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Given the Southwest’s arid climate, water is one of our most precious resources. APS facilities strive to minimize water usage through water conservation activities including cycling water in power plant cooling towers several times before discharging it, adapting evaporative coolers to reduce blow-down at large facilities and capturing car wash water.
At the Palo Verde Nuclear Generating Station, we use treated effluent, purchased from seven cities in the Phoenix metropolitan area for cooling. A 35-mile pipeline carries treated waste water from a City of Phoenix sewage treatment facility to Palo Verde, where we use an advanced waste water treatment process capable of preparing 90 million gallons of water each day for use in the plant. The adjacent Redhawk natural gas-powered facility uses treated effluent from the Palo Verde treatment plant to meet its cooling needs as well.
In 2003, the Palo Verde plant’s water reclamation facility processed a total of about 20 billion gallons of treated effluent for power plant use, preserving enough potable water for about 75,000 homes. The Silverhawk Power Plant about 30 miles northeast of Las Vegas is an air-cooled combined-cycle plant. It uses about 200 to 250 acre feet of water per year at full capacity, compared to 3,300 acre feet per year for a similar water-cooled plant.
Water Discharge
Although we reuse our water supplies as much as possible to avoid wasting this resource, eventually some water must be discharged to control the salinity of the water used in the power plant processes.
The methods for disposal of blowdown water from the plants vary depending on the circumstances. The newest combined-cycle power plants use equipment (brine concentrators and crystallizers) to recover up to 95 percent to 98 percent of the blowdown water for reuse in the plant. The salts are then disposed to either a licensed offsite landfill or to on-site evaporation ponds.
Other plants, such as the Palo Verde Nuclear Generating Station (PVNGS), discharge the blowdown to lined evaporation ponds. The cooling water in the PVNGS cooling towers is recycled until its salinity is 20 or more times the salinity of the source water before it is discharged as blowdown to the lined evaporation ponds.
At other plants, we must blowdown to surface waters, or return the water to irrigation canals for reuse. These discharges are made according to the requirements of National Pollution Discharge Elimination System (NPDES) permits. The water quality of the blowdown is monitored to verify it meets the stringent water quality requirements of the NPDES permit. In one case, the blowdown is discharged to the local sewer system. This discharge is permitted by and must meet the requirements of an industrial sewer discharge permit.
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