US EPA has finalized federal Water Quality Criteria for nonylphenol, a biodegradation intermediate of nonylphenol ethoxylates, which are commonly used surfactants. To provide information in support of this initiative, an assessment was made of the ability of wastewater treatment plants to remove these and other alkylphenol ethoxylate (APEO) surfactants that are used widely in domestic and industrial applications. This paper, based on a monograph prepared for the Alkylphenols & Ethoxylates Research Council (Melcer et al, 2006), summarizes the results of this work and provides guidance on the factors influencing treatment plant operation and on optimum values of these factors to ensure high removals of APEOs. In general, for activated sludge systems, it was found that criteria such as high solids retention time (SRT) and hydraulic retention time (HRT) that apply to the degradation of many complex man-made compounds also apply to APEOs; that is, a minimum SRT of approximately 10 days and a minimum HRT of 8-10 hours were required to ensure high levels of ultimate APEO degradation.