Improvement of nitrogen and phosphorus removal in the anaerobic-oxic-anoxic-OXIC (AOAO) process by stepwise feeding

This investigation incorporated a stepwise feeding strategy into the biological process containing anaerobic/oxide/anoxic/oxide (AOAO) stages to enhance nitrogen and phosphorus removal efficiencies. Synthetic wastewater was fed into the experimental reactors during the anaerobic and anoxic stages and the substrates/nutrients were successfully consumed without recycling either nitrified effluent or external carbon source. An intrinsic sufficient carbon source developed during the anoxic stage and caused the NOx (NO2-N+NO3-N) concentration to be reduced from 11.85mg/l to 5.65mg/l. The total Kjeldahl nitrogen (TKN) removal rate was between 81.81%-93.96% and the PO4-P removal ratio ranged from 93%-100%. The substrate fed into the anaerobic with a Q(1) flow rate and a Q(2) into the anoxic reactor. The three difference experiments contained within this study produced Q(1)/Q(2) that varied from 7/3, 8/2, and 9/1. The AOAO process saved nearly one-third of the energy compared with typical biological nutrient removal (BNR) system A(2)O processes.