PSYCHROPHILIC ANAEROBIC PRETREATMENT OF LOW-STRENGTH WASTEWATER USING THE ANAEROBIC MIGRATING BLANKET REACTOR

The feasibility of a compartmentalized anaerobic migrating blanket reactor (AMBR) was studied for the treatment of low-strength wastewater under low-temperature conditions. During an operating period of 186 days, we fed a 20-liter AMBR non-fat dry milk as a synthetic wastewater at low temperatures (15°C and 20°C). The concentration of the influent was constant at COD and BOD5 concentrations of 600 and 285 mg/liter, respectively. The soluble chemical oxygen demand (SCOD) removal efficiency was 73% at the end of the operating period at a 4-h hydraulic retention time (HRT), while total COD (TCOD) and methane-based COD (MCOD) removal efficiencies were 59% and 36%, respectively. At a 4-h HRT, staged conditions promoted a complete removal of propionic acid in the final compartments of the reactor. The specific methanogenic activity of the granules increased slowly until the end of the operating time, improving the removal rate. Biomass was retained effectively, as the sludge retention time (SRT) was always exceeding 50 days during step decreases of the reactor HRT from 12 to 4h. A long SRT promoted stability during changes in flow in which the SCOD removal remained above 70%. During a 1-day peak flow study, the HRT was reduced from 4 to 1 h during which solids levels in the effluent increased and the SRT decreased to 12.6 days. However, 1 day after the peak flow the performance was almost similar as before the peak flow. AMBR treatment of low-strength wastewater at low temperatures was found to be attractive, because of staged conditions and the ability of the system to retain biomass sufficiently during changes in flow.