Electro-Fenton Treatment of Contaminated Mine Water to Decrease Thiosalts Toxicity to Daphnia Magna

Treatment of organic contaminants using electro-Fenton (EF) is efficient but generate toxic by-products. Two mine effluents from northern Quebec with different concentrations of thiosalts (MElow and MEhigh) were tested for acute toxicity to Daphnia magna, before and after EF treatment, using pre-optimized parameters (carbon fiber brush cathode, single-side coated Nb/boron-dopped diamond plate anode, current intensity = 0.3 A, and initial [Fe2+] = 0.2 mM). The higher toxicity of untreated MElow compared to MEhigh, despite its lower thiosalts content (58 vs 199 mg/L), suggests the presence of an unidentified toxic species, which was removed during EF treatment. EF treatment of MEhigh, initially non-acutely toxic (50% mortality), resulted in the elimination of D. magna mortality. A preliminary techno-economic analysis conducted for northern Quebec vs the rest of Canada and the USA showed that energy consumption was the main contributor (52‒95%) to the total costs. Electricity-related operating costs nearly doubled (55%) for northern Quebec relative to the rest of Canada. These findings provide new insights for the potential application of the EF for the treatment of thiosalts in mine water, for operations in central jurisdictions and in remote northern areas