Treatment of Anaerobically Digested Swine Wastewater Using Intermittent Aeration and Membrane Bioreactors

Abstract

Three 120 L/d intermittent aeration and membrane bioreactors were employed to study the treatment of anaerobically digested swine wastewater, in an attempt to optimize operating parameters. The systems were preset to work under nine operational conditions: hydraulic retention time (HRT) was set at 15 h, 20 h and 24 h; on/off of intermittent aeration time ratios being at 1h/1h, 1h/3h and 1h/4h; sludge retention time (SRT) was 30 d, 50 d and 70 d; on:off time ratios for effluent being at 5:3 min, 7:3 min and 10:3 min). When influent COD and NH4+-N reached 1240-1830 mg/L and 722-1360 mg/L, respectively, the averaged COD and NH4+-N volumetric loading rates (VLR) were 1.30 and 0.48 kg/(m3d), respectively, in nine experiments. More than 70% COD removal and 50% NH4+-N removal were observed, when operational conditions became appropriate. When HRT was 24 h or 20 h, on:off of intermittent aeration time ratio was 1:4 h, SRT was 50 d or 70 d, and on:off of effluent was 5:3 min., COD and NH4+-N removal rates were higher, as indicated by experimental data. COD removal by microorganisms averaged 67.3%, as shown by mass balance calculation. COD rejection of membranes accounted for an averaged 70.6% during the nine experiments. Microorganisms have been proven to be a major contributor to COD removal. Membranes are able to effectively prevent discharge pollutants with effluent.