[Study on the operation of a methanogenic EGSB reactor under acid condition at pH 6.0]

In this paper the methanogenic process under acid condition at pH 6.0 was studied. Inoculated with neutral granular sludge, a 3.1 L EGSB reactor was operated for 345 days, the pH value in the reactor was gradually lowered down, and the acid-tolerant methanogenic granular sludge was achieved, and the anaerobic EGSB reactor was operated stably under lower pH and lower alkalinity. At pH 6.0, influent COD 3000 mg/L, COD OLR 5 kg/(m3 x d), the average COD removal efficiency of the EGSB reactor was 95.0%, while the effluent alkalinity (CaCO3) was only 328.5 mg/L, the biogas production per gram removal COD was 372.2 mL with 57.6% methane content. At pH 6.0, influent COD 4000 mg/L, COD OLR 7.5 kg/(m3 x d), the average COD removal efficiency was 90.9%, and the effluent alkalinity (CaCO3) was 404.8 mg/L, the biogas production per gram removal COD was 446.3 mL with 55.9% methane content. The EGSB reactor was operated at pH 6.0-6.1 for 112 days, which showed the stable methanogenic process was feasible at low pH and low alkalinity.