Anaerobic membrane bioreactor for the treatment of low strength wastewater

Abstract

This research investigated the fundamentals of anaerobic membrane bioreactor (AMBR) operated at low trans-membrane pressure (TMP) and cross-flow velocity (CFV) using poly-tetrafluoroethylene (PTFE) membrane for the treatment of low strength wastewater. Specific methanogenic activity (SMA) test was used to examine the methanogenic activity profiles of suspended and attached sludge in AMBR treating synthetic municipal wastewater at 25 and 15°C. It was hypothesized that accumulated biomass on the membrane surface could act as a secondary membrane as well as a biofilm which removed chemical oxygen demand (COD) biologically. The results showed that attached sludge on the membrane surface had lower activity than suspended sludge. Attached sludge on the membrane surface contained less extractable extracellular polymeric substance (EPS), especially protein content, than the suspended sludge, which could be related to the decreased methanogenic activity. Membrane in AMBR system is likely not only to retain all biomass in the reactor, but also complement decreased biological removal efficiency by rejecting soluble organics. AMBR was operated at COD loading rates of 1-2 kg/m·d for 280 days. Permeate TCOD concentration was always less than 40 mg/L, and no noticeable volatile fatty acids (VFAs) were detected regardless of hydraulic retention time (HRT) variations, while soluble COD was accumulated in the reactor at lower HRT. The particle size reduction was relatively less than other studies reported even after long operation time due to the low operation CFV. Approximately 30% of COD was not recovered as methane irrespective of applied HRTs, due to the COD loss by dissolved methane, sulfate reduction. The observed