Reusing Municipal Wastewater for Power Generation Cooling Towers - Opportunities and Obstacles
NC Currents, Summer 2012
Jul 1, 2012
Power plants and other cooling tower users are being pinched for available water resources. Many traditional sources, such as surface and groundwater may be over-allocated, too costly, or unavailable due to periodic droughts or regulatory considerations. Non-traditional sources are under consideration, including surface runoff capture, acid mine drainage, and municipal or industrial wastewater treatment plant effluents. The major focus of these non traditional sources is municipal wastewater treatment plants (WWTP). Both cooling tower users and municipalities can benefit environmentally and financially from this arrangement, especially if the source and use point are reasonably close to each other.
There are 5,400 US power plants, but only 60 of these obtain their cooling water from treated municipal wastewater sources. These are mostly located in Florida, California, Texas and Arizona, but other less water constricted states, such as Massachusetts, New Jersey, and Minnesota, also have power plants using reclaimed municipal wastewater. Most power plants further disinfect reclaimed municipal wastewater and use some treatment chemicals at the power plant. A recent University of Pittsburgh study points to possibly 50% of existing power plants can obtain all of their cooling water from WWTPs within a 16 km (10 mile) radius. As many as 78% of all existing power plants could rely on all their cooling water from WWTPs if the radius is extended to 25 miles, while 80% of all proposed power plants can obtain their cooling water from wastewater treatment plants in a 10 mile radius. Typically, power plants use 95 liters, or 25 gallons per kW produced, on average for all types of power generation. Most water is used by cooling, but other demands exist for boiler makeup, ash transport, chemical addition, and other uses. Slightly less than half of all power plants, (43% at last count), use once through cooling. Most newer plants use closed cycle cooling that recirculates water 4-8 times before discharging a blowdown amount to reduce total dissolved solids (TDS) buildup. This blowdown may require additional treatment before discharge, or if returned to the municipal wastewater plant, may pose toxicity problems from a higher TDS load, biocides, or other power plant treatment chemicals.
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