The effectiveness of Fenton's reagent pretreatment on the biodegradability of selected nonylphenol ethoxylates (NPEs) ethylene oxide/propylene oxide (EO/PO) block copolymers and a nonsurfactant compound polypropylene glycol (PPG) was examined. Chemical oxidation kinetic studies were conducted that showed that the Fenton reaction was rapid at the base conditions used (approx. 1000 mg/L COD 1000 mg/L H2O2, H2O2,/Fe-II molar ratio of unity) based on dissolved organic carbon, chemical oxygen demand, H2O2 and Fe-II removals. Batch aerobic bioassays were conducted to assess both the rate and the extent of biodegradability of the chemically preoxidized and unoxidized samples. A 12-L sequencing batch reactor (SBR) was operated aerobically to provide acclimated biomass for use in the bioassays. EO/PO block copolymers, PPGs and (to a lesser degree) NPEs were found to be biorecalcitrant, that is, resistant to biomineralization. Advanced oxidation pretreatment using Fenton's reagent was highly effective at enhancing the biodegradability of EO/PO block copolymers and PPG. The biodegradability of NPEs, however; decreased with low oxidant dosages and increased with higher oxidant dosages. Economic estimates showed that chemical costs would comprise more than 90% of the overall treatment costs for an integrated Fenton/activated sludge treatment system. (C) 1999 Elsevier Science Ltd. All rights reserved.