Anaerobic migrating blanket reactor treatment of low-strength wastewater at low temperatures.

The feasibility of the compartmentalized anaerobic migrating blanket reactor (AMBR) was studied for the treatment of low-strength soluble wastewater under low-temperature conditions. During an operating period of 186 days, a 20-L AMBR was fed nonfat dry milk substrate as a synthetic wastewater at low temperatures (15 and 20 degrees C). The concentration of the influent was constant at chemical oxygen demand (COD) and 5-day biological oxygen demand (BOD5) concentrations of 600 and 285 mg/L, respectively. The soluble COD (SCOD) removal efficiency was 73% at the end of the operating period (15 degrees C) at a 4-hour hydraulic retention time (HRT), while the total COD (TCOD) removal efficiency was 59%. At a 4-hour HRT, staged conditions promoted complete removal of propionic acid in the final compartments of the reactor. The specific methanogenic activity of granules increased slowly until the end of the operating time, improving the removal rate. Biomass was retained effectively, as evidenced by the solids retention time (SRT) that was always greater than 50 days even during step decreases of the reactor HRT from 12 hours to 4 hours. A long SRT also promoted system stability during changes in flow, which was observed by SCOD removal efficiencies staving greater than 70%. During a hydraulic stress test, the HRT was reduced from 4 hours to 1 hour for one day (24 HRTs) in which volatile suspended solids (VSS) in the effluent increased from an average background level of 8.7 g/d to 35 g/d and the SRT decreased from 50.5 days to 12.6 days. However, mixed liquor volatile suspended solids concentration decreased only by 1 g/L, and hence a similar COD removal efficiency and biogas production was found one day after the hydraulic stress (as compared to one day before the hydraulic stress).