REAL-TIME CONTROL OF AEROBIC-ANOXIC SLUDGE-DIGESTION USING ORP

This research documents the use of oxidation-reduction potential (ORP) to control two lab-scale aerobic-anoxic sludge digesters. The reactors were operated in sequencing batch reactor fashion, and one reactor had the ratio of air-on/air-off arbitrarily ''fixed'' at 3 h for each portion of the cycle. The other reactor operated in a real-time manner with 3 h of air-on and the air-off time determined by computer detection of the nitrate breakpoint in the orp-time profile. Reactor performances were evaluated from a chemical (mass balance) removal perspective [total and volatile suspended solids (TSS and VSS), nitrogen, and phosphorus] coupled with a consideration of the control stability achieved when the reactors were subjected to spikes of sodium nitrate, ammonium chloride, and hydrogen peroxide. The reactors showed comparable chemical removals, however the real-time control reactor displayed a greater ability to accommodate the disturbances investigated.