Transformation of roxarsone during UV disinfection in the presence of ferric ions

The transformation of roxarsone (ROX) during UV disinfection with Fe(III) has been investigated. Fe(OH) 2+ , as the main Fe(III) species at pH = 3, produces HO under UV irradiation leading to the oxidation of ROX. Dissolved oxygen plays a very important role in the continuous conversion of generated Fe 2+ to Fe 3+ , which ensures a Fe(III)-Fe(II) cycle in the system. The presence of Cl − /HCO 3 − /NO 3 − has little influence on the ROX transformation, whereas PO 4 3− achieves an obvious inhibitory effect. The transformation of ROX leads to the formation of inorganic arsenic consisting of a much higher amount of As(V) than As(III). LC-MS analysis shows that phenol, o -nitrophenol and arsenic acid were the main transformation products . Both the radical scavenger experiment and electron spin resonance data confirm that the HO is responsible for ROX transformation. The toxic transformation products are found to have potential environmental risks for the natural environment, organisms and human beings.