Carnegie Mellon University, in a joint effort with the University of Pittsburgh, is conducting a study of the use of treated municipal wastewater as cooling system makeup for coal fired power plants. This project builds upon a study sponsored by the U.S. Department of Energy entitled, “Reuse of Treated Internal or External Wastewaters in the Cooling Systems of Coal-Based Thermoelectric Power Plants,” which showed that treated municipal wastewater is the most common and widespread source in the United States. Data analysis revealed that 81 percent of power plants proposed for construction by the Energy Information Administration (EIA) would have sufficient cooling water supply from one to two publicly owned treatment works (POTW) within a 10-mile radius, while 97 percent of the proposed power plants would be able to meet their cooling water needs with one to two POTWs within 25 miles of these plants. Thus, municipal wastewater will be the impaired water source most likely to be locally available in sufficient and reliable quantities for power plants. Results of initial studies indicate that it is feasible to use secondary treated municipal wastewater as cooling system makeup. The biodegradable organic matter, ammonia-nitrogen, and phosphorus in the treated wastewater pose challenges with respect to enhanced biofouling, corrosion, and scaling, although current research is demonstrating that these problems can be controlled through aggressive chemical management. It is currently unclear whether tertiary treatment of municipal waste water prior to its re-use can be a cost-effective option to aggressive chemical management of the bulk cooling water volume.

The project will further examine the feasibility of using treated municipal wastewater as cooling system makeup water by conducting experimental studies and economic and social analyses. The primary goal of this project is to evaluate the benefits and costs of implementing tertiary treatment of municipal wastewater prior to using it in recirculating cooling systems at power plants versus an expanded chemical regimen for managing the quality of the entire cooling water volume with municipal wastewater as part of the makeup. Specific project objectives include:

• Determine the benefits and costs of subjecting secondary treated municipal wastewater to additional treatment (to remove ammonia by nitrification, biological oxygen demand by Granular Activated Carbon adsorption or microfiltration, and particles by filtration) prior to use as cooling water makeup.
• Determine different chemical treatment regimens required to manage cooling water quality for different levels of tertiary treatment ranging from no tertiary treatment to inclusion of nitrification, organic compound removal by adsorption, and filtration.
• Perform comparative life cycle cost analyses for different levels of tertiary treatment versus the corresponding chemical treatment regimens.
• Determine the critical economic, technical, and social factors that need to be considered in a comparative evaluation of tertiary treatment of makeup water versus cooling water chemistry control by chemical treatment (e.g., future changes in freshwater availability and cost, value of treated wastewater in the future, or social support for water reuse efforts).

Secondary Treated Municipal Wastewater as a Potential Source for Cooling Water in Power Plants

In the first phase of the project, detailed information about the use of treated municipal wastewater at several power plants where such water is used as cooling system makeup water will be collected and evaluated; plans will also be made for the field studies at the Franklin Township Municipal Sanitation Authority (FTMSA) wastewater treatment facility.  The second phase of the project includes the performance of laboratory studies, followed by related field studies with pilot-scale cooling towers at the FTMSA site to assess the benefits of tertiary treatment of the wastewater in reducing chemical treatment required for cooling water quality management.  Initial studies for life cycle cost analyses will also be performed.  Finally, life cycle cost analyses will be performed for the implementation of varying levels of tertiary treatment of municipal wastewater prior to use as makeup water for cooling systems.  An assessment of the technical and social factors that need to be considered in a comparative evaluation of tertiary treatment of makeup water versus cooling water quality control by chemical treatment will also be conducted.