Prechlorination

Prechlorination: The addition of chlorine at the headworks of a treatment plant prior to other treatment processes. Done mainly for disinfection and control of tastes, odors, and aquatic growths, and to aid in coagulation and settling.

prechlorination
chlorination of water prior to filtration, or chlorination of sewage prior to treatment.
precipitant ...

See also: Chemical oxygen demand, Sewer, Suspension, Discharge, Sewage