Application of photochemical waste water oxidation UV and/or visible light, especially TiO₂/UV and the Photo-Fenton reaction(Fe²⁺/H₂O₂/UV-VIS), have been investigated. Degradation results of 4-Chlorophenol and some other model compounds at laboratory scale arediscussed. A photoreactor with immobilized TiO₂ has led to a higher quantum efficiency than the suspension treatment. Experiments with different waste waters(e.g. landfill leachates, plastics industry, etc.) using the Fe²⁺/H₂O₂/UV-VIS system in a photoreactor prototype are reported.