Passive co-treatment of Zn-rich acid mine drainage and raw municipal wastewater

A microcosm-scale, three-stage batch reactor system was constructed to test the viability of the passive co-treatment of Zn-rich acid mine drainage (AMD) and raw municipal wastewater (MWW). AMD from an abandoned adit on Cerro Rico de Potosí with pH 3.58 and acidity of 1080mg/L as CaCO₃ equivalent containing 12, 68, 17 and 550mg/L of dissolved Al, Fe, Mn and Zn respectively was mixed at a 5:1 ratio with raw MWW from Potosí, Bolivia with 5.6 and 38mg/L nitrate and phosphate, respectively. Compared to the influent mix to account for dilution, dissolved Al, Fe, Mn and Zn concentrations were decreased by 99.7%, 99.9%, 4.5% and 33.9%, respectively. PHREEQC geochemical modeling indicated the formation of various solid-phase metallic complexes. Nitrification occurred despite inhibitory Zn concentrations. Phosphate was decreased to below detection limits and pH increased to 7.06. The study revealed the feasibility of non-synthetic AMD and raw unscreened MWW passive co-treatment in relatively low ambient temperatures (8.2 to 10.3°C).