AWWA JAW56401

Drinking water that contains algae can have disagreeable tastes and odors. Because many algae contain significant quantities of taste- and odor-causing compounds and toxins within their cells, it is preferable to remove algae intact rather than through cell lysis. In addition, to avoid frequent filter clogging and to minimize disinfection byproduct concentrations, it is preferable to remove the algae prior to the filtration and disinfection steps of the water treatment process. Intact algae cells can be removed by coagulation, flocculation, and sedimentation. However, coagulation processes are frequently disrupted by the presence of algae because raw water pH tends to increase during algae blooms and because algae can excrete polysaccharides that increase coagulant demand. Therefore, utilities require strategies for the effective coagulation of algae. The authors discuss their findings of optimizing coagulant dosing by means of charge titrations. They maintain that online coagulant dose control, via online streaming current measurements, will allow utilities to maintain proper coagulant doses when raw water algae concentrations and/or background water quality vary. In optimizing coagulation conditions, the following factors were evaluated: streaming current value, coagulation pH, and initial algae concentration. Experiments were performed with both laboratory-cultured Anabaena flos-aquae that were spiked into a natural water and a natural algae bloom water that contained primarily Anabaena spp. and Synedra spp. Includes 52 references, tables, figures.