Electrolysis-assisted UV/sulfite oxidation for water treatment with automatic adjustments of solution pH and dissolved oxygen

Abstract

Sulfite as a precursor to generate sulfate radical (SO4–) for water treatment has gained attention. Here we report a metal-free and highly efficient electro/UV/sulfite process to produce SO4– for water treatment. UV/sulfite reaction induces sulfite radical (SO3–), which is transformed into SO4– by the presence of oxygen due to water electrolysis. Electro/UV/sulfite process generates a steady-state SO4– concentration of 0.2 to 1.1 × 10−12 M in our tests. Solution pH affects sulfite species distribution, and higher pH mediates improved yield of steady-state SO4– concentration. Effect of sulfite concentration exhibits a bell-shaped pattern toward SO4– production due to self-scavenging. The oxidation capability of electro/UV/sulfite process is manifested by removing representative micropollutants (i.e., ibuprofen, salicylic acid, and bisphenol A) and Escherichia coli model pathogen, in both synthetic and natural water matrices. This novel electro/UV/sulfite process has obvious advantages, since it avoids metal ion catalysts, supplies reaction with electrolytically generated nascent oxygen, and overcomes the acidic pH requirement, that are challenging to traditional metal/sulfite processes. Considering the features of environmental friendliness and low cost, the proposed electro/UV/sulfite process should lead to successful applications in the future.