Abstract:The hydrogen ion production rate (HPR) and the pH were measured by a novel automatically respirometric- titrimetric system, and shortcut nitrogen removal in an SBR was studied in the laboratory. An SBR was used to treat synthetic wastewater containing 360mg/L COD and 40mg/L NH4+-N at 20℃ with DO lower than 2.0mg/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 NH4+-N removal ratios were both higher than 90%. Based on the HPR online monitoring data, the estimated NH4+-N 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.