Prediction of the fate of alcohol ethoxylates in sewage treatment plants

Alcohol ethoxylates (AE) are used in large amounts in detergents and cleaning agents and are disposed into the aquatic environment. It is known that sewage treatment plants (STPʹs) eliminate surfactants from wastewater to a high extent. In this study SimpleTreat, a Mackay level III box model, was applied to simulate the fate of AE in STPʹs. SimpleTreat uses data on physico-chemical properties, the emission rate of a chemical into the sewer system and the biodegradability of the chemical. When Monod biodegradation kinetics were applied, predictions of the elimination of the AE approximate those found in a monitoring study. The Henryʹs Law constant (H) of AE were calculated from data on vapour pressure and critical micelle concentrations. The H values of the AE did not exceed 10−4 Pa m3/mol. Elimination of AE via volatilization in the aeration tank is therefore negligible. Depending on the structure of the AE, elimination of the AE in STPʹs proceeds mainly via sorption on the primary sludge and biodegradation.