Removal of less commonly addressed metals via passive cotreatment

The viability of removing less commonly addressed metals (e.g., Cd, Cu, Ni, and Pb) in a passive cotreatment concept was tested using a microcosm-scale, three-stage batch reactor system in which acid mine drainage from an abandoned adit on Cerro Rico de Potosí and raw municipal wastewater from Potosí, Bolivia, were introduced at a 5:1 ratio. The acid mine drainage had pH 3.58, acidity 1080 mg L^-1 as CaCO₃ equivalent, and elevated concentrations of dissolved Al, Fe, Mn, Zn, Cd, Cu, Ni, and Pb, among other metals/metalloids. The municipal wastewater had pH 9.05 and alkalinity 418 mg L^-1 as CaCO₃ equivalent, with 5.6 and 38 mg L-1 of nitrate and phosphate, respectively. Previous analyses noted substantial pH increase, phosphate removal, denitrification, and removal of Al, Fe, Mn, and Zn. Prompted by these results, subsequent analyses were conducted for the current study, which noted that dissolved concentrations of Cd, Cu, Ni, and Pb decreased by 78.5, 18.3, 25.5, and 45.9%, respectively. Additionally, concentrations of Ce, Cr, Gd, and La decreased throughout the system. The study revealed the broader applicability of passive cotreatment of acid mine drainage and municipal wastewater, specifically for removing metals that are often difficult to address with conventional passive treatment approaches, such as Cd, Cu, Ni, and Pb. Results could be applicable for treatment alternatives in developing and developed countries where these waste streams occur in close proximity.