Enhanced Phosphorus Removal From Municipal Wastewater via Cotreatment of Mine Drainage During Primary Clarification

Cotreatment of mine drainage (MD) in existing wastewater treatment plants (WWTPs) could provide treatment benefits for both waste streams. The alkalinity that is innate to most WW may be sufficient to neutralize MD acidity, elevating pH and correspondingly decreasing concentrations of dissolved metals. Additionally, PO₄ in WW interacts with Fe and Al in MD and is removed from solution, potentially decreasing the need for enhanced biological treatment or chemical precipitation techniques. However, there are concerns about how adding MD to a WWTP may impact the treatment efficiency of the WWTP. Hence, the objective of this study was to determine the impact of AMD addition on the kinetics of BOD removal, in addition to the extent of metals, acidity, and PO₄ removal when WW and MD were mixed in a bench-scale primary clarifier. MD was mixed with primary influent WW in 10:90 and 40:60 MD:WW ratios and allowed to settle for 2 h before the supernatant was transferred to BOD respirometers. The pH remained circumneutral 2 h after mixing, ranging from 7.44 to 8.27 for 10% MD and 6.66 to 7.36 for 40% MD. The BOD oxidation rate was unaffected by MD addition, with first-order kinetic rates ranging from 0.50 to 0.77 day^-1 for raw WW, 0.54 to 0.97 day^-1 for 10% MD, and 0.45 to 0.95 day^-1 for 40% MD. PO₄ removal increased linearly with the molar ratio of ([Fe] + [Al])/[PO₄-P] for the conservative mixture of raw WW and MD and reached > 99% removal when (([Fe] + [Al])/[PO₄-P]) > 2. Overall, this work establishes a practical framework for leveraging mine drainage chemistry within conventional wastewater primary treatment to enhance phosphorus capture without compromising downstream biological performance. The approach offers a scalable pathway for utilities to turn a problematic influent into a controllable unit-process benefit, supporting tighter nutrient limits with minimal new infrastructure and chemical inputs.