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

The performance of an immobilized-cell reactor for simultaneous carbon nitr ogen removal in synthetic wastewater with an intermittent aeration (IA) pro cess under real-time control of oxygen supply was investigated. The oxidati on-reduction potential (ORP) was monitored during operation. The ORP-time p rofile showed distinctive turning points, which directly correlated with th e changes in the system chemistry and biological activity. The reactor was conducted by cyclic fixed-time aeration-nonaeration operation at the beginn ing, 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 nitr ate breakpoint of the aeration cycle. Once the breakpoint was found, the re actor was aerated for a fixed period. The treatment process could effective ly avoid the anoxic fermentation state under the real-time control. The cyc le time was reduced around 30%. The duration of aeration period was found t o 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 b etter nitrogen removal efficiency than the fixed-time control operation, bu t 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 dis turbance of the influent loading occurred. (C) 2001 Elsevier Science Ltd. A ll rights reserved.