Removal of Some Heavy Metals from Industrial

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Republic of Iraq Ministry of Higher Education & Scientific Research University of Technology Building & Construction Engineering Department

Removal of Some Heavy Metals from Industrial Wastewater By Aquatic Plants (Duckweed)

Thesis submitted to the Department of Building & Construction Engineering of the University of Technology In partial fulfillment of the requirements for the degree of Master of Science In Environmental & Sanitary Engineering

By

Alaa Fadhil Ibrahim Al - Saadi H.Diploma in Environmental Engineering, 2001 B.Sc. Civil Engineering, 1992

Supervised By

Asst. Prof. Dr. Faris Hamoodi Al - Ani Asst. Prof. Dr. Mahmoud Salih Al - Khafaji

December 2015

‫بسم هللا الرحمن الرحيم‬ ‫سمآء مآء فأ ْحيا ِب ِه‬ ‫وٱ هّللُ أنزل ِمن ٱل َّ‬ ‫ٱأل ْرض ب ْعد م ْوتِهآ(ج) ِإ َّن فِي ذ ِلك آليةً‬ ‫ِلهق ْو ٍم ي ْسمعُون‬ ‫صدق هللا العلي العظيم‬ ‫سورة النحل‪:‬اآلية ‪65‬‬

Dedication To my Late Parents; may Allah bless their souls… To my beloved Wife… To my Daughters & Sons… I dedicate my work

Alaa F.I

Committee Certification We hereby certify that we read the thesis entitled “Removal of Some Heavy Metals from Industrial Wastewater By Aquatic Plants (Duckweed)”, and the examining committee had examined the student (Alaa Fadhil Ibrahim Al-Saadi) in its contents and that in our opinion meets the standards of a thesis for the degree of Master in Science in Sanitary and Environmental Engineering. Signature:

Signature:

Name: Asst. Prof. Dr. Faris H. Al – Ani

Name: Asst. Prof. Dr.

Mahmoud S. Al - Khafaji Date:

/

/2016

Date:

/

(Supervisor and member)

/2016 (Supervisor

and member)

Signature:

Signature:

Name: Asst. Prof. Dr.Basim H. Al-Obaidy

Name: Dr. Zainab

Bahaa Date:

/

/2016 (Member)

Date:

/

/2016

(Member)

Signature: Name: Prof. Dr. Riyad Hassan Al-Anbari Date:

/

/2016 (Chairman)

Approved for the University of Technology-Baghdad

Signature: Name: Prof. Dr. Riyad Hassan Al-Anbari Head of Building and Construction Engineering Department Date:

/

/2016

Certification We hereby certify that the thesis entitled “Removal of Some Heavy Metals from Industrial Wastewater By Aquatic Plants (Duckweed)”, was prepared by (Alaa Fadhil Ibrahim AlSaadi) in partial fulfillment for the degree of Master in Science in Sanitary and Environmental Engineering is a bona fide record of work carried out by him under our supervision.

Signature:

Signature:

Name: Asst. Prof. Dr. Faris H. Al – Ani

Name: Asst. Prof. Dr.

Mahmoud S. Al - Khafaji Date:

/

/2016

Date:

/

/2016

In view of the available recommendations, I forward this thesis for debate by examining committee.

Signature: Name: Asst. Prof. Dr. Faris H. Al – Ani Head of the Sanitary and Environmental Engineering Branch Date:

/

/2016

Certificate This is to certify that the thesis entitled “Removal of Some Heavy Metals from Industrial Wastewater By Aquatic Plants (Duckweed)”, prepared by (Alaa Fadhil Ibrahim AlSaadi) has been read and corrected linguistically to meet English style.

Signature: Name: Yaghdan R. Mahdi (Linguistic Supervisor) Date:

/

/2016

Acknowledgment I would like to express my deep appreciation and gratitude for my supervisors Dr. Faris H. Al-Ani, Dr. Mahmoud S. Al-Khafaji for their continuous encouragement and observations through the stages of work on the completion of thesis, also I express my great thanks and gratitude to the Head of the Environmental Research Center at the University of Technology, Dr. Abdul Hameed Jawad Al-Obaidi and all employees of the center and especially employees of the laboratory of water and soil, and laboratory of spectroscopy, also employees of the Laboratory of sanitary engineering in the Building and Construction Engineering Department. Special thanks to the members of the General Company for the manufacturing of batteries in Waziriya, especially the Department of Environment for their great help to supply the industrial wastewater as well as to employees of the General Directorate for Industrial Development in the Ministry of Industry and Minerals for their cooperation in facilitating the task of getting the industrial wastewater from one of the private tanneries in Nahrawan region, and also thanks to the employees of Al- Rustumiya Wastewater Treatment Station / Third Extension for their invaluable assistance in obtaining duckweed plant.

I

Abstract The treatment of industrial wastewater by a simple constructed wetland system (CWS) for the removal of heavy metals consisting of clarification and duckweed system; depending on the principle of plug flow system with dispersion factor equals to zero. The study was done under experimental conditions by using pilot plant which was designed, constructed and operated. The pilot plant was operated with constant hydraulic retention time of 2 hr and 10 days for clarifier and duckweed tanks respectively. Pollutants concentrations in raw industrial wastewater had direct impact on the physical, nutrients and heavy metals removal in the system. The average wastewater flow was 250 m3/day; while the chemical oxygen demand (COD) and heavy metals of raw industrial wastewater concentrations were 15210 mg/L and 0.0229 mg /L, 0.5377 mg/L, 0.1274 mg /L, 0.2583 mg /L for Cd, Cr, Ni and Pb respectively. The tests results for the clarifier tank show that the performance in removing other parameters seemed to be very low because that the clarifier requires more detention time. This study was conducted to evaluate the treatment efficiency of the wetland and wetland aquatic plants to play an important role in heavy metals removal process. It is known that duckweed (Lemna minor) absorb specific heavy metals at the fastest rates. In this research, the potential of duckweed (Lemna minor) has been investigated to accumulate Cd, Cr, Ni and Pb present in a combined industrial wastewater brought from tanneries and batteries manufacturing plants. The duckweed sample was collected and brought from the final clarifiers of Al-Rustumiya Wastewater Treatment Plant/Third Extension. The average removal efficiency of COD for duckweed tanks was 97.49%, and the average reduction of both temperature and pH were 11.54%, II

22.35% respectively; while the average removal of each of : EC, TDS, NH4-N, NO3-N, and PO4-P were 61.6%, 16.76%, 56.45%, 89.48% and 85.61% respectively; also for Cd, Cr, Ni and Pb were 44.93%, 32.26%, 74.48%, and 79.1% respectively as the heavy metals removal efficiencies were increased in acidic solution (pH range from 6.6 to 8.6); and DO increased from 0.02 mg/L to 7.07mg/L. The results show that duckweed proved to be a good accumulator of Pb, and Cr, a moderate accumulator of Ni, and a poor accumulator of Cd, since that the Bioconcentration Factor which is defined as the ration of heavy metal concentration in the biomass (duckweed tissues) to the concentration of heavy metal in the feed solution (wastewater mass surrounding); (BCF) values were 7.63, 5.33, 4.7 and 0.12 for Pb, Cr, Ni and Cd respectively(BCF>1.0 shows a good accumulation).

III

Table of Contents Acknowledgment.....……………………………………………...…………...... Abstract.………………………………………………………………………... Table of Contents…………………………………….………………………... List of Tables…………………………………………..………………………. List of Figures………………………………………..………………………… List of Photos……………………………………..……………………………. Nomenclatures……………………………..…………………………………... Chapter One – Introduction 1-1: General……………………………………………………………………... 1-2: Industrial Wastewater and Quality Problems…..…………………………... 1-3: Need for Research on Industrial Wastewater Treatment Systems for Developing Countries …………………………………………………………... 1-4: Heavy Metal Removal from Wastewater…………………………………... 1-5: The Problem………………………………………………………………... 1-6: Research Objectives……………………………………………………… Chapter Two – Theory & Literature Review 2-1: General…...………………………………………………………………… 2-2: Importance of Metals……………………………………………………….. 2-3: Sources of Metals ………………………………………..………………… 2-4: Wetlands-Water “living filters”…………….………………………………. 2-4-1: Factors Influencing Water Quality……………………………………….. 2-4-2: Constructed Wetland Systems (CWSʼs)………..………………………... 2-4-2-1: Advantages and Disadvantages of Constructed Wetland Systems…….. 2-4-2-2: Types of Constructed Wetland Systems ........…………………………. 2-4-2-3: Constructed Wetland Systems Components…………………………… 2-4-3: Mechanisms of Pollutants Removal by Constructed Wetland Systems … 2-4-3-1: Suspended Solids Removal……………………………………………. 2-4-3-2: Soluble Organic Matter……………………………………………….. 2-4-3-3: Nutrients Removal…………………………………………………….. 2-4-3-4: Pathogen Removal……………………………………………………... 2-4-3-5: Metals Removal………………………………………………………... 2-5: Aquatic Plants………………………………………………………………. 2-6: Using Duckweed as A Biosorbent………………………………………….. 2-7: Duckweed for Industrial Wastewater Treatment…………………………… 2-8: Literature Review on Duckweed Performance…..………………………… Chapter Three : Experimental Works 3-1: Methodology………………………………………………………………... 3-2: Design Considerations…………………………………………………..….. IV

I II IV VI VII VIII IX 2 3 5 6 7 7 10 10 11 13 14 16 17 18 19 21 21 23 24 30 31 39 41 43 44 49 50

3-3: Pond Design …………………….………………………………………….. 3-4: Similarity Laws.……………..……………………………………………... 3-5: The Design Set-up of Full-Scale & Model-Scale…………………………... 3-6: Design Calculations of Pilot Plant..………………………………………... 3-7: Pilot Plant...………………………………………………………………... 3-7-1: Clarifier Tank…………………………………………………………….. 3-7-2: Duckweed tanks………………………………………………………….. 3-8: Industrial Wastewater Sampling and Analysis……………………………... 3-9: Duckweed Sampling and Analysis…………………………………………. 3-10: Laboratory Apparatuses .………………………………………………….. 3-11: Plant Tissue Analysis .……………………………………………………. Chapter Four : Results and Discussion 4-1: General……………………………………………………………………... 4-2: The Clarification Removal Efficiency……………………………………… 4-3: Duckweed Effect on COD Removal Efficiency……………………………. 4-4: Duckweed Effect on Temperature Reduction Efficiency…………………... 4-5: Duckweed Effect on pH Reduction Efficiency…………………………….. 4-6: Duckweed Effect on EC Reduction & TDS Removal Efficiency………….. 4-7: Duckweed Effect on DO Increase Efficiency……………………………… 4-8: Duckweed Effect on Nutrients Removal Efficiency……………………….. 4-9: Duckweed Effect on Heavy Metals Removal Efficiency…………………... 4-10: pH Effect on Heavy Metals Removal Efficiency…………………………. 4-10-1: pH Effect on Cadmium Removal Efficiency…………………………… 4-10-2: pH Effect on Chromium Removal Efficiency…………………………... 4-10-3: pH Effect on Nickel Removal Efficiency………………………………. 4-10-4: pH Effect on Lead Removal Efficiency………………………………… 4-11: Bioconcentration Factor (BCF)…………………………………………. 4-12: Comparison of the Effluent Wastewater Characteristics with Allowable Iraqi Limits………………………………………………………………………. Chapter Five : Conclusions & Recommendations 5-1: Conclusions………………………………………………………………… 5-2: Recommendations and Future Work……………………………………….. References Annex A : Pilot plant photos Annex B : Duckweed photos Annex C : Iraqi Regulations

V

51 56 57 60 65 67 70 71 72 72 78 81 83 86 88 90 90 94 96 100 106 106 107 108 109 110 112 117 119 122 144 150 154

List of Tables Table (2.1) Table (2.2)

Metals of importance in wastewater management…………. Typical waste compounds produced by commercial, industrial, and agricultural activities; that have been classified as priority pollutants…………………………….. Table (2.3) Characteristics of different types of natural wetlands and their ability to retain non-point source pollutants………….. Table (2.4) Pollutant removal mechanisms…………………………….. Table (2.5) The major nitrogen conservative transformations and retention processes in CWS………………………………... Table (2.6) Heavy metals removal efficiencies in different types of CWS………………………………………………………... Table (2.7) Different roles of aquatic plants used in wastewater treatment…………………………………………………… Table (2.8) Literature Review Summary……………………………… Table (3.1) Different duckweed treatment systems depending on type and amount of wastewater…………………………………. Table (3.2) Basic prototype to scale model relationships………………. Table (3.3) Analytical Methods According to the Standard Method…... Table (4.1) The characteristics of collected industrial wastewater fed to pilot plant and tested at 24/09/2014………………………………………………... Table (4.2) Clarification pollutants concentrations & removal efficiencies………………………………………………... Table (4.3) COD measured concentrations & % removal in duckweed tanks……………………………..….……………………… Table (4.4) Temperature measured concentrations & % reduction in duckweed tanks …………………………..………………. Table (4.5) pH measured concentrations & % removal in duckweed tanks ……………………………..………………………... Table (4.6) TDS measured concentrations & % removal in duckweed tanks ………………………………..……………………… Table (4.7) EC measured concentrations & % reduction in duckweed tanks ……………………………..………………………... Table (4.8) DO measured concentrations & % increase in duckweed tanks ………………………………………………………. Table (4.9) NH4-N measured concentrations & % removal in duckweed tanks ………………………………….……………………. Table (4.10) NO3-N measured concentrations & % removal in duckweed tanks ………………………………………………………. Table (4.11) PO4-P measured concentrations & % removal in duckweed tanks ………………………………………………………..

VI

11

12 15 22 26 38 40 45 51 57 71

81 86 87 89 91 92 93 95 96 98 99

Table (4.12) Cd measured concentrations & % removal in duckweed tanks ………………………………………………………. Table (4.13) Cr measured concentrations & % removal in duckweed tanks ……………………………………………………….. Table (4.14) Ni measured concentrations & % removal in duckweed tanks ………………………………………………………. Table (4.15) Pb measured concentrations & % removal in duckweed tanks ………………………………………………………. Table (4.16) Concentrations of heavy metals in duckweed tissues……… Table (4.17) BCF values of heavy metals accumulated in duckweed tissues………………………………………………………. Table (4.18) Comparison with Iraqi Standards set for wastewater effluents used for agricultural irrigation…………………… Table (4.19) Comparison with Iraqi Standards set for wastewater effluents discharged into watercourses…………………… Table (4.20) R, R2 and y = f(x) Parameters Fitted Polynomials Regression Models with Time & % Removal in Duckweed Tanks……………………………………………………….

101 102 103 104 111 112 113 114

115

List of Figures Figure (2.1)

Figure (2.2) Figure (2.3) Figure (2.4) Figure (2.5) Figure (3.1) Figure (3.2)

Figure (3.3) Figure (3.4) Figure (3.5) Figure (3.6) Figure (3.7) Figure (4.1) Figure (4.2)

Different types of CWS(A, FWS with free-floating plants; B, FWS with submerged plants; C, FWS with emergent plants; D, Horizontal SSF; E, Vertical SSF)………………………… Summary of the major physical, chemical and biological processes controlling pollutant removal in CWS……………. Nitrogen transformation/removal mechanisms in CWS…….. Metal removal mechanisms in CWS………………………… Lemna minor spreading in worldwide……………………….. Ideal plug-flow system for combined duckweed-based wastewater treatment and protein production……………….. Example of batch-operated pond for duckweed cultivation at village level, (100 m2 at 0.5 m depth). (a) Length (b) Width section of duckweed pond…………………………………… Biological Process in Duckweed Wastewater System………. Values of kτ in the Wehner and Wilhelm equation verses percent remaining for various dispersion factors……………. Schematic diagram of the clarifier tank……………………... Schematic diagram of the Storage (Holding) and Duckweed tanks………………………………………………………….. Schematic diagram of the pilot plant system………………… (a) COD vs Time, (b) COD% Removal vs Time with fitted polynomial…………………………………………………… (a) Temperature vs Time, (b) Temperature% Reduction vs

VII

19 20 25 32 42 52

53 59 60 66 67 68 87

Figure (4.3) Figure (4.4) Figure (4.5) Figure (4.6) Figure (4.7) Figure (4.8) Figure (4.9) Figure (4.10) Figure (4.11) Figure (4.12) Figure (4.13) Figure (4.14) Figure (4.15) Figure (4.16) Figure (4.17)

Time with fitted polynomial…………………………………. (a)pH vs Time, (b)pH% Reduction vs Time with fitted polynomial…………………………………………………… (a)TDS vs Time, (b)TDS% Removal vs Time with fitted polynomial…………………………………………………… (a)EC vs Time, (b)EC% Reduction vs Time with fitted polynomial…………………………………………………… (a)DO vs Time, (b)DO% Increase vs Time with fitted polynomial…………………………………………………… (a)NH4-N vs Time, (b) NH4-N % Removal vs Time with fitted polynomial…………………………………………….. (a)NO3-N vs Time, (b) NO3-N % Removal vs Time with fitted polynomial…………………………………………….. (a)PO4-P vs Time, (b) PO4-P % Removal vs Time with fitted polynomial…………………………………………………… (a)Cd vs Time, (b) Cd % Removal vs Time with fitted polynomial…………………………………………………… (a)Cr vs Time, (b) Cr % Removal vs Time with fitted polynomial…………………………………………………… (a)Ni vs Time, (b) Ni % Removal vs Time with fitted polynomial…………………………………………………… (a)Pb vs Time, (b) Pb % Removal vs Time with fitted polynomial…………………………………………………… Cd % Removal vs pH % Reduction with fitted polynomial…. Cr % Removal vs pH % Reduction with fitted polynomial…. Ni % Removal vs pH % Reduction with fitted polynomial…. Pb % Removal vs pH % Reduction with fitted polynomial….

89 91 93 94 95 97 98 99 101 102 104 105 106 107 108 110

List of Photos Photo (2.1) Photo (3.1)

Photo (3.2)

Photo (3.3) Photo (3.4) Photo (3.5)

Three duckweed genera together: Spirodela (largest), Lemna (mid-sized) and Wolffia (smallest), scale in millimeters…… Duckweed-covered serpentine plug-flow lagoon in the USA; for tertiary treatment of effluent from three facultative lagoons followed by a wetland buffer. Design flow is reported at19,000 m3/d, with peak flows reaching 38,000 m3/d………………………………………………………….. Batch-operated pond for duckweed cultivation at village level showing dense duckweed cover and pour-flush latrine influent for nutrient supply in the background (Bangladesh)... Pilot plant of the duckweed wastewater treatment system…... Industrial Wastewater fed into the Clarifier Tank…………… Analytical Balance…………………………………………... VIII

42

52

53 69 70 73

Photo (3.6) Photo (3.7) Photo (3.8) Photo (3.9) Photo (3.10) Photo (3.11) Photo (3.12) Photo (3.13)

PH, EC, and TDS meter……………………………………... Laboratory Oven…………………………………………….. Multi-parameter Bench Meter (Model C99)………………… Multi-parameter Bench Meter (HI 83200)…………………... DO Meter (Multi 3430 SET F)………………………………. COD Meter & Incubator (SN11/25370) & (ET 108)………... Atomic Absorption Spectrophotometer model (AA 6300)….. Grinded duckweed fronds after drying in Electrical laboratory oven……………………………………………….

Nomenclatures Description a BOD BOD5 BAC BCF TF UBOD COD

Symbol Model scale Biochemical oxygen demand Five days biochemical oxygen demand Bioaccumulation Coefficient Bioconcentration Factor Translocation Factor Ultimate-Biochemical oxygen demand Chemical oxygen demand

CH4 H2S FeS CO2 Dt

Methane gas Hydrogen sulfide Ferrous Sulfide Carbon dioxide Detention time

d EC FC FeS Fr

Diameter, dispersion factor, depth Electrical conductivity Fecal coliform bacteria Ferric sulfide Froude number

HCl HCLO4 HNO3 H2S

Hydrochloric acid Perchloric acid Nitric acid Hydrogen sulfide

IX

74 75 75 76 76 77 78 79

Description HRT kt ks tsummer twinter Tsummer Twinter L W S/So NO3-N NH4-N PO4-P O-PO4-3 N2

Symbol Hydraulic retention time, day or hour Reaction rate coefficient at a given temperature Solubility product Detention time in Summer, days Detention time in Winter, days Temperature in Summer Temperature in Winter Length, m Width, m BOD% remaining, Percent remaining Nitrates nitrogen concentration Ammonia as nitrogen Phosphate as phosphorus Orthophosphate Nitrogen gas

pH

Hydrogen potential

P.V.C

Polyvinyl chloride

Q

Industrial wastewater flow

R R2

Coefficient of correlation Coefficient of determination

DO SS TDS TSS

Dissolved oxygen suspended solids Total dissolved solids Total suspended solids

TKN Eh

Total Kjeldahl Nitrogen Redox potential

As V Ʋpipe W

Surface area Volume Velocity in pipe Width

X

Description Qm Qp Vm Vp Dtm Dtp hm hp Hm Am Ap dm dp

Symbol Clarifier flow in model scale Clarifier flow in pilot plant Clarifier volume of wastewater in model scale Clarifier volume of wastewater in pilot plant Clarifier detention time in model scale Clarifier detention time in pilot plant Clarifier depth of wastewater in model scale Clarifier depth of wastewater in pilot plant Clarifier depth in model scale Clarifier area in model scale Clarifier area in pilot plant Clarifier diameter in model scale Clarifier diameter in pilot plant

Vʹm Vʹp Dtʹm Dtʹp hʹm hʹp Hʹm Lʹm Wʹm Wʹp

Duckweed tank volume of wastewater in model scale Duckweed tank volume of wastewater in pilot plant Duckweed tank detention time in model scale Duckweed tank detention time in pilot plant Duckweed tank depth of wastewater in model scale Duckweed tank depth of wastewater in pilot plant Duckweed tank depth in model scale Duckweed tank length in model scale Duckweed tank width in model scale Duckweed tank width in pilot plant

Lme Lpe Wme Wpe dme dpe

Equalization tank length in model scale Equalization tank length in pilot plant Equalization tank width in model scale Equalization tank width in pilot plant Equalization tank depth of wastewater in model scale Equalization tank depth of wastewater in pilot plant

EU US UV П Ø

European Union United States Ultra violet Pi (3.14159265359) Pipe diameter

XI

Chapter One Introduction

Chapter One

Introduction CHAPTER ONE INTRODUCTION

1-1: General Water pollution has been recognized as a problem for decades. The use of heavy metals in industries increase their concentration in water bodies. Metals cannot be degradedand require immobilization to reduce or remove their toxicity (Ankita Suhag, 2011). Industry nature and receiving stream water uses reflect the removal of

wastewater

constituents before discharge, among those are the heavy metals, which the annual total toxicity of all anthropogenically metals exceeds the combined total toxicity of all radioactive and organic wastes generated each year, as to meet drinking water standards (Nriagu & Pacyna, 1988). Urbanization and industrialization significantly contribute to the formation of unsanitary conditions in many areas (Robert A. Corbit, 2004). The term heavy metal has been defined as those metals with a density > 6000 kg/m3 (Davies, 1987), some of which are essential to life processes, others have no beneficial role and all may adversely affect plants and animals

at

higher

concentrations

(Davies,

1984).

The

major

anthropogenic sources of heavy metals discharged into water, air and soil include releases from the combustion of fossil fuels and incineration of wastes, mining and mine wastewater, metal coatings, smelting and refining, paint and ink manufacturers, petroleum refining, iron and steel manufacturing,

photographic

industry,

leather

tannery,

battery

manufacturing and wood preservatives (Krishnan et al., 1993). Practically every industry discharges one trace metal into the soil and the other into _____________________________________________________________________ 2

Chapter One

Introduction

the water; with 70% of each metal emitted to the atmosphere is deposited on land and the remaining 30% of it will remain in the aquatic environment (Nriagu & Pacyna, 1988). Constructed wetland systems(CWS) are successfully used for different types of wastewater; among them is the industrial wastewater (Dunbabin and Bowmer, 1992),with heavy metals as primary pollutants in industrial effluents. Heavy metals accumulate in natural watercourses after discharge of wastewater, leading to potential toxicity in receiving ecosystems and eventually humans (Kadlec and Knight, 1996). Whether designed for the treatment of domestic wastewater or metal-laden industrial effluents, therefore CWS should eliminate the discharge of heavy metals into the natural environment. natural receiving waters limited assimilative capacity indicate a need to develop technologies that treat wastewaters before they are being discharged into the natural receiving waters(Kadlec and Knight, 1996). Conventional technologies require concrete, steel, chemicals and energy contributing in non-renewable resources depletion (De Pauw and De Maeseneer, 1992). Moreover, in the developing countries high technological requirements and significant investment, operational and maintenance costs seriously hamper introducing conventional wastewater treatment systems exploring the use of CWS in industrial wastewater treatment (Kivaisi, 2001).

1-2: Industrial Wastewater and Quality Problems Human industrial activities produce in general diverse pollutants. Depending on the industrial activities, these pollutants may be toxic organic,

suspended

solids

and heavy metals (Eckenfelder, 1989).

Depending on the processing, these wastewaters contain

typical

_____________________________________________________________________ 3

Chapter One

Introduction

pollutants such as BOD, COD, oil and grease, TSS, nitrogen, phosphorus and heavy metals (Kadlec and Wallace, 2008), causing particular threats to the environment. The industrial wastewater quality depends on the utilized chemicals; also the process itself. Depending on the season and the fashion, changes often happen in the composition of industrial wastewater even of the same process. In tanning industry; process water consumption, and consequently wastewater effluent discharges, varies greatly between tanneries, based on the processes involved, raw materials, and products. Generally, water consumption is the greatest in the pre-tanning areas, but significant amounts of water are consumed also in the post tanning processes. Wastewater from the beamhouse processes (e.g. soaking, fleshing, dehairing, and liming) and from associated rinsing is generally collected together having significant loads of organic matter and suspended solids. Wastewater from tan yard processes, deliming and bating may contain sulfides, ammonium salts, and calcium salts and is weakly alkaline. After pickling and tanning processes, the main wastewater contaminants depend on the tanning techniques used. Finishing wastewaters may contain lacquer polymers, solvents, color pigments and coagulants. (IFC & World Bank group, 2007). The battery industry wastewater is highly polluted in terms of, COD, BOD, TSS, Pb, Cr, and Zn, chlorine, sulfates and arsenic. The value of these parameters is very high as compared to the values in National Environment Quality Standards (NEQS, 1999).The levels of pollutants in lead acid battery wastewater also vary depending upon the process adopted in battery making (Rahangdale et., al., 2012). The main environmental concern is to reduce the environmental impact; discharge limits imposed on industrial wastewater are becoming ever _____________________________________________________________________ 4

Chapter One

Introduction

more stringent (Okeo-tex, 2006a, b, c). Moreover, in the future reuse of purified effluents will be of increasing relevance due to raising water prices as well as to preserve natural water resources.

1-3: Need for Research on Industrial Wastewater Treatment Systems for Developing Countries In developing countries; wastewater treatment systems are not really operational even at small scales. Furthermore, the industrial wastewater generated may be dumped untreated into natural wetlands; causing serious problems of water pollution, because all the wastewater is directly discharged into natural water bodies, without any prior treatment. Therefore, there is a need for monitoring the water quality within and surrounding the wetlands receiving this polluted water in order to assess the extent of the metal pollution. Furthermore, many developing countries are facing problems related with the treatment of industrial wastewaters mainly due to high investment required for the installation and operating costs of the conventional industrial wastewater treatment plants and the need of skilled personnel that’s also required (UNESCO-IHE-Sekomo, 2012). In trying to do so, this study proposed to simulate ponds (wetlands) receiving industrial wastewater coming from tanneries, and batteries focusing on heavy metals pollution, specifically Cd, Cr, Ni, and Pb, and trying to solve the issue of improving the removal efficiency of heavy metals from industrial wastewater by a low-cost option for the purification of wastewater (Gijzen, 1996); by using a combination of a clarifier with duckweed tanks (an aquatic plants found in shallow ponds) (Gijzen, 2001).

_____________________________________________________________________ 5

Chapter One

Introduction

1-4: Heavy Metal Removal from Wastewater Conventional biological/chemical treatment methods for heavy metals removal, such as ion exchange, precipitation, phyto-extraction, ultrafiltration, reverse osmosis, and electro-dialysis are very expensive (Schnoor, 1997), because of the non-degradability properties of heavy metals; especially when the dissolved metals concentrations are in range of (1-100 mg/L) (Nourbakhsh et al., 1994).

Adding to thatm the

conventional treatment technologies produce toxic chemical sludges of which the disposal/treatment is rather costly. Therefore, heavy metals contaminated wastewater need an effective affordable technological solution. Wetland plants are able to accumulate heavy metals. However, one of their major shortcomings, include metal accumulation and uptake by plants which play a minor role in wetlands and ponds systems (Mays and Edwards, 2001). Waste stabilization ponds and wetlands systems are applied because of their easy maintenance and no need of skilled personnel when compared to various advanced systems for treatment of wastewater that have been developed in Europian Union and United States and which requires high capital investments, maintenance costs and skilled personnel (Veenstra and Alaerts, 1996). Wetland systems have been successfully used for water quality improvement. These act as reservoirs, part of wastewater treatment technology and also help to maintain the natural and biogeochemical links between land, water and biota. They also serve as available natural resource for wildlife and people (Connor and Luczak, 2002).

_____________________________________________________________________ 6

Chapter One

Introduction

1-5: The Problem Effective treatment of industrial wastewater remains a difficult target to achieve in most developing countries. While there are many reasons for this, but still the specialized personnel generally agree that the most important overriding factor is cost. Conventional treatment systems, which generally rely on heavy aeration, are prohibitively expensive to install, and both difficult and costly to operate and maintain. Duckweed based industrial wastewater treatment systems make realistic solutions to these issues. They are inexpensive to install as well as to operate and maintain, also they do not require imported components. They are functionally simple, yet stable in operation; and they can provide tertiary treatment performance that is equal or superior to conventional wastewater treatment systems now recommended for large scale applications. Due to Iraq's lack of such studies on the effect of industrial pollutants in wastewater treatment plants, the environment and using phytotechnology in treatment and removal of pollutants; this study will be among the first which has been done in such approach.

1-6: Research Objectives This research is aimed at the improvement of the mechanisms involved in the removal of heavy metals by natural systems. The study addresses the issue of improving the removal efficiency of heavy metal from industrial wastewater in developing a low cost and alternative treatment system for metal removal from a combination of tannery and battery wastewater. The overall goal of the study is to develop a simulation model that can be used as a planning tool for the design of

_____________________________________________________________________ 7

Chapter One

Introduction

pond or simple lagoon (CWS) for effective control and treatment of industrial wastewater. The main objectives of this research are: 1. Presenting and surveying the ability of a group of tiny aquatic plants commonly known as “Duckweedˮ for industrial wastewater treatment. 2. To determine the heavy metal removal capacity of a pond system seeded with duckweed to show the effect of dissolved oxygen, pH

and

other contaminants on

the

heavy

metal

removal

efficiency in order to select a pre-treatment technology. 3. To develop an integrated cheap alternative for heavy metals removal combining some units of conventional wastewater treatment plants such as clarifier together with a macrophyte pond seeded with duckweed plants. 4. To compare the effluent characteristics with their values set for primary treatment by Iraqi Regulations No.(3), (2012) and No.(25), (1967) and its ammendments; effluent quality that is measured for irrigation and discharged into watercourceses.

_____________________________________________________________________ 8

Chapter Two Theory & Literature Review

Chapter Two

Theory & Literature Review CHAPTER TWO THEORY & LITERATURE REVIEW

2-1: General Trace quantities of many important constituents of most waters, among them, are metals such as cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), and zinc (Zn) , which are also classified as priority pollutants. However, most of these metals are necessary for growth of biological life, while for example; the lack of adequate quantities of them may hamper growth of algae. The presence of any of these metals in excessive quantities interferes with many beneficial uses of water because of its toxicity. Therefore, it is recommended often to measure and control the concentrations of these substances (Metcalf & Eddy, 2004).

2-2: Importance of Metals Table (2.1) summarizes which metals are of importance in the treatment, reuse, and disposal of treated effluents and bio-solids (Metcalf & Eddy, 2004). Macro and micro quantities of metals, such as iron, chromium, copper, zinc, and cobalt are fundamental for appropriate growth of microorganisms, but the highly concentrated presence of same metals can be toxic. The using of treated wastewater effluent for irrigation and landscape watering requires determining a variety of metals to assess any adverse effects that may occur from them. It’s important to determine metals such as arsenic, copper, selenium, calcium, lead,

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mercury, molybdenum, nickel, cadmium, and zinc found in composted sludge applied in agricultural applications (Metcalf & Eddy, 2004). Table 2.1: Metals of importance in wastewater managementa (Metcalf & Eddy, 2004). Nutrients necessary for biological growth Microb

Used to determine if biosolids are suitable for land application

Metal

Symbol

Arsenic

As

0.05



Cadmium

Cd

1.0



Calcium

Ca

Chromium

Cr



Cobalt

Co



Copper

Cu



1.0



Iron

Fe

Lead

Pb



0.1



Magnesium

Mg

Manganese

Mn

Mercury

Hg

Molybdenum Nickel Potassium

Mo Ni K

Selenium

Se

Sodium

Na

Tungsten

W



Vanadium

V



Zinc

Zn



a c

Macro

Concentration Used to threshold of determine inhibitory effect on SAR for land heterotrophic application of organisms, mg/l effluent



√ 10c, 1d

√ √





√ √ √

0.1



1.0

√ √

√ √







1.0



From Crites and Tchobanoglous (1998). bOften identified as trace elements needed for biological growth. Total chromium. dHexavalent chromium.

2-3: Sources of Metals The discharges from residential dwellings, groundwater infiltration, and commercial and industrial discharges are sources of trace metals in wastewater. Table (2.2) identifies any heavy metals sources (Metcalf & Eddy, 2004). For example, industrial wastes often containing cadmium,

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Table 2.2: Typical waste compounds produced by commercial, industrial, and agricultural activities; that have been classified as priority pollutants (Metcalf & Eddy, 2004). Name

Formula Use

Arsenic

As

Barium

Ba

Cadmium

Cd

Chromium

Cr

Lead

Pb

Mercury

Hg

Selenium

Se

Silver

Ag

Concern

Alloying additives for metals especially lead and copper as shot, battery grids, cable sheaths, boiler tubes. High-purity(semiconductor) grade Getter alloys in vacuum tube, deoxidizer for copper, Frary’s metal, lubricant for anode rotors in x-ray tubes, spark-plug alloys Electrodeposited and dipped coatings on metals, bearing and low-melting alloys, brazing alloys, fire protection system, nickel-cadmium storage batteries power transmission wire, TV phosphors, basis of pigments used in ceramic glazes, machinery enamels, fungicide, photography and lithography, selenium rectifiers, electrodes for cadmium-vapor lamps and photoelectric cells Alloying and plating element on metal and plastic substrates for corrosion resistance, chromiumcontaining and stainless steels, protective coating for automotive and equipment accessories, nuclear and high-temperature research, constituent of inorganic pigments Storage batteries, gasoline additives, cable covering, ammunition, piping, tank linings, solder and fusible alloys, vibration damping in heavy construction, foil, babbitt and other bearing alloys Amalgams, catalyst electrical apparatus, cathodes for production of chlorine and caustic soda, instruments, mercury vapor lamps, mirror coating, arc lamps, boilers Electronics, xerographic plates, TV cameras, photocells, magnetic computer cores, solar batteries(rectifiers, relays), ceramics(colorant for glass), steel and copper, rubber accelerator, catalyst, trace element in animal feeds Manufacture of silver nitrate, silver bromide, photochemicals; lining vats and other equipment for chemical reaction vessels, water distillation, etc.; mirrors, electric conductors, silver plating electronic equipment; sterilant, water purification, surgical cements, hydration and oxidation catalyst, special batteries, solar cells, reflectors for solar towers, low-temperature brazing alloys, table cutlery, jewelry, dental, medical, and scientific equipment, electrical contacts, bearing metal, magnet windings, dental amalgams, colloidal silver used as a nucleating agent in photography and medicine, often combined with protein.

12

Carcinogen and mutagen. Longterm-sometimes can cause fatigue and loss of energy; dermatitis. Flammable at room temperature in powder form. Long-termIncreased blood pressure and nerve block. Flammable in powder form. Toxic by inhalation of dust or fume. A carcinogen. Soluble compounds of cadmium are highly toxic. Long-termconcentrations in the liver, kidneys, pancreas, and thyroid; hypertension suspected effect Hexavalent chromium compounds are carcinogenic and corrosive on tissue. Long-termskin sensitization and kidney damage Toxic by ingestion or inhalation of dust or fumes. Long-term-brain and kidney damage; birth defects Highly toxic by skin absorption and inhalation of fume or vapor. Long-term-toxic to central nervous system, may cause birth defects Long-term-red staining of fingers, teeth, and hair; general weakness; depression; irritation of nose and mouth Toxic metal, Long-termpermanent gray discoloration of skin, eyes, and mucous membranes

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chromate, lead, and mercury should be removed by pretreatment on-site of the industry rather than be mixed with the municipal wastewater (Metcalf & Eddy, 2004).

2-4: Wetlands-Water “living filters” For many centuries; natural wetlands have been used indirectly as wastewater final discharge sites. Wastewater depuration capacity observations of natural wetlands have led to pollutant assimilation of these ecosystems potentials and their stimulation of the artificial wetlands systems development of wastewaters sources treatment. Constructed wetlands on the contrary to natural wetlands are man-made systems that are designed, constructed and operated to imitate uses of natural wetlands for needs or desires of human , as influential, cheap means to clean-up municipal wastewaters, also point and non-point source wastewaters, such as industrial effluents. Natural wetlands play the role of buffer regions surrounding water bodies and as a purifying phase for traditional municipal wastewater treatment plants effluents, before discharging into receiving water courses. In fact, conventional wastewater treatment plants are inefficient to remove various organic compounds coming from industries such as tannery, and battery and due to their inefficiency; consequently contaminating receiving water bodies, focusing on wetlands ability to effective removal of many of these complexes, reaffirming the important role of wetlands in water quality conservation (Ana Dordio, et. al., 2008). Wetlands significance has been appreciated in controlled shapes, for example the Marshes formed by the concourse of the Tigris and Euphrates in southern Iraq (Sundaravadivel and Vigneswaran, 2001).

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Constructed Wetland Systems design simplicity and installation low costs, operation, and maintenance makes them a suitable alternative for both developed and developing countries (USEPA, 2000).

2-4-1: Factors Influencing Water Quality The biotic status of wetland affects the availability of nutrient; also affects anaerobiosis within soil, and pH of both water and soil (Kivaisi, 2001). Soil characteristics greatly influence wetland prevailing vegetation type, and microorganism populations that can live on the water-soil phase. The removal of certain types of pollutants is acid-base properties, and redox potential and the capacity of absorption dependent. Macrophytes are the dominant vegetation in wetlands typically acclimatized to saturated conditions in water and capable of preserving anaerobic soil conditions as a result of the environmental stresses. Active root function depends on rhizosphere oxygenation which is considered essential, and counteracting the effects of soluble phytotoxins (Ana Dordio, et. al., 2008). The major role in the biogeochemical transformations of nutrients is done by microorganisms (Vymazal, 2007), and the organic compounds metabolism (Stottmeister et al., 2003). Wetlands types, characteristics and their abilities to overcome different non-point pollution problems are illustrated in Table (2.3) (IETC-UNEP, 1999). The prediction of water pollution restraints is very hard by natural wetlands; in spite of their observed water depuration general abilities, Natural wetlands cannot be considered as a consistent approach to

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wastewater treatment because of their extreme variable characterized functional components; which leads to the controlled environment of constructed wetlands, such a treatment that can work in a reliable and reproducible manner (Ana Dordio, et., al., 2008). Table 2.3: Characteristics of different types of natural wetlands and their ability to retain non-point source pollutants (IETC-UNEP, 1999) Type of Wetland

Characteristics

Ability to retain non-point source pollutants

Wet meadows

Grassland with waterlogged soil; standing water for part of the year

Denitrification only in standing water; removal of nitrogen and phosphorus by harvest

Fresh water marshes

Reed-grass dominated, often with peat accumulation

High potential for denitrification, which is limited by the hydraulic conductivity

Forested wetlands

Dominated by trees, shrubs; standing water, but not always for the entire year

High potential for denitrification and accumulation of pollutants, provided that standing water is present

Salt water marshes

Herbaceous vegetation, usually with mineral soil

Medium potential for denitrification; harvest possible

Bogs

A peat-accumulating wetland with minor flows

High potential for denitrification but limited by small hydraulic conductivity

Shoreline wetlands

Littoral vegetation of significant importance for lakes and reservoirs

High potential for denitrification and accumulation of pollutants, but limited coverage

Although; natural wetlands are capable of providing high levels of wastewater treatment, natural wetlands are preserved areas, thus banned wastewater implementation in many countries. (Hammer and Bastian, 1989), an increasing attention in the use of man-made wetlands for wastewater treatment is promoted as there is anxiety over potential deleterious impacts of wastewaters pathogens and toxic compounds with long term wetlands degradation (USEPA and USDA-NRCS, 1995).

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Whilst the discharge of wastewater into naturally originated wetlands is banned globally, the understanding of the processes of pollutants assimilation and removal, led to suggest the design of new natural water treatment systems (Vymazal et al., 1998a). Proposing the use of constructed wetland systems for wastewater treatment is achieved by using the knowledge with the assimilative capacity of natural wetlands.

2-4-2: Constructed Wetland Systems (CWSʼs) The need for creation of artificial wetlands has been generated due to recent anxieties over wetlands losses, which are meant to imitate the roles and significances of naturally originated wetlands. CWS are artificially built-up of emergent, saturated substrates and/or submerging flora, fauna, and water that emulate natural wetlands for human usage and interests (Hammer and Bastian, 1989). CWS which constructed as specified by particular specified definitions (Sundaravadivel and Vigneswaran, 2001); to recompense for naturally originated wetlands; which were altered for agriculture and urban uses, and hence for flood control facility (Constructed flood control wetland); conserve native plant and animal kingdom (Constructed habitat wetlands); water quality improvement and wastewater treatment system (Constructed treatment wetlands; and production of food and fiber (Constructed aquaculture wetlands). CWS have acceptable limits of capabilities; including applications for domestic wastewater and urban storm-water, drainage wastewaters of agriculture, etc. and for tertiary treated municipal wastewater to be

16

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refined, and returned to river water and other water resources (Coveney et al., 2002).

2-4-2-1: Advantages and Disadvantages of Constructed Wetland Systems. Advantages:CWSʼs have many advantages when compared to more traditional technologies of wastewater treatment (Haberl et al., 2003) such as: • often be less costly to construct than conventional treatment, low expenses in operation and maintenance; • constructed, operated simply, involve natural processes; • able to tolerate fluctuations in flow with high buffering capacity; • able to treat wastewaters with various pollutants; • produce minimal of excess sludge; • water reuse and recycling are facilitated; • provide habitat for many wetland organisms; • provide recreational and educational opportunities; • monitoring pollutant accumulation to preserve ecological health of the system.

Disadvantages:Also; CWSʼs are restricted to be used by some limitations: • generally require large land area for efficient treatment; • may be relatively slow to provide treatment, require long period to achieve optimal treatment efficiencies; • reduced efficiencies in colder seasons due to less rhythmic performance than in conventional treatment; 17

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• vulnerable to storm, wind, and floods; • to tolerate water withdrawals its require a base flow of water; • may prepare breeding conditions for mosquitoes and pests; • the biological components are more vulnerable to be affected by pollutants toxicity.

2-4-2-2: Types of Constructed Wetland Systems CWSʼs principal categorization is based upon the flow type according to the substrate bed; common types of CWS are: • Free water surface (FWS) wetlands (also called surface flow (SF) wetlands or aerobic wetlands). FWS Proximally identify the appearance of natural wetlands due to the presence of macrophytes of free floating type or rooted on the bottom soil layer of wetland, with water flows horizontally through, and above the substrate (Figures (2.1A, B & C)). The upper water layer is aerobic; but the deeper water layer and the substrate are commonly anaerobic (USEPA and USDA-NRCS, 1995). • Subsurface flow (SSF) wetlands (also known as vegetated submerged bed (VSB) systems). SSF do not match natural wetlands due to the absence of stagnant water; they are erected with a substrate (usually sand or soil, gravel, small rocks,); implanted with macrophytes, and the wastewater being out from under the lower region of the supporting material surface in touch with the roots of the plants (USEPA and USDA-NRCS, 1995). Implanted SSF systems with emergent aquatic plants can be sub-

18

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categorized in accordance with their modes of flow of water (Figure 2.1D&E). (Cooper et al., 1996): a- Horizontal SSF systems b- Vertical SSF systems c- Hybrid systems Generally, FWS wetlands require extra land to accomplish the adequate pollution removal as SSF wetlands, but FWS are easier and less costly to plan and construct (USEPA and USDA-NRCS, 1995).

Figure 2.1: Different types of CWS (A, FWS with free-floating plants; B, FWS with submerged plants; C, FWS with emerged plants; D, Horizontal SSF; E, Vertical SSF)(USEPA and USDA-NRCS, 1995).

2-4-2-3: Constructed Wetland Systems Components Constructed Wetland Systems are well engineered wastewater treatment systems that are planned and erected to exploit the natural systems that take place in natural wetlands. A constructed wetland consists of a well-designed pond that consists of main elements which are soils or other selected substrate, water column and wetland vegetation. Other significant components that support the wastewater treatment are 19

Chapter Two

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such as the naturally developed microorganisms; their coordinated performance (substrate, macrophytes and microbial population) through various processes (chemical, physical and biological), is reliable for wastewaters purification accomplished in a CWS. The concerted action of all these components (substrate, macrophytes and microbial population adapted to the wastewater toxicity) through a variety of chemical, physical and biological processes, is responsible for the depuration of wastewaters achieved in a CWS (Figure2.2). (Ana Dordio, et. al., 2008).

Figure 2.2: Summary of the major physical, chemical and biological processes controlling pollutant removal in CWS (Ana Dordio, et. al., 2008).

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2-4-3: Mechanisms of Pollutants Removal by Constructed Wetland Systems Wetlands are effective in treating organic matter, nutrients and suspended solids; and also to reduce trace organic pollutants, metals, and pathogens. An overview of the major operations in the wetland environment for pollutant removal mechanisms is shown in Figure (2.2) & Table (2.4) (Ana Dordio, et. al., 2008).

2-4-3-1: Suspended Solids Removal Municipal and part of industrial wastewaters commonly consist of considerable amounts of suspended solids, which usually will be very efficiently addressed in a CWS by settling, usually with more than 90% efficiencies (Mantovi et al., 2003). The removal of settleable suspended solids in a CWS will be done by sedimentation and filtration, which are the major responsible mechanisms, while at least partially, by bacterial growth and collisions with the adsorption to other solids; the nonsettling/colloidal solids will be removed (Vymazal et al., 1998b). Mostly; CWS erected with a sedimentation tank installed upstream of the system to enhance larger suspended solids removal and diminishing the chance to clog wetland cells, and diluting the raw influent if it is considered too strong; which will contribute by a considerable share in the organic matter removal of pathogens and nutrients (primarily N and P). In some situations; the suspended solids high removal efficiencies in SSF systems have also shown not to be so much responsive to seasonal fluctuations (Merlin et al., 2002).

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Table 2.4: Pollutant removal mechanisms (Sundaravadivel and Vigneswaran, 2001) Wastewater pollutant Total Suspended Solids (TSS) Soluble Biodegradable Organic Matter (measured as BOD) Nutrients: Nitrogen (N)

Phosphorus (P)

Metals

Pathogens (microbial population)

Organic xenobiotics

Removal mechanism • Sedimentation • Microbial degradation (aerobic, anoxic and anaerobic • Adsorption • Plant uptake Odor and insects may be a problem due to the free water • surface • Ammonification (mineralization) • Nitrification/ denitrification • Nitrate-ammonification • Plant/microbial uptake • Media adsorption/ion exchange • Ammonia volatilization • ANAMMOX • Media adsorption • Plant and microbial uptake • Sedimentation • Precipitation • Adsorption and cation exchange • Complexation • Precipitation/co-precipitation • Oxidation and hydrolysis • Plant uptake • Microbial oxidation/reduction (microbial-mediated processes) • Sedimentation and filtration • Sedimentation • Filtration • Natural die-off • Predation • UV irradiation • Excretion of antibiotics form roots by roots of macrophytes • Adsorption • Sedimentation • Volatilization • Biodegradation • Adsorption • Plant uptake • Photolysis • Chemical reactions • Sedimentation

22

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2-4-3-2: Soluble Organic Matter In the urbanized territories; factories, houses and roads run-off lead to harsh pollution mostly in rainy weathers after dry weather periods. Industrial effluents are an additional origin of severe organic contamination such as in tanneries and abattoirs, food and beer industries, dairies, textile and paper mills and farms; which may be routed via the wastewater treatment works or they may be released, with or without treatment, directly into a waterway (Ana Dordio, et. al., 2008). The microorganism’s microbial process decomposes organic matter; in which simple inorganic molecules result from the breakdown of the more complex organic particles, which consumes considerable amounts of dissolved oxygen (Mason, 2002). One of the major problems caused by effluents with high BOD loads occurs as organic matter is gradually decomposed by the microorganisms in a much similar way to the processes occurring in biological treatment processes in wastewater treatment plants. This microbial process, in which the more complex organic molecules are broken down into simple inorganic molecules, involves a considerable consumption of dissolved oxygen. When high loads of organic pollution are present, oxygen may be used at a higher rate than it can be replenished from the atmosphere or the photosynthetic activity of aquatic plants, thus causing its depletion with severe consequences for the water stream biota, including reduced fitness and, in extreme cases, asphyxiation (Mason, 2002). The sedimentation of organic waste at the bottom of streams may also alter its characteristics, with potential harmful effects to its biota Soluble degradable organic matter in wastewater is removed mainly through 23

Chapter Two

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microbial degradation whereas uptake of degradable organic matter by macrophytes is negligible compared to biological degradation (Metcalf and Eddy, 1991). The microorganisms responsible for the degradation are generally associated with slimes or films that develop on the surfaces of substrate particles, vegetation and litter (Metcalf and Eddy, 1991). In CWS; the removal efficiency of soluble organics is generally high, usually exceeding 80%, with variable efficiency according to the CWS type, because of their designs and operational parameters (Vymazal, 2005c); Seasonal variations in BOD removal efficiency by CWS in the presence of various macrophytes species (Duckweed, Cat tail/Reed-mace, Water lily, Water primrose, Reeds and papyrus, Seaweeds, etc.) have been reported by several investigators, with consistent treatment deterioration being observed in late winter months (Kuehn and Moore, 1995).

2-4-3-3: Nutrients Removal The

considerable

origins

of

nutrients

contamination

in

watercourses generated in the urbanized areas from domestic, industrial effluents, storm drainage and agriculture; often, nitrogen and phosphorus are the controlling parameters in a macrophyte system, and eutrophication in water bodies or other unwanted changes in the ecological system may be due to the addition of excess nutrients (Mason, 2002).

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A. Nitrogen Removal in Constructed Wetland Systems Nitrogen forms are the major contaminants in most wastewaters which is biochemically inter-convertible, including nitrogen gas (N2). Nitrogen organic and inorganic forms exist in dissolved forms; whilst inorganic forms exist as minute separate particles. Particulate forms removal is achieved by settling and burial, while the dissolved forms are removed and regulated by different effective biogeochemical reactions that occur in the substrate and water column (Figure (2.3)); which their biological and physicochemical characteristics and vegetation type affect the relative rates of these processes.

Figure 2.3: Nitrogen transformation/removal mechanisms in CWS (Cooper et. al.996)).

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The major transformations of nitrogen; which nitrogen will not be liberated from CWS are summarized in Table (2.5). Table 2.5: The major nitrogen conservative transformations and retention processes in CWS (Vymazal (2007)). Process Ammonification (mineralization) Nitrification Nitrate-ammonification Plant/microbial uptake (assimilation) Ammonia adsorption Organic nitrogen burial

The

linked

Transformation Organic-N → ammonia-N Ammonia-N → nitrite-N → nitrate-N Nitrate-N → ammonia-N Ammonia-N, nitrite-N, nitrate-N → organic-N

nitrification-denitrification

process

and

ammonia

volatilization with gaseous nitrogen expulsion lead to the most effective nitrogen removal. The volatilization process high efficiency in this type of systems major factor is the presence of a free water surface in FWF systems.

Nitrification – is usually defined as the biological oxidation of ammonium to nitrate with nitrite as an intermediate in the reaction sequence. Nitrification is performed primarily by chemoautotrophic bacteria, which derive energy from the oxidation of ammonia and/or nitrite and carbon dioxide is used as a carbon source for synthesis of new cells. The process consists of two main sequential steps (Ana Dordio et al., 2008): NH4+1+ 3/2 O2 → NO-2 + 2 H + H2O

+

……………………..(2.1)

NO-2 + 1/2 O2 → NO-3

……………………..(2.2)

NH4+1+ 2 O2 → NO-3+ 2 H+ + H2O

26

……………………..(2.3)

Chapter Two

Theory & Literature Review

The first step, the oxidation of ammonium to nitrite, is executed by strictly chemo-lithotrophic (strictly aerobic) bacteria which are entirely dependent on the oxidation of ammonia for the generation of energy for growth. In soil, species belonging to the genera Nitrosospira, Nitrosovibrio, Nitrosolobus, Nitrosococcus and Nitrosomonas have been identified (Vymazal, 2007). The second step in the process of nitrification, the oxidation of nitrite to nitrate, is performed by facultative chemo-lithotrophic bacteria, Nitrobacter, which can also use organic compounds, in addition to nitrite, for the generation of energy for growth (Vymazal, 2007). Nitrification rates in wetlands were reported to be in the range of (0.01– 2.15 g N/ m2.d) with the mean value of (0.048 g N/ m2.d) (Tanner et al., 2002). Nitrification is influenced by concentrations of ammonium-N, BOD concentration, temperature, pH value, water alkalinity, inorganic C source, moisture, microbial population, dissolved oxygen and toxic compounds potential. Nitrification is strictly an aerobic process in which the end product is nitrate; this process is limited when anaerobic conditions prevail (Ana Dordio et al., 2008).

Denitrification – is a bacterial facilitated anoxic process of nitrate reduction that may ultimately

produce

molecular

nitrogen

(N2)

through a series of intermediate gaseous nitrogen oxide products. This respiratory process reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter (Brady and Weil, 2002).

27

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The organisms that carry out this process are commonly present in large numbers and are mostly facultative anaerobic bacteria in genera, such as Pseudomonas, Bacillus, Micrococcus and Achromobacter.

These

denitrifying bacteria are chemo-heterotrophs, which obtain their energy and carbon from the oxidation of organic compounds. Other organisms are autotrophs, such as Thiobacillus denitrificans, which obtain their energy from the oxidation of sulfide. The exact mechanisms vary depending on the conditions and organism involved (Brady and Weil, 2002). It is generally agreed that the actual sequence of biochemical changes from nitrate to elemental gaseous nitrogen is (Vymazal, 2007): 2 NO-3 => 2 NO-2 => 2 NO => N2O => N2 ………………………. (2.4) Environmental factors known to influence denitrification rates include the absence of O2, redox potential, substrate moisture, temperature, pH value, presence of denitrifiers, substrate type, organic matter, nitrate concentration and the presence of overlying water (Vymazal, 2007). The estimation of denitrification rates in CWS varies widely in the literature between 0.003 and 1.02 g N/ m2.d (Vymazal, 2007). Denitrification

is

the

predominant

microbial

process

that

modifies the chemical composition of nitrogen in a wetland system and the major process whereby elemental nitrogen is returned to the atmosphere (Ana Dordio, et. al., 2008).

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B. Phosphorus Removal in Constructed Wetland Systems In Constructed Wetland Systems; water courses eutrophication is also caused by the availability of phosphorus in immoderate quantities as another nutrient and its tendency of removal will not be as high as nitrogen removal due to there is no direct metabolic route available to remove it biologically. Wetlands removal of phosphorus is accomplished by a various kinds of physical, chemical and biological processes. Organic and inorganic phosphorus are typical forms of phosphorus ideally exist in wastewaters, which often present as orthophosphate but also as polyphosphates (Cooper et. al., 1996). Organic phosphorus undergoes enzyme hydrolysis, so it is not readily bioavailable. In wetlands; cycling relationship of organic and inorganic phosphorus is due to the free orthophosphate, which is exclusively phosphorus major form that is thought to be exhausted straightway by algae and aquatic plants (Vymazal, 2007). The phosphorus availability from organic phosphorus is affected by the rate of mineralization and biodegradability which rises as a consequence of the nutrient loading. The CWS generally have a greater potential to remove nitrogen than phosphorus because nitrogen can be converted to nitrogen gas and be emitted to the atmosphere as a consequence of the coupled nitrification-denitrification process. The phosphorus only sustainable removal routine is plant uptake and later harvesting; where in FWS systems with free-floating macrophytes will be a particularly significant pathway of phosphorus removal (Vymazal, 2007).

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2-4-3-4: Pathogen Removal Waterborne diseases are the major danger in many worlds’ regions. Pathogenic bacteria, viruses, protozoa pathogens and helminth are the important organisms from a public health standpoint (Rivera et al., 1995). In rivers; the main origin of faecal pathogenic microorganisms contamination come from wastewater discharges, and which pose a public health threat (Sleytr et al., 2007). The treatment of wastewater pathogens in CWS is essentially a two stage process. Most pathogens are particles ranging from very small viruses to the large eggs and cysts of helminths. One of the stages of pathogen treatment is particle removal. This occurs via the same processes as for removal of suspended solids, namely sedimentation, filtration, surface adhesion and aggregation. A series of other processes are important in influencing the viability of pathogens as infectious agents which may occur in a stage either before or after pathogenic particles removal. The major mechanisms in this stage are the hostility of the environmental conditions (temperature, pH, dissolved oxygen concentration, redox potential, salinity, turbidity), predation by nematodes, protists and zooplankton and infection by other organisms, antibiosis, exposure to UV radiation and natural die-off (Ottova et al., 1997). The indicator microorganisms are completely inspected such as coliforms and enterococci regarding CWS removal efficiency especially of microorganisms’ removal (Perkins & Hunter, 2000; Langergraber & Haberl, 2001; Hench et al., 2003).

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In CWS; the removal efficiency of faecal bacteria is generally reported to be high, commonly exceeds 85%, and is commonly lower for faecal streptococci and comparatively more for faecal coliforms (Vymazal, 2005b). Treatment efficiencies rely upon many design and operational factors among them; CWS type, temperature, hydraulic regime, hydraulic retention time, mass and hydraulic loading rate, substrate, and type of vegetation.

2-4-3-5: Metals Removal Human activities are in charge of a considerable raise in metals concentration up to a level where they begin to set an environmental impact and public health concern; also they are naturally present in the environment. Rather than the naturally originated, pollution by metals is mostly related with such activities as urbanization, soil disturbance, mining, industrial production, fossil fuels burning and use of manufactured products such as paints, pesticides, etc. In fact; some metals are indispensable to some biological processes in low concentrations (e.g. chromium, zinc, copper, and nickel); at low levels copper is a plants micronutrient which is indispensable to the photosynthetic electron transport system, while it will be considered as an effective herbicide at higher levels. Some chemical metal forms are also considered as a great toxicant such as inorganic mercury which is less toxic than the methylated form of mercury (Mitra, 1986). Metals toxic effects will lead to chronic effects as a consequence of a long-term exposure. Cancer, damage to the immune systems, disruption of the endocrine system, disorders of the nervous system, liver and

31

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kidney damage, and birth defects are examples of metals chronic health effects. The main mechanisms that may provide routes for metal elimination from the wastewater are illustrated in Figure (2.4) (Cooper et al. (1996)). In general; the substrate is believed to be an environmental installed manmade metals sink. The capacity of metal detention can be determined by a number of physical and chemical processes; a major metals fraction will immediately be adsorbed onto the solid phase, while a slight portion of the metals still be dissolved and will be available to uptake by the plant (Ana Dordio, et. al., 2008).

Figure 2.4: Metal removal mechanisms in CWS (Cooper et al. (1996)). 32

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A. Physical Removal Processes Sedimentation – is one of the heavy metals removal major processes in wastewater in both natural wetlands and CWSs (Kadlec and Knight, 1996; Hammer, 1997; ITRC, 2003), where other mechanisms such as precipitation/co-precipitation and flocculation will be preceded by sedimentation, and agglomeration of heavy metals into particles large enough to settle down (Walker and Hurl, 2002). As a consequence removing and trapping heavy metals from wastewater into wetland sediments, thus the aquatic ecosystem will be retained (Sheoran and Sheoran, 2006). Wetland length and particle settling velocity will efficiently enhance the sedimentation.

B. Chemical Removal Processes A wide range of chemical processes are involved in the removal of heavy metals in the wetlands: Sorption –is one of the wetlands extremely significant removal processes which leads to ion transfer from water to the soil/sediments; which some types of pollutants will be retained in a short-term detention or immobilized in a long-term immobilization (Sheoran and Sheoran, 2006). Either by chemisorption or cation exchange; heavy metals in sediments will be adsorbed. Previously in the process; other small cations (such as, K+, NH4+, Na+, etc.) will substitute the metal cation with in their locations in the clays mineral structures and groups of humic acids negatively charged (Sheoran and Sheoran, 2006). The adsorption strength by non-specific adsorption or cation exchange relies on the medium physical and chemical parameters (e.g. pH, metals

33

Chapter Two

Theory & Literature Review

properties concerned and other soluble ligands concentration and properties, and metals) (Sheoran and Sheoran, 2006). Mostly in general; copper and lead tend to be adsorbed substantially, while zinc, cadmium, and nickel are commonly grasped weakly which reveals that probably these metals are furthermore to be unstable and bioavailable (Sheoran and Sheoran, 2006). Metals adsorption differs with the outflow water pH fluctuations (Machemer and Wildeman, 1992). Oxidation and hydrolysis of metals –Metal oxidation states apparently will have impact on the metal chemical aqua behavior. Particularly, a metal may be ideally hydrolyzed to form hydroxides or insoluble oxides under some states of oxidation; while it can be extra-soluble in other states of oxidation. For example, insoluble compounds which formed from iron, aluminum and manganese by hydrolysis lead to form sorts of hydroxides, oxides, and oxy-hydroxides. Redox potential, the presence of various anions; and pH have effect on iron removal (Sheoran and Sheoran, 2006). Precipitation and co-precipitation – is a wetland major process of sediments heavy metals removal. Heavy metals bioavailability for many aquatic ecosystems is restricted by the insoluble metal precipitates formation. Precipitation relies upon metal ions concentration and relevant anions, metal involved solubility product (Ks), and pH of the wetland (Brady and Weil, 2002). Secondary minerals, such as nickel, copper, manganese, Fe oxides and cobalt will commonly co-precipitate heavy metals; while manganese oxides will co-precipitate nickel and iron (Stumm and Morgan, 1981). The precipitation of carbonate is particularly influential for nickel and

34

Chapter Two

Theory & Literature Review

lead removals (Lin, 1995), but considerable amounts of manganese and copper carbonates accumulated in some natural wetlands were reported (Sobolewski, 1999). Appropriate substrate may raise sulfate reducing bacteria growth in anaerobic conditions. Hydrogen sulfide will be generated by these bacteria, which most heavy metals will react with it resulting to form highly insoluble sulfides of metal (Stumm and Morgan, 1981). Metals such as arsenic, zinc, lead, copper and cadmium may form highly insoluble sulfides which will be in contact with H2S of low concentrations (ITRC, 2003).

C. Biological Removal Processes The most important pathway for heavy metal removal in the wetlands is the biological removal; where it's probably that plant uptake will play the major distinguished role, whilst wetlands sediments form major heavy metals sinks (Gray et al., 2000), heavy metals will be absorbed by aquatic plants roots and shoots also. The aquatic plants use processes which are not inevitably the one for different metals and various species. Metals phyto-extraction from sediments as well as water by submerged rooted plants may have high potentials, while metals can be extracted only by floating plants from water (Sriyaraj and Shutes, 2001). Metal removal rate by plants differs excessively, which depends on the rate of plant growth and heavy metals concentration in plant tissue. Metal uptake rate per wetland unit area is predominantly much elevated for herbaceous plants, or macrophytes such as duckweed (Lemna minor), (Zayed et al., 1998; Stoltz & Greger, 2002; Sheoran and Sheoran, 2006). 35

Chapter Two

Theory & Literature Review

Duckweed body mass can tolerate high concentrations of several metals without exhibiting adverse growth impacts (Sheoran and Sheoran, 2006). An understanding of the biological processes controlling heavy metals removal in wetlands will substantially increase the probability of success of treatment wetland applications. Furthermore, a working knowledge of biogeochemical cycling, the movement and transformation of nutrients, metals and organic compounds among the biotic (living) and abiotic (non-living) components of the ecosystem, can provide valuable insight into overall wetland functions and structure. This level of understanding is useful for evaluating the performance of heavy metal removal by constructed wetlands and for assessing the functional integrity of human-impacted, restored and mitigation wetlands (Ana Dordio, et. al., 2008).

D. Microbial Activity in Constructed Wetland Systems Microorganism uptake heavy metals actively (bioaccumulation) and/or passively (adsorption). The microbial cell walls, which mainly consist of polysaccharides, lipids and proteins, offer many functional groups that can bind heavy metal ions, and these include carboxylate, hydroxyl, amino and phosphate groups. Among various microorganismmediated methods, the biosorption process seems to be more feasible for large scale application compared to the bioaccumulation process, because microorganisms will require addition of nutrients for their active uptake of heavy metals, which increases the biological oxygen demand or chemical oxygen demand in the waste. Further, it is very difficult to maintain a healthy population of microorganisms due to heavy metal toxicity and other environmental factors. Fungi of the genera Penicillium, 36

Chapter Two

Theory & Literature Review

Aspergillus and Rhizopus have been studied extensively as potential microbial agents for the removal of heavy metals from aqueous solutions. The genetic diversity of endophytic bacteria had been evaluated from the copper-tolerant species of Elshotzia apliendens and Commelina communis, reporting increased dry weights of roots and aboveground tissues compared to uninoculated plants. Further, they also reported significant amounts of (ranging from 63% to 125%) Cu content in inoculated plants compared to un-inoculated ones (Dixit et al., 2015). Microorganisms also provide a measurable amount of heavy metal uptake and storage; it is their metabolic processes that play the most significant role in removal of heavy metals (Sheoran and Sheoran, 2006). This provides an important biological mechanism for removal of a wide variety of heavy metals, including those found in municipal and industrial wastewater. Microbial activity in wetlands reduces metals to non-mobile forms (Sheoran and Sheoran, 2006). Reduction of metals to non-mobile forms by microbial activity in wetlands

has

been reported by Sobolewski (1999). Metals like

chromium and uranium become immobilized when reduced through processes biologically catalyzed by microorganisms (Fude et al., 1994). Root growth affects the properties of the rhizospheric zone and stimulates the growth of the microbial consortium, for which researches had shown that the population of microorganisms in the rhizosphere is several orders of magnitude greater than in the surrounding environment. In turn, rhizospheric microorganisms may interact symbiotically with roots to enhance the potential for metal uptake. In addition, some microorganisms may excrete organic compounds which increase bioavailability, and

37

Chapter Two

Theory & Literature Review

facilitate root absorption of essential metals, such as Fe and Mn as well as nonessential metals, such as Cd. Microorganisms can also directly influence metal solubility by altering their chemical properties. For example, a strain of Pseudomonas maltophilia was shown to reduce the mobile and toxic Cr+6 to nontoxic and immobile Cr+3, and also to minimize environmental mobility of other toxic ions such as Hg +2, Pb+2, and Cd+2. In addition, it has been estimated that microbial reduction of Hg+2 generates a significant fraction of global atmospheric HgO emissions (Lasat, 2000). Illustrative results about the removal efficiencies of several heavy metals obtained in various CWS are shown in Table (2.6). Table 2.6: Heavy metals removal efficiencies in different types of CWS (Ana Dordio, et. al., 2008). Pollutant

Type of CWS

Reduction rate

References

Lead

CWS (small-scale plot)

≥ 90%

(Liu et al., 2007)

HSSF

≥ 70%

(Mantovi et al., 2003)

FWS FWS Grenhouse experiment HSSF HSSF VSSF HSSF VSSF FWS HSSF FWS FWS Grenhouse experiment HSSF

67% 48 % > 43 % 59 % 49 % ≥ 80% 79 % ≥ 95 % 95 % 93% 58 % 86 % 100% 52%

(Maine et al., 2006) (Maine et al., 2007) (Hadad et al., 2007) (Mantovi et al., 2003) (Lesage et al., 2007) (Lee and Scholz, 2007) (Mantovi et al., 2003) (Lee and Scholz, 2007) (Maine et al., 2006) (Lesage et al., 2007) (Maine et al., 2007) (Maine et al., 2006) (Hadad et al., 2007) (Mantovi et al., 2003)

CWS (small-scale plot) Grenhouse experiment HSSF CWS (small-scale plot) HSSF

≥ 90% ≥ 35% 86 % ≥ 90% 24 %

(Liu et al., 2007) (Hadad et al., 2007) (Mantovi et al., 2003) (Liu et al., 2007) (Mantovi et al., 2003)

Nickel

Copper Iron Aluminum Chromium

Zinc

Cadmium

38

Chapter Two

Theory & Literature Review

Some variation was presented in removal efficiencies from about low values (~ 25%) to almost full removal of some metals. Usually the efficiencies will rely upon different parameters such as the metal loads of the influent, vegetation type used, the type of CWS and environmental conditions; but efficiencies still be high (> 70%). The removal percentage of metals by plant uptake will entail a frequent harvesting of the plant. The plant biomass harvested amount with high concentrations of metal inputs in the designed CWS, should thereafter be disposed of as hazardous waste and draw a suitable treatment (Ana Dordio, et. al., 2008).

2-5: Aquatic Plants The search for new technologies involving the removal of toxic metals from wastewaters has directed attention to Aquatic plants have also proven usefulness

aquatic

plants.

in removing organic

wastes from water. Some examples are cattails, calla lilies, arrowhead, ginger lilies, pickerelweed, water hyacinths, water lettuce, water spinach, duckweed, aquatic mosses and liverworts. Some aquatic plants roles are presented in Table (2.7) (Best, et. al. (1999)). These systems can be used for schools, motels, hospitals, office complexes, mobile home parks, etc. The vegetation resulting from wetland systems can be utilized as compost or as animal feed supplements, or digested to produce methane. The aquatic plants usually work on the principle of biosorption, based on metal binding capacities of various biological matters. Biosorption can be defined as the ability of biological matters to accumulate heavy metals from wastewater through metabolically mediated or physicochemical pathways of uptake. The major advantages of biosorption over 39

Chapter Two

Theory & Literature Review

conventional treatment methods include low cost, high efficiency, minimization

of

chemical and /or biological sludge, no additional

nutrient requirement, and regeneration of biosorbent and possibility of metal recovery (Ankita et. al., 2011). Duckweed has been adopted worldwide as an effective and low cost system for the treatment of domestic wastewater (Alaerts et al., 1996), which is employed as a biosorbent and has been considered a better alternative than any other aquatic plant due to its high tolerance to coldness than water hyacinth, more easily harvested than algae, capable of rapid growth (0.1 to 0.5 g. g-1 .day-1) and small size of plant (Ankita et. al., 2011). Table (2.7) presents the different roles of aquatic plants used in wastewater treatment. Table 2.7: Different roles of aquatic plants used in wastewater treatment CWS (Ana Dordio, et. al., 2008). Aquatic Plants Typha or Cattail or Bullrush Duckweed Water hyacinth Drumsticks Hydrilla

Use in Treatment Arsenic and dirt Nitrates, Phosphates, toxins, Pb, Cu, U, Ni, Fe, K, removes algae as well, mosquito breeding, odor control, prevents evaporation of water Removes Cd, Cr, Co, Ni, Pb, Hg, Cyanide, enhances nitrates Extract from the seeds is used as a flocculants in a low-cost form of water treatment, bacterial reduction Resistant to high salinity in water… not much effective in treating waste water

Jatropha

Land reclamation and bio fuel production

Bamboo

Bamboo filter for water desalination

Calla lily

Nitrate, ammonium, total Kjeldahl nitrogen (TKN), dissolved oxygen (DO), redox potential (Eh), hydrogen potential (pH), and COD, (research being done on surfactant removal)

40

Chapter Two

Theory & Literature Review

2-6: Using Duckweed as A Biosorbent Nutrient

removal

from

wastewater prevents eutrophication

from occurring downstream where the wastewater is discharged into water bodies such as rivers and reservoirs.

One nutrient removal

system that has been researched extensively over the past 60 years utilizes duckweed plants (Lemnaceae). Duckweed (botanically known as Lemnaceae) is a stem less, aquatic flowering plant. Duckweed is a small and free floating and grows on the surface of still or slow moving water in carpet-like groups. Duckweed is a worldwide spreading plant as shown in Figure (2.5) (Ankita et. al., 2011). Common Duckweeds; especially the genera Lemna minor are Stem-less and seed bearing plant; has 1 to 3 leaves measuring (1/16) to (1/8) inches in length (Photo (2.1)); with 1 to 6 roots that may grow from each plant. Duckweed systems depend on three basic principles: nutrient uptake, harvesting, and solids management (Best, et. al., 1999). Duckweed grows naturally in dense colonies and almost in every region with a growing season of at least five months. Duckweed is a monocot; floats on water, having one of the fastest growth rates of any other macrophyte. Duckweed is the common name for the Lemnaceae family of plants, with species like Lemna minor, Lemna Gibba, Spirodela Polyrhizza, and Wolffia (genus name) (Best, et. al., 1999). Generally reproduction

rate

of

duckweed

is extraordinary as they are able to cover 1 acre in just 45 days if unrestrained (Birkett et. al., 2003).

41

Chapter Two

Theory & Literature Review

Figure 2.5: Lemna minor spreading in worldwide (Landolt, E. & Kandeler, R. 1987).

Photo 2.1: Three duckweed genera together: Spirodela (largest), Lemna (mid-sized) and Wolffia (smallest), scale in millimeters (Lemna Corp. 1994).

42

Chapter Two

Theory & Literature Review

Water contained in the fresh duckweed fronds is about 92% to 94%. A wild colony of duckweed growing on poor-nutrient water have a solid fraction typically ranges from 15 to 25 % of protein and from 15 to 30 % of fiber. Depending on the species involved, duckweed will have a protein content of 35 to 45 % and a fiber content of 5 to 15 %; when it grows under ideal conditions and harvested regularly. The profitable characteristics of duckweed are high productivity, high protein content, wide geographic distribution and control of negative

impacts

from

conventional

wastewater treatment ponds (Braeckevelt, et. al., 2007).

2-7: Duckweed for Industrial Wastewater Treatment There is hardly any research pertaining to industrial wastewater treatment for specific industries (Gijzen and Khondker 1997). A high BOD and nutrient load effluents may necessitate suitable primary treatment to decrease the organic load. The duckweed growth upper BOD limit of tolerance is anonymous. Niklas (1995), reported that Lemna gibba grow on waters with a COD of over 500 mg/L. However, it is essential to dilute primary effluent assure that BOD5 at the head of a plug-flow treatment system comprised of a duckweed is retained below 80 mg/L (Skillicorn et al., 1993). A high BOD load of industrial wastewaters with low nutrient content; are less suitable to favor duckweed growth (Iqbal, 1999). Initially, in order to separate some of the settleable solids, floating material, and settleable fraction of pathogens, it is essential to use raw wastewater primary treatment. In the case of plug-flow system; it is significant to prevent degradation of initial treatment pathways by 43

Chapter Two

Theory & Literature Review

implementing an efficient sedimentation. It is also important to release organically bound nitrogen and phosphorus by adequate pretreatment by microbial hydrolysis, as the availability of NH4+1 and O-PO4-3 for fast duckweed growth was suggested to be the controlling step (Alaerts et al. 1996).

2-8: Literature Review on Duckweed Performance Several researchers had been reported on duckweed efficiency in removing different wastewater pollutants, including physical parameters such as temperature, pH, EC, DO and TDS; nutrients and heavy metals. It was shown by the results that duckweed can be successfully implemented to remove wastewater pollutants. Without the addition of nutrients, almost no duckweed growth was observed on the paper mill wastewater. Duckweed growth may be restrained by high concentrations of BOD, oil, grease, and detergents. Nevertheless, toxins will settle on the sediments with the decaying plants unless that it's important to harvest the biomass at regular intervals (Mdamo, 1995). COD removal in shallow batch systems was promoted by duckweed considerably (Korner et al., 2003). The aquatic plants have the capability to accumulate necessary metals for their growth and development; among these metals are iron, manganese, zinc and copper (Kara et. al., 2003). Results from metal analysis in plant tissues revealed a high accumulation of copper and a low accumulation of nickel within the plant (for concentrations causing no growth inhibition) and a corresponding

44

Chapter Two

Theory & Literature Review

decrease of metals in the water. Lemna gibba could be a good candidate for the removal of low concentrations of copper from polluted water. The duckweed contribution for the organic matter removal is because of their capability to straight use of simple organic compounds, as well as the microbial degradation processes of organic matter (Oron et. al., (1988)). BOD removal efficiency was found to be higher in duckweed based ponds than in algae based ponds (Zimmo et. al., (2005)). Lemna minor is one of floating aquatic plants which cover the surface of the water and form an insulating layer prevent light penetration, leading to reduce water temperatures (Kara, et. al., 2003). Table (2.8) shows literature review summary. Table 2.8: Literature Review Summary Reference

Azeez M. and Sabbar A. (2012)

Mdamo, 1995

Pandey, 2001

Kara et. al., 2003

Parameter Symbol Reduction

Concentration

Notes

Cadmium

As

99.6%

----

----

Lead

Pb

98.7%

----

----

Nitrate

NO3

57.1%

----

----

COD

----

32.7%

----

----

Phosphate

PO4

30%

----

----

Suspended solids

SS

38%

----

----

Temperature

----

----

17.2˚C

----

pH

----

----

13.4

----

----

150 mg/L

----

>98%

----

COD

----

(70-80)%

----

Iron

Fe

----

----

Manganese

Mn

----

----

Zinc

Zn

----

----

Copper

Cu

----

----

BOD

45

---Duckweed growth on paper mill effluents was only observed when BOD was relatively low (150 mg/L) and nutrients were added externally. Removal was observed when 2mg/m2 of both N and P were added daily. Removal range in discharged duckweed treatment system. Aquatic plants have the capability to accumulate necessary metals for their growth and development.

Chapter Two

Theory & Literature Review

Table 2.8: literature review summary (Contd.) Reference

Parameter

Symbol

Reduction

Concentration

Notes

Copper

Cu

----

0.3 mg/L

Nickel

Ni

----

0. 5 mg/L

Copper & Nickel

Cu & Ni

----

----

Copper

Cu

----

----

Sooknah & Wilkie, 2004

Electrical conductivity

EC

70.8%

----

Culley et al., 1981

Temperature

----

----

34°C

Landolt & Kandel, 1987

Phosphorus

P

----

----

Ammonia

NH4

----

----

Phosphorus

P

----

----

Koner & Vermaat, 1998

Phosphate

PO4

52%

----

Patel & Kanungo, 2010

Nitrate

NO3

----

----

Nitrate

NO3

----

----

Ammonia

NH4

----

----

Total dissolved solids

TDS

----

2110 mg/L

Assessed Lemna gibba tolerance and phytoaccumulation ability to copper and nickel tolerated concentrations. High accumulation of copper and a low accumulation of nickel within the plant for concentrations causing no growth inhibition. Lemna gibba could be a good candidate for the removal of low concentrations of copper from polluted water. Three types of floating plants used to treat diary wastewater reduced electrical conductivity from 2510 μS/cm to 733μS/cm. Upper temperature tolerance limit for duckweed growth due to Lemna minor. Lemna sp. necessitates high phosphorus concentration to grow in water. Lemna minor monoculture systematically removed the largest quantities from storm water in 8 weeks. Lemna gibba and microorganism coexist with it reduced phosphate to 75% and plants used 52% of it for growth process. Nutrients removal experiment from domestic wastewater by Lemna gibba removed a great quantity from wastewater and coalesced it into its biomass that was attributed to plant's capacity to provide suitable conditions for nitrate reduction. Co–existence with microorganisms plays a significant role in nitrogen transformation or plants direct uptaking which use large quantities of nitrogen compounds during growth period. Total dissolved solids minimum concentration after 30 days of treatment due to plant capacity to take some organic and in organic ions, it may be absorbed high concentration of sodium ion during growth.

Khellaf & Zerdaoui ,2009

Perniel et al., 1998

Juren, K., 1999

Seidel, K., 1976

46

Chapter Two

Theory & Literature Review

Table 2.8: literature review summary (Contd.) Reference Saygideger, 1996

Parameter Symbol Reduction pH

----

Concentration In nature

3.5 - 10

Optimum

4.5 – 7.5

----

Lead

Pb

95%

----

Nickle

Ni

7%

----

Cadmium

Cd

100%

----

Iron

Fe

98%

----

Copper

Cu

74%

----

Zinc

Zn

62%

----

Mercury

Hg

53%

----

pH

----

12%

----

BOD

----

37%

----

COD

----

49%

----

Nitrate

NO3

100%

----

Phosphate

PO4

36%

----

Total dissolved solids

TDS

53%

----

Loveson, 2013

47

Notes Lemnaceae family is susceptible to survive in completely wide range of pH. Heavy metals efficiently highest reduction rates after 8 days of treatment.

Efficiently highest reduction rates after 8 days of treatment of nutrients and other factors.

Chapter Three Experimental Work

Chapter Three

Experimental Work CHAPTER THREE EXPERIMENTAL WORK

3-1: Methodology A wastewater treatment pilot plant was constructed and operated at the Sanitary Engineering Laboratory of the Building & Construction Engineering Department at University of Technology, where the duckweed plants Lemna minor were cultured and harvested. The pilot plant was set up and filled with 200Liters of industrial wastewater generated from the tanning industry and batteries plants. The reactors were stocked with Lemna minor at 1000 g fresh weight per square meter of duckweed tanks. The culture tanks were exposed to temperature range of 20-30˚C and light regime by using four standard 4-feet long 40 watts fluorescent tubes-6 inches apart for 8 hours lighting period and 16 hours of darkness (A standard 4-feet long, 40 watts fluorescent tube provides 10 lamp Watts per square foot for 8 hours lighting period and 16 hours of darkness; as experiments and tests have demonstrated that most vegetables and flowering plants need 25 to 30 fluorescent light Watts per square foot. House plants and seedlings do well with 15-20 Watts, and germinating seeds need the least 10-15 watts per square foot (McCaskey et. al., 1994)). The laboratory work extended for 120 days, including design, construction, and installation & operating of the pilot plant. Regular monitoring of the performance of duckweed was carried out with analysis of dry matter first at the beginning and last at the end of the day55; to find heavy metals (Cd, Cr, Ni, and Pb), concentrations accumulated in plant tissues (fronds). Mixed composite samples from the tanneries and batteries wastewater phase (influent and effluent) were held for pH

49

Chapter Three

Experimental Work

equalization (tanning wastewater is normally basic solution; while battery manufacturing wastewater is highly acidic) and presettling in an initial equalization tank (presettling tank) for one day then subjected to analysis of ammonia, nitrate, and phosphate concentrations and other controlling parameters (temperature, pH, EC, DO, TDS, COD and heavy metals). The analyses of these parameters were carried out at the end of each run time of 3days. Interpretation and analysis of results was carried out by using Grapher 10 software to find coefficient of correlation and coefficient of determinant respectively with best fit 2nd degree polynomial.

3-2: Design Considerations The crucial factors in the design of duckweed treatment systems are the type and quantity of wastewater to be treated (Table (3.1)); and it is necessary to ensure daily nutrient inputs and use of biomass for infrastructural requirements (Iqbal, 1999). It is suggested by Metcalf & Eddy (1991) that duckweed systems, use mainly the duckweed-based principle for wastewater treatment, can be designed as conventional stabilization ponds with the addition of a floating grid system to control the effects of wind. They can be operated as batch (stagnant ponds) or plug-flow (continuous flow) systems. It should be ensured that there is an easy access to pond surface for purposes of good operation and maintenance in site selection and design of a duckweed treatment pond system. Therefore, it is more convenient to use a narrow, channel-like pond design than wider ponds; allowing for easier access to water surface for operation and maintenance work.

50

Chapter Three

Experimental Work

Table 3.1: Different duckweed treatment systems depending on type and amount of wastewater (Iqbal, 1999).

3-3: Pond Design As aforesaid, for duckweed treatment; two basic principles for pond design and operation are used, plug-flow and batch systems. For larger wastewater flows originating from communities and (peri-) urban areas; a plug-flow design (continuous flow through) appears to be the more convenient treatment option, as it ensures a modified and more continuous distribution of the nutrients (Photo. (3.1)). Also enhanced contact surface between wastewater and floating plants is achieved in plug-flow design, herewith, diminishing short-circuiting. To assure plugflow conditions it is necessary to use a high plug-flow length to width ratio of (10:1) or more (Hammer 1990). An excellent treatment results with a length to width ratio of (38:1) was reported by Alaerts et al. (1996). 51

Chapter Three

Experimental Work

Ideal plug-flow design should include multiple wastewater inlet points with recirculation of the final effluent to ascertain optimum treatment efficiency and protein production as shown in Figure (3.1).

Photo 3.1: Duckweed-covered serpentine plug-flow lagoon in the USA; for tertiary treatment of effluent from three facultative lagoons followed by a wetland buffer. Design flow is reported at (19,000 m3/d), with peak flows reaching (38,000 m3/d). (Photograph: Lemna Corp. 1994).

Figure 3.1: Ideal plug-flow system for combined duckweed-based wastewater treatment and protein production (Hammer 1990).

52

Chapter Three

Experimental Work

Batch-operated ponds are a feasible option to postulate duckweed aquaculture in rural areas were already existing ponds can predominantly be used and, so, saving capital costs for additional earth work (Photo (3.2), Figure (3.2)).

Photo3.2: Batch-operated pond for duckweed cultivation at village level showing dense duckweed cover

and nutrient supply pour-flush latrine influent in the background

(Bangladesh) (Photograph: Lemna Corp. 1994).

Figure 3.2: Example of batch-operated pond for duckweed cultivation at village level, (100 m2 at 0.5 m depth). (a) length and, (b) width section of duckweed pond (Edwards et al. 1987). 53

Chapter Three

Experimental Work

In comparison with a continuous flow through system, duckweed growth may be enhanced near the nutrient inlet points as a result of reduced nutrient mixing and distribution. To allow for duckweed harvesting from the embankment; a narrow pond design is also preferred here. The organic, nutrient, and hydraulic loading rates, system depth and harvesting rate are the controlling parameters on the HRT. Relatively long retention times in the range of 20 to 25 days are presumed for duckweed (plug-flow) systems; in which to ensure suitable pathogen removal and treatment efficiency (Metcalf & Eddy 1991). The critical factor regarding water depth is to assure pond vertical mixing to allow the wastewater to be treated and to come into contact with the duckweed fronds. It is recommended to use an outlet structure so as to vary the operating depth (Metcalf & Eddy 1991). Pond depths range reported to be from 0.3 to 2.7 m up to even 5 m (Lemna Corp. 1994). The majority reported optimal depths ranging from 0.4 to 0.9 m, inclusion that a maximum depth of one meter is adequate for appropriate temperature buffering. Higher depths are also a reasonable choice for systems with relatively low BOD loads, a low recirculation rate and high land costs. However, for high organic loads, high recirculation rate and for regions with inexpensive land prices; shallow system depths are better convenient. For plant systems without artificial aeration; average organic loading rates expressed in terms of BOD5 should not exceed 100 to 160 kg/ha·d, so as to acquire an effluent quality of 30 mg BOD/L or less (Gijzen and Khondker 1997). At lower loading rates; odors can arise particularly where the sulphate concentration in the wastewater is greater than 50

54

Chapter Three

Experimental Work

mg/L. It appears that duckweed is less appropriate for wastewaters treatment with high BOD loads. Stabilization of the duckweed on the water surface is of utmost importance because duckweed is very liable to wind drifts and water currents. Drifts may be restrained by using floating grids in regions with moderate winds, which will split the pond surface into cells or compartments by floating bamboo. A patented UV-stable high density polyethylene grid system has been developed by Lemna Corporation. However; the costs of such a system per hectare appear to be too high for low-income countries, this firm grid system still to be resistant to environmental extremes (Prism 1990). For middle-income countries, a more robust and costly grid system may be as economical as more appropriate choice on a long term than a less expensive bamboo grid system which must be replaced frequently. The pigments will be degraded due to exposure to direct sunlight and hence also, the total nutritional value, but not the protein (Skillicorn et al., 1993). Thus, it would eliminate the ability of duckweed to remove nutrient from wastewater. The optimum solar radiation for duckweed growth is 138 Watts per square meter (12.8 Watts per square foot) at optimum temperature 26˚C (Landesman et al, 2005). Experiments and tests have demonstrated that most vegetables and flowering plants need 25 to 30 fluorescent light Watts per square foot. House plants and seedlings do well with 15-20 Watts, and germinating seeds need the least 10-15 watts per square foot (McCaskey et. al., 1994).A standard 4-feet long, 40 watts fluorescent tube provides 10 lamp Watts per square foot for 8 hours lighting period and 16 hours of darkness (McCaskey et. al., 1994).

55

Chapter Three

Experimental Work

3-4: Similarity Laws Results were obtained from hydraulic scale model tests usually, scaled up to actual prototype by the use of similarity laws developed from principles of dynamic similitude. The relationship most commonly used is expressed as dimensionless parameters, which by their numerical values characterize the type of the flow under consideration (Hurbert, 1974). The dimensionless parameters most commonly used in hydraulic experimentation are Froude number, Reynolds number, and Weber number. These parameters are derived from consideration of gravity forces, viscosity and surface tension forces, in conjunction with the force of inertia. Froude’s number law is written as: (Kawamura, 1981). Fr = v / (L*g) 0.5………… (3-1) Where: v: system velocity, (m/s) L: system main linear dimension, (m) g: acceleration due to gravity, (m/s2) The law expresses the condition of gravity and inertia forces, as Froude number is the same for both model and prototype and the ratio of gravity forces to inertia forces is the same, and the paths of flow are similar (Kawamura, 1981).The relationship between hydraulic scale model and prototype (basic model scale parameters that should be kept constant are shown in Table (3.2)).

56

Chapter Three

Experimental Work

Table 3.2: Basic prototype to scale model relationships (Kawamura, S., 1981). Model Scale *

Parameter Length scale

1: a

Area scale

1: a2

Volume scale

1: a3

Time scale

1: a1/2

Velocity scale

1: a1/2

Discharge scale

1: a5/2

Acceleration scale

1: a0

Force scale

1: a3

Work scale

1: a4

* In this research model scale suggested to be 1:24; that’s the value of scale factor (a) will be 24

3-5: The Design Set-up of Full-Scale & Model-Scale A. Constraints: -Temperature of industrial wastewater range from 7-18 ˚C in winter and from 13-24 ˚C in summer (Suhag, et. al., 2011). • Twinter =7-18 ˚C; take Twinter =16 ˚C • Tsummer =13-24 ˚C; take Tsummer =24 ˚C - k1 values for untreated wastewater is generally about (0.12-0.46 d-1) (base; e) with typical value of 0.23 d-1 @ 20 ˚C to give BOD5 removal of about 68% of UBOD first stage demand(Metcalf & Eddy, 2004). The temperature correction is given below in equation (3-2): k1T=k1.ӨT-20………… (3-2) Where: k1T: reaction rate coefficient at a given temperature (d-1). k1: first-order reaction rate coefficient at 20˚C (d-1). Ө: temperature coefficient factor. T: temperature (oC). and the value of Ө had been found to vary from 1.056 in temperature range between 20-30˚C to 1.135 in temperature range between 4-20˚C

57

Chapter Three

Experimental Work

(Schroepfer et al., 1964). A value of Ө often quoted in the literature is 1.047(Phelps and Streeter, 1944).

B. Duckweed Plug Flow System In plug flow reactor, the velocity is constant at any given cross section and no mixing of fluid elements occur longitudinally along the flow path. Thus, all elements of fluid have the same residence time in the reactor. Since composition of the fluid varies from position to position along the reactors (Sundstrome and Klei, 1979). Fluid particles pass through the tank and are discharged in the same sequence in which they enter. This type of flow is approximated in long tanks with a high length to width ratio (Metcalf & Eddy, 2004). The conditions in a plug flow system are mainly facultative because organisms in this zone must be capable of adjusting their metabolism to the change in oxygen conditions (Peavy et. al., 1986). Although the surface cover of duckweed, hinders air interchange between the water and the atmosphere, but it is possible that duckweeds can supply oxygen to the wastewater by the transportation of atmospheric oxygen to the root zone (Dalu & Ndamba, 2002). This means that the zones that near to the duckweed mat is mainly aerobic. Stagnant conditions in the sludge along the bottom prevent oxygen transfer to that region and anaerobic conditions prevail there. Organic acids and gases, products of decomposition in the anaerobic zone, are released and became soluble food for organisms in the aerobic zone. Biological solids produced in the aerobic zone ultimately settle to the bottom where they die, providing food for the anaerobic benthic organisms (Peavy et. al., 1986). Dissolved oxygen decreases near bottom; so forming reduced products such as NH4, CH4, H2S, FeS, and N2 (Al-Khateeb, 2004). A special 58

Chapter Three

Experimental Work

relationship exists between the bacteria and algae in the aerobic zone; in which that the bacteria use oxygen as an electron acceptor to oxidize the wastewater organics to stable end products such as CO2, NO-3, and PO4-3, algae in turn use these compounds as a material source and, with sunlight as an energy source, producing oxygen as an end product (Peavy et. al., 1986) (Figure (3.3)). The process of treatment in duckweed covered sewage lagoons is a duckweed-mediated process, either directly through the nutrients recovery by plant uptake or indirectly by release of oxygen in the water column (Alaerts et al., 1996). To avoid nutrient shock loading on the duckweed, a recycled quantity of duckweed treated liquid is recommended to be mixed with the influent wastewater to lower the influent nutrient concentrations (Cheng et al., 1999).

Figure 3.3: Biological Process in Duckweed Wastewater System (Smith and Moelyowati, 2001)

Thirumurthi (1969) developed (Figure (3.4), in which the term kτ is plotted against S/So (% remaining) for dispersion factors varying from

59

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zero for an ideal plug flow reactor to infinity for a completely mixed reactor. These relationships shown in (Figure (3.4)) can be used for ponds design with the application of equation (3-2) (Peavy et. al., 1986). The design of wetlands using aquatic plants such as duckweed depends on the principle of plug flow system with dispersion factor equal to zero; to achieve 85% BOD removal (Metcalf & Eddy, 2004).

Figure (3.4): Values of kτ in the Wehner and Wilhelm equation verses percent remaining for various dispersion factors (Metcalf & Eddy, 2004).

3-6: Design Calculations of Pilot Plant By applying temperature correction given in equation (3-2): k1T = 0.23(1.047)T-20 • For winter Twinter =16 ˚C; k16˚C =0.23(1.047)16-20= 0.191 d-1 • For winter Tsummer =24 ˚C; k24˚C =0.23(1.047)24-20= 0.276 d-1

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As mentioned previously in chapter two; the design of wetlands using aquatic plants such as duckweed depends on the principle of plug flow system with dispersion factor equals to zero to achieve 85% BOD removal (Metcalf & Eddy, 2004). Referring to Figure (3.4) for plug flow system with dispersion factor of zero and 85% BOD removal (15% remaining S/So); the value of (k1t=1.8). Then, the detention time will be as follows: • twinter=(1.8/0.191)=9.4 days • tsummer=(1.8/0.276)=6.5 days Then the maximum detention time will be 9.4 days≈10 days. The industrial wastewater flow suggested will be 250m3/day; with average operating period of 8hrs to be drawn completely by 10 minutes as detailed below: A. Equalization (Pre-settling)Tank • Tanneries to produce 175m3/day (as per two batches, each batch produces 87.5m3/day/batch per 4hrs operating period). • Batteries to produce 75m3/day (as per 8hrs operating period). Then; Volume of wastewater will be: V=((250 m3/day)*(10min/hr))/(8hr/day*60min/hr)= 5.21m3 This will be the effective volume of wastewater to be withdrawn from equalization tank as it works also as lifting station with 10minutes withdrawal time, and the wastewater effective depth to be drawn will be 1.5m Then; surface area, As = (Volume/Depth) = (V/d) = (5.21/1.5)=3.47m2 Let L=2W (aspect ratio) As=L*W=2W*W=2W2 → 3.47=2W2 →W=1.32m, L=2.64m

61

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B. Clarifier Tank • To obtain efficient S.S. removal choose detention time = 10 hr. (Barnes & Wilson, 1976). V =Q*Dt = (250*10/24) = 104.2 m3. Typical depth= 3.5m (Metcalf & eddy, 2004; suggests 3-4.9m). Surface area for the clarifier = (104.2/3.5) = 29.8 m2. d = (4 *29.8/π)1/2 = 6.16m C. Connection Pipe • A P.V.C pipe shall be adopted in the design because of the light weight, strong, durability, and highly resistant to corrosion (Peavy, 1986). A 110mm (4 in.) pipe diameter will be adopted. Area = π *(0.11)2/4 = 0.0095 m2 Ʋ pipe = 250/0.0095 = 26315.8 m/d = 0.305 m/s. D. Duckweed tanks • As calculated previously; the maximum detention time is 10 days; also (Suhag, Gupta & Tiwari, 2011) suggested that the maximum detention time is 10 days. Duckweed Tank Volume = V =Q*Dt = (250m3/day*10days) = 2500 m3 (Karia & Christian, 2009) suggest using maximum facultative pond depth of 3m Surface area for duckweed tank= (2500/3) = 833.33 m2 Use two tanks in parallel; each with surface area of 416.67 m2 Let L=3W (aspect ratio) As=L*W=3W*W=3W2→ 416.67=3W2 →W=11.79m, L=35.37m Distance between each tank = 0.5 tank width (Lyerly, 2004) = 5.9m Using floating booms for duckweed shading to protect duckweed from intense sun light, high temperature, and wind (Skillicorn et al., 1993). 62

Chapter Three

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E. Pilot Plant • As mentioned previously; for model scale dimensions, Hurbert, (1974) suggested model scale factor (1:a),(1:24), by applying similarity laws, the dimensions of a pilot plant are as follows: 1-Equalization Tank: Lme=(Lpe/a)…….from Table (2.9) Lme=(2.64/24)=0.11m≈0.12m Wme=(Wpe/a)…….from Table (2.9) Wme=(1.32/24)=0.055m≈0.06m dme=(dpe/a)…….from Table (2.9) dme =(1.5/24)= 0.0625m = 6.25cm As the equalization tank works as lifting station (batch type), the suggested dimensions will be 0.5m x 0.5m x 0.6m 2-Clarifier Tank: Qm =(Qp/a2.5)…….from Table (2.9) Qm =(250/242.5)=0.0886 m3/day Vm =( Vp/a3)…….from Table (2.9) Vm =(104.2/243)=0.00754 m3 Dtm=(Dtp/a0.5)…….from Table (2.9) Dtm = (10/240.5)= 2.04 hr. ≈ 2hr. hm=(hp/a)…….from Table (2.9) hm=(3.5/24)=0.146m=14.6cm Hm=hm+Free board Hm = 14.6 cm + 3.5 cm =18.1cm≈20cm Am=(Ap/a2)…….from Table (2.9) Am =(29.8/242)= 0.052 m2 dm=(dp/a)…….from Table (2.9) dm =(6.16/24)= 0.257m = 25.7cm≈30cm 63

Chapter Three

Experimental Work

For V-notch weirs: • The available circumference of clarifier is 2.83m (2π x radius of clarifier). • The total number of 90˚ V-notches at a rate of 20cm center to center. •

Total number of notches= 5 notches/m x 2.83m= 14.15 ≈ 14 notches.

• The head over the V-notches at the peak design flow. Peak discharge per notch at peak flow=(0.0886m3/day / 14) =0.00633m3/day per notch =7.33 x 10-8 m3/sec per notch The discharge through a V-notch is ……………..(3-3) where; Q=flow per notch, m3/sec Cd=coefficient of discharge=0.6 H=head over notch, m Ө=angle of the V-notch=90˚ 7.33 x 10-8 m3/sec= (8/15) x 0.6 x (√2x9.81) x tan (90/2) x H5/2 H=0.00122m=0.12cm • Checking the depth of the notch. The total available depth of the notch is 10cm; while maximum liquid head over the notch is 0.12cm (adequate). 3-Duckweed Tanks: Vʹm =( Vʹp/a3)…….from Table (2.9) Vʹm =(833.33/243)=0.0603 m3 Dtʹm=(Dtʹp/a0.5)…….from Table (2.9) Dtʹm = (10*24/240.5)= 49 hr. = 2.04days≈2days hʹm=(hʹp/a)…….from Table (2.9) 64

Chapter Three

Experimental Work

hʹm=(3/24)=0.125m=12.5cm Duckweed root length = 2 cm (Landesman et al., 2005). Hʹm=hʹm+Plant Roots length+Free board Hʹm = 12.5 cm + 2 cm + 3.5 cm =18cm≈20cm For each duckweed tank; Lʹm=(Lʹp/a)…….from Table (2.9) Lʹm=(35.37/24)=1.47m≈1.5m Wʹm=(Wʹp/a)…….from Table (2.9) Wʹm=(11.79/24)=0.49m≈0.5m Then; each duckweed tank dimensions shall be 1.5m x 0.5m x 0.2m. According to dimensional analysis; effluent parameters concentrations depend on length and width, area, volume, detention time, velocity of flow, discharge, wastewater and tank depths, and acceleration due to gravity, force and work. The Pilot plant for the system of clarifier tank and duckweed tanks as consecutive system was fabricated outside the university and installed inside laboratory as shown in Figures (3.1), (3.2), & (3.3) and Photo (3.1).

3-7: Pilot Plant: The pilot plant is fabricated from galvanized steel sheets (gage 160.0625mm) by welding, painted from outside and inside; from outside by white anti-rust painting, while from inside by epoxy protective coating suitable for use in contact with chemicals (resistant to wide range of chemicals and waterproof) known as X-Shield Epoxy Seal PW; applied in a single layer of 400microns by roller (www.x-calibur.us), as shown in Figures (3.1), (3.2) & (3.3) (refer to Annex A for more photos of the Pilot Plant).

65

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Figure 3.5: Schematic diagram of the clarifier tank.

66

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3-7-1: Clarifier Tank. Industrial wastewater had been brought from one of the tanneries in Al-Nahrawan region and Batteries Factory in Al-Wazyriah district with combined flow of 0.0886 m3/day (3.69 LPH) that was fed into the holding (presettling) tank to mix the wastewater and remove the floating matter, and large settleable particles after that the wastewater was fed into the clarifier tank as shown in Photo (3.2) which was made from galvanized steel sheets as mentioned previously. It consists of a cylindrical basin with diameter and depth 90 & 44 cm respectively. A small perforated cylinder was placed in the center of the clarifier with diameter and depth 25 & 44 cm respectively.

Figure 3.6: Schematic diagram of the Storage (Holding) and Duckweed tanks.

67

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This cylinder is connected to the hopper; which is the bottom part of the clarifier tank used for sludge processing. The hydraulic residence time for the clarifier tank is 2hr.

68

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69

Chapter Three

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Photo 3.4 : Industrial Wastewater fed into the Clarifier Tank

3-7-2: Duckweed tanks. The wastewater from clarifier tank was fed into the duckweed tanks which were covered with Lemna minor (Refer to Annex B). This tank was made from galvanized steel sheets, each duckweed tank dimensions are 1.5m x 0.5m x 0.2m. During the operation of the system the duckweed sample was taken at the beginning and at the end of operating period, while not leaving any surface area exposed. Harvesting took place at the end of each run manually so that plants were approximately about 412g/m2 (150%) coverage rate of the surface area of the tank (Zhao Y. & Zhao H., 2013).

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3-8: Industrial Wastewater Sampling and Analysis. Samples of wastewater were taken for analysis, as the first was untreated wastewater taken from presettling (equalization) tank after one day of settling (the wastewater left for one day in order to settle the large settleable matters originated especially in the tannery wastewater). The second sample was taken after the clarifier tank taken from clarifier tank effluent (before entering duckweed tanks); while the rest samples of duckweed industrial treated wastewater were taken from duckweed tanks at a three days periods of runs. The analyses of these samples were immediately done in the laboratories of the Environmental Research Center at the University of Technology. The samples of wastewater were stored in polyethylene bottles of 250ml and 500ml respectively. Tests include (temperature, pH, EC, DO, TDS, COD, NH4-N, NO3-N, PO4-P, and heavy metals (Cd, Cr, Ni, and Pb)) are done according to the standard methods shown in Table (3.3). The experimental procedures for laboratory analyses were carried out according to standard methods for examination of water and wastewater manual (APHA, 1992), and the results were tabulated as shown in chapter four for statistical analysis and comparison with the acceptable Iraqi limits for reuse in irrigation of special crops. Table (3.3): Analytical Methods According to the Standard Method, (APHA, 1992) Pollution parameter

Method

pH, Temperature and EC

pH, Temperature and EC meter.

DO

DO meter

TDS

TDS meter

COD

COD meter + incubator.

NH4-N, NO3-N, and PO4-P

Multi-parameter Bench Photometer

Cd, Cr, Ni, Pb

Atomic Absorption Spectrophotometer

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3-9: Duckweed Sampling and Analysis. Duckweed plant was brought from Al-Rustumiya Wastewater Treatment Plant-Third Extension, which is found in the final clarifiers as the plant is widely available in Baghdad City. Two samples of duckweed were taken for analysis of the heavy metals accumulated in plant tissues. The harvested samples were taken before placing duckweed in duckweed tanks (initial sample; weighed for wet and dry weight), and the second one taken after the death of the plant. The harvested sample was first weighed for wet weight; and then washed with tap water, and then washed with distilled water to ensure removing any attached materials and compounds on the surface of the fronds of the duckweed that will give erroneous results when tested to find the values of the heavy metals, then air dried for about 20 minutes in order to remove excess water. Then the duckweed samples were dried in an oven at 105 ˚C for about 12 hours to determine the dry weight. The oven dried duckweed sample then grinded and weighed to begin the plant tissues analysis for heavy metals. The procedure was adopted from the Iraqi Journal of Market Research and Consumer Protection, Vol. 2, No. (3) 2010. The analyses of these samples were immediately done in the laboratories of the Environmental Research Center at the University of Technology.

3-10: Laboratory Apparatuses Several types of laboratory apparatuses are used in testing industrial wastewater samples for several pollutants and duckweed plant tissues (fronds) samples for heavy metals; but firstly calibrated. The apparatuses used are shown below:

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1. Electronic balance. High-quality electronic precision Analytic Balance (Model DS 452Series) with digital indicator in the range (0.0001–220.0000) gm, with simple-touse multifunction control panel and large and bright display with multilines manufactured by Precisa Company (Indian Origin) (Photo 3.3) was used.

Photo 3.5: Analytical Balance

2. pH, EC, and TDS meter. Portable pH, EC, TDS and temperature meter was used to measure pH, EC, TDS and temperature of wastewater type (HI 9811Portable pH/EC/TDS/°C meter) manufactured by Hanna Instruments as shown in Photo (3.4).

Complete, versatile, with a large LCD and splash proof

portable combination meter designed with the utmost precision and 73

Chapter Three

Experimental Work

simplicity. The instrument provides measurements for pH, EC and TDS ranges, which are easily selectable through the keypad on the front panel. Conductivity

measurements

are

automatically

compensated

for

temperature changes with a built-in temperature sensor.

Photo 3.6: PH, EC, and TDS meter.

3. Electrical Laboratory Oven Electrical laboratory oven is used in drying the samples of duckweed fronds with temperature ranges of +5ºC above ambient to +300ºC, manufactured by Binder GmbH in Germany. The Laboratory Oven is fitted with a programmable microprocessor PID controller with color LED display for programming and monitoring the test parameters. The Laboratory Oven is supplied with two off internal shelves (Photo (3.5)).

4. Multi-parameter Bench Meter. Multi-parameter Bench Meter as shown in the Photos (3.6) & (3.7), model (C99) & (HI 83200) manufactured by Hanna Instruments is used for the measurement of wastewater nutrients.

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Photo 3.7: Laboratory Oven.

Photo 3.8: Multi-parameter Bench Meter (Model C99).

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Photo 3.9: Multi-parameter Bench Meter (HI 83200).

5. Dissolved oxygen meter. Digital dissolved oxygen (DO) meter model (Multi 3430 SET F) manufactured by WTW GmbH in Germany is used to determine the concentrations of dissolved oxygen (DO) in wastewater samples as shown in Photo (3.8). It supports optimal measuring in the easiest way along with efficient documentation.

Photo 3.10: DO Meter (Multi 3430 SET F).

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6. COD Meter & Reactor Chemical Oxygen Demand (COD) meter model (SN11/25370) & reactor model (ET 108), both manufactured by Lovibond GmbH in Germany are used to determine a wide range of chemical oxygen demand (COD) in wastewater samples as shown in Photo (3.9). It supports optimal measuring in the easiest way along with efficient documentation.

Photo 3.11: COD Meter & Incubator (SN11/25370) & (ET 108).

7. Atomic Absorption Spectrophotometer Atomic Absorption Spectrophotometer model (AA 6300) for multielement analysis, manufactured by Shimadzu in Japan, is used to determine a wide range of heavy metals in wastewater samples by quantitative determination of main, transition and trace elements as a part of the daily routine analyses in every control laboratory as shown in Photo (3.10).

8. Glass burette. Glass burettes graduated in the range of (0-50) ml and (0-5) ml are used for all titration procedures.

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9. Laboratory Tests Accessories. Most types of laboratories glasses e.g. (cylinders, test tubes, filtration funnels, Pyrex beaker, etc.), and filter papers number (41, 42) were used in the lab work.

Photo 3.12: Atomic Absorption Spectrophotometer model (AA 6300).

3-11: Plant Tissue Analysis Plant tissue analysis is done in the laboratories of the Environmental Research Center at the University of Technology to determine dry weight duckweed fronds heavy metals in. The procedure was adopted from the Iraqi Journal of Market Research and Consumer Protection, Vol. 2, No. (3) 2010. The following steps were followed: 78

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1. Initially washing the plant fronds to get rid of the attached materials on the fronds well and then dried in the oven at a temperature 105˚C. 2. Grinding the dried fronds after air cooled and then weighing 2gm. 3. Acidify with 40ml of nitric acid (HNO3), cover and left for 24 hours in darkness for soaking. 4. Heating the sample until the escalation of vapors and then left to cool 5. Adding 3 ml of perchloric acid (HCLO4) and heated again with lifting the lid to dry. 6. The remaining left to cool then adding 2 ml of hydrochloric acid (HCL) with the addition of (2-3) ml of distilled water and heating until melting. 7. Cooling the sample, filtering the solution and completing the solution filtrate up to 50 ml of distilled water by a 50ml volumetric flask, now it’s ready

for

the

measurement

model

by

atomic

absorption

spectrophotometer apparatus, as shown in Photo (3.11).

Photo 3.13: Grinded duckweed fronds after drying in Electrical laboratory oven.

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Chapter Four Results and Discussions

Chapter Four

Results and Discussions CHAPTER FOUR Results and Discussions

4-1: General The industrial combined tannery and battery wastewater influent to the pilot plant characteristics are shown in Table (4.1) as kept in equalization tank (presettling tank) for one day to let for mixing, pH equalization and also to settle heavy matters (especially from tanneries such as flesh, wool, skin and hair remnants); then let to enter the clarifier as primary sedimentation process for two-hour retention time as mentioned previously in chapter three. Table (4.1): The characteristics of collected industrial wastewater fed to pilot plant and tested at 24/09/2014 (after one day residence time in equalization tank)* Parameter

Concentrations

Temperature, ˚C

28.8

pH

8.8

EC, µS/cm

8700

DO, mg/L

0.01

TDS, mg/L

8090

COD, mg/L

15210

NH4-N, mg/L

10

NO3-N, mg/L

33

PO4-P, mg/L

30

Cd, µg/L

22.9

Cr, µg/L

537.7

Ni, µg/L

127.4

Pb, µg/L

258.3

*All measurements are average of two samples.

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Wastewater effluent from clarifier enters the duckweed tanks (biological treatment tanks) to begin the treatment and removal of pollutants; where the duckweed plants Lemna minor were cultured and harvested as the duckweed sample was used. Samples of raw wastewater fed to equalization tank were collected and tested as shown in Table (4.1). Treatment process started at 23/09/2014 as wastewater left for one day residence time in equalization tank and then fed into the clarifier next day. Treatment process lasted for 55 days including both wastewater and plant tissues tests part of them include the tests of heavy metals concentrations in both wastewater and plant tissues analyses used to predict removal percentages and the BCF values. Wastewater Samples Collection Wastewater Samples first were taken from the clarifier at the beginning of sedimentation process (before clarifier) and after 2hrs residence time in clarifier (after clarifier) to show the impacts of sedimentation on duckweed based treatment of the industrial wastewater which will be fed to duckweed tanks after 2 hrs. When the wastewater fed into duckweed tanks; a regular samples collection take place at 3-days’ time period from the duckweed tanks to be tested for all the parameters required for the study including the heavy metals concentrations. Principle of Sampling and Sample Type A grab sample collected at a particular time and place to represent only the composition of the source at that time and place. This involved manual sampling and minimal equipment. Care had been taken so that the grab sample is representative of the whole.

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Equipment Sample bottles: two 500ml new PVC bottles used for all samples taken with four 100ml new PVC bottles for small ready samples prepared for tests. A sampling beaker (250ml, 500ml or 1000ml) used for depth sampling. Procedure • Sampling was carried out taking care to avoid personal risk or injury arising from the nature of the sample itself or the location of the sample point. • Sample bottles/containers were clearly labelled and identified. The time/date was recorded together will all relevant details of location and sampling conditions that may be present at time of sampling, e.g. wastewater temperature. • Sample bottles were securely sealed following sampling and stored securely for safe transport to the laboratory in cooler boxes where necessary. • Samples were analyzed within 24 hours of sample collection, as a general rule.

4-2: The Clarification Removal Efficiency The use of clarifier was suggested in order to remove settleable solids that can be easily deposited and in addition to remove floating materials, thus reducing heavy suspended solids that will restrain the subsidiary treatment process and consequently reducing duckweed treatment efficiency. The characteristics of the influent industrial wastewater were quite high and the wastewater was highly contaminated as shown from the values

83

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shown in Table (4.1) taken in 24/09/2014(the values shown in Table (4.1) are the average of two samples). The removal and variation increase percentages were calculated by the following formulas (Tanhan et. al., 2007) % Removal= ((Co-Cf)/Co)*100 ……(4.1) Where:Co=Initial pollutant parameter concentration Cf=Final or after time period pollutant concentration While percent increase in dissolved oxygen was calculated by the following formula: % Increase= ((Cf-Co)/Co)*100 …….(4.2) Where:Co=Initial dissolved oxygen concentration Cf=Final or after time period dissolved oxygen concentration Grapher 10 software used to compare between pollutants mean values. While the characteristics of the effluent wastewater from clarifier (after 2 hours residence in clarifier tank), shown in Table (4.2) as average effluent percent variation in temperature of 0.694%, pH and Ec of 3.41% & 16.78% respectively; an average effluent percent increase in DO of 100%, while showing an average effluent % removal in nutrients and heavy metals as shown in Table (4.2) by using formula (4.1) & (4.2). The percent variation of physical parameters (temperature, pH and EC) seemed to be very low because that the clarifier requires more detention time. The tests results for the clarifier tank show that the performance in removing other parameters slightly increases with running time due to high influent pollutants concentrations which causing septicity case; consequently decreases the efficiency of clarifier tank in removing other pollutants parameters. In general clarification did not significantly 84

Chapter Four

Results and Discussions

affected pH (slight variation in pH of 0.694%). A slight variation in TDS of 2.23% (as the solids concentration increases the removal efficiency decreases in the wastewater, especially if there is a significant amount of industrial waste) (Eckenfelder, 2000). Tanks having shorter detention periods (0.5 to 1 hr) shall have less removal efficiency of suspended solids (Metcalf & Eddy, 2004). Also age (time in collection tank) of wastewater when it reaches the pilot plant; older wastewater becomes stale or septic, solids do not settle properly because gas bubbles cling on the particles and tend to hold them in suspension. (Office of Water Programs). The removal efficiency of both TDS and COD which are 2.23% & 12.3% respectively are less than those reported by Eckenfelder, (1989) of about 10% to 15% for total Solids and of about 20% to 50 % for BOD while COD will be about 24% to 59% ; taking average of 85% of BOD /COD for which if BOD/ COD is > 60% then the waste is fairly biodegradable, and can be effectively treated biologically; and if BOD/COD ratio is between 30 and 60%, then seeding is required to treat it biologically, because the process will be relatively slow, as the acclimatization of the microorganisms that help in the degradation process takes time, while if BOD/COD < 30%, biodegradation will not proceed, thus it cannot be treated biologically, because the wastewater generated from these activities inhibits the metabolic activity of bacterial seed due to their toxicity or refractory properties ( Abdalla & Hammam, 2014). Some organic nitrogen, organic phosphorus, and heavy metals associated with solids are also removed during primary sedimentation but colloidal and dissolved constituents are not affected (Al-Saaedi, 2007).

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Table (4.2): Clarifier pollutants concentrations & % removal efficiencies

Temperature, ˚C

Clarifier effluent concentrations 28.6

% Removal efficiency 0.694

pH

8.5

3.41

EC, µS/cm

7240

16.78

DO, mg/L

0.02

100

TDS, mg/L

7910

2.23

COD, mg/L

13340

12.3

NH4-N, mg/L

9.46

5.4

NO3-N, mg/L

30.5

7.58

PO4-P, mg/L

28.5

5

Cd, µg/L

22.7

0.87

Cr, µg/L

525.2

2.33

Ni, µg/L

111.7

12.32

Pb, µg/L

252.6

2.21

Parameter

4-3: Duckweed Effect on COD Removal Efficiency COD reduction continued as the clarifier tank effluent fed into the duckweed tanks for biological treatment. Wastewater influent and effluent COD concentration ranged between (13340-335) mg/L and plant death concentration (530) mg/L respectively (values are average of two samples) as shown in Table (4.3) and Figure (4.1)a; while the removal rate achieved of COD was 94.83%, which is higher than the value reported by Pandey, ( 2001), Dalu & Ndamba, (2002) , Ran et al, (2004), and Azeez & Sabbar, (2012). Figure (4.1)b shows the removal efficiency increased with time. The effluent COD level at day-30 became high because the duckweed reached the death phase in the tanks which increases organic load due to the release of those pollutants that have been adsorbed on plant fronds back to the wastewater after death.

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Table (4.3): COD measured concentrations & % removal in duckweed tanks * COD, mg/L Influent Effluent

COD% removal

Date

Time, Days

25/09/2014

1

13340

-----

-----

29/09/2014

4

-----

10250

23.16

03/10/2014

8

-----

8060

39.58

07/10/2014

12

-----

1930

85.53

12/10/2014

17

-----

420

96.85

17/10/2014

22

-----

370

97.23

20/10/2014

25

-----

342

97.44

22/10/2014

27

-----

335

97.49

25/10/2014

30**

-----

530**

94.83**

*All measurements are average of two samples. **Start of plant death.

Figure (4.1): (a) COD vs Time, (b) COD% Removal vs Time with fitted polynomial

COD concentrations showed a gradual decrease during periods of prolonged treatment (Figure (4.1)a). Data revealed that duckweed effectively reduced COD by 97.49% before reaching death condition.

87

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Results and Discussions

In agreement with the present research, (Oron et. al., (1988) mentioned that the duckweed contribution for the removal of organic matter is due to their ability to direct use of simple organic compounds. The result showed a significant correlation between COD removal and time as coefficient of correlation value was R = 0.974379(R2= 0.949414).

4-4: Duckweed Effect on Temperature Reduction Efficiency The duckweed tanks influent wastewater temperature was (28.6)˚C, while the effluent temperature was (25)˚C, as shown in Table (4.4) and Figure (4.2)a, which indicates that the temperature dropped during run time of the pilot plant due to the complete coverage of duckweed plants which weaken influent temperature by preventing the effect of the air temperature on the wastewater below the duckweed mat (Skillicorn et al., 1993). Temperature range was within temperature tolerance limit for duckweed growth as mentioned by Culley et al., (1981) who found that the upper temperature tolerance limit for duckweed growth was around 34°C, and that may be due to Lemna minor was one of floating aquatic plants which cover the surface of the water and form an insulating layer prevent light penetration, leading to reduce water temperatures (Kara, 2003). The wastewater temperatures results approximately coincide with that of the temperature that the duckweed can grow in. Data revealed that temperature reduction shown about 11.54%. A significant correlation between temperature variation and time had been showed. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was

88

Chapter Four

Results and Discussions

R = 0.987061 (R2 = 0.961591) observed from the results in this research as shown in Figure (4.2)b. Table (4.4): Temperature measured concentrations & % reduction in duckweed tanks * Temperature, ˚C Influent Effluent

Date

Time, Days

Temp.% reduction

25/09/2014

1

28.6

-----

-----

29/09/2014

4

-----

27.7

3.15

03/10/2014

8

-----

27.3

4.55

07/10/2014

12

-----

26.5

7.69

12/10/2014

17

-----

26.2

9.06

17/10/2014

22

-----

25.6

10.49

20/10/2014

25

-----

25.7

10.14

22/10/2014

27

-----

25.3

11.54

25/10/2014

30**

-----

25**

9.747**

*All measurements are average of two samples. **Start of plant death.

Figure (4.2): (a) Temperature vs Time, (b) Temperature% Reduction vs Time with fitted polynomial. 89

Chapter Four

Results and Discussions

4-5: Duckweed Effect on pH Reduction Efficiency The Lemnaceae can survive in nature in fairly wide pH range, Lemnaceae species can survive in pH range of (3.5 to 10). The optimum pH range is (4.5 to 7.5) (Saygideger, 1996, Suhag, et. al., 2011). The duckweed can survive in pH range of (6.5-7.5) as reported by Leng et al., (1995). pH values were ranged between (6.6-8.5) for both influent and effluent, while at day-30 the effluent pH was 6.7, where duckweed start to enter death phase(Table (4.5) and Figure (4.3)a). The pH values, shown in Fig (4.3)a within the range (6.6-8.5) as mentioned previously , are affected by buffering factor such as CO2, HCO3 because some plants have capability to moderate the impact throughout ion releasing and taking for the balance completion within environment (Ji, et. al., 2007). A significant correlation between pH variation and time had been showed. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was R=0.98401 (R2 = 0.968279), observed from the results in this research as shown in Figure (4.3)b.

4-6: Duckweed Effect on EC Reduction & TDS Removal Efficiency Determination of the electrical conductivity of the water gives an indication on TDS (Peavy, 1986), also gives an indication on mineral ions content in water (Dalu & Ndamba, 2002). Both the average influent and effluent TDS were 7910mg/L and 6584mg/L respectively, with death value of 7430mg/L; while regarding the electrical conductivity, the average influent and effluent EC were

90

Chapter Four

Results and Discussions

7240µS/cm and 2780µS/cm respectively, with death value of 3700µS/cm as shown in Table (4.6) & (4.7), Figures (4.4)a &(4.5)a respectively. Table (4.5): pH measured concentrations & % removal in duckweed tanks * pH Influent

Effluent

pH% reduction

1

8.5

-----

-----

29/09/2014

4

-----

8.2

3.53

03/10/2014

8

-----

7.9

7.06

07/10/2014

12

-----

7.5

11.76

12/10/2014

17

-----

7.4

12.94

17/10/2014

22

-----

6.8

20

20/10/2014

25

-----

6.7

21.18

22/10/2014

27

-----

6.6

22.35

25/10/2014

30**

-----

6.7**

21.18**

Date

Time, Days

25/09/2014

*All measurements are average of two samples. **Start of plant death.

Figure (4.3) : (a)pH vs Time, (b)pH% Reduction vs Time with fitted polynomial.

91

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The TDS removal was 16.76%, decreased to 6.07% at death phase; while EC reduction was 61.6%, and deceased to 48.90% at death phase as shown in Tables (4.6) & (4.7), and Figures (4.4)b & (4.5)b, which indicates that the duckweed has a slightly effect on removing dissolved solids in wastewater and consequently requires more treatment to reduce TDS. As shown in Figures (4.4)b & (4.5)b, both TDS removal and EC reduction increase with time, but decrease after Day-20 for EC. TDS removal result is lower than that reported by (Dalu & Ndamba, 2002) which is (40%) and EC reduction result is higher than that reported by (Dalu & Ndamba, 2002) which is (22%) due to some conditions were unsuitable for duckweed growth to remove wastewater pollutants and death of some duckweed plants in the tanks. Table (4.6): TDS measured concentrations & % removal in duckweed tanks * TDS, mg/L Influent Effluent

TDS% removal

Date

Time, Days

25/09/2014

1

7910

-----

-----

29/09/2014

4

-----

7750

2.02

03/10/2014

8

-----

7680

2.91

07/10/2014

12

-----

7608

3.82

12/10/2014

17

-----

7500

5.18

17/10/2014

22

-----

6890

12.90

20/10/2014

25

-----

6740

14.79

22/10/2014

27

-----

6584

16.76

25/10/2014

30**

-----

7430**

6.07**

*All measurements are average of two samples. **Start of plant death

TDS values decrease because of the plant susceptibility to uptake some organic and inorganic ions, and it is susceptible to note high concentrations of sodium ion during the growth phase (Seidel, K. 1976). A significant correlation between TDS & EC variation and time had been showed. The results of the correlation-regression analysis indicated a 92

Chapter Four

Results and Discussions

positive relationship where the value of the correlation coefficient was R=0.76453 and 0.989585 (R2 = 0.584504 and 0.979279) for TDS and EC respectively as observed from the results.

Figure (4.4) : (a)TDS vs Time, (b)TDS% Removal vs Time with fitted polynomial. Table (4.7): EC measured concentrations & % reduction in duckweed tanks * EC, µS/cm Influent Effluent

EC% reduction

Date

Time, Days

25/09/2014

1

7240

-----

-----

29/09/2014

4

-----

6930

4.28

03/10/2014

8

-----

5760

20.44

07/10/2014

12

-----

4700

35.08

12/10/2014

17

-----

3450

52.35

17/10/2014

22

-----

2980

58.84

20/10/2014

25

-----

2840

60.77

22/10/2014

27

-----

2780

61.60

25/10/2014

30**

-----

3700**

48.90**

*All measurements are average of two samples. **Start of plant death.

93

Chapter Four

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Figure (4.5) : (a)EC vs Time, (b)EC% Reduction vs Time with fitted polynomial.

4-7: Duckweed Effect on DO Increase Efficiency DO values ranged between (0.02-7.07)mg/L for both influent and effluent, this due to oxygen produced by duckweed is released into the water, while at day-30 the effluent DO was 7.01mg/L to duckweed eventual senescence, and starting to enter death phase (Parr et. al., 2002), as shown in Table (4.8) and Figure (4.6)a, which showed that the DO concentrations within the range (0.02-7.07)mg/L were very low at the beginning due to covering the whole surface of water with a 1 cm thick duckweed mat (Parr et. al., 2002). A significant correlation between DO variation and time had been showed.

94

Chapter Four

Results and Discussions

Table (4.8): DO measured concentrations & % increase in duckweed tanks * DO, mg/L Influent Effluent

DO% increase

Date

Time, Days

25/09/2014

1

0.02

-----

-----

29/09/2014

4

-----

0.03

50

03/10/2014

8

-----

0.05

150

07/10/2014

12

-----

0.09

350

12/10/2014

17

-----

6.54

32600

17/10/2014

22

-----

7.04

35100

20/10/2014

25

-----

7.05

35150

22/10/2014

27

-----

7.07

35250

25/10/2014

30**

-----

7.01**

23270**

*All measurements are average of two samples. **Start of plant death.

Figure (4.6) : (a)DO vs Time, (b)DO% Increase vs Time with fitted polynomial.

The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was R = 0.87488 (R2 = 0.765412) as observed from the result. 95

Chapter Four

Results and Discussions

4-8: Duckweed Effect on Nutrients Removal Efficiency Both influent and effluent ammonia (NH4-N) were 9.46mg/L and 4.12 mg/L respectively and death value of 5.3mg/L, with removal of 56.45% as shown in Table (4.9) and Figure (4.7)a. A significant correlation between (NH4-N) removal and time had been showed. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was R = 0.92202 (R2 = 0.850118) as observed from the results in this research as shown in Figure (4.7)b. Table (4.9): NH4-N measured concentrations & % removal in duckweed tanks * NH4-N, mg/L Influent Effluent

NH4-N % removal

Date

Time, Days

25/09/2014

1

9.46

-----

-----

29/09/2014

4

-----

8.36

11.63

03/10/2014

8

-----

7.85

17.02

07/10/2014

12

-----

7.2

23.89

12/10/2014

17

-----

5.19

45.14

17/10/2014

22

-----

4.62

51.16

20/10/2014

25

-----

4.3

54.55

22/10/2014 27 ----4.12 25/10/2014 30** ----5.3** *All measurements are average of two samples. **Start of plant death.

56.45 36.60**

Both influent and effluent nitrate (NO3-N) was 30.5mg/L and 3.21 mg/L respectively and death value of 4.2mg/L, with removal of 89.48% as shown in Table (4.10) and Figure (4.8)a. This value is higher than the value reported by (Gijzen & Ikramullah, 1999) 74% and (Lyerly, 2004); 62% respectively. The nitrate removal increases with the time as illustrated in Figure (4.8)b.

96

Chapter Four

Results and Discussions

Figure (4.7) : (a)NH4-N vs Time, (b) NH4-N % Removal vs Time with fitted polynomial.

However, nitrogen content in the plants decreased with high nitrogen loads due to high ammonia concentrations inhibiting nitrogen uptake by the plants because of ammonia toxicity to the plants (Al-Nozaily et al., 2000). In agreement with the present study, the results demonstrated that the duckweed efficiently removed nitrate from wastewater and incorporated into its biomass attributed to the plant's ability to provide the right conditions to reduce nitrate as a result of cooperation with the presence of micro-organisms which play a vital role in nitrogen conversion or plants direct up- taking using large amounts of nitrogen compounds such as NO3, NH4 during the period of growth (Juren, K. 1999). A significant correlation between (NO3-N) removal and time had been showed. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was

97

Chapter Four

Results and Discussions

R=0.95704 (R2 = 0.91592) as observed from the results in this research as shown in Figure (4.8)b. Table (4.10): NO3-N measured concentrations & % removal in duckweed tanks * NO3-N, mg/L Influent Effluent

NO3-N % removal

Date

Time, Days

25/09/2014

1

30.5

-----

-----

29/09/2014

4

-----

28

8.20

03/10/2014

8

-----

25.8

15.41

07/10/2014

12

-----

22

27.87

12/10/2014

17

-----

5.6

81.64

17/10/2014

22

-----

3.4

88.85

20/10/2014

25

-----

3.25

89.34

22/10/2014

27

-----

3.21

89.48

25/10/2014

30**

-----

4.2**

86.23**

*All measurements are average of two samples. **Start of plant death.

Figure (4.8): (a) NO3-N vs Time, (b) NO3-N % Removal vs Time with fitted polynomial. 98

Chapter Four

Results and Discussions

Influent and effluent phosphates (PO4-P) were 28.5mg/L and 4.1 mg/L respectively and death value of 5.2mg/L, with removal of 85.61% as shown in Table (4.11) and Figure (4.9)a; Table (4.11): PO4-P measured concentrations & % removal in duckweed tanks * PO4-P, mg/L Influent Effluent

PO4-P % removal

Date

Time, Days

25/09/2014

1

28.5

-----

-----

29/09/2014

4

-----

24.3

14.74

03/10/2014

8

-----

22.5

21.05

07/10/2014

12

-----

12.6

55.79

12/10/2014

17

-----

8.7

69.47

17/10/2014

22

-----

4.9

82.81

20/10/2014

25

-----

4.3

84.91

22/10/2014

27

-----

4.1

85.61

25/10/2014

30**

-----

5.2**

81.75**

*All measurements are average of two samples. **Start of plant death.

Figure (4.9) : (a)PO4-P vs Time, (b) PO4-P % Removal vs Time with fitted polynomial. 99

Chapter Four

Results and Discussions

this value was higher than the range reported by (Reddy & De Busk, 1985; Reddy & Smith, 1987; Alaerts et al., 1996; Korner & Vermaat, 1998; Vermaat & Hanif, 1998) (9-61)% (PO4-P), and that reported by (Lyerly, 2004)16%. The phosphate removal increases with the time as illustrated in Figure (4.9)b; but percent removal begin to increase slightly near day-22 due to high ammonia concentrations inhibiting phosphate uptake by the plants because of ammonia toxicity to the plants (Al-Nozaily et al., 2000). A significant correlation between (PO4-P) removal and time had been showed. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was R=0.98351 (R2 = 0.967293) as observed from the results in this research as shown in Figure (4.9)b.

4-9: Duckweed Effect on Heavy Metals Removal Efficiency The heavy metals of influent concentrations were 22.7µg/L, 525.2 µg/L, 111.7 µg/L and 252.6 µg/L for (Cd, Cr, Ni and Pb) respectively and effluents12.5 µg/L, 355.8 µg/L, 28.5 µg/L and 52.8 µg/L; while death values were 14.7µg/L, 474.2 µg/L, 41.7 µg/L and 80.2 µg/L for (Cd, Cr, Ni and Pb) respectively. Removal percentages were 44.93%, 32.26%, 74.48%, and 79.1%, for (Cd, Cr, Ni and Pb) respectively as shown in Tables (4.12), (4.13), (4.14) & (4.15) and Figures (4.10)a, (4.11)a, (4.12)a & (4.13)a respectively. The value of cadmium percent removal was 44.93%, which is lower than the range reported by (Chaudhuri et. al., 2014) which was 47-78%; and lower than that reported by (Loveson et al., 2013, and Miranda, M. G. et. al., 2000) which were 53% and 53.5% respectively, while it was higher than that reported by (Sekomo et. al., 2012) which was 33%. 100

Chapter Four

Results and Discussions

Table (4.12): Cd measured concentrations & % removal in duckweed tanks * Cd, µg/L Influent Effluent

Cd % removal

Date

Time, Days

25/09/2014

1

22.7

-----

-----

29/09/2014

4

-----

22.4

1.32

03/10/2014

8

-----

19.2

15.42

07/10/2014

12

-----

18.7

17.62

12/10/2014

17

-----

18.2

19.82

17/10/2014

22

-----

13.5

40.53

20/10/2014

25

-----

12.7

44.05

22/10/2014

27

-----

12.5

44.93

25/10/2014

30**

-----

14.7**

35.24**

*All measurements are average of two samples. **Start of plant death.

Figure (4.10)b shows the Cd % Removal vs Time with fitted polynomial, with correlation coefficient R of 0.93529(R2 of 0.874768) as observed from the results in this research.

Figure (4.10) : (a)Cd vs Time, (b) Cd % Removal vs Time with fitted polynomial.

101

Chapter Four

Results and Discussions

The removal percentage of chromium was 32.26%, which is lower than that reported by (Sekomo et. al., 2012) which was 94% and within the range reported by (Upatham et. al., 2002) which was 12.9-47.4%. Table (4.13): Cr measured concentrations & % removal in duckweed tanks * Cr, µg/L Influent Effluent

Cr % removal

Date

Time, Days

25/09/2014

1

525.2

-----

-----

29/09/2014

4

-----

513.3

2.266

03/10/2014

8

-----

492.4

6.25

07/10/2014

12

-----

454.6

13.44

12/10/2014

17

-----

430.2

18.09

17/10/2014

22

-----

380.5

27.55

20/10/2014

25

-----

375.4

28.52

22/10/2014

27

-----

355.8

32.26

25/10/2014

30**

-----

474.2**

9.71**

*All measurements are average of two samples. **Start of plant death.

Figure (4.11) : (a)Cr vs Time, (b) Cr % Removal vs Time with fitted polynomial. 102

Chapter Four

Results and Discussions

Figure (4.11)b shows the Cr % Removal vs Time with fitted polynomial, with correlation coefficient R of 0.83255(R2 of 0.693144)as observed from the results in this research. The value of nickel percent removal was 74.48%, which is lower than that reported by (Leela et. al., 2013) which was 98.8%, and higher than that reported by Loveson et al. (2013) which was 7%. Figure (4.12)b shows the Ni % Removal vs Time with fitted polynomial, with correlation coefficient R of 0.95707(R2 of 0.916014)as observed from the results in this research. The value of lead percent removal was 79.1%, which is higher than that reported by (Sekomo et. al., 2012 and Miranda, et. al., 2000) which were 36%, and 55.2% respectively. Lead percent removal was lower than that reported by (Leela et. al., 2010, Hurd & Stemberg, 2008, and Banerjee & Sarkar, 1997) which were 85%, 95%, and 95.5% respectively. Table (4.14): Ni measured concentrations & % removal in duckweed tanks * Date

Time, Days

25/09/2014

1

29/09/2014

Ni, µg/L Influent Effluent

Ni % removal

-----

-----

4

111.7 -----

58.2

47.90

03/10/2014

8

-----

48.7

56.40

07/10/2014

12

-----

39.3

64.82

12/10/2014

17

-----

36.2

67.59

17/10/2014

22

-----

30.3

72.87

20/10/2014

25

-----

29.7

73.41

22/10/2014

27

-----

28.5

74.48

25/10/2014

30**

-----

41.7**

62.67**

*All measurements are average of two samples. **Start of plant death.

103

Chapter Four

Results and Discussions

Figure (4.12) : (a)Ni vs Time, (b) Ni % Removal vs Time with fitted polynomial. Table (4.15): Pb measured concentrations & % removal in duckweed tanks * Pb, µg/L Influent Effluent

Pb % removal

Date

Time, Days

25/09/2014

1

252.6

-----

-----

29/09/2014

4

-----

245.7

2.73

03/10/2014

8

-----

210.1

16.83

07/10/2014

12

-----

178.5

29.33

12/10/2014

17

-----

149.1

40.97

17/10/2014

22

-----

56.7

77.55

20/10/2014

25

-----

53.2

78.94

22/10/2014

27

-----

52.8

79.10

25/10/2014

30**

-----

80.2**

68.25**

*All measurements are average of two samples. **Start of plant death.

104

Chapter Four

Results and Discussions

Figure (4.13) : (a)Pb vs Time, (b) Pb % Removal vs Time with fitted polynomial.

Figure (4.13)b shows the Pb % Removal vs Time with fitted polynomial, with correlation coefficient R of 0.961847(R2 of 0.92515) as observed from the results in this research. The results under experimental conditions show that duckweed found to be a good accumulator of Pb, and Ni, a moderate accumulator of Cd, and a poor accumulator of Cr, which make it an ideal plant for the bioremediation of combined industrial wastewater effluent from tanneries and batteries manufacturing plants. It has been proven through an experimental work in laboratory that the ability of Lemna minor to moderate the impact of high concentrations of heavy metals as reported by Khellaf and Zerdaoui (2009) which this research agreed with in terms of the aquatic plants capacity to accumulate heavy metals and using it as phytoremedator and monitoring tool of heavy metals pollution such as Hanaf (2009), Aziz (2004), and Mahmood (2008).

105

Chapter Four

Results and Discussions

4-10: pH Effect on Heavy Metals Removal Efficiency 4-10-1: pH Effect on Cadmium Removal Efficiency The duckweed tanks influent cadmium concentration was 22.7µg/L and effluent concentration was 12.5µg/L; while death value was 14.7µg/L. Removal percentage was 44.93% as shown in Table (4.12) and Figure (4.14). The value of cadmium percent removal was 44.93%, which is within the range reported by (Upatham et. al., 2002); which was 35.1-65.4% for pH range of (4-7). A significant correlation between cadmium removal percentages and pH % reduction shown in Table (4-5) had been shown. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was R = 0.974429 (R2 = 0.949233) as

Figure (4.14) : Cd % Removal vs pH % Reduction with fitted polynomial.

106

Chapter Four

Results and Discussions

observed from the results in this research which is shown in Figure (4.14), implies that pH would play a vital role in the removal of cadmium from wastewater.

4-10-2: pH Effect on Chromium Removal Efficiency The influent chromium concentration was 525.2µg/L and effluent concentration was 355.8µg/L; while death value was 474.2µg/L. Removal percentage was 32.26% as shown in Table (4.13) and Figure (4.15).

Figure (4.15) : Cr % Removal vs pH % Reduction with fitted polynomial.

Cadmium percent removal was within the range reported by (Upatham et. al., 2002) which was 12.9-47.4% for pH range of (1.5-6).

107

Chapter Four

Results and Discussions

A significant correlation between chromium removal percentages and pH % reduction shown in Table (4-5) had been shown. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was R = 0.80706 (R2 = 0.65134) as observed from the results in this research which is shown in Figure (4.15), implies that pH would play a vital role in the removal of cadmium from wastewater.

4-10-3: pH Effect on Nickel Removal Efficiency The influent nickel concentration was 111.7µg/L and effluent concentration was 28.5µg/L; while death value was 41.7µg/L. Removal percentage was 74.49% as shown in Table (4.14) and Figure (4.16).

Figure (4.16) : Ni % Removal vs pH % Reduction with fitted polynomial.

108

Chapter Four

Results and Discussions

Nickel percent removal was lower than that reported by (Leela et. al., 2013) which was 98.8% for pH of (6) for 22 days by uptake as rootabsorption and bioaccumulation. A significant correlation between nickel removal percentages and pH % reduction shown in Table (4-5) had been shown. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was R = 0.91874 (R2 = 0.844083) as observed from the results in this research which is shown in Figure (4.16), implies that pH would play a vital role in the removal of cadmium from wastewater.

4-10-4: pH Effect on Lead Removal Efficiency The influent lead concentration was 252.6µg/L and effluent concentration was 52.8µg/L; while death value was 80.2µg/L. Removal percentage was 79.1% as shown in Table (4.15) and Figure (4.17). Lead percent removal was lower than that reported by (Leela et. al., 2013) which was 98.8% for pH of (6) for 22 days by uptake as rootabsorption and bioaccumulation. Lead percent removal was lower than that reported by (Leela et. al., 2010) which was 85% for pH of (5), and that reported by Hurd & Stemberg, (2008) which was 95% for pH of (6.5) after 7 days, while it was lower than that reported by Banerjee & Sarkar,(1997) which was 95.5% for pH of (5.5). A significant correlation between lead removal percentages and pH % reduction shown in Table (4-5) had been shown. The results of the correlation-regression analysis indicated a positive relationship where the value of the correlation coefficient was R = 0.988340 (R2 = 0.976816) as observed from the results in this research which is shown in Figure 109

Chapter Four

Results and Discussions

(4.17), implies that pH would play a vital role in the removal of cadmium from wastewater.

Figure (4.17) : Pb % Removal vs pH % Reduction with fitted polynomial.

4-11: Bioconcentration Factor(BCF) Bioconcentration Factor is defined as the ratio of heavy metal concentration in the biomass (duckweed tissues) to the concentration of heavy metal in the feed solution (wastewater mass surrounding). Bioconcentration Factor (BCF) provides an index of the ability of duckweed to accumulate the metal with respect to the metal concentration in the substrate (Zayed et. al., 1998). By definition, the higher the BCF value, the more heavy metals are taken up. It was found that BCF values increase with decrease in heavy metals concentration in acidic medium.

110

Chapter Four

Results and Discussions

Table (4.16): Concentrations of heavy metals in duckweed tissues * Heavy Metal

Duckweed Tissues Heavy Metals Concentrations, µg/L Initial Final

Cd

16.8

18.3

Cr

838.4

2733.6

Ni

329.6

463.5

Pb 410.3 813 *All measurements are average of two samples.

Table (4.16) shows the accumulated concentrations of heavy metals in duckweed tissues; the first is the initial concentration in the original plant sample brought from Al-Rustumiya Treatment Wastewater Plant and the other is the accumulated concentration in duckweed tissues after uptake with time running in pilot plant. Bioconcentration Factor (BCF) was calculated by the following formula (Zayed et. al., 1998): BCF= (Heavy metal concentration in plant tissue) / (Heavy metal initial concentration in external solution) BCF=(Cpf-Cpi))/ Crs ……(4.3) Where:Cpi=Premier (original) heavy metal concentration in plant tissue, µg/L Cpf=Heavy metal accumulated concentration in plant tissue after treatment, µg/L Crs= Residual heavy metal concentration in solution after treatment, µg/L Crs set forth for the values of the effluent concentrations of Cd, Cr, Ni and Pb respectively before death status of duckweed which were presented in Tables (4.12), (4.13), (4.14), (4.15) respectively.

111

Chapter Four

Results and Discussions

BCF Sample of Calculation for cadmium Cpi=16.8 µg/L (from Table (4.16)) Cpf=18.3 µg/L (from Table (4.16)) Crs=12.5 µg/L (from Table (4.12) - at day 22/10/2014 before death status) BCF = ((18.3-16.8) / (12.5)) = 0.12

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