WASTEWATER TREATMENT PROCESSES EMPLOYING HIGH RATE CHEMICAL SOFTENING SYSTEMS

摘要

A ballasted flocculation system that chemically softens water and causes hardness particles to precipitate from the water and crystallize. In the course of crystallizing, the hardness particles grow and form ballasted floc that are separated from the water in the form of sludge by a clarification unit, producing a clarified effluent. The separated sludge including the hardness crystals is directed to a separator where the sludge is separated into two streams with each stream having hardness crystals contained therein. In one process design, one stream includes relatively small hardness crystals and the other stream includes relatively large hardness crystals. The stream having the relatively small hardness crystals is directed to a first reactor and mixed with the incoming water and a softening reagent. The stream having the relatively large crystals is directed to a second downstream reactor and mixed with water and a flocculant which facilitates the growth of the hardness crystals.