Ozonation of activated sludge in the recycle stream

Intermittent ozonation of a part of the recycle sludge was performed two times a week for a laboratory-scale reactor at an average ozone dose of 0.019 g O3(gSSozonated)-1. Under these conditions a decrease of about 50% in sludge growth was obtained for the ozone-treated system, in comparison with the control. As a consequence less sludge had to be removed from the test reactor. Only a slight decrease in quality of effluent was noticed. A comparative cost calculation was made, based on these results, between an ozone-treated activated sludge system and a traditional activated sludge system.