Zero discharge of cooling water by sidestream softening

Abstract

Cooling water discharges are major environ mental problems, constituting from 60 to 90% by volume of industrial discharges. This amounts to 3.8 to 11.4 X 106 m3/y (1 to 3 X 109 gal/yr) of cooling water blowdown in the U. S. Heat, toxic chemicals, and organic and inorganic materials are contained in these discharges. Sidestream softening of cooling water elimi nates blowdown discharges to the environ ment. The lime-soda softening process re moves calcium, magnesium, and silica, which are the primary causes of scale formation on heat-exchange surfaces. The treated water then can be recycled to the cooling water sys tem. The only discharges are drift (fine drop lets entrained in the air circulating through the cooling tower) and sludge from the softener. The sidestream softening process is currently in operation at one power and two industrial plants, and is in the design/construction phase at several others. It is adaptable to most water supplies, but is most suitable for makeup waters that are not high in chlorides or dis solved solids concentrations. The process uses low-cost raw materials, lime and soda ash. It is gaining acceptance both as an economic alternative to blowdown treatment and as a way to meet zero discharge standards.