The application of ORP in activated sludge wastewater treatment processes

This study researched, at full and pilot scale, the potential for using ORP to control the operation of activated sludge aeration tanks. Results indicate that ORP values can clearly show the COD removal occurring along the length of an aeration tank; ORP values increased dramatically as organic matter was removed. Based on the experimental data obtained on site during more than a half year of study, the ORP and COD in the aeration tank effluent followed a good linear relationship. Because ORP control is much easier and quicker than using COD measurements, the Delta ORP of the influent and effluent and the ORP values of the effluent could be used to in situ indicate the pollutant removal efficiency and the effluent quality, respectively. ORP changes occurring under different COD and DO concentrations were also examined using a pilot column. The pilot column data confirmed the results from the aeration tanks. The ORP values of the mixed liquor increased during biodegradation of the organic matter, and then leveled off when biodegradation was finished. However, under high COD (higher than 1000 mg/L) loading conditions, the biodegradation continued throughout the whole aeration cycle, and the ORP values continued increasing throughout the cycle. The data from systems operating under several DO conditions indicated that supplying a very high DO concentration (higher than 6.0 mg/L) is not necessary for biodegradation.