Partial nitritation with aerobic duration control of carbon-captured blackwater: Process operation and model-based evaluation

Abstract

Partial nitritation and anammox (PN/Anammox) is the most appropriate process for nitrogen removal from blackwater. However, information on control strategies of PN of blackwater is scarce. In this study we selected aerobic duration control, with pH and dpH/dt as control variables, as our PN strategy. To demonstrate PN with aerobic duration control, investigate impact factors, and optimize start-up and the operation process, a laboratory-scale PN-SBR (sequencing batch reactor), fed on real carbon-captured blackwater (321 mg COD/L, 219 mg N/L, pH 8.18, and alkalinity 804 mg CaCO3/L) was set up. A model-based evaluation was implemented. With aerobic duration control, the PN-SBR was successfully started in ∼2 weeks, reaching an average nitrite accumulation ratio (NAR) of 93.8% at 30 °C with a sludge retention time of 8.1 days. Low dissolved oxygen (0.30 mg/L) had minimal effect on the NAR, but significantly prolonged the reaction period. One week, on-site free nitrous acid and free ammonia sludge shock treatments had limited effect on the PN process, and could not prevent lasting washout of the nitrite-oxidizing organisms. When the temperature was decreased from 20 °C to 15 °C, the NAR decreased from 95.6% to 88.6%, due to the nitrite-oxidizing organisms in the influent, as indicated by our modeling results. We found pH to be a better controlling variable than dpH/dt as it not only shortened the reaction period, but also resulted in good PN performance. Fixed pH is also an appropriate control variable for the fluctuating alkalinity-to-ammonium ratio. In conclusion, aerobic duration control is an appropriate strategy to achieve PN of carbon-captured blackwater.