Real-time control of an immobilized-cell reactor for wastewater treatment using ORP

The performance of an immobilized-cell reactor for simultaneous carbon–nitrogen removal in synthetic wastewater with an intermittent aeration (IA) process under real-time control of oxygen supply was investigated. The oxidation–reduction potential (ORP) was monitored during operation. The ORP–time profile showed distinctive turning points, which directly correlated with the changes in the system chemistry and biological activity. The reactor was conducted by cyclic fixed-time aeration–nonaeration operation at the beginning, followed by real-time control technology using ORP setpoint. A moving window along the slope of the ORP curve was employed to search for the nitrate breakpoint of the aeration cycle. Once the breakpoint was found, the reactor was aerated for a fixed period. The treatment process could effectively avoid the anoxic fermentation state under the real-time control. The cycle time was reduced around 30%. The duration of aeration period was found to be optimum at 3 h under the consideration of the removal efficiencies of COD and total nitrogen. The real-time control system not only exhibited a better nitrogen removal efficiency than the fixed-time control operation, but it also showed a stable effluent quality during the change of HRT from 3 to 8 h. Good operation stability was demonstrated even when a very high disturbance of the influent loading occurred.