Electro-Fenton treatment of contaminated mine water to decrease thiosalts toxicity to Daphnia magna

Treatment of organic contaminants using the electro-Fenton (EF) process is efficient but generates toxic by-products. The aim of the present study was to assess the residual toxicity associated to the treatment of real mine effluents using EF and to perform a preliminary techno-economic analysis to compare the costs of different techniques. 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. 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, or that higher thiosalts concentrations mitigate the toxicity of other toxicants. 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 operating costs. Electricity-related 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.