In order to prevent the scum generation due to Gordona (Nocardia) amarae, experiments were made to add ozone in the aeration tank from 1990 to 1994, and scum suppression effects, sludge settleability improvement effects, etc. were reported (Goi et al., 1994; Okouchi et al., 1996). The studies made so far did not clarify the scum suppression mechanism of added ozone. Based on the measurements of the number of Gordona, mycolic acid, etc., an attempt was made to investigate this mechanism. By adding ozone, the number of Gordona was suppressed in general to below 1 x 10(5) CFU/mg-SS. In the presence of mycolic acid produced by Gordona amarae at a rate of about 178-236 mu g in 1g activated sludge, no scum generation was seen. Within an experimental range of ozone added at a rate below 3 mg/l, it was considered that the scum suppression effect was due more to the decomposition of mycolic acid, which is a metabolite of Gordona amarae, than to the effect of the number of Gordona amarae being reduced by the disinfectant action of ozone. (C) 1998 Published by Elsevier Science Ltd. All rights reserved. [References: 9]
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