The wastewater is allowed to enter the top of the cooling tower at a rate of 1 to 4 gallons per minute per square foot of tower. As the water flows through the packing, air is injected into the system countercurrent to the water. The ammonia gas is subsequently striped from wastewater. After stripping is completed, the pH of the effluent is readjusted in order to conform to local effluent standards. Filtration can be accomplished by using filter beds made of diatomaceous earth, sand or mixed media.
Wastewater flows through the filter bed where suspended solids are entrapped.
After a period of operation, flow through the filter is obstructed by the entrapped material. When this occurs, the filter must be taken off line and backwashed before filtration can continue. If this cleaning is not completed, short-circuiting within the filter bed may occur, resulting in poor effluent quality. Filtration can achieve suspended solid values of 1 to 20 milligrams per liter depending on the efficiency of biological processes that preceded it. A microstrainer can also be used to provide the same results achieved by a filter bed.