Determination of the fate of alcohol ethoxylate homologues in a laboratory continuous activated-sludge unit study.

Environmental monitoring indicates that the distribution of alcohol ethoxylate (AE) homologues in wastewater treatment plant (WWTP) effluents differs from the distribution in commercial AE products, with a relative higher proportion of fatty alcohol (AOH, which is AE with zero ethoxylation). To determine the contribution of AE-derived AOH to the total concentration of AE and AOH in WWTP effluents, we conducted a laboratory continuous activated-sludge study (CAS). This consisted of a test unit fed with AE-amended synthetic sewage and a control unit fed with only synthetic sewage to avoid AE contamination from the feed. The removal efficiencies of some 114 AE homologues were determined by the application of a specific and sensitive analytical method. The extent of the removal of AE ranged from 99.70% for C18 compounds to >99.98% for C12−16. Relatively high-AOH concentrations were observed in the effluents from blank and test units. By building the concentration difference from the test minus the control unit, the AE in the CAS effluent originating from AE in the influent was determined. Thus, it could be shown that AOH represented only 19% of the total AE (EO0−18) in the CAS, while monitoring in 29 WWTP effluents (European, Canadian, and US) revealed in total a mean AOH fraction of 55% (5–82%) of the total AE (EO0−18). This shows that only a small fraction of AOH in WWTP effluents originates from AE entering the WWTP.