Effect of Recirculation Ratio on Simultaneous Methanogenesis and Nitrogen Removal Using a Combined Up-Flow Anaerobic Sludge Blanket–Membrane Bioreactor

Abstract

Abstract Simultaneous methanogenesis and nitrogen removal using a combined system consisting of an up-flow anaerobic sludge blanket (UASB) and aerobic membrane bioreactor (MBR) was investigated for treating synthetic municipal wastewater. A more reliable effluent quality of above 98.0% total organic carbon (TOC) and 98.0% NH4+-N removal was achieved consistently throughout the experiments. Total nitrogen (TN) removal of up to 82.8% could also be achieved when the recycling ratio was increased from 0 to 800%. Analysis of the biogas composition showed that the degradation of NOX−-N through denitrification did not have any obvious effect on the total methane production up to a recycling ratio of 400%. A higher recycling ratio of 800% resulted in an increase of CO2 and a decrease of CH4, due to more sludge being washed out from the UASB into the MBR and recycled back into the UASB, which resulted in a higher dissolved oxygen (DO) concentration in the UASB. Hence, an optimal recycling ratio of 400% was suggest...