The removal of non-ionic surfactants (NS), as well as a long-chained ethoxylates, short-chained NS and poly(ethylene glycols)(PEG), was investigated in two sewage treatment plants (STP) of the activated sludge type and one trickling filter type. The indirect tensammetric method (ITM), and the ITM combined with the Bismuth Active substances (BiAS) separation scheme (BiAS-ITT) were used for the determination of NS and their metabolites. on average, 85% reduction of total Ns was determined in the activated sludge type STP and 53% reduction in the case of the trickling filter type STP. significant concentrations of NS metabolites (short-chained NS and PEG) were determined in raw sewage, which indicate that NS biodegradation had already started in the sewer system. Both tensammetric methods prove to be a useful tool in monitoring Ns and their metabolites in STP.