Shortcut nitrification–denitrification in a sequencing batch reactor by controlling aeration duration based on hydrogen ion production rate online monitoring

The hydrogen ion production rate (HPR) and the pH of the aeration phase in a sequencing batch reactor (SBR) were simultaneously measured by a novel respirometric–titrimetric instrument. The results showed that HPR could indicate the end of ammonia oxidation with a greater accuracy and sensitivity than pH. An SBR was used to treat synthetic wastewater containing 360 mg/L chemical oxygen demand (COD) and 40 mg/L at 20°C with dissolved oxygen (DO) lower than 2.0 mg/L. Controlling the aeration duration based on HPR online monitoring, shortcut nitrification–denitrification was successfully performed for approximately two months with a stable nitrite accumulation rate (NAR) above 88%, and the COD and removal ratios were both higher than 90%. Based on the HPR online monitoring data, the estimated concentrations in nitrification were closely related to the measured concentrations, with a correlation coefficient of 0.9722, and the estimated values were lower than the measured values mainly because of the titration delay at the beginning of the aeration phase.