To investigate the feasibility of anaerobic wastewater treatment technology for low strength sugar refinery wastewater (0.4 - 0.5 g COD/L), an 8.8 L volume of anaerobic granular sludge bed reactor was operated at 20°C for 400 days. The operation mode was combination of one pass flow (UASB, 50 min) and effluent-recirculation (EGSB, 10 min) mode. The aerobic down-flow hanging sponge (DHS) reactor was installed as a post-treatment. During the started-up period, reactors were fed with synthetic wastewater at overall HRT of 3 hours (anaerobic 2 hours, aerobic 1 hour). After day 85, feed was changed to real wastewater together with supplement of nutrients, trace elements and NaHCO3. The sufficient COD removal efficiency (85% SD±6.2) and stable process performance were elicited from the granular sludge bed reactor.Also, post-treatment (DHS reactor) offered good quality of effluent (45 mg COD/L, 7 mg BOD/L) and it achieved the discharge standard. Increasing of sulfate concentration of wastewater caused higher contribution of sulfate reducing bacteria for COD removal. The sludge concentration and settleability were well maintained thoroughly. However, floatation of large size granule was observed in the later part of experiment. This phenomenon may attribute to the high growth yield of retained sludge at 20°C.

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