An effluent gas stream treatment system for treatment of gaseous effluents such as waste gases from semiconductor manufacturing operations. The effluent gas stream treatment system comprises an oxidation unit to which an oxygen-containing gas such as ozone may be added, with input of energy (e.g., thermal, radio frequency, electrical, microwave, etc.), to effect oxidation of oxidizable species in the effluent, such as halocompounds (e.g., chlorofluorocarbons, perfluorocarbons), CO, NF3, nitrogen oxides, and sulfur oxides). The effluent gas stream treatment system may include a wet scrubber associated with the oxygen-containing gas source, so that the gas stream is contacted with the oxygen-containing gas during the wet scrubbing operation, to enhance removal of oxidizable species in the gas stream during treatment.