Chemicals are added as the water enters two rapid mixers: lime for softening, aluminum sulfate as a primary coagulant, and potassium permanganate to oxidize taste and odor compounds. Chemical reactions begin to change certain of the hardness compounds in the water from soluble to insoluble precipitates called “floc.” Floc absorbs color and entangles bacteria and other suspended matter. As the floc settles, the hardness is reduced, resulting in finished water hardness of about five grains per gallon (90 parts per million).Flocculators
The water then passes through three basins called flocculators. Large, motor-driven paddles rotate slowly, causing the floc to come into contact with all suspended matter. The long, narrow basins ensure that the softening and coagulation agents have sufficient time to complete the chemical reaction and prevent the floc from settling. Powdered activated carbon is added primarily for taste and odor control. However, it also has the capacity to adsorb dissolved synthetic organic chemicals, such as pesticides. Ferric chloride is added as a flocculant aid.