Controlling factors for simultaneous nitrification and denitrification in a two-stage intermittent aeration process treating domestic sewage

This bench-scale research investigated the controlling factors for simultan eous nitrification and denitrification (SND) in a 2-stage, intermittent aer ation (IA) process, designed for nitrogen and phosphorus removal. The 2-sta ge process consisted of an anaerobic zone followed by an oxidation-reductio n potential (ORP) controlled, intermittently aerated, completely mixed (IAC M), tank. The three independent variables examined were the average ORP lev el, organic substrate (acetate and methanol) dosage and aeration cycle. The sewage used was completely of residential origin. Nitrogen balance clearly indicated that the nitrogen loss, due to SND in the aeration tank, contrib uted 10% to 50% of the influent TKN to the overall nitrogen removal. Signif icant differences in both nitrification and denitrification in the IACM tan k were observed, when different average ORP levels were applied to the aera tion control; this proved that absolute ORP can be used as a real-time cont rol parameter for SND. Under low DO and intermittent aeration conditions, a cetate and methanol additions improved nitrification over the entire dosage range and denitrification at relatively low dosages. Finally, a longer aer ation cycle, with a zero-DO period, appeared to favor sequential nitrificat ion and denitrification (SQND), not SND. (C) 1999 Elsevier Science Ltd. All rights reserved.