Carbon dioxide impacts both passive treatment system effectiveness and carbon footprint

摘要

Artesian discharges of net-alkaline, ferruginous waters from abandoned underground lead-zinc mines were examined in field mesocosms and a full-scale passive treatment system. Influent waters were calculated to contain ≈290 mg/L dissolved CO_2 (pCO_2 of 0.16 atm). Degassing of CO_2 improved iron and trace metal removal performance. Despite proton acidity produced by oxidative iron removal, pH values increased to >6.5, thus enhancing the rate of iron removal. Degassing resulted in return of ≈ 84,000 kg of CO_2 to the atmosphere on an annual basis, while maximum biological productivity would result in carbon sequestration of ≈ 4,500 kg a~(-1) in the full-scale system.