BACKGROUND: Removal of recalcitrant chemicals is an essential step in conventional wastewater treatment plants. Among these, pesticides are of great environmental concern. Different treatment options were compared in this work: the combination of advanced oxidation processes (AOPs) with biological treatment, an aerobic process and anaerobic biological treatments. The role of chemical processes in improving solution biodegradability was verified. Oxidation by-products were identified and biological process kinetics are reported. The performance of biological processes and their kinetics were studied. RESULTS: Chemical oxidation increased the solution biodegradability index to 0.25. Oxidation by-products were identified as maleic acid, phenol and a mixture of catechol, resorcinol and hydroquinone. The combined processes resulted in 98% organic matter removal. Pesticide degradation followed pseudo-first-order kinetics with a rate constant in the range 0.5-1.2 L g(-1) TVSS h(-1). An anaerobic process was found to be an attractive option with 92% removal efficiency. The aerobic process had a long adaptation time (>200 days), 80% removal efficiency and an average pseudo-first-order rate constant of 0.18 L g(-1) TVSS h(-1). CONCLUSION: Comparison of the investigated processes favoured the use of combined AOPs and biological and/or aerobic biological treatment due to its practical operating conditions. (C) 2009 Society of Chemical Industry