Treatment of low-strength soluble wastewater using an anaerobic baffled reactor (ABR)

Abstract

Treatment of low-strength soluble wastewater (COD ≈ 500 mg/L) was studied using an eight chambered anaerobic baffled reactor (ABR). At pseudo steady-state (PSS), the average total and soluble COD values (COD T and COD S) at 8 h hydraulic retention time (HRT) were found to be around 50 and 40 mg/L, respectively, while at 10 h HRT average COD T and COD S values were of the order of 47 and 37 mg/L, respectively. COD and BOD (3 day, 27 °C) removal averaged more than 90%. Effluent conformed to Indian standards laid down for BOD (less than 30 mg/L). Reactor effluent characteristics exhibited very low values of standard deviation indicating excellent reactor stability at PSS in terms of effluent characteristics. Based on mass balance calculations, more than 60% of raw wastewater COD was estimated to be recovered as CH 4 in the gas phase. Compartment-wise profiles indicated that most of the BOD and COD got reduced in the initial compartments only. Sudden drop in pH (7.8–6.7) and formation of volatile fatty acids (VFA) (53–85 mg/L) were observed in the first compartment due to acidogenesis and acetogenesis. The pH increased and VFA concentration decreased longitudinally down the reactor. Residence time distribution (RTD) studies revealed that the flow pattern in the ABR was neither completely plug-flow nor perfectly mixed. Observations from scanning electron micrographs (SEM) suggest that distinct phase separation takes place in an ABR.