Membrane bioreactors for anaerobic treatment of wastewaters

Anaerobic treatment of municipal wastewaters or other wastewaters of weaker strength has conventionally been difficult, especially in regions of cooler climate. Issues with solids retention and sufficient biomass concentration and activities required for treatment are usually of primary concern in these situations. However, the recent incorporation of membranes in the anaerobic treatment of municipal wastewater has made this technology feasible through the absolute retention of biomass within the reactor. Among the many advantages this technology has over its aerobic membrane bioreactor (MBR) counterpart, the most attractive may be the absence of an energy requirement for aeration. Although the anaerobic membrane bioreactor (AnMBR) is a promising technology, limited understanding of the interactions between the reactor biomass and the filtration membranes in the AnMBR has generally confined it to the lab scale level. To this end, the subject of examination for this study is the feasibility of AnMBR treatment of municipal wastewaters, with a strong focus towards membrane operation at moderate operating temperatures. Two experiments were conducted during this study. The first was the long-term operation of two commercially available membranes (hollow fibre and flat sheet) operated in parallel within the reactor. The achievable operational OLR range for the AnMBR was about 1.25 kg COD/m³-d. COD removal efficiency for the AnMBR system during biomass acclimatization was 84% with the addition of supplemental acetate in the feed. This decreased to 43% after the removal of supplemental acetate at a reactor temperature of 25 °C. Biogas production of the system decreased by 20% subsequent to a temperature decrease of 5 °C, due likely to decreased methanogenic activities. The second experiment was to assess the mechanism(s) of membrane flux decline and to compare them with mechanisms identified for the same membranes applied in an aerobic MBR system. The major difference between filtration of the aerobic and anaerobic mixed liquor was the membrane surface cake layer fouling. The observed anaerobic mixed liquor resistance was nearly 100 times greater than the aerobic contribution. It was observed that the mechanism of flux decline of the organic membrane in an anaerobic environment was due to surface cake layer fouling.Applied Science, Faculty ofCivil Engineering, Department ofGraduat