Investigation of Photo–Fenton–Like Process Efficiency in Diazinon Pesti- cide Removal from Aqueous Solutions Leila Kazemizad 1 , Yasaman Ghaffari 1 , Majid Kermani 2* , Mahdi Farzadkia 2 , Ayoub Hajizadeh 1 , 1 Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. 2 Department of Environmental Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran. Received 12 October 2016; Revised 10 November 2016; Accepted 24 November 2016; Available online 27 December 2016 ABSTRACT: Diazinon pesticide and its metabolites have been identified in aquatic systems worldwide. It was related to toxicity for aquatic organisms, animals, and humans. Waters contaminated with such persistent insecticides should be treated with suitable treatment processes. In this research, Diazinon removal from aqueous solutions by the photo–Fenton–like process (UV/H 2 O 2 /Fe 0 ) was investigated. This experimen- tal laboratory scale study was performed on synthetic wastewater in a batch system. The reaction was done in the cylindrical UV irradiation photo–reactor with 2.5 L useful volume at 25 ±2 °C. The effects of H 2 O 2 , pH, ZVI, retention time and initial Diazinon concentration on removal efficiency were studied. The results showed that the optimal parameters for this process were as follows: [Fe 0 ]/[H 2 O 2 ] molar ratio of 1:1, pH 4, the reaction time of 30 min, and initial concentration of 10 mg/L. Diazinon removal and COD reduction in this condition were achieved 83.05% and 71.34%, respectively. Photo–Fenton like process can be suggested as a pretreatment step for the biological removal or post treatment of Diazinon and other pesticides with a similar structure in the aqueous environments. Also, considering the high potential of the photo–Fenton– like process in the reaction with pollutants, a modifying pilot system to ensure concurrent proper rotation speed and UV radiation seem to be necessary. KEYWORDS: Diazinon, Photo–Fenton Like Process, AOPs, ZVI, Organophosphate Pesticide Introduction One of the organophosphate pesticides that is vastly used to treat a variety of insects in different regions is Diazinon [1]. Despite Diazinon has low persistence in the environment compare to the organochlorine pesticides, it is a non–specific insecticide and highly toxic to animals and humans. The main toxic action of Diazinon is inhibition of acetylcholinesterase activity [2]. Diazinon (O, O–diethyl O–[2–isopropyl–6–meth- ylpyrimidin–4–yl] thiophosphate) is classified by the World Health Organization as “moderately hazardous” class II. It was related to toxicity for aquatic organisms in the concentration of 350 ng/L, with an LC 50 in killifish (48 h) of 4.4 mg/L. Fatal human doses were found to be in the range from 90 to 444 mg/kg. Diazinon is relatively water soluble (40 mg/L at 25 °C), non–polar, moderately mobile and persistent in soil. Hence, it is of concern for groundwater and surface resources derived drinking water [3–5]. Diazinon and its metabolites have been identified in aquatic systems worldwide [4]. Therefore, wa- ters contaminated with such persistent insecticides should be treated with suitable treatment processes [6, 7]. Conventional water treatment processes have no enough efficacy for the degradation and removal of emerging water micro–pollutants including Diazinon [8]. In recent years, dif- ferent methods have been developed and studied for removal of Diazinon such as biodegradation [9], sonochemical degra- dation [10], photodegradation [11], Fenton reagents and its derivatives [12–14], adsorption [15], electrocoagulation [4], and photocatalytic degradation [7]. A number of studies have *Corresponding Author Email: majidkermani@yahoo.com Tel.: +98 2186 704 627; Fax: +98 2188 622 707 Note. Discussion period for this manuscript open until January 31, 2017 on JSEHR website at the “Show Article” http://dx.doi.org/10.22053/jsehr.2016.33383 J. Saf. Environ. Health Res. 1(1): 17–22, Autumn 2016 DOI: 10.22053/jsehr.2016.33383 ORIGINAL RESEARCH PAPER indicated the potential for using advanced oxidation process- es (AOPs) to destroy micro–pollutants completely such as pes- ticides. AOPs use combinations of oxidants, catalysts, and ultravio- let irradiation to produce hydroxyl radicals (OH • ) in solutions and have offered interest for the degradation of non–biode- gradable or hazardous organic pollutants in wastewater. The organic compounds are oxidized and mineralized by free rad- icals to carbon dioxide, water, and mineral salts. The Fenton reaction (Fe 2+ /H 2 O 2 ), and Fenton–like reactions (Fe 0 /H 2 O 2 or Fe 3+ /H 2 O 2 ) have been widely applied in the treatment of biore- fractory wastewater in the field of AOPs [13]. The main advan- tage of Fenton processes can be linked to the fact that the re- action occurs at room conditions of temperature and pressure which results a less expensive treatment. furthermore, a short time is necessary for the reaction [16]. However, Fenton sys- tems have two major limitations: (a) more iron sludge produc- tion and (b) slow Fe +3 ions reduction by H 2 O 2 [13, 17]. Hence, ultraviolet (UV) irradiation is offered for dominance on the system limitations. The use of UV irradiation causes ferric iron (Fe +3 ) that had poor efficiency in Fenton process, returned to activity segment and transformed to ferrous iron ion in which enhance process efficiency. Moreover, UV irradiation affords hydroxyl radicals gain [13]. Thus, Fenton systems plus UV irradiation considering ad- vantages such as favorite health and environmental aspects, high efficiency for various pollutants removal from water and wastewater, and other advantages have a very desirable pros- pect in water and wastewater industries. The presence of high concentrations of chemical, synthetic, and toxic pollutants, which have an inhibitory effect on microorganism’s biologi- cal activity, have made frequent use of these systems in treat- ing industrial wastewater. Although, great studies have been performed heretofore about AOPs application sake pesticides