Anaerobic Treatment of Actual Domestic Wastewater with EGSB Reactor at Ambient Temperature

Abstract

To assess the feasibility of actual domestic wastewater treatment by an expanded granular sludge bed (EGSB) reactor at ambient temperature, the startup and stable operation performance of an EGSB reactor seeded with digestion sludge treating actual domestic wastewater was monitored in the range of 13~25degC. The results showed that there was no adaptive stage to treat actual domestic wastewater using the granules incubated through feeding brewery wastewater at 25degC. With 131~618 mg.L -1 influent COD, only 1.1 h HRT, 2.6~12.27 kgCOD-m -3 -d -1 high organic loads, the EGSB reactor could gain a favorable operation effect: 20~180 mg.L -1 low effluent COD, 1.38~1.59 mmol/L effluent VFA and 66-85% high COD removal efficiency. And which meant a successful startup of the EGSB seeded with digested sludge for the treatment of actual domestic sewage under ambient temperature. It only took three months. About live months stable operation, along with operation temperature stepwise decreased from 25 to 13degC, the EGSB reactor treating actual domestic wastewater run well. With 88~952 mg.L -1 influent COD concentrations, gradually shortened HRT from 3.4 to 0.4 h and even with a high organic loads up to 38.1 kg COD-m -3 -d -1 the EGSB reactor could keep 28~103 mg.L -1 effluent COD concentrations and attain 61~93% COD removal efficiency. Simultaneously the effluent VFA could maintain at the range of 0.72~1.46 mmol.L -1 all the while. The optimal operation conditions were low HRT of 0.5~0.8 h, high influent flow of 15~24 L.h -1 and low recycle ratio of 0~0.6. The proportion of larger granules could increase with the lowering temperature, but the settled velocity began to decrease, low COD concentration and low temperature were the dominating factors. The granules were still hold in the EGSB reactor without any washout though settled velocity decreased to 18 m.h -1 at 13degC.