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ABSTRACT Background and aim: Today, chlorine is the most common material used for effluent disinfection. Chlorination is an established and effective method for effluent disinfection. But the use of chlorine for disinfection of effluent due to several major concerns should be reassessed. The aim of this study was to compare long-term benefits and costs of chlorination/de chlorination with those of UV by pilot studies. Material and Methods: This pilot study consisted of pre-treatment units clarification and filtration systems with two types of low pressure and medium pressure UV lamps designed and installed at the wastewater treatment plant in the north of Isfahan. Results:Medium pressure UV systems with dose of 230 mw.s/cm2 for disinfection of filtered effluent with SOR of 1090 lit/m2.hr is more economical than a low pressure system and chlorination/dechlorination process and has the least environmental and health adverse effects. Conclusion: In wastewater treatment plants use of UV disinfection technology should be considered in preference to chlorination, especially if the dechlorination of chlorinated effluent is required. Before application of this system pilot studies on actual effluent at plant sites are required. Keywords: Effluent disinfection, UV radiation, Chlorination, pilot study Received: Oct 3, 2010 Accepted: Nov 5, 2011 Conflict of interest: Nill