Photochemical Degradation of Arsenic and Selenium with Advanced Reduction Processes—Effects of Reagents

Abstract

A new class of water treatment processes called advanced reduction processes (ARPs) combine activation methods, such as ultraviolet (UV) irradiation, with reducing reagents to produce highly reactive reductants. This article reports on the application of ARPs to immobilize arsenic and selenium. Batch screening experiments were conducted under anaerobic conditions to evaluate the effectiveness of different ARPs in removing arsenic and selenium and to identify the most promising ARP for this purpose. The combination of sulfite with UV irradiation was not able to effectively remove arsenic and selenium. Although the ferrous iron/UV ARP was able to continuously remove all target compounds, the dithionite/UV ARP was observed to be the most promising method for removal of arsenic and selenium. However, resolubilization of both target compounds was observed with the dithionite/UV ARP. The dithionite/UV ARP rapidly removed soluble arsenic and selenium by reducing them to solid phases (As4S4, elemental Se). This was followed by resolubilization that was probably caused by oxidation of the solids by sulfite radicals or by reaction of sulfite with elemental selenium to form soluble species.