Abatement of circumneutral mine drainage by Co-treatment with secondary municipal wastewater

Abstract

Acid mine drainage is a persistent and problematic source of water pollution. Co-treatment with municipal wastewater at existing wastewater treatment plants has several advantages; however, potential impacts on plant physicochemical and biological processes have not been well explored. The primary purpose of this bench-scale study was to examine the impact of co-treatment by combining a mild acid mine drainage at various ratios with municipal wastewater, followed by sludge settling and supernatant comparative analysis using a variety of effluent water quality parameters. These measurements were combined with carbonate system and adsorption isotherm modeling to elucidate the mechanisms underlying the experimental results. Acid mine drainage addition decreased municipal wastewater effluent PO₄^3- concentrations below 0.2 mg/L with greater than 97% removal, demonstrating co-treatment as an alternative solution for municipal wastewater nutrient removal. Biochemical oxygen demand remained similar to controls with <10% variation after co-treatment. Coagulation from metals in acid mine drainage was incomplete due to PO₄^3- adsorption, confirmed by comparing experimental results with Langmuir isotherm behavior. Sweep flocculation was the dominating particle aggregation mechanism, and co-treatment led to improved particle clarification outcomes. Improved clarification led to up to 50% Fe removal. Final pH had little variation with all conditions having pH > 6.0. Carbonate system modeling adequately explains pH effects, and can also be applied to varying acid mine drainage matrices. The impact of acid mine drainage addition on the municipal wastewater microbial community was also investigated which provided evidence of microbial adaptation. This study demonstrates post-aeration co-treatment enables mitigation of mild acid mine drainage without adversely affecting wastewater treatment plant processes. Reported results also frame required future studies to address extant questions prior to full-scale adaptation.

Keywords: Acid mine drainage; Adsorption isotherm; Co-treatment; Iron; Oxygen demand; Phosphate adsorption.