A Balancing Act: Achieving Both Low Level Phosphorus and Metals Limits at Upper Blackstone

Upper Blackstone conducted bench-scale testing of six coagulants and side-by-side piloting of three phosphorus removal technologies (ACTIFLO®, CoMag® and Aqua MegaDisk®) with the objective of determining the optimal combination of chemical type and treatment process to meet its NPDES permit. The stringent limits include 0.1 mg/L for total phosphorus and metals limits of 7.2 μg/L (copper), 0.2 μg/L (cadmium), and 87 μg/L (aluminum). All six coagulants achieved the phosphorus goal; however, alum, ferric chloride and RE-100 were selected for piloting. All three removal processes achieved the phosphorus goals, but performance was affected by the coagulant utilized. The ballasted flocculation processes performed better with alum and ferric chloride, and the filters performed better with RE-100. The treatment process utilized did not impact metals compliance, but the coagulant used and the addition of sulfide-based polymer did. Upper Blackstone selected ACTIFLO with ferric chloride based on an economic and non-economic evaluation.