The photochemical treatment of hazardous waste can be optimized by taking into account various factors that influence the rates of photochemical reactions. Physical factors that facilitate photochemical treatment include: (1) maximizing the irradiated surface to volume ratio of the system; (2) selecting a light source with a spectrum that strongly overlaps the absorption spectrum of the chromophore; and (3) vigorously mixing the reaction mixture. Although hazardous wastes are degraded by direct absorption of light, the overall rate of light-induced reactions can usually be accelerated by adding to the treatment system various dissolved or particulate substances that, on light absorption, produce reactive excited states or free radical intermediates that react with the waste. Examples of such additives include ozone, perixides, semiconducting metal oxides such as titanium dioxide, and various organic photosensitizers that efficiently photoproduce excited triplet states.