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Water is a precious resource in the Southwest, and APS' facilities strive to minimize water usage through a variety of water-conservation activities. APS' major use of water is in electricity generation. One way in which APS conserves water is through careful water chemistry and treatment. This allows for a high level of water recycling in our electricity-generation process. We reuse our water supplies as much as possible to avoid wasting water, however, some water must be discharged (this is called "blowdown water") 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 98 percent of the blowdown water for reuse in the plant. The salts are then disposed at either a licensed offsite landfill or in on-site evaporation ponds. Other plants, such as the Palo Verde Nuclear Generating Station, discharge the blowdown to lined evaporation ponds. The cooling water in the Palo Verde 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 must meet the requirements of an industrial sewer discharge permit.
Water use was also an important consideration in the design of our new power plants, and APS strived to incorporate water conservation measures in these new plants, resulting in power plants that utilize less water per MWh generated.
APS has been able to reduce water use in power plant generation over the past two years as a result of higher capacity factors (leading to better resource efficiency) at our coal plants, and the addition of several new, more efficient natural-gas generation units.
Use of Treated Effluent
Another way we conserve water is to reuse treated effluent water from municipal wastewater treatment plants. APS is one of the largest users of treated effluent in the United States for use in power generation. This significantly reduces the amount of surface and groundwater required in our generation activities. As shown in the chart below, almost 60 percent of our total power plant water comes from treated effluent. At the Palo Verde Nuclear Generating Station and our Redhawk natural gas-powered facility, 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 at both Palo Verde and Redhawk.
Each year, Palo Verde's water reclamation facility processes about 20 billion gallons of treated effluent for power plant use, preserving enough potable water for about 75,000 homes.
Other Water Conservation Efforts
APS also has a variety of other water conservation efforts at facilities across our system. For example, in 2005 our Four Corners Power Plant initiated a non-native vegetation removal project at Morgan Lake, which is projected to save up to 13,000 acre-feet of water annually when completed, as well as improve the recreation activities at the lake.
APS also incorporates water conservation and use ideas into facility building and maintenance as part of our participation in the LEED program.
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