Advanced Wastewater Treatment under Different Dissolved Oxygen Conditions in an Innovative Step-Feed Process

An innovative step-feed Anaerobic-multiple Anoxic/Oxic-Membrane Bioreactor [An-M(A/O-MBR] process was developed to treat synthetic domestic wastewater. Performance of the lab-scale system was investigated at different dissolved oxygen (DO) concentration (0.4-2.4mg/L) in the aerobic tank of the multiple A/O zone. The results showed that, under the conditions imposed, the DO level has no obvious influence on COD removal and the removal efficiency was more than 94% throughout the operation. However, DO levels have great influence on nitrogen and phosphorus removal. Better nitrification performance(>99%) could be obtained when DO was in the range of 0.8 similar to 2.4mg/L. High total nitrogen (TN) and total phosphorus (TP) removal performance can be obtained when DO was in the range of 0.8 similar to 1.2mg/L, the average removal efficiency was 74.81% and 71.41%, respectively. In this condition, DO can meet the demand of nitrification and phosphorus uptake simultaneously, and the simultaneous nitrification and denitrification (SND) occurred in the aerobic tanks under lower DO concentration. Meanwhile, since the DO circulated from the aerobic tank to the anoxic tank decreased, denitrification was enhanced and the nitrate quantity in the sludge recycle system decreased, resulting in the decrease of carbon substrate competition between denitrifcation and phosphorus release in the anaerobic zone. Ultimately, the performance of TN and TP removal was enhanced.