EVALUATION OF TOXIC-SUBSTANCES IN EFFLUENTS FROM A WASTE-WATER TREATMENT-PLANT

The experimental investigation of effluent from municipal wastewater t reatment plants and nightsoil treatment plants was conducted from the viewpoint of safe effluent water quality to evaluate the strategies an d regulations for wastewater reuse. A bacterial assay named umu-test, which can detect error-prone repair dependent on DNA damage by some ch emicals, was applied to samples from treatment plants. Concentrates of secondary effluent of municipal sewage treatment plant revealed stron g genotoxicity, and its activity could be observed every day of the we ek. Also, the samples from secondary effluent separated by ultrafiltra tion in a nightsoil treatment plant showed positive genotoxicity. Newl y developed strains which are Salmonella typhimurium in umu-test are h ighly sensitive to aromatic amines and can detect the genotoxic activi ty induced by these compounds. By using this method, the genotoxic pot ency of above samples was examined, The toxicity on aromatic amines co uld be detected in the matter contained in raw nightsoil. This shows t hat human feces involve some genotoxic substances and the genotoxicity could not be reduced through the biological treatment with nitrificat ion and denitrification, nor removed by the ultrafilter separation pro cess. A coagulation-sedimentation process could partially remove the t oxic substances from the solution and activated carbon adsorption coul d almost remove the substances. The liquid chromatography column was a pplied to fraction the concentrated substances to elute the toxic subs tances from samples. Some genotoxic fractions related to aromatic amin es would be observed more clearly by this method. In order to reuse th e effluent from the treatment plant of the very close side to human bo dy, the reduction of those genotoxicities is expected from the viewpoi nt of human health. From the results of ozone application to the efflu ent, it was found that the genotoxicity could be clearly reduced to a negative level at the ozone consumption ratio of 1 mgO(3 consumed)/mgC .