Improvement of nitrogen-removal efficiency using immobilized microorganisms with oxidation–reduction potential monitoring

The use of an immobilized-cell reactor for simultaneous carbon–nitrogen removal in wastewater with the monitoring of oxidation–reduction potential (ORP) in an intermittent aeration (IA) process was investigated. Under alternating aerated and nonaerated conditions, the ORP-time profile showed distinctive turning points that directly correlated with changes in the system chemistry and biological activity. The aeration ratio, defined as aeration time/cycle time, was optimum at 50% for obtaining the maximum efficiency of denitrification accompanied by sufficient nitrification. High simultaneous carbon–nitrogen removal efficiency could be achieved using the immobilized-cell reactor by applying the IA process. More than 90% of COD-removal efficiency and over 80% of total-nitrogen-removal efficiency were obtained using three aerobic–anoxic cycles per day at an aeration ratio of 50% and with a hydraulic retention time of 10 h. Journal of Industrial Microbiology & Biotechnology (2000) 25, 229–234.