Removal of Cu and Zn from mine water using bench-scale bioreactors with spent mushroom compost: a case study in an abandoned mine region, South Korea

Mine water containing copper and zinc exceeding the permissible discharge limit has been discharged from the S mine site in South Korea. To evaluate the feasibility of applying passive treatment methods for treating water discharged from this mine, bench-scale experiments were conducted by using columns simulating successive alkalinity-producing systems (SAPS) and bioreactors. As substrate materials, limestone and spent mushroom compost (SMC) were applied, with their structures and mixing ratios varied. The efficiency of metal removal for each column was then evaluated. SAPS (column B) and bioreactors (columns C and D) exhibited Cu removal efficiencies of 99.7%, 98.0%, and 97.1%, respectively, while the limestone reactor (column A) had an average removal efficiency of 81.3%. Except for the re-dissolution events, Zn removal efficiencies were 99.5%, 97.6%, and 88.4%, respectively, while the limestone reactor had an average removal efficiency of 29.2%. Facilitated by a pH increase caused by the dissolution of limestone, the bacterial sulfate reduction (BSR) reaction was shown to be effective at removing metal in the SAPS and bioreactor columns; the process was revealed through the presence of sulfide in the effluent. When comparing bioreactors with different compost mixing ratios, columns with greater SMC ratios had higher removal efficiencies, as well as higher alkalinity, which shows the importance of SMC in metal removal. Overall, this study will be helpful in determining on-site treatment methods for Cu- and Zn-rich mine water by reusing waste materials, SMC, through bacterial metal reduction reactions, as well as considering the potential lifespan of the treatment facility.