Aeration represents the main part of energy consumption in the low-load activated sludge process. Because of its ability to remove the various kinds of pollution (carbonaceous, nitrogenous) with a high dependability level, this process is the most widespread throughout France, particularly in its tropical overseas regions. A previous study led the authors to set up a graph which links energy savings and effluent quality (carbonaceous and nitrogenous pollution removal). This graph appears useful as well to monitor biological phosphorus removal in the low-load activated sludge process including an anaerobic basin.

In order to optimize pollution removal and energy savings, ORP regulation has been carried out since January 1983 on the Yffiniac plant (West of France). It was preferred to dissolved oxygen (D.O.) regulation because of the low values of D.O. observed in this plant and the difficulties of operating D.O. regulation.

A laboratory and full-scale study shows that ORP regulation is possible and particularly accurate as a contribution to optimizing pollution removal, energy savings and operating conditions. Since then other ORP Regulations have been installed. The observations we made specify which cases lend themselves to successful ORP regulation.

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