AUTOMATIC REGULATION OF ACTIVATED-SLUDGE AERATION - SINGLE-TANK NITRIFICATION-DENITRIFICATION

Several activated sludge processes using intermittent aeration were de veloped during the last decade to improve nitrogen removal. Timers, ox idation-reduction or oxygen probes are often used to switch aeration o n and off at present times or by upper and lower limits. These regulat ion systems cannot adjust the oxygen supply to the biological oxygen d emand and cannot realize the supply when 'requested' by the influent. A new controller/regulator system (OGAR : Optimized manaGement of Aera tion by Redox) based on the variation with time of the oxidation reduc tion potential was developed : EH = f(time). This OGAR system controls the aeration periods and therefore optimizes the nitrification and de nitrification reactions in the sludge processes. The operation of the OGAR programmable controller can be summarized by three functions: Ana lysis --> Diagnosis --> Action It is a true diagnostic tool and a deci sion making aid. Its simple design enables it to be adapted easily to any site and to be highly user-friendly. OGAR was applied to an existi ng wastewater treatment plant located at Nezel-la-Falaise near Paris ( west suburb). Overall performance of the plant before and after implem entation of automatic aeration control by OGAR yields the following co nclusions: removal of COD was improved by 45% reduction in COD from 10 0 mg/l to 55 mg/l ammonia nitrogen concentration was reduced from 42 m g.l-1 to 2 mg.l-1 and nitrate nitrogen concentration was reduced to le ss than 5 mg.l-1