Step feeding strategy for enhancing nitrogen and phosphorus removal in AOAO process

This study describes a biological process containing anaerobic/oxide/anoxic/oxide (AOAO) stages, which incorporates a stepwise feeding strategy to enhance nitrogen and phosphorus removal efficiencies. In the experimental reactors, synthetic wastewater was fed into the anaerobic stage and anoxic stage separately, while the substrates and nutrients were successfully consumed without recycling either nitrified effluent or external carbon sources. Experimental results demonstrated that the anoxic stage was provided an intrinsic sufficient carbon source and caused NOx (NO2-N + NO3-N) concentration to reduce from 11.85 mg/l to 5.65 mg/l. The total Kjeldahl nitrogen (TKN) removal rate was between 81.81% and 93.96%, while the PO4-P removal ratio was between 93% and 100%. The substrate fed into the anaerobic at flow rate Q1 and into the anoxic at flow rate Q2. In addition, three different ratios were performed with Q1/Q2 varied from 7/3, 8/2 to 9/1. The AOAO process clearly saves nearly one-third of the energy compared to the typical Biological nutrient removal (BNR) system A2O process.