Development of aerobic granular sludge for the removal of antibiotic sulfamethoxazole from municipal wastewater
Jafari Kang, Abbass
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Aerobic granular sludge (AGS) was developed in anoxic/anaerobic/oxic sequencing batch reactors (SBR) for the removal of antibiotic sulfamethoxazole from municipal wastewater. First, the stability and biological nutrient removal (BNR) efficiency of aerobic granules at low organic loads (when applied to municipal wastewater) was studied. For this aim, granules obtained with high-strength (COD = 1400 mg/L) wastewater were fed with medium (COD = 700 mg/L) and then low-strength (COD = 400 mg/L) municipal wastewater. The granules rapidly acclimated to the medium-strength wastewater. However, feeding with low-strength wastewater reduced the food/microorganisms (F/M) ratio from 0.4 to 0.2 gCOD/gVSS d and granules disintegration occurred. Re-granulation was obtained after poor settling biomass was washed out and the F/M ratio reached 0.4 gCOD/gVSS d. Second, the BNR treatment performance of the granules was evaluated under two operation strategies: i) continuous anaerobic feeding and ii) anaerobic contact. Results indicated that, anaerobic contact increased anaerobic COD utilization from 17-24% to 45-53% with improving mass transfer and consequently, improved phosphorus removal from 63 to 93%. The anaerobic contact also improved the effluent quality from 87 to 46 mg/L VSS with prevention of flocs formation. With the application of anaerobic contact retention time (SRT) increased from 15 to 32 days. Third, the removal of SMX in aerobic granular sludge was compared with conventional activated sludge in anoxic/anaerobic/oxic SBRs under the same operation conditions. For three months, 2μg/L SMX was spiked into the reactors’ feeds (synthetic municipal wastewater). The presence of SMX had no significant impact on treatment performance of the suspended and granular biomass in terms of removing organics and nutrients. Overall, with 12 h of hydraulic retention time (HRT), mean removal efficiencies of 84±8% and 73±10% were obtained for the granular and suspended biomass, respectively. Results of SMX elimination during eight hours of a cycle consisting of anaerobic/anoxic and aerobic phases showed that SMX removal was obtained only under aerobic condition while mixing under anoxic/anaerobic condition did not remove SMX. This confirms the insignificance of SMX removal via anoxic/anaerobic transformation and/or sorption onto activated sludge. The pseudo-first order SMX biodegradation constant rate constants (kbio) in the granular and suspended biomass at steady-state operating condition, were 2.25±0.30 and 1.34±0.39 L/gVSS.d, respectively. The mean value of kbio obtained with granular sludge was significantly greater than that with the suspended biomass. These results, suggest that aerobic granular sludge, which has advantages such as high biomass retention and high biomass concentration, could be used as an efficient process for the removal of such organic micropollutants.