A technique to determine nitrogen removal rates in systems performing simultaneous nitrification and denitrification

Abstract

This paper reports on a possible technique to determine specific nitrification and denitrification rates (SNR and SDNR) in an oxidation-reduction potential (ORP) controlled, intermittent aeration (IA) tank, in which simultaneous nitrification and denitrification (SND) occurred. In addition, SNRs in a three-stage Bardenpho aerobic zone and SDNRs in its anoxic zone were determined. This research was done at bench scale. The technique involves a steady-state run and two additional transient-state tests (created by either ammonia or nitrate shock loading). The rates obtained, using this technique, are the maximum rates possible in a continuous process under certain, improvised conditions. The technique is extremely flexible and generates data relating the rate to substrate concentration in one steady-state run. Data analysis was performed using the integral method; an excellent agreement between predicted and experimental data was found. Zero-order kinetics could describe nitrification in an ammonia concentration range of 1–30 mg/L and denitrification in a nitrate concentration range of 10–30 mg/L. The SNRs in the intermittently aerated, complete-mix (IACM) tank (0.39–1.69 mg g–1 h–1) were considerably lower than those in the 3-stage Bardenpho aerobic zone (3.4–3.81 mg g–1 h–1) due mainly to imposed dissolved oxygen limitations. The SDNRs in the IACM tank were in a range of 0.16–1.26 mg g–1 h–1, which were also considerably lower than that in the 3-stage Bardenpho anoxic zone (2.0–2.5 mg g–1 h–1). Key words: acetate, denitrification, intermittent aeration, kinetics, methanol, nitrification, ORP control, simultaneous nitrification and denitrification.