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ScienceDirect APCBEE Procedia 10 (2014) 126 – 130

ICESD 2014: February 19-21, Singapore

Hydrodynamic Properties of Aerobic Granules Cultivated on Phenol as Carbon Source Farrukh Basheer and I. H. Farooqi *

Department of Civil Engineering, Aligarh Muslim University, Aligarh 202 002 India

Abstract The cultivation and hydrodynamic properties such as morphology, fractal dimension, porosity, size distribution, and settling velocity of stable aerobic granules, developed in a column type sequencing batch reactor SBR was investigated in this study. A column type SBR was operated with organic loading rate of 1.8 kg phenol/m3day with phenol as a sole carbon source. The granules were fractal and porous aggregates and had a fractal dimension and porosity of 2.47 and 0.70.9 respectively. The settling velocities of aerobic granules were in the range of 2.38x10 -02m/s-7.1x10-02m/s. This was in good agreement with the settling velocities predicted by Stoke’s law for porous but impermeable spheres. This may be due to the EPS (Extracellular Polymeric Substances) produced by bacteria form a gel matrix that clogs the pores within the granules which resulted in reduced permeation and settling velocities. © Authors. Published by Elsevier B.V. This isand/or an open access articleunder under the CC BY-NC-ND license ©2014 2014The Published by Elsevier B.V. Selection peer review responsibility of Asia-Pacific (http://creativecommons.org/licenses/by-nc-nd/3.0/). Chemical, Biological & Environmental Engineering Society Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords: Aerobic Granules; Phenol; Porosity; Sequencing Batch Reactor (SBR); Settling Velocity

1. Introduction The use of aerobic biological treatment can be traced back to the late nineteenth century.. These days a new innovation in aerobic process has been developed known as aerobic granular sludge technology. It has many advantages over the conventional activated sludge process i.e. it can withstand fluctuating loads; lesser space requirement; lower biomass production due to high biomass retention [1]. Settling velocity is a critical

Corresponding author. E-mail address: [email protected]

2212-6708 © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2014.10.029

Farrukh Basheer and I.H. Farooqi / APCBEE Procedia 10 (2014) 126 – 130

factor that regulates sludge liquid separation and effluent quality in biological wastewater treatment processes. The settling velocity of aerobic granules depends upon its drag coefficient, and hence the calculation of drag coefficient has been an important parameter for microbial granules. In this study, aerobic granules were cultivated in SBR with phenol as only carbon source. Aerobic granules developed were analysed for hydrodynamic and other properties. 2. Materials and Methods 2.1. Reactor Setup and Operation A laboratory scale SBR with an effective volume of 2 L was used to cultivate aerobic granules. The internal diameter of the reactor was 5 cm and the working H/D (Height/Diameter) was about 20. Fine air bubbles for aeration and mixing were supplied by diffusers placed at the reactor bottom. Superficial air velocity was maintained in the range of 2-3 cm/s. A reactor was operated sequentially in 8 h cycles which consist of 5 min of influent filing, 472-447 min of aeration, 5-30 min of settling and 3 min of effluent withdrawal. Effluent was discharged at 50 cm from the bottom of the reactor with a volumetric exchange ratio of 50%. Seeding biomass was obtained from the municipal wastewater treatment plant, Okhla, New Delhi, India. The sludge was acclimatized to phenol in batch culture for a period of one month. The acclimatized sludge was used as inoculum for the reactor. The reactor was fed with phenol as a sole carbon source by using a synthetic wastewater with following nutrient composition. Phenol, NH4Cl, MgSO4·7H2O, K2HPO4, and KH2PO4 at a weight ratio of 1:0.4:0.26:3.3:2.7. The media was supplemented with 1 ml/ L of micronutrients, as described previously [2]. 2.2. Characteristics of granules 2.2.1. Terminal Settling Velocity of granules The settling velocity study of granules was performed in a vertical glass column filled with tap water. The glass column which was 100cm in height to insure that terminal settling velocity could be reached, and 5.0 cm in internal diameter to minimize the wall effect on granule settling. Before the settling test each granule was analysed using Cenisco binocular petrological microscope with SANYO digital camera. The photographs were analysed using image analysis system (Averz Software). More than 40 granules diameter were determined using image analysis system. After the settling test the dry mass of aerobic granule was measured. The granule was dried at 105o C for 1.5 h on a pre-weighted membrane filter and its dry mass ‘Wd’ was measured. 2.2.2. Granule Strength and Density Granule strength is defined as the ability of granules to resist disintegration. It is defined as an integrity coefficient (IC) (%) which is the residual volatile suspended solids (VSS) after sample was agitated for 5min at 200 rpm to a total VSS of the intact granules prior to agitation [3] .The stronger granules have higher ICs. The density of aerobic granules was determined using (Volumetric Displacement Method). 2.2.3. Stroke’s law for porous but impermeable granules. The terminal settling velocity, Us of single impermeable particle aggregate can be predicted by the following generalization of Stoke’s law for wide range of Reynold’s number [4]. Us= √(4g(ρa-ρ1)d/3ρ1Cd ) where ρa and ρ1 are the densities of the aggregate and the liquid respectively , g is the gravitational constant

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and d is the size of the aggregate . The calculation of Cd, which is the function of Reynolds number, Re = ρa Utd/μ, where Ut is the actual settling velocity and μ is the fluid viscosity. The empirical drag Coefficient Cd is adjusted for higher Reynolds number (Re>1) according to CD=24/Re +6/(1+ √Re )+0.4. Porosity of aerobic granule can calculated from its dry mass by equation given by (Li and Yuan 2002)[4], ε=1- 6fWd/ (πρad3) where f is the ratio between the wet mass and dry mass of the cells. It has been determined f =3.45 for aerobic bacteria comprising microbial aggregates.

Fig. 1. Microscopic image of fully developed granules on day 145 and Macrostructure photo of granules in 90mm Petri dish on day 145. 1.2

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3. Results and Discussion 3.1. Characteristics of Aerobic Granules. The aerobic granules cultivated in SBR were having a size range from 1.1 mm-5.56 mm. On day 145, the settling experiments were carried out on aerobic granules cultivated in SBR. The size of granule varies from 1.1 mm to 5.56 mm. The aerobic granules were compact in structure and having a stable and clear outer surface (Figure 1). The integrity coefficient (IC) and granules density was found to be 95% and 1067 kg/m 3 respectively. The settling velocity of granules was found to be in the range of 2.38x10 -02m/s-7.1x10-02m/s. It has been observed that as the size increased, the settling velocity also increased. Figure (2a) shows the variation velocities of terminal settling and predicted Stoke’s law with diameter of granules. The difference between the observed and predicted settling velocities increased slightly as the aerobic granules became larger. The Reynolds number Re for aerobic granules varied in the range of 30-450. The variation of drag coefficient Cd with Reynolds number is shown in Figure (3a). The dimensionless ratios between the observed and the predicted settling velocities, Г, were in the range from 0.7-1.1 (Figure 2b). Based on the slope of logarithmic relationship between the dry mass ‘Wd’and size ‘d’ of aerobic granule as shown in Figure( 4a), the fractal

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dimension ‘D’ of the aerobic granule was calculated as 2.47. The porosity of aerobic granules varied from 0.71 to 0.90 (Figure 4b) 3.2. Discussion Settling velocity is an important parameter that regulates the solid liquid separation in the biological wastewater treatment. The advantage of aerobic granules over the conventional activated sludge flocs is its high settling properties. The settling velocities of aerobic granules varied from 3.7x10-03 to 6.6x10-02 m/s, which were much higher than those of activated sludge flocs( 1.7x10 -03 to 4.2 x10 -03m/s). In this study the settling velocity of granules varied from 2.38x10-02m/s-7.1x10-02m/s. The observed settling velocities were in general similar with the predicted value obtained by Stoke’s law for porous and impermeable aggregates (Figure 2a). The observed slope of settling velocity-size relationship was 0.0127 which was close to the predicted slope of 0.0152. This similarity shows that aerobic granules in the SBR did not have an internal permeation that was significant in affecting their settling velocities. It may be due to the EPS (Extracellular Polymeric Substances) produced by bacteria form a gel matrix that clogged the pores within the granules [5]. Chiu et al (2006) [6]found that as the size of granule increased mass transfer limitation takes place, the biomass inside large granules may not be able to receive sufficient substrate and oxygen to contribute to waste organic degradation. Xiao et al 2008 [7] proposed that it can be assumed that the biomass within the penetration depth (δ =200μm) from the surface is active biomass, whereas the sludge below δ inside the granule is largely inactive due to substrate and oxygen limitation. Johnson et al (1996) [8] found that highly permeable inorganic aggregates settle 4-8 times faster than predicted by Stoke’s law. The dimensionless ratios between the observed and the predicted settling velocities, Г, were in the range from 0.7-1.1 (Figure 2b), which is closed to unity (Average of 0.9). 2.5

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The fractal dimension ‘D’ was calculated using the slope and intercept of the plot between W d and d as shown in Figure (4a) and was found to be 2.47. The fractal dimensions were within the range as reported in the literature. Li and Ganczarczyk (1987) [9] reported wide range of fractal dimensions 1.4-2.8 for particle aggregates in water and wastewater treatment process. Microbial flocs in activated sludge process have fractal dimension of about 2.25 [4] . Zahid et al (1994) [10] reported the fractal dimension of biofim formed by attached bacterial growth to be high upto 2.8. Anaerobic granules formed by biohydrogen production are reported to have a fractal dimension that increased from 2.11 to 2.48 with increasing organic loading 5-15 g COD/L [5]. Xiao et al (2008) [7] reported fractal dimension of 2.42 for bacterial granules which is comparable to results of this study. The granules studied in the present study were porous in nature; with porosity ranging from 0.71-0.91. Xiao et al (2008) [7] reported the range of porosities values for fungal

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aerobic and bacterial aerobic granules as 0.78-0.97 and 0.68-0.92 respectively. Earlier Li and Yuan et al (2002) [4] found porosity greater than 0.95 for conventional activated sludge flocs. The porous structure of aerobic granule was able to facilitate the passage of the oxygen and substrates as well as the release of the metabolic products [11]. 0.95

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4. Conclusion This study showed that compact well settling aerobic granules can be cultivated in SBR on phenol as a sole carbon source. After 30 days of operation aerobic granules were formed in the reactor. At phenol loading of 1.8 kg phenol/m3day removal efficiency of 79% was achieved. The aerobic granules cultivated in SBR were having a size range from 1.1 mm-5.56 mm. The aerobic granules were fractal and porous in nature. The settling velocities of aerobic granules were in good agreement with the settling velocities predicted by Stoke’s law for porous but impermeable spheres. It is supported by earlier work that extracellular polymeric substances released by microorganisms, can fill the pores within the aerobic granules which resulted in reduced permeation and settling velocities. References [1] Liu Yu, Tay JH. State of art of biogranulation technology for wastewater treatment. Biotechnol. Advan 2004; 22:533-563 [2] Moy BYP, Tay JH, Toh SK, Liu Y. Tay STL . High organic loading influences the physical characteristics of aerobic granules. Lett. Appl. Microbiol 2002; 34(6): 407–412. [3] Ghangrekar MM, Asolekar SR, Ranganathan KR, Joshi SG. Experience with UASB reactor start up under different operating conditions. Water Sci Tec 1996; 34:5-6: 421-428 [4] Li XY, Yuan Y. Settling velocities and permabilities of microbial aggregates. Water Res 2002; 36: 3110-3120. [5] Zhang JJ, Li XY, Oh SE, Logan BE. Physical and hyrdrodynamic properties of flocs produced during biological hydrogen production. Biotechnol . Bioengg 2004; 88: 854-860. [6] Chiu ZC, Chen MY, Lee DJ, Tay STL, Tay JH, Show KY. Diffusivity of oxygen in aerobic granules Biotechnol. Bioeng 2006; 94: 505 [7] Xiao F, Yang SF Li XY .Physical and hydrodynamic properties of aerobic granules produced in sequencing batch reactors. Separation and Puri. Tech. 2008; 63: 634-641. [8] Johnson CP, Li XY, Logan BE. Settling velocities of fractal aggregates. Environ Sci Tech 1996; 30: 1911-1918. [9] Li DH , Ganczarczyk JJ . Stroboscopic determination of settling velocity, size and porosity of activated sludge flocs . Water Res. 1987; 21: 257-262 [10] Zahid WM Ganczarczyk .A technique for a characterization of RBC biofilm surface. Water Res 1994; 28: 2229-2231. [11] Su, KZ and Yu HQ. Formation and characterization of aerobic granules in a sequencing batch reactor treating , soyabeanprocessing wastewater. Environ. Sci. Technol 2005; 39: 2818-2827