Three photooxidation processes, UV/H2O2, UV/S2O82- and UV/O-3 were applied to the treatment of model wastewater containing non-biodegradable organic pollutant, azo dye Acid Orange 7 (AO7). Dye degradation was monitored using UV/VIS and total organic carbon (TOC) analysis, determining decolorization, the degradation/formation of naphthalene and benzene structured AO7 by-products, and the mineralization of model wastewater. The water quality during the treatment was evaluated on the bases of ecological parameters: chemical (COD) and biochemical (BOD5) oxygen demand and toxicity on Vibrio fischeri determining the EC50 value. The main goals of the study were to develop an appropriate mathematic model (MM) predicting the behavior of the systems under investigation, and to evaluate the toxicity and biodegradability of the model wastewater during treatments. MM developed showed a high accuracy in predicting the degradation of AO7 when considering the following observed parameters: decolorization, formation/degradation of by-products and mineralization. Good agreement of the data predicted and the empirically obtained was confirmed by calculated standard deviations. The biodegradability of model wastewater was significantly improved by three processes after mineralizing a half of the initially present organic content. The toxicity AO7 model wastewater was decreased as well. The differences in monitored ecological parameters during the treatment indicated the formation of different by-products of dye degradation regarding the oxidant type applied. (C) 2010 Elsevier B.V. All rights reserved.