Application of a yeast-based assay protocol developed to monitor total oestrogenic activity induced by 17β-oestradiol in activated sludge supernatants from batch experiments

Batch experiments were carried out with activated sludge from laboratory reactors and a full-scale treatment plant spiked with 17 beta-oestradiol (E2). An oestrogen-sensitive yeast-based assay protocol, described in detail in a related publication, was used to measure reduction of E2-induced total oestrogenic activity from the sludge supernatant over a 15 d period after which the sludge was re-spiked to check for possible enhancement of reduction by pre-exposed sludge during an additional 15 d period. The reduction was generally improved by increasing sludge solids concentrations and by continuous mixing. For a 100 ngE2/l spike there was > 40% reduction of oestrogenic activity within 15 d, which improved to > 70% by pre-exposing the sludge. The oestrogenic activity produced by a dose of 100 mu gE2/l was readily removed by most sludges within 15 d. However, re-spiking the activated sludge with the same E2 concentration caused some sludges to lose reduction capacity.