SINGLE-STAGE ANAEROBIC PASSIVE CO-TREATMENT OF ACID MINE DRAINAGE AND MUNICIPAL WASTEWATER

The passive co-treatment of municipal wastewater (MWW) and acid mine drainage (AMD) is an emerging treatment approach that has shown recent promise. The approach involves allowing a self-designed microbial ecosystem to synergistically improve these waters by passively manipulating redox conditions. To investigate the efficiency and rates of reactions of anaerobic co-treatment, 24 replicate anaerobic 1L-cubitainers containing a 5:2 MWW:AMD mixture and inert Kaldnes plastic media were sealed and incubated for 30 days. The AMD had 37 mg/L aluminum, 20 mg/L iron, 2.6 mg/L manganese, and 670 mg/L sulfate with a pH of 2.7. The MWW had 1200 mg/L of chemical oxygen demand, 7.4 mg/L phosphate as P, pH of 6.9, and 375 mg/L of alkalinity as calcite equivalent. After a sharp decrease from the initial mix pH of 6.9 to 6.3, the pH increased linearly back to 6.9. Following pH, alkalinity also dipped from the initial mix of 153 to 128, but then increased linearly to 249 mg/L as calcite equivalent due to bacterial sulfate reduction. Sulfate decreased from 230 to 149 mg/L. Iron decreased to 0.05 mg/L upon mixing due to the effect of increased pH on trivalent iron. Iron later increased near the midpoint of the incubation, likely from the activity of iron reducing bacteria acting on iron oxyhydroxides. However, the iron released into solution subsequently precipitated via iron-sulfide formation. Hydrogen sulfide concentrations increased dramatically over time, supporting sulfate reduction and iron-sulfide precipitation as treatment mechanisms. Phosphate decreased to below detection limits (< 0.5 mg/L as P) immediately upon mixing. Chemical oxygen demand decreased from 389 in the influent mix to 242 mg/L. Overall, results revealed interesting iron treatment dynamics and provided reaction rates central to expanding this technology to field-scale application.