Gamma irradiation of textile mill effluents under oxygen pressures up to 1500 psi, with and without activated charcoal present, was studied as a method for removing color and removal of substances contributing to the chemical oxygen demand (COD). Both color and COD reduction are directly related to the radiation dose and pressure of the oxygen over the dye solution samples during irradiation. The study revealed a new method for in-situ reactivation of charcoal by gamma-radiation-induced oxidation of organic compounds adsorbed on charcoal. This discovery permits a large reduction in the gamma source size required for processing textile mill effluents because the water fraction of the effluent does not need to be irradiated to the same degree as the organic material contained in the effluent. A mathematical model for the process was developed.