Lysing of filamentous bacteria with the nonionic surfactant, polyoxyetylene dodecyl eter was tested for four different major filamentous bacteria; type1701,
Thiothrix, type 021N and
Microthrix parvicella. The nonionic surfactant was capable of lysing filamentous bacteria in the bench scale continuous culture tank by addition of the surfactant, whose dose rates were determined in the preliminary batch tests. Based on this result, tests were carried out in four full-scale treatment plants, and the filamentous bacteria were successfully lysed by using the nonionic surfactant. The settleability of the bulking sludge was improved and the overflow of the sludge was greatly reduced. It was proved that the nonionic surfactant could be utilized to solve filamentous bulking in the activated sludge process.
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