Influence of Temperature and Disintegrated Sludge in Enhanced Biological Phosphorus Removal (EBPR) Systems

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1 The 10 th International PSU Engineering Conference May 14-15, 2012 Influence of Temperature and Disintegrated Sludge in Enhanced Biological Phosphorus Removal (EBPR) Systems Nittaya Boontian School of Environmental Engineering, Institute of Engineering, Suranaree University of Technology, Muang Nakhon Ratchasima District, Nakhon Ratchasima, 30000, Thailand Abstract A biological phosphorus removal pilot plant was used to study the effects of temperature and use of disintegrated sludge (DS) as a carbon source upon phosphorus accumulating organisms (PAOs). The values of calibrated stoichiometric and kinetic parameters at 17 and 23 C showed an important dependence on additional carbon sources from influent DS and temperature. The phosphorus removal process was efficiently performed in the two experiments carried out showing a maximum value for Y PAO and q PHA at 23 C. The PAOs calibrated parameters indicated the presence of glycogen accumulating organisms (GAOs) in the process. This is because the Y PAO values at 17 and 23 C with and without influent DS were higher than values predicted by ASM2d. At 17 C the biological phosphorus removal efficiency was more effective than at 23 C. The Arrhenius constant values ( ) obtained for the PAOs represented the temperature influences on biological phosphorus removal processes. q PHA is more influence by the temperature than the maximum rate for phosphorus release. The values for q PHA were and with and without influent DS, respectively. In addition, the values for Y PAO with and without DS were and 1.010, respectively. Keywords: Arrhenius constant; ASM2d; Disintegrated sludge; Enhanced biological phosphorus removal; Temperature 1. Introduction Successful biological nutrient removal (BNR) wastewater treatment plants (WWTPs) are based upon a number of parameters. Short-chain volatile fatty acids (VFAs) are suitable carbon sources for BNR [1]. Phosphorus accumulating organisms (PAOs) can utilize VFAs directly under anoxic condition without hydrolysis and fermentation processes [2]. In addition, VFAs can significantly enhance biological phosphorus removal (EBPR) processes [3]. Disintegration sludge (DS) with mechanical deflaking can release soluble chemical oxygen demand (SCOD) as well as VFAs [4]. EBPR processes are successful using influent DS [4]. Temperature is a fundamental factor that affects all living organisms [5]. It influences the rates of enzymatically catalysed reactions and the rate of diffusion of substrate into the cells [6]. In EBPR processes, the diverse bacterial consortium consists of psychrophilic, pyschrotrophic and mesophilic heterophic bacteria [6]. Temperature strongly influences the population composition of these groups due to their optimum growth temperatures [6]. Temperature is one of the crucial factors to control microorganisms in EBPR processes [7]. The influence of temperature on the kinetics of EBPR has also been investigated in numerous studies with contradictory conclusions. Higher phosphorus removal efficient was reported at high temperatures (20-37 C) [8]. Another study of the impact of long term temperature changes on the stoichiometry and kinetics of different processes at 5, 10, 15, and 20 C was done [9]. At temperatures between 15 and 20 C, aerobic phosphorus uptake rate shows a maximum value ( g P g -1 active biomass h -1 ). Other anaerobic and aerobic conversion rates increased with increasing temperature (5 to 20 C). Maximum specific phosphorus release rate increasing from to g P g -1 active biomass h -1 and maximum specific poly-hydroxy-butyrate (PHB) consumption rate increasing from to g PHB g -1 active biomass h -1. At 5 C, acetate was utilized in the anaerobic stage. Unutilized acetate was then consumed in downstream aerobic stages. At low temperatures, the efficiency of EBPR improves in relation to Arrhenius constant [5] -Usach [7] reported that among process temperatures of 13, 20 and 24.5 C, that the highest efficiency was observed at 13 C. Additionally, temperature is influential in controlling competition between PAOs and glycogen accumulating organisms (GAOs). PAOs are the microorganisms responsible for the phosphorus removal processes [10]. GAOs can take up organic substrate anaerobically without phosphorus release and are related to deterioration of EBPR processes (Mino et al., 1998). GAOs were a predominant microbial group when the temperature was gradually increased from 20 C to 35 C [11]. The PAOs was washed out from the systems when temperature was gradually increased. This is because the portion of energy required for maintenance increased substantially. Subsequently the energy availability for biomass growth rate was reduced [11]. Another study

2 also reported that when temperature was increased from 22±1 C to 29±1 C and then was followed by a decrease to 14±1 C, the dominant cell group was changed from PAOs to GAOs [12]. - [13] reported that PAOs were the dominant microorganisms at low temperature (10 C) regardless of the influent carbon source or ph. PAOs become the dominant organisms under temperature conditions less than 20 C and the efficiency of EBPR processes is enhanced [14], [15] - [16] - [10] found that temperature effects did not confer metabolic advantages to GAOs over PAOs when considering their aerobic metabolism. Competitive advantages were due to anaerobic processes. So far, even considering the work of other researchers, the effects of temperature on EBPR have not yet been completely elucidated. Verification of mathematical models has been found to be a useful tool for the investigation of advanced control strategies for wastewater treatment plants (WWTPs) [7], [17]. Activated Sludge Model No. 2d (ASM2d) is one of the most useful models. It can be used to describe the kinetics and behavior of autotrophs, heterotrophs, and PAOs involved in biological wastewater treatment [18]. The strict standards for EBPR wastewater treatment plant effluents require better process control. Use of ASM2d is one of the most promising approaches to elaborate optimising strategies. The influence of temperature and inclusion of DS as a carbon source on PAOs in EBPR has not been reported. This study aims to calibrate ASM2d for PAOs behavior in order to investigate combined effects of temperature and influent disintegrated sludge on EBPR. The pilot-scale Modified University of Cape Town (MUCT) processes were carried out at two different temperatures. The experimental results were calibrated using ASM2d. Arrhenius equation constants in relation to influence of temperature and influent DS on PAOs behavior were calculated after obtaining the calibrated parameters. 2. Materials and Methods 2.1 The MUCT pilot scale The experiments were done with a MUCT pilot scale process. The pilot scale consisted of two series of reactors using influent DS (test) and influent with no DS (control), respectively. A schematic diagram of reactor configuration is shown in Figure 1. The process consisted of five reactors in series. These included anaerobic, 1 st anoxic, 2 nd anoxic, aerobic phases and clarifier stages. They had effective volumes of m 3, m 3, m 3, m 3 and m 3, respectively. The operating conditions included influent wastewater flow rate (Q IN = 0.60 m 3 h -1 ), return activated sludge flow rate (Q R = 0.51 m 3 h - Influent Anoxic recirculation flow Aerobic recirculation flow Anaerobic 1 st Anoxic 2 nd Anoxic Aerobic Clarifier Return activated sludge Excess sludge Figure 1 A schematic diagram of the MUCT systems. 1 ), anoxic recirculation flow rate (Q 1 = 0.60 m 3 h -1 ) and aerobic recirculation flow rate (Q 2 = 0.60 m 3 h -1 ). An equivalent mixed liquor suspended solid (MLSS) in both test and control was maintained. Average temperature was maintained at 17 C. Another set of experiments was conducted at a higher constant temperature (23 C). The solid retention time (SRT) in test and control experiments was 45-days and 16- days, respectively. Experiments conducted at 17 o C were done over a 4 month period in the winter season. Additionally, observations made at 23 o C were done over a four month period during summer months. This was done to maintain appropriate MLSS levels. Both series of experiments were conducted under the same conditions. DS was fed to the test series only. In order to develop EBPR, acetic acid was fed to the influent at an equivalent level in both the test and control. Acetate concentrations in municipal wastewater were not high enough to enable EBPR. The control was fed with acetic acid only added to the influent. For the test, acetic acid and DS were added to the influent. DS contained acetic acid as one if its components. Influent, anaerobic stage, aerobic stage and effluent were sampled on a daily basis. 2.2 Simulation methodology This methodology is followed other research [19]. Aquasim [20] was used to calculate the sensitivity analysis. GPS-X (Hydromantis, Inc., Hamilton, Canada) was used as the simulation tool. The ASM2d model was calibrated with the parameter significance ranking resulting from calculations. The iterative algorithm using GPS-X was re-evaluated until the sensitivity parameter no longer affected the simulation output. 2.3 Temperature coefficient The effect of temperature on reaction rates for small temperature differences can be expressed by the Arrhenius equation: (1) where k 1 and k 2 are reaction rates at temperatures T 1 and T 2. is a temperature coefficient. The values were calculated by fitting equation (1) to the data. This allowed comparison of temperature coefficients for different processes considered in mathematical models [21]. In this study, of different processes at 17 and 23 C were presented. Effluent

3 3. Results and Discussion 3.1 Wastewater characteristics Simulation of operating periods was completed for steady state processes. The influent characteristics of disintegrated sludge (DS) and without disintegrated sludge (WDS) at 17 and 23 C are summarized in Table 1. Table 1 Wastewater components of DS and WDS. Symbol 17 and 23 C Unit DS WDS S O2in 0 0 g O 2 m -3 S Ain g COD m -3 S Fin g COD m -3 S Iin g COD m -3 S NH4in g N m -3 S NO3in 0 0 g N m -3 S PO4in g P m -3 S N2in 0 0 g N m -3 X Iin g COD m -3 X Sin g COD m ASM2d calibration Kinetic and stoichiometric ASM2d parameters having high influence on process outputs were determined and considered as sensitivity parameters. Parameter sensitivity ranking was obtained from sensitivity analysis. Resulting sensitivity parameters were used for ASM2d calibration. Sensitivity analysis and calibration followed an approach discussed by other research [19]. The kinetic and stoichiometric parameters obtained for autotrophs and PAOs are experiments done at 17 and 23 C with and without influent DS was performed once steady state was achieved. There are no calibration results for heterotrophic organisms at 17 and 23 C conditions. This is because heterotrophic activity is not significantly different at these two temperatures. PAOs kinetic parameters obtained at 17 C indicate that the yield coefficient (Y PAO ) and poly-hydroxyalkanoates (PHA) storage (q PHA ) decreased. In contrast, a saturation coefficient for ammonium (substrate), K NH4 AUT, in autotrophs was lower at 23 C than at 17 o C. Values of Y PAO, Y PO4, and K MAX in PAOs are different in ASM2d because of the presence of GAOs [17], [22]. K MAX refers to the maximum ratio X PP /X PAO. GAOs are treated in the same manner as PAOs in ASM2d in that they cannot store polyphosphate (poly-p). On the basis of this ASM2d assumption, PAOs and GAOs are not different [17]. Glycogen is not represented as an intracellular storage product in ASM2d. Thus, GAOs and glycogen were presented in PAOs [17], [22]. Observed Y PAO values at 17 and 23 C with and without influent DS are higher than predicted by ASM2d (Table 2). One exception is that Y PAO without influent DS at 17 C is lower than predicted by ASM2d. GAOs are present Table 2 Stoichiometry and kinetic parameter. Sym ASM2 d 17 C 23 C DS WDS DS WDS Y PAO Y PO Y PHA q PHA q PP µ PAO d -1 b PAO d -1 b PP d -1 b PHA d -1 Unit COD g P g -1 COD P g X PHA g -1 X PAO d -1 g X PP g -1 X PAO d -1 K PS g P m -3 Y A µ AUT d -1 b AUT d -1 N K O g O 2 m -3 K NH g N m -3 in pilot-scale WWTPs. Under anaerobic conditions, both PAOs and GAOs can store VFAs internally in the form of PHA. PAOs utilize energy from poly-p and glycogen degradation. In contrast, GAOs utilize energy from glycogen degradation only. When increasing GAO population, Y PO4 values are decreased [17], [21]. In this study Y PO4 (0.4) was found to have a similar value to that predicted by ASM2d. The behavior of Y PO4 with respect to ASM2d is different from that seen for Y PAO. Y PO4 values in other studies were reported to be 0.42 and 0.46 g P g -1 COD in Elche B and Elda WWTPs, respectively [17]. It was concluded that GAOs were absent in Elche B WWTPs since the value of Y PO4 was close to the predicted ASM2d value (0.4). Additionally, Elda WWTPs contained GAOs, even though Y PO4 was much higher than the expected value for a mixed population of PAOs and GAOs. This caused a higher ph (7.95). Y PAO at 17 C was lower than at 23 C. This result suggests that even though the values of kinetic parameters decrease as temperature is reduced, the efficiency of EBPR processes is higher at lower temperatures. PAOs occur at 10 C or less because they are psychrotrophic. Under these conditions, PAOs growth rate is higher than non-paos in EBPR systems [5]. This results in an increased PAOs population at lower temperatures [5]. The EBPR performance at 20 C was lower than at 10 C even though the kinetic parameter values increased when temperature was increased from 10 to 20 C [5]. The reason for higher efficiency of EBPR performance at lower temperature was related to reduce competition

4 for substrate by non-paos under anaerobic conditions. The Arrhenius relationship (Equation 1) was employed using the ASM2d parameters. A set of calibrated parameters is required in order to use this equation. The constant values of the Arrhenius equation were calibrated parameter resulting from experiments conducted at 17 and 23 C (Table 3). The Arrhenius constant values of PAOs expressed in Table 3 can be categorized into two groups. The first group, consists of temperature independent parameters ( = 1). Stoichiometric and kinetic parameters, with the exception of Y PAO with influent DS are included. The second group, includes temperature dependent parameters ( 1) Table 3 Arrhenius constant value ( Symbol DS WDS Y PAO Y PO4 1 1 Y PHA 1 1 q PHA q PP 1 1 µ PAO 1 1 b PAO 1 1 b PP 1 1 b PHA 1 1 K PS 1 1 Y A 1 1 µ AUT 1 1 b AUT 1 1 K O2 AUT 1 1 K NH4 AUT ) for PAOs. Values of q PHA and Y PAO (without influent DS) are included. PAOs processes in ASM2d, the mean value of the Arrhenius constant obtained for q PHA and Y PAO ( = and with and without influent DS, respectively) are closer to the ASM2d values. The literature values for q PHA and Y PAO Arrhenius constants are given in Table 4. Under anaerobic conditions, values obtained for the rate constant for storage of PHA (q PHA ) and the maximum rate for phosphorus release (estimated as the product Y PO4 *q PHA ) were the same values with and without influent DS. They were and 1.023, respectively. It was observed, that the temperature influence on the maximum rate for PHA storage is similar to influence of temperature on the maximum rate of phosphorus release. This result is different from that of other researchers (Table 4). Under aerobic conditions, values obtained for the rate constant for storage of polyphosphate (q pp ) was equal to 1. This value is different from that reported in other studies (Table 4). Table 4 Comparison of Arrhenius constant value ( ) q PHA P release Y PAO Poly-P Ref This 3 This [7] 1.080± ± ±0.012 [8] ± ± ±0.006 [9] [18] 1.095± ± ±0.017 [23] [24] [25] 1 DS, 2 WDS, 3 This study 4. Conclusions In this work, a biological phosphorus removal pilot plant was used to study the effects of temperature and use of disintegrated sludge (DS) as a carbon source upon PAOs. Experiments were carried out at 17 and 23 C. The ASM2d model was calibrated at 17 and 23 C under conditions with and without DS in the influent stream. Arrhenius equation constants were obtained for phosphorus removal processes influenced by temperature and DS. It was found that temperature and influent DS influences biological phosphorus removal. The Arrhenius equation constants ( ) of the yield coefficient (Y PAO ) with and without DS were and 1.010, respectively. The Arrhenius equation constants for poly-hydroxy-alkanoates (PHA) storage (q PHA ) with and without DS were and 1.023, respectively. Acknowledgements The work was fully supported by Suranaree University of Technology, Thailand. References [1] Tong, J. and Chen, Y Enhanced biological phosphorus removal driven by short-chain fatty acids produced from waste activated sludge alkaline fermentation. Environmental Science and Technology, 41(20): [2] Brdjanovic, D., Slamet, A., van Loosedrecht, M.C.M., Hooijmans C.J., Alaerats G.J., Hejinen J.J Modeling COD, N and P Removal in a Full-Scale WWTP Haarlem Waaderpolder. Water Research, 34(3): [3] Feng, L., Chen, Y., Zheng, X Enhancement of waste activated sludge protein conversion and volatile fatty acids accumulation during waste activated sludge anaerobic fermentation by carbohydrate substrate addition: the effect of ph. Environmental Science and Technology, 43(12): [4] Kampas, P., Parsons, S.A., Pearce, P., Ledoux, S., Vale, P., Cartmell, E. and Soares, A An internal carbon source for improving

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