Co-Treatment of Acid Mine Drainage With Municipal Wastewater Using the Activated Sludge Process: Preliminary Treatability Studies

Abstract

Co-treatment of acid mine drainage (AMD) and municipal wastewater (MWW) using the activated sludge (AS) process is an innovative approach to AMD remediation that utilizes the alkalinity of MWW and the adsorptive properties of AS biomass to remove acidity and metals from AMDimpacted waters. Preliminary treatability studies have been conducted to simulate the effects of introducing AMD to different stages of the AS process. Mixing high-strength synthetic AMD (pH 2.8, 540 mg L-1 Fe, 200 mg L-1 Al, 30 mg L-1 Cu, 60 mg L-1 Zn, 30 mg L-1 Mn) with settled MWW over a range of dilutions, simulating conditions in the primary sedimentation stage of the AS process, led to rapid and significant removal of metals from solution (average removal: 38 mg L-1 Al, 5 mg L-1 Cu, 56 mg L-1 Fe, 4 mg L-1 Mn, and 7 mg L-1 Zn). Mixing synthetic AMD with AS biomass at different solids concentrations, simulating AMD loading to the secondary (biological) treatment stage and/or to a subsidiary mixing tank, also removed significant fractions of metals from solution (average removal: 28 mg L-1 Al, 5 mg L-1 Cu, 25 mg L-1 Fe, 3 mg L-1 Mn, and 4 mg L-1 Zn at a mixed liquor suspended solids concentration of 6 g L-1). Activated sludge respiration inhibition tests indicated high tolerance to spiked additions of synthetic AMD, demonstrating that acute toxicity is mediated by the neutralization and metal removal reactions that occur during mixing. Acclimatization studies indicated that AS sensitivity to spiked additions of AMD decreased after a 25-day period of continuous AMD loading. Laboratory-scale process evaluation studies are underway to demonstrate the feasibility of co-treatment for full-scale application in the treatment of AMD.