The fate of xenobiotic organic compounds in wastewater treatment plants.

The effective operation of wastewater treatment plants plays an important role in minimising the release of xenobiotic compounds into the aquatic environment. Considerable effort has been expended in developing models to quantify the overall removal and fate of these compounds in biological treatment plants. A synthesis and modification of these approaches has been made and a generalised fate model for organic compounds in an activated sludge plant is presented. The influence of the different removal mechanisms, such as sorption, volatilisation and advection for chemicals with different physico-chemical properties is investigated and the important role of biotransformation is discussed. The effect of some operating parameters has been found to have an important influence upon the concentration of xenobiotic released in the sludges and final effluent. This may have significance for a wide range of ecotoxic compounds and in particular the class of compounds increasingly recognised as having the potential to disrupt endocrine activity in some aquatic vertebrates.