Protection of clean aquifers requires radical minimization of water consumption, overall reduction of wastewater and, furthermore, minimization of wastewater loading. Many organic pollutants in wastewater present a specific problem because of their toxicity, bioaccumulation and poor biodegradability. The scope of this paper is to investigate and identify the benefits offered by advanced oxidation processes (AOPs) as destructive methods for treatment of wastewater loaded with recalcitrant organic pollutants. The study was performed on model wastewater containing p-chlorophenol as a representative of organic chemical industry intermediates. Several UV based AOPs were studied: UV, UV/H2O2, UV/O3, UV/H2O2/O3 and UV/Fenton. Optimal process conditions for the highest mineralization efficiency in the investigated range (pH, [H2O2] and [Fe2+]) have been determined on the basis of HPLC measurements and the following ecological parameters: total organic carbon (TOC), adsorbable organic halides (AOX), chemical oxygen demand (COD) and biochemical oxygen demand (BOD5). Toxicity is one of the most important ecological parameters in determining the level of water pollution. In this study, toxicity tests were performed on the zooplankton Daphnia magna in order to evaluate efficiency of the applied treatments. The UV/ Fenton and UV/H2O2/O3 processes were found to be the most appropriate processes for degradation and mineralization of p-chlorophenol. Complete degradation was achieved after 15 minutes ofUV/Fenton process treatment, while 92.1% TOC and 98.3% AOX removals were obtained after treatment of 60 minutes.