Photocatalytic treatment of organoselenium in synthetic mine-impacted effluents

Abstract

Biological selenium reduction processes are commonly employed as the best available technology (BAT) for selenium removal; however, as a by-product they produce trace amounts of organoselenium compounds with orders of magnitude greater bioaccumulation potential and toxicity. Here, we assessed buoyant photocatalysts (BPCs) as a potential passive advanced oxidation process (P-AOP) for organoselenium treatment. Using a synthetic mine-impacted water solution, spiked with selenomethionine (96 μg/L) as a representative organoselenium compound, photocatalysis with BPCs fully eliminated selenomethionine to <0.01 μg/L with conversion to selenite and selenate. A theoretical reaction pathway was inferred, and a kinetics model developed to describe the treatment trends and intermediates. Given the known toxic responses of Lepomis macrochirus and Daphnia magna to organoselenium, it was estimated that photocatalysis could effectively eliminate organoselenium acute toxicity within a UV dose of 8 kJ/L (1–2 days solar equivalent exposure), by transformation of selenomethionine to less hazardous oxidized Se species. Solar photocatalysis may therefore be a promising passive treatment technology for selenium-impacted mine water management. HIGHLIGHTS Buoyant photocatalysts (as a passive advanced oxidation process) used to treat selenomethionine (SeMet), a bioavailable by-product from biological Se treatment, in synthetic mine-impacted water, to below <0.01 ppb.; A treatment pathway for SeMet oxidation to Se(IV) and Se(VI) proposed from Se speciation data.; Solar dose of 1–2 days estimated to remove acute toxicity to Lepomis macrochirus and Daphnia magna.;

Keywords

• organoselenium
• passive treatment
• photocatalysis
• selenium
• selenomethionine