The partial oxidation of a variety of “non-biocorapatible” organics using hydrogen peroxide was evaluated as a pretreatment step prior to biological oxidation of these organics. The compounds tested were 2,4-dichlorophenol, dinitro-ortho-cresol and two unknown phenolic waste-waters of industrial origin. Fenton's Reagent, FeSO4, was used as the catalyst for production of reactive free-radical species at pH 3.5. The residual by-products of hydrogen peroxide oxidation were evaluated based on toxicity (MicrotoxR), and biodegradability (fed-batch reactors) in relation to a typical municipal sludge and a “standard” acclimated laboratory sludge. In all cases, the by-products were about an order of magnitude less toxic than the initial compounds. For example, given 650 mg/l of 2,4 dichlorophenol, the initial EC50 was 0.32% and the uptake rate (based on total organic carbon) by municipal sludge was 0.0 versus an EC50 of 2.5% and an uptake rate of 3.47 mg TOC/g VSS-hr after reaction with hydrogen peroxide.