A night soil treatment plant which collects a high amount of human urine and excreta, is a very unique system to Japan and the object of this investigation on the fate and behavior of the human estrogens in the water treatment process. Water and sludge samples at different treatment phases were taken at a night soil treatment plant. Their hydrophobic fractions were assayed using an in vitro yeast assay (yeast estrogen screen) and an enzyme immunoassay (ELISA) employed for the detection of overall estrogenic activity and 17β-estradiol (E2), respectively. Estrogenic activity observed by the yeast assay was quantified as E2 concentration equivalent, which was comparable with E2 concentration measured by the ELISA, in order to estimate the contribution of E2 to the total activity. Based on the ELISA results, a sketch of the mass balance of E2 in the treatment system was drawn and treatability of E2 was discussed.

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