Sustainable Solutions for the 21 st Century Integration of Water Treatment Systems with Energy Derived from Municipal Wastes

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1 Sustainable Solutions for the 21 st Century Integration of Treatment Systems with Energy Derived from Municipal Wastes Paul L. Hauck CDM Smith Tampa, Florida USA Abstract Hillsborough County is a Florida municipality that has seen rapid growth and utility demands over the past 50 years. In response, it has implemented an innovative project to reduce the cost of wastewater treatment using renewable energy produced from municipal solid waste. The county developed a modern energy-from-waste (EfW) facility 25 years ago, in recognition that solid waste was capable of producing significant amounts of renewable energy in the form of electricity, and to limit landfill disposal. The electricity was sold to a local utility to help offset the costs of solid waste disposal to local rate payers. The EfW facility was also located adjacent to one of the county s advanced wastewater treatment plants (AWTP), allowing the county to take advantage of reclaimed water at the EfW facility for cooling and other process uses. Five years ago, faced with continuing growth, the county expanded their EfW facility by approximately 50 percent. They decided to disconnect the adjacent AWTP from the local electric grid, and use renewable electricity supplied from the adjacent EfW facility to reduce the cost of wastewater treatment at the AWTP. This synergistic arrangement resulted in savings to both the Solid Waste and Resources Departments. Keywords: renewable energy from wastes, water treatment Introduction There are many paradigms emerging within the disciplines of what was once the purview of public works. These changes are being driven by a growing awareness of the need to address climate change; reduce greenhouse gasses; improve municipal energy efficiency; and develop renewable energy projects, including renewable energy derived from municipal wastes. Faced with an aging, but rapidly expanding infrastructure, and the mandate to efficiently manage their assets, municipal governments are caught in a perplexing situation of becoming more efficient while working under the pressure of smaller budgets, fewer resources, and less staff. Methods Many communities are faced with the need to develop alternate water supplies to accommodate future growth. With the availability of high-quality water supply sources less available, greater quantities of energy are generally required to process lower quality water sources using advanced technologies. This paradox presents an opportunity for public works to explore the synergies of using renewable energy from wastes to power advanced water treatment facilities for the benefit of the local environment and economy. Page 1 of 7

2 This paper explores the synergies that can be realized by the integration of renewable energy systems derived from municipal solid waste with several municipal water treatment processes. The evolution of the modern energy-from-wastes (EfW) industry has not been without major hurdles. Often referred to as incineration, the first generation of plants typically did not recover energy, nor did they have efficient and modern air pollution controls. In the 1980s, many of the current generation EfW facilities were constructed and equipped with efficient energy recovery systems and modern air pollution controls. Today, in the Unites States, EfW facilities convert approximately 13 percent of the nation s waste at 86 operating EfW facilities, processing more than 25 million tons of solid waste with a generation capacity in excess of 2,700 megawatts (MW). Recent benchmarking studies have shown the U.S. EfW industry s continual advancement toward improved emissions, efficiencies and other benefits for their respective communities. Some of the trends in the EfW industry are noted below. Increasing EfW trends include: Number of EfW facility expansions More stringent emission limits and green-house gas (GHG) reporting Higher heating value (HHV) of waste Higher boiler and turbine-generator availability Greater use of reclaimed water for cooling Higher gross and net electric generation per ton of solid waste Recognition and classification of electricity from EfW as renewable energy Marketable value of the environmental attributes of EfW electricity Addition of non-ferrous metal recovery systems Integrated solid waste management systems on an eco-campus Decreasing EfW trends include: Lower air emissions Lower reagent consumption Lower water consumption Lower electric payments The U.S. EfW market appears to be on the verge of renaissance, with several plants currently under construction for expansion of capacity, one new facility to break ground in the spring of 2012, and several new projects under consideration. One of the key drivers in the cost-effectiveness of EfW is the price paid for renewable electricity. As noted above, one of the recent trends in the U.S. electric power industry has been a decline in retail sales of electricity for the first time in modern history. This has led to a low demand for new electric power plant capacity. Unless there is a turnabout in the methodology for determining how municipal EfW facilities are paid for the renewable energy, the opportunity to use all or some of the electric power behind the meter (internally) within public works may present the highest and best use of this renewable electricity. One such opportunity for internal use of electricity will be for the treatment of municipal water resources. This broad class of vital municipal services includes treatment of wastewater, reclaimed water, stormwater and potable water. Page 2 of 7

3 Matching a modern EfW facility s electrical output with water treatment demand varies significantly based on the source of the raw water, quality, treatment and pumping system compatible with the community s existing water distribution system. Energy input for water treatment plants varies widely with the raw water quality and treatment process type required to meet potable water standards. The typical range of energy input for various water treatment processes including raw water withdrawal and transfer, treatment, disinfection and distribution is summarized below. Figure 1 below illustrates the relationship between the size of an EfW facility processing 1,000 tons per day (tpd) of municipal solid waste and a number of potential water treatment processes, assuming that all of the net electricity produced by the EfW was used for water treatment. Source Groundwater Surface Brackish Treatment Technology Conventional softening, filter, and disinfection Conventional softening, filter, and disinfection Reverse osmosis / membrane Seawater Reverse osmosis / membrane Seawater Multi-stage flash evaporation (MSF) Multiple effect distillation (MED) Reclaimed Reverse osmosis / membrane Reclaimed Wastewater Electrical Energy Intensity kwh/mg (kwh/m 3 ) ( ) ( ) 4,000 10,000 ( ) 10 20,000 ( ) 20, ,000 ( ) 10,000 15,000 ( ) MSF/MED 15,000 20,000 ( ) Biological treatment / disinfection 1,000 5,000 ( ) Page 3 of 7 Figure 1 Size of Treatment Process Powered by 1,000-tpd (907 mtpd) EfW As shown, the net electrical output of a modestly sized 1,000-tpd (907 mtpd) EfW facility may provide more electrical energy than needed to meet the community s demand for convention potable water and wastewater treatment services. For communities in need of securing additional water supplies from alternate water sources, including lower quality surface water, brackish water, reclaimed water, or seawater, the compatibility of EfW and advanced water treatment processes improves as the demand for energy increases. An ever-growing percentage of the global population curently resides along coastal states. Much of this population resides in large- and mediumsized coastal communities, where the demand for additional water supply may be provided by seawater treatment technologies. In these communities, the use of reverse osmosis

4 (R/O), multi-stage flash (MSF) evaporation and multiple-effect distillation (MED) processes may be ideally suited to use 100 percent of the electricity from an EfW facility that is sized to treat the municipal solid waste generated in the community. Results The Hillsborough County Florida municipal EfW facility was originally constructed from 1985 to 1987 to process 1,200 tpd (1089 mt/day) of municipal solid waste (MSW). The facility, as originally designed, generates 29 MW of renewable electricity sold to a local utility. The EfW facility is located adjacent to an 8 million-gallon-perday (mgd) (30,283 m3/day) advanced wastewater treatment plant (AWTP), which provides the EfW facility with up to 1.1 mgd (4,164 m3/day) of reclaimed water. The reclaimed water is used for multiple purposes in the EfW process. The largest user at approximately 1 mgd (3,785 m3/day) is makeup water to the EfW s cooling system (wet evaporative cooling tower). The second largest user at approximately 56,000 gpd (212 m3/day) is dilution water, which is used in the spray dryer scrubber air pollution control unit. Additional use of approximately 11,000 gpd (41.6 m3/day) is plant floor wash down water, and another 5,300 gpd (20.1 m3/day) for ancillary cooling of equipment. The facility landscape irrigation water supply is also provided by the AWTP reclaimed water system. The AWTP facility also accepts sanitary waste along with process wastewater from the EfW facility. The EfW facility was recently expanded from 2007 to 2009 to accommodate the continuing growth of the local community and solid waste generation. An additional 600 tpd (544 mt/day) of waste processing capacity was added, along with a separate steam turbine generator for the production of an additional 17 MW of renewable electricity. During the addition of the new expansion unit, Hillsborough County Resource Services staff worked in conjunction with the Solid Waste staff to investigate the technical and economic feasibility of internally using some of the EfW renewable electricity to power the AWTP facility. After review and analysis, the decision was made to disconnect the AWTP facility from the local utility grid, and to power the facility entirely with renewable electricity from the EfW facility. Figure 2 is a recent aerial photograph of the two adjacent municipally owned facilities. AWTP Facility EfW Facility Figure 2 - Hillsborough County, Florida 1,800-tpd (1,633 mt/day) EfW Located Adjacent to 8-mgd (30,283 m3/day) AWTP. Backup diesel generator power was already available at the AWTP plant to provide full operating capacity for periods when the EfW facility is not available (for example, during periodic turbine generator outages that are performed approximately every 5-6 years for maintenance). A total of four diesel-powered emergency generators are located at the AWTP site and can provide up to 2,500 kw of electricity for periods when the EfW Page 4 of 7

5 facility is at reduced load due to planned and unplanned maintenance outages. Figure 3 is a photograph of one of the four dieselpowered backup generators located at the AWTP. Figure 3 - One of Four Diesel Powered Backup Generators Located at the AWTP. Commencing in the summer of 2009, the AWTP facility was placed entirely on the EfW electrical system and has been consuming approximately 1.7 MW of electricity. This synergistic relationship allows the new Public Utilities Department (combined solid waste and water resource services groups) to share in two ways. The solid waste group currently sells the remaining power to the local electric utility for a little less than 6 cents per kilowatt-hour (kwh), whereas the AWTP was formerly purchasing electricity from the local electric utility for approximately 9 to 11 cents per kwh under several commercial tariff rates. The current kwh rate for the EfW electricity utilization benefits the Public Utilities Department in two ways. The Solid Waste Enterprise system receives additional revenues because the self-service rate paid by the Service Enterprise system is slightly higher than current electric market rates; and, the Service Enterprise system has significantly lowered its energy cost by approximately 50 percent because the self-served facilities no longer purchase commercial energy from a local electric utility. The estimated overall annual benefit to the Public Utilities Department is approximately $600,000 per year assuming an average use of 1.7 MW of electricity valued at 4 cents/kwh differential (cost of electricity purchased by the AWTP minus the current EfW power sales price). Other services recently powered include a water treatment facility that serves its local potable water system, a customer service center, and a warehouse complex utilizing approximately 0.3 MW of electricity. The estimated overall annual benefit to the Public Utilities Department is an additional $100,000 per year assuming an average use of 0.3 MW of electricity valued at a differential of 4 cents/kwh. In response to this initial successful synergistic project, Hillsborough County Public Utilities Department is evaluating the potential to continue expanding the internal use of its renewable electricity by up to an additional 5 MW of electric power for other essential municipal services that are managed on its municipal campus. Modifications to the existing electrical switchgear and transmission system required for the new electrical supply to the AWTP located south of the EfW facility were completed during the expansion project in 2009 by the EfW operator, Covanta Energy Inc. However, a new electrical switchyard and transmission line was required for the additional electrical supply to the county facilities located north of the EfW facility. Page 5 of 7

6 Figure 4 shows the new 13.2 kv electrical substation in the foreground, with the existing switchyard in the background. Figure 4 - New 13.2 kv Substation (foreground) for Internal Use of Electricity by Hillsborough County, Florida. Discussion and Conclusions For communities considering similar synergistic arrangements, the potential cost savings can be significant, depending upon the percentage of EfW net electrical output that can be used behind the meter for treatment of water and wastewater resources. Figure 5 - Potential Benefits for use of Renewable Electrical Energy from EfW Facilities. The above figure illustrates the potential savings to Public Works for a variety of EfW facility sizes based upon the percentage of electricity that is used for the treatment of water resources. As shown, the savings can be significant, potentially tens of millions of dollars per year. As a point of reference, the Hillsborough County Florida EfW internal use of electricity is currently only 5.1% of the total net generation. The county continues to explore additional opportunities for ways to use a greater percentage of their renewable energy for other municipal services and public work projects. A synergistic approach to managing several municipal processes on a single campus is compatible with the goals of sustainability, waste reduction, and development of alternate water supplies, while answering the challenge of the water-energy nexus. In addition to this successful Florida project, there are numerous opportunities to integrate energy from waste with water treatment processes for various alternate water sources, including surface water, wastewater, reclaimed water, stormwater, brackish water, and seawater as viable options for the future era of sustainable public works. Advanced treatment requiring greater demands of energy for water resource treatments is becoming common when processing lower quality raw water, while meeting higher environmental standards for a growing family of water chemistry parameters and chemicals of concerns. Ultraviolet light, ozone, ultrasonics, membrane technology and other electrically derived disinfection and filtration Page 6 of 7

7 technologies continue to evolve, with the net effect of increasing the overall energy intensity of future municipal water treatment systems. Figure 6 illustrates how a future integrated municipal water utility may be configured and operated with renewable electricity from EfW. EfW electricity or steam, along with biomethane from landfill gas or anaerobic digesters for drying WWTP biosolids. Operation of recycling facilities (construction and demolition waste, household hazardous waste, electronic waste, and material recovery facilities). Operation of municipal buildings via combined heat and power (CHP) using steam, hot and chilled water. Acknowledgments Hillsborough County, Florida Public Utilities Department (Paul Vanderploog Director, Rebecca Garland, Operations Division Director, and Patricia V. Berry, Solid Waste Management Group Manager) Figure 6 - Future Integrated Campus for Municipal Utilities. Disclosures The author has nothing to disclose. Often referred to as the water-energy nexus, water and energy are inextricably linked in the goal of public works to provide a clean and affordable municipal water supply. High quality solid waste management and water treatment delivery are also two key processes critical to the successful development of sustainable economic development on local, regional, state and national levels. In addition to the uses of EfW electricity for water treatment and associated distribution systems, other uses for energy derived from municipal wastes on an integrated campus may include: Page 7 of 7