Using Coagulation, Flocculation, and Settling to Remove Toxic cyanobacteria

Cyanobacteria (blue‐green algae) produce toxins and tastes and odors that can significantly impair water quality. The removal of cyanobacterial cells without cell damage could significantly reduce the concentration of tastes, odors, and toxic cell metabolites present in treated water. Cultured cyanobacterium, hepatotoxic Microcystis aeruginosa , was mixed with reservoir water to simulate water entering a treatment plant during an algal bloom. A bench‐top jar‐test apparatus (flocculation) and a full‐scale pilot plant (flocculation–sedimentation–filtration) rated at 600 mL/min were used to evaluate the effectiveness of conventional water treatment processes in removing cyanobacterial cells. Removal of cells by flocculation using a jar‐test apparatus with aluminum sulfate dosed at concentrations used in water treatment practice varied between 70 and 83%. Results obtained from the pilot experiment indicated 99.9% of the cells were removed. More important, no additional release of microcystin (toxin) was found in the finished water.