The main objective of this research was to investigate the capabilities of three chemical oxidation processes as pretreatment technologies with the goal of making wastewaters containing persistent organic compounds amenable to biotreatment. The processes investigated are ozonation, ultraviolet radiation/ hydrogen peroxide (UV/H2O2) and Fenton reaction. The studies were focused on two organic compounds: Dichloro diethyl ether (DCDE) and methyl tertiary butyl ether (MTBE). Synthetic solutions, and a real groundwater and an industrial wastewater were used for experimentation. The experimental method involved oxidation of solutions of the target organic compounds at various percentages by the three oxidation processes. The pre-oxidized solutions of the organic compounds were subjected to biodegradation and toxicity studies. Four different respirometric tests (two Short-term, one Mid-term, and one Long-term) and a bench scale Sequencing Batch Reactor (SBR) test were used for full assessment of the effectiveness of the chemical oxidation processes. Activated sludge,  as acclimated and non-acclimated to the organic compounds, was used as the test culture.