The fate of three endocrine-disrupting compounds (EDCs), namely 4-n-nonylphenol (4-n-NP), triclosan (TCS) and bisphenol A (BPA), was studied in activated sludge process. The effect of sludge retention time (SRT) on their sorption and biodegradation was also investigated. Three continuous-flow activated sludge systems were used, operating at SRT of 3, 10 and 20 days, respectively. Batch experiments with biomass originated from the aforementioned systems showed that 4-n-NP and TCS are significantly sorbed on the suspended solids, while BPA to a lesser extent. The sorption affinity of target compounds did not seem to be affected by SRT, with the exception of 4-n-NP for which higher values of sorption coefficients were calculated at SRT of 3 days. The operation of continuous-flow systems in the presence of 10-40 mu g L(-1) of EDCs indicated that more than 90%, 94% and 97% of BPA, TCS and 4-n-NP, respectively, can be removed during the activated sludge process in systems operating at SRT of 3-20 days. Determination of EDCs in the dissolved and particulate phase and calculation of their mass flux revealed that biodegradation was the principal removal mechanism of EDCs. For SRT values used in this study, this parameter does not seem to affect significantly percentage biodegradation of BPA. On the other hand, biodegradation of 4-n-NP and TCS was enhanced at SRT of 20 days. Calculation of biotransformation rates showed that the highest values for all EDCs were calculated at SRT of 3 days. (C) 2009 Elsevier Ltd. All rights reserved.