The effects of Fentonʹs reagent pretreatment on the biodegradability of nonionic surfactants

The effectiveness of Fentonʹs 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,/FeII molar ratio of unity) based on dissolved organic carbon, chemical oxygen demand, H2O2 and FeII 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 Fentonʹs 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.