Nitrogen removal from temperate anaerobic–aerobic two‐stage biological systems: impact of reactor type and wastewater strength

Abstract BACKGROUND There is a need to examine the impact of anaerobic reactor type and wastewater strength on anaerobic–aerobic two‐stage biological systems for temperate wastewater treatment An expanded granular sludge blanket reactor and an anaerobic membrane bioreactor for crude wastewater treatment with downstream aerobic biological treatment were studied together with increasing the organic concentration by fortifying the crude wastewater with primary sludge. RESULTS A chemical oxygen demand and ammonia compliant effluent was produced from the anaerobic–aerobic two‐stage process. Due to the enhanced organics removal achieved by the membrane, a lower denitrification rate, k d , was recorded for the anaerobic membrane bioreactor effluent treatment. However, the residual organic carbon in the anaerobic effluents from both the expanded granular sludge blanket reactor and the anaerobic membrane bioreactor treating crude wastewater was not of sufficient quality to support denitrification. Complete nitrification was achieved during downstream treatment of the fortified effluent. In addition, fortification increased k d to values analogous to exogenous carbon substrates. CONCLUSIONS It is postulated that fortification currently presents the most sustainable strategy for anaerobic–aerobic two‐stage biological systems due to a combination of enhanced methane production and denitrification. © 2013 Society of Chemical Industry