Synergistic effects of polyaluminum chloride and Phoslock on phosphate and cyanobacteria removal in eutrophic lake water

Abstract

Polyaluminum chloride (PACl) and Phoslock® are two promising technologies for lake restoration. The objective of this study was to evaluate the synergistic effects of PACl and Phoslock on phosphate and cyanobacteria removal and solids' settling rates during coagulation treatment of water from Lake Kampeska, South Dakota. The lake water, spiked with Anabaena sp., was treated with PACl, Phoslock, and PACl+Phoslock, under controlled laboratory conditions. PACl with 70% basicity at a dose of 8 mg Al/L achieved phosphate, chlorophyll a, and turbidity removal efficiencies of 93.8%, 90.7%, and 93.5%, respectively. The corresponding removal efficiencies of Phoslock at a dose of 800 mg/L were 70.5%, 73.2%, and 90.0%, respectively. The combination of PACl (4 mg Al/L) and Phoslock (300 mg/L) resulted in 88.5%, 99.4%, and 99.5% removal efficiencies for phosphate, chlorophyll a, and turbidity, respectively. These removal efficiencies were 12.6%–23.5% or 10.5%–55.4% higher than PACl or Phoslock alone. The combined use of PACl and Phoslock also exhibited high tolerances to the variations in pH and dissolved organic carbon levels during coagulation. Coagulation treatment produced flocs that settled out of suspension. These flocs were resuspended to simulate hydraulic disturbance. The sedimentation rates following resuspension were in the order of PACl+Phoslock > PACl > Phoslock. Treatment with PACl+Phoslock improved turbidity reduction at a settling time of 30 min by 48.5%–61.6% after initial treatment compared with PACl and Phoslock. The results of this study suggest that the combined use of PACl and Phoslock is an effective strategy to remove phosphate and cyanobacteria in lake water. © 2019 American Water Works Association.