Reduction of Phosphate from Surface Water using ...

Reduction of Phosphate from Surface Water using Natural Adsorbents Sudheesh C1, Prashanth N2

Abstract : The increased content of phosphorus in a water ecosystem leads to extensive algae growth or eutrophication. So removal of phosphate from surface water is crucial. We have conducted a column study using two different adsorbents: Crab Shell-Sand and Vermiculite. Experiments were done with the phosphate stock solution prepared from potassium di hydrogen phosphate. Crab Shell (0.5 mm)-Sand (1:1) and Vermiculite (0.5 mm) with flow rates 2 mL/min showed maximum removal efficiency of 93.1% and 95.7% respectively. Exhaustion time for Crab Shell-Sand was 32 h and Vermiculite was 20 h. Thomas model was used as an isotherm, maximum adsorption capacity of Crab Shell-Sand and Vermiculite were 24.53 mg/g and 16.29 mg/g. After 8 days it is found that the Crab Shell column gets clogged due to bio fouling which reduces the flow rate and cause bad odor. Hence, Vermiculite was considered as a better optimal adsorption material. Regeneration of Crab Shell-Sand can withstand only up to 3 cycles but Vermiculite can withstand up to four cycles. Finally, pond water was tested in both the column of Crab Shell-Sand (1:1) and Vermiculite which shows same results as that of using phosphate stock solution in the column. SEM analysis was also proved the adsorption-desorption of phosphate onto Crab Shell and Vermiculite. Keywords: phosphate, eutrophication, crab shell-sand, vermiculate, thomas model, bio fouling, SEM analysis. I. INTRODUCTION

1.1 GENERAL Surface waters contain certain level of phosphorus in which is an important constituent of living organisms. In natural conditions, the phosphorus concentration in water is balanced. When the input of phosphorus to waters is higher than it can be assimilated by a population of living organisms, the problem of excess phosphorus content occurs. This causes algal bloom or Eutrophication. Phosphorus is an essential nutrient for growth of organisms in most ecosystems. Itis a very important material for many industries as well. The extensive industrial useof phosphates inevitably results in large amounts of phosphate-bearing wastes, whichare usually discharged into municipal and industrial water effluent streams. The excess content of phosphorus in receiving waters leads to extensive algae growth (eutrophication).

When algal blooms exhaust the supply of phosphorus, they die and start to decompose. During decomposition, dissolved oxygen is removed from the water by microorganisms that break down the organic material. The lack of dissolved oxygen makes it difficult for aquatic organisms to survive and henceforth water bodies become unusable. This thereby causes the imbalance in the ecosystem to be disturbed calling for the need for purification of water streams.

1.2 LITERATURE REVIEW Various physical, chemical and biological treatment processes have been developed to remove phosphate from water. Chemical precipitation most often employs compounds such as calcium, aluminum, and iron (7). In the late 1950s, the development of biological phosphorus removal was established and it was found that under certain conditions, activated sludge could take up a

1 Department of Civil Engineering, Sathyabama University, Chennai, Tamil Nadu, India, [email protected] 2 Department of Civil Engineering, Sathyabama University, Chennai, Tamil Nadu, India, [email protected]

Journal of Indian Water Works Association

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considerable amount of phosphorus (3). It is possible to remove phosphate from aqueous solution as hydroxyl apatite (HAP) by crystallization reaction with calcium ion when seed crystalline substance coexists in the solution (2). Ion exchange process has also been investigated for phosphate removal from aqueous medium (1). Magnetic separation methods have also been tried out where lime is used to precipitate calcium phosphate attached to magnetite and separated using an induced magnetic field8. Removal of phosphate from aqueous solution by means of adsorption has been investigated in recent years by using various sorbents, which include bio-adsorbents e.g. wood particles, microalgae, Scenedesmus, seaweed, carrageenan and waste materials or byproducts such as coir pith carbon, fly ash , blast furnace slags etc.

reservoirs where drinking water is obtained it is no more than 0.025 ppm and systems supporting aquatic life it is 0.01 ppm.

ZnCl2 activated carbon developed from coir pith, Orange waste immobilized with Zirconium, the tamarind nut Shell activated carbon (TNSAC), Iron impregnated coir pith, Waste Iron humate (IH) from young brown coal, Fe-Mn binary oxide Adsorbent with Fe/Mn molar ratio 6:1, calcite- Natural Adsorbent (4), basic oxygen furnace slag, Oyster Shell waste, Titanium mesostructure prepared with different surfactant template, La (III) modified Zeolite adsorbent (LZA).

The surface water samples were collected by grab sampling technique from various locations like Thamaraikulam, Vannarkulam, OldTambaram and Adyarpoonga from Chennai in India for characteristics of water samples.

II. METHODOLOGY

2.1 GENERAL

Surface water from various sources was collected, analyzed for their physio- chemical parameters using standard methods (APHA, 2005). Phosphate reduction from surface waters was carried out using waste-crab shell and naturally occurring mineral-vermiculite as adsorbents. Powdered materials of different sizes were used in the column study. Column was packed with the adsorbent material and phosphate stock solution was fed into the column. Finally, reduction of phosphate Adsorption is one of the techniques, which is concentration was measured using stannous chloride comparatively more useful and economic for phosphate method and regeneration of adsorbent material is also removal. Crab shell is widespread in nature and has studied. been recently utilized for the treatment of wastewater, such as heavy metals or phenols. The fact that the crab The sample water after passing through the test shell has adsorption properties gives raise an idea that it apparatus was studied for five parameters. They include could be utilized as an adsorbent for trapping phosphorus. pH by a pH meter, temperature by a thermometer, Crab shell has been used to adsorb materials such as phosphate by stannous chloride method, BOD and DO lead (5), nickel (9) and phosphate has been adsorbed by by wrinkler’s method and finally COD by open reflux method. materials such as digested sugar beet tailing bio-char.

2.2 MATERIALS USED Adsorbents used for the experiment are Crab Shell (Pediculus pubis) with sand of size (0.5mm) and naturally occurring vermiculite.

Vermiculate have been used to adsorb materials such as aluminum, Cadmium, Copper and Lead and Reagents used for the chemical analysis after the phosphate. completion of the test are Manganese Sulphate, Potassium Iodide, Sodium azide, NaOH pellets, Sodium The standard limits for phosphates according to United thiosulphate, Starch, Concentrated Sulphuric acid, States environmental protection agency, 2012 (USEPA) Phosphate buffer, Calcium chloride, magnesium are for Streams/rivers it is 0.1 ppm, lakes/reservoirs it Sulphate, Ferric chloride for DO and BOD analysis. is 0.025 ppm, Streams entering Lakes it is 0.05 ppm, Phosphate analysis uses ammonium Molybdate, Stannous Streams which do not empty into reservoirs for drinking chloride, Glycerol and concentrated Sulphuric acid. The it is no more than 0.1 ppm, Streams discharging into COD analysis uses ferrous Ammonium Sulphate, COD reservoirs for drinking it is no more than 0.05 ppm, for acid, silver sulphate, Mercuric sulphate, Potassium di


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chromate and a Ferroin indicator. The phosphate stock solution is prepared using potassium di hydrogen phosphate. The column study used 1 ppm concentration of phosphate solution. The column reusability study used 0.1% Dilute HCl.

was optimized to 1mL/min and 2mL/min.

2.3 TEST APPARATUS PREPARATION

III. RESULTS

Reusability of adsorbent material: The adsorbed phosphate both from crab shell and vermiculite was leached out by using 0.1% of dilute HCl followed by distilled water washing. The column was subjected to Apparatus required consists of a column- Height (40 further phosphate removal for several times. Eluted cm), Inner Diameter (2 cm), a pH Meter anda pH probe, phosphate was neutralized with 0.1 M NaOH and a thermometer and a Spectrophotometer. phosphate was determined by Stannous Chloride method.

Crab shell:Fresh Crab Shells were collected from local The various physic-chemical parameters of sample fish market located near Marina beach. The shells were waters were found out to be as follows, washed several times with water and sun dried for about 24 hours and crushed into various sizes (1 mm, 0.5 mm, Table 1 Physic-chemical parameters of sample water 0.125 mm) for carrying out adsorption studies. Vermiculite:Vermiculite was collected from Tamil Nadu Minerals Ltd. Ambattur, Chennai. Vermiculite was sieved into various sizes like 1 mm; 0.5 mm and 0.25 mm were used as an adsorbent in column. Column used: A column of height of 40 cm and inner diameter of about 2 cm was used in the current study. Column was packed to a height of 25 cm. Hence the volume of packing space is around 78.5 mL. A down flow column and an upward flow column were prepared.

2.4 TESTING PROCEDURE Experiments with crab shell: After packing the column, treated samples were collected at every 1 hour intervals and phosphate concentration was analyzed using the stannous chloride method. Here phosphate stock solution prepared from Potassium di-hydrogen phosphate was used. Effect of flow rate in the column packed with a mix of crab shell and sand (0.5mm) in the ratio of 1:1 was adjusted to 1 mL/ min and 2 mL/ min to find the column performance at different flow rates when the size of crab shell was 1 mm. other sizes of the crab shell used were 1mm, 0.5 mm, 0.25mm. The ratio of crab shellsand was tested for 1:1 and 3:1 ratio’s to find the removal efficiency with respect to percentage of Crab shell-Sand used.

Characteristics

Thamarai Vannar Kulam Kulam

OldTambaram Tank

pH

7.1

7.4

7.7

DO (mg/L)

3.2

3.0

3.9

Temperature (o C)

24.7

29.5

29.2

BOD (mg/L)

168

96

92

Phosphate (mg/L) 1.2

0.8

0.6

Among the four ponds, ThamaraiKulam and AdyarPoonga showed high phosphate concentration namely 1.2 and 1.4 mg/L respectively.

3.1 COLUMN STUDY USING CRAB SHELL 3.1.1 COLUMN STUDY IN DOWN FLOW: Column was packed using Crab shell (0.25 mm) and Sand in the ratio of 1:1 (by volume equal to 78.5 mL). Continuous flow of 1ppm concentration phosphate solution was fed into the column. The column was maintained at a flow rate of 0.2 mL/min. Sample was collected after treatment at every 4 hours interval. Figure 3.1.1 shows that phosphate removal efficiency for 1st 4 hours was 86.2% and decreased subsequently in the next 3 cycles of 4 hours interval. Removal efficiency for 2nd, 3rd and 4 th cycles were 83.45%, 81.38% and 78.62% respectively.

3.1.2 COLUMN STUDY IN UP FLOW: Column Experiments with vermiculite: Column was packed with packed with Crab shell (0.5 mm)-Sand in the ratio of vermiculite of sizes 1 mm and 0.5 mm and the flow rate 1:1 by volume. Flow rate was adjusted to 1 mL/min.


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Figure 3.1.1 Phosphate removal (%) using Crab Shell (0.250 mm)-Sand

Phosphate removal efficiency of up flow and down flow column was compared in the figure 3.1.2. Sample was collected after treatment at 1 hour interval. Phosphate removal efficiency of up flow and down flow column for 1st 1 hour was 65.15% and 46.75% respectively. Column study was performed for first 6 hours. Removal efficiency of up flow column at 2nd, 3rd, 4th, 5th and 6th intervals were 65.15%, 64.39%, 62.9%, 56.06% and 53.79% respectively. Removal efficiency of down flow column at 2nd, 3rd, 4th, 5th and 6th intervals were 44.23%, 41.93%, 38.57%, 35.85% and 35.42% respectively. Thus, the efficiency of up flow column was higher than the down flow column due to its high retention time.

rate between 1mL and 2mL, changes in concentration of crab shell: sand between 1:1 and 3:1, changes in size of crab shell between 0.25mm, 0.5mm and 1mm. These were then studied for exhaust time and volume of effluent treated. The following tabular column provides a summary of the basic study done using the Crab Shell columns. The summarized results of column study with their exhaust time and amount of water treated until it reached the exhaust time has been shown in Table 2. From the above results it was concluded that Crab Shell (0.5 mm) – Sand with ratio 1:1, flow rate 2 mL/min, Size of Crab Shell 0.5mm was optimal in phosphate removal.

3.1.3 Many other parameters such as change in flow

Figure 3.1.2 Phosphate removal using Crab Shell (0.5 mm)-Sand in down flow and up flow column


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Table 2 Properties of column packed with Crab Shell and Sand. Crab Shell – SandRatio

Flow rate

Size of Crab Shell

Exhaust time(h)

Volume of Effluent treated (mL)

1:1

1mL/min

1mm

17

1020

1:1

2mL/min

1mm

17

2040

3:1

1mL/min

1mm

25

1500

3:1

2mL/min

1mm

17

2040

1:1

1mL/min

0.5mm

32

1920

1:1

2mL/min

0.5mm

32

3840

3:1

1mL/min

0.5mm

32

1920

3:1

2mL/min

0.5mm

32

3840

1:1

2mL/min

0.25mm

28

3360

3.2 COLUMN STUDY USING NATURAL MINERAL – VERMICULITE

3.3 THOMAS MODEL FOR ADSORPTION STUDY

Study or vermiculite was done varying the concentration, Successful design of a column adsorption process flow rates, size of vermiculite and the data has been requires prediction of the concentration-time profile or tabulated below, breakthrough curve for the effluent. The maximum adsorption capacity of an adsorbent is also needed in Table 3 Properties of column packed with Vermiculite. design. Traditionally, The Thomas model is used to calculate adsorption rate constant and solid phase Vermiculite/ Flow rate Size of Exhaust Volume of concentration of adsorbate on the adsorbent from Vermiculite – Crab time(h) Effluent SandRatio Shell treated continuous mode studies (6) Sorption is usually not limited (mL) by chemical reaction kinetics but is often controlled by interphase mass transfer (25). The model is as follows, OnlyVermiculite 1mL/min 1mm 12 720 OnlyVermiculite 2 mL/min 1mm

12

1440

OnlyVermiculite 1mL/min

20

1200

0.5mm

OnlyVermiculite 2 mL/min 0.5mm VermiculiteSand (1:1)

1.25 mL /min

20

0.25mm 13

C

= 1/[1+exp

T

2400 975

Here,

t=

( kt (qmr- coV) ) ]

(1)

v r

The equation (1) becomes, The summarized results of column study with their exhaust time and amount of water treated until it reached exhaust time’s as shown in Table 3. So, finally it was concluded that 0.5 mm size vermiculite column with a flow rate 2 mL/min was optimal in phosphate removal Slope = KT Co And Intercept = KT q m r using vermiculite. Where ‘Ct’ is effluent concentration (mg/L), ‘Co’ is influent concentration (mg/L), ‘KT’ is Thomas rate constant (L/min.mg), ‘q’ is maximum adsorption capacity Journal of Indian Water Works Association

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(mg/g), ‘m’ is mass of adsorbent (g), ‘V’ is effluent

volume (mL) and ‘r’ is flow rate (mL/min).

Figure 3.3.1 shows the thomas model graph for 1 mm size Crab Shell with varying flow rates (1 mL/min and 2mL/min) and varying Crab Shall-Sand ratio (1:1 and 3:1).

Figure 3.3.2 shows the thomas model graph for 0.5 mm size Crab Shell with varying flow rates (1 mL/min and 2mL/min) and varying Crab Shall-Sand ratio (1:1 and 3:1).

Figure 3.3.3 shows the thomas model graph for Vermiculite with varying flow rates (1 mL/min and 2mL/min) and varying size (1 mm and 0.5 mm).


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Table 4 various parameters studied under Thomas Model using Crab Shell and Vermiculite. Adsorbent

Flow rate (mL/min)

Size of Adsorbent (mm)

KT (L/min.mg)

q(mg/g)

R2

Crab Shell – Sand(1:1)

1

1

0.0028

4.99

0.9557


2

1

0.0034

9.41

0.92


1

1

0.003

11.31

0.8295


2

1

0.002

23.12

0.9041


1

0.5

0.0024

14.01

0.9629


2

0.5

0.0026

24.53

0.9526


1

0.5

0.0038

15.64

0.9496


2

0.5

0.0032

29.06

0.9701

Vermiculite

1

1

0.0037

4.93

0.9632

Vermiculite

1

0.5

0.0055

9.94

0.9697

Vermiculite

2

0.5

0.006

16.29

0.9586

In Crab Shell (0.5 mm)-Sand (3:1) and flow rate 2 mL/ min, the value of q was 29.06 mg/g and therefore was considered optimal. When considering study with vermiculite, vermiculite of size 0.5 mm and flow rate 2 mL/min has q value of 16.29 mg/g which was high and considered better. Crab Shell shows higher adsorption capacity but after 8 days in Crab shell there is clogging of column due to Biofouling which reduces flow rate of the column and it is not acceptable. So, Vermiculite packed column was found to show optimal and

acceptable results.

3.4 MASS BALANCE OF PHOSPHATE IN PACKED COLUMN Mass balance of phosphate was done by finding out the amount of phosphate loaded, phosphate adsorbed in the column and phosphate eluted from the column. After each regeneration using 0.1% HCl, the above mass balance was done and represented in graphical form as shown below.

Figure 3.4.1 Mass balance for Crab Shell (0.5 mm)-Sand (1:1) with flow rate 2 mL/min.


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Figure 3.4.2 Mass Balance of VermiculiteVermiculite (0.5 mm) with flow rate 2 mL/min.

Figure 3.5.1 Regeneration cycle of Crab Shell

3.5 REGENERATION OF ADSORBENT

Regeneration of both Crab Shell – Sand and Vermiculite was done by using 0.1% dilute HCL and the adsorption study was carried out. This was done for Crab Shell – Sand of flow rate 2mL/min, ratio 1:1 and size 0.5mm and Vermiculite with flow rate 2mL/min and size 0.5 mm.

The column packed with vermiculite where column was regenerated four times and and Regeneration efficiency for 1st, 2nd, 3rd cycle and 4th cycle were 99.8%, 99.8%, 99.4 % and 98.2%.

3.6 SEM ANALYSIS FOR CRAB SHELL AND VERMICULITE

Surface morphology of Crab Shell and Vermiculite before and after adsorption-desorption studies were examined using scanning electron microscopy with 2000 x SE Column packed with Crab Shell where column can be magnification. regenerated 3 times and Regeneration efficiency for 1st, 2nd and 3rd cycle were 99.3%, 99.7% and 98.47%. In the 3rd cycle phosphate adsorption decreases to 78.26% which were 93.04% and 92.19% in 1st and 2nd cycle respectively. Journal of Indian Water Works Association

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Figure 3.5.2 Regeneration cycle of Vermiculite

Figure 3.6.1 Crab Shell beforeAdsorption (left) and afterAdsorption (right)

Figure 3.6.2 Vermiculite before Adsorption (left) and afterAdsorption (right)

32 h.Vermiculite (0.5 mm) with 2 mL/min flow rate showed phosphate removal efficiency of 96%. Maximum It was concluded that, Crab Shell (0.5 mm) - Sand (1:1) adsorption capacity was 16.29 mg/g by Thomas model with 2 mL/min flow rate showed phosphate removal with an exhaust time of 20 h. Crab Shell can be efficiency of 93.1%. Maximum adsorption capacity was regenerated and used up to three cycles whereas 24.53 mg/g by Thomas model with an exhaust time of IV CONCLUSION


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Vermiculite can be regenerated and used up to 4 cycles for phosphate adsorption with out reduction in their removal efficiency. SEM analysis was also proved the adsorption-desorption of phosphate onto Crab Shell and 6. Vermiculite. V REFERENCES 1.

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2.

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of lead on the surface of crab shell particles’, Proc. Biochem. Vol.2, pp. 671–677. Sivakumar P. and Palanisamy P.N. (2009) ‘Adsorptive Removal of Reactive and Direct Dyes Using NonConvental Adsorbent-Column Studies’, Journal of scientific & Industrial Research, Vol. 68, pp. 894-899.

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8.

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9.

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10. Vijayaraghavan K., Palanivelu K. and Velan M. (2006) ‘Biosorption of copper (II) and cobalt (II) from aqueous solutions by crab shell particles’, Bioresource Technology, vol.97, pp. 1411–1419.

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