An A₂O-MBR system for simultaneous biological nitrogen and phosphorus removal from brewery wastewater at various nitrate recirculation ratios

Abstract

Anaerobic/Anoxic/Oxic – Membrane BioReactor (A2O-MBR) system including A2O unit at short solids retention time (SRT) for accumulation of PO43--P and MBR at long SRT for nitrification of NH4+-N was used to enhance simultaneous removal of nitrogen and phosphorus from brewery wastewater. The model of A2O-MBR system made from polyacrylic with the capacity of 49.5 liters was operated with organic loading rate of 0.75 kgCOD/m3.day. Nitrate recycling ratio was increased from 100 to 300% while sludge recirculation ratio was maintained at 100%. The results showed that for the nitrate recycling ratios of 100, 200, 300%, average NH4+-N and total nitrogen (TN) removal efficiencies of the model were 95.7 and 72.4, 99.2 and 86.7, 99.3 and 89.6%, respectively. The removal efficiencies of chemical oxygen demand (COD) and total phosphorus (TP) were over 90 and 75%, respectively, regardless of nitrate recirculation ratio. The output values of COD, NH4+-N, TN and TP were within the limits of Vietnam National Technical Regulation on Industrial Wastewater (QCVN 40:2011/BTNMT), column A, throughout the experiments. The model with recommended system configuration and optimum operational conditions could treat not only nitrogen but also phosphorus well due to appropriate nitrate recycling ratios.