Sustainable Solutions for the 21st Century

By the year 2020, the future of an integrated solid waste management system will continue to evolve by reducing its carbon footprint and focusing on renewable energy in response to the global drive toward sustainability. Reducing the waste management carbon footprint may originate from many fronts. Opportunities may include the wholesale deployment of collection vehicles using natural gas fuels and making fewer collections per week, installation of landfill gas-to-energy systems, and other renewable energy systems (wind and solar) even on a small scale sufficient to power the electrical needs of only the ancillary landfill offices and other on-site facilities. And lastly the beginning of comprehensive public utilities planning may soon result in the development of public works and utilities campuses that take advantage of the synergies presented by recovering energy from waste and powering contiguous water and wastewater plants, along with numerous other public energy users, from jails to administrative offices.

The recent promotion of alternate waste-conversion technologies for the production of biomethane, syngas, and liquid biofuels from municipal waste by an increasing number of developers may result in additional opportunities for communities to manage their waste. The list of waste conversion technologies includes advanced combustion, anaerobic digestion, catalytic depolymerization, fermentation, gasification, and pyrolysis. Advanced combustion is a currently demonstrated technology. Several of the emerging technologies are currently being evaluated in various stages of testing, with funding provided by the US Department of Energy and private investors. The pathway to commercial success for emerging technologies typically requires five to 10 years. By 2020, it is possible that several of the emerging waste-conversion technologies will advance to commercial status.

However, the focus of our crystal ball is to look ahead for mass-burn advanced combustion-the proven workhorse of the waste-to-energy (WTE) industry-to continue to evolve and be implemented into a municipal utility campus. Unless there is a turnabout in the methodology for determining how municipal WTE facilities are paid for the renewable energy derived from local wastes, the opportunity to use the power behind the meter or 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, and our vision of this sustainable and synergistic approach is explored below.

Opportunity Presented by the Water-Energy Nexus
By the year 2020, the global public works community will be faced with the daunting task of providing both solid waste management and water resource services to a global population projected to be in excess of 8 billion. Looking to a sustainable future, renewable energy in the form of steam, heat and electricity derived from advanced WTE facilities can be used to internally power municipal water treatment processes with energy derived from the nonrecycled fraction of local municipal wastestreams. For those cases where the internal use of the electricity results in savings compared with the purchase of electricity from the local electrical utility, the savings may be shared between the solid waste and water resources departments.

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. 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. Advanced treatment requiring greater demands of energy for potable water production is becoming the norm for processing lower-quality raw water supplies while meeting higher environmental standards for a growing family of water chemistry parameters and chemicals of concern. Ultraviolet light, ozone, ultrasonics, membranes, and other electrically derived disinfection and filtration technologies continue to evolve, with the net effect of increasing the overall energy intensity of municipal water treatment.

In summary, the following are emerging paradigms affecting municipal solid waste management and water resources:

• Increasing landfill diversion and recycling goals
• Local, regional and national energy independence goals via clean renewable energy
• Growing awareness of sustainability and climate change initiatives
• Need for development of alternative water supplies
• Need for local, sustainable economic development and high quality jobs

Water Treatment Process Electric Demands
Energy input for water treatment plants varies widely with the raw water quality and treatment process types 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 in Table 1.

WTE/Water Treatment Process Synergy

Matching a modern WTE facility’s electrical output with water treatment process demand can vary significantly based on the water source, quality, treatment process and pumping requirements associated with the community’s existing water distribution system.

Figure 1 below illustrates the relationship between the size of the WTE facility and the potential water treatment process if all of the electricity were used for water treatment.

As shown, the WTE facility can provide energy far in excess of a community’s demand for convention potable water and wastewater treatment services. For communities in need of securing additional water supplies from alternate water sources-such as lower-quality surface water, brackish water, or seawater-the compatibility of WTE and water treatment plant (WTP) improves due to the greater demand for energy. An ever-growing percentage of the global population currently resides along coastal states. Much of this population resides in large- and medium-sized coastal communities, where the demand for additional water supply may require seawater distillation technologies. In these communities, the use of reverse osmosis (R/O), multi-stage flash (MSF) evaporation and multiple-effect distillation (MED) processes may be ideally suited to use 100% of the WTE electricity.

Advanced Water Treatment
Looking to the future of a more constrained and efficient municipal water resource system, water treatment approaches may include reclaimed water distribution systems for local, residential, commercial, and agricultural irrigation; reservoir storage for reclaimed water and excess stormwater during wet seasons; and stormwater treatment systems for removal of excess nutrients and pollutants in light of recent environmental mandates to control these discharges. In such an arrangement, the demand for energy in the form of electricity and steam will increase significantly and provide opportunity for a WTE facility to provide integrated campus needs.

Figure 2 illustrates how such a future water resource system and WTE facility could be integrated into a single utility campus.

The majority of communities currently do not employ WTE and have large MSW streams that are currently being disposed of in landfills. As the local and state goals for landfill diversion gain momentum as part of a drive for sustainability, the development of regional WTE facilities may also become viable when combined with regional water supply and distribution projects. In these cases, there is likely sufficient MSW available, which could allow a WTE facility to be sized to match the demand of the community’s existing and future water resource needs.

Figure 3 below illustrates a recent example of this synergistic relationship in Hillsborough County, Florida. This publicly owned, municipal waste-to-energy facility was originally constructed from 1985 to 1987 to process 1,200 tons per day of municipal solid waste. The facility generates 29 MW of renewable electricity, which is sold to the local utility. The WTE facility is located adjacent to an advanced wastewater treatment (AWT) plant that provides reclaimed water for use in the WTE facility’s cooling system, along with other ancillary uses that include facility landscape irrigation, plant floor washing, and process water for use in the facility’s air pollution control system. The AWT facility also accepts sanitary sewage waste and process wastewater from the WTE facility.

A Recent Success Story
The Hillsborough County WTE facility was recently expanded in 2007 to accommodate the continuing growth of the local community’s solid waste. An additional 600 tons per day of capacity was added, along with a separate steam turbine generator for the production of an additional 17 MW of renewable electricity. Shortly after the addition of the new expansion unit, Hillsborough County water services staff approached the solid waste staff to investigate the technical and economic feasibility of using some of the WTE renewable electricity to power the AWT facility. After review and analysis, the decision was made to disconnect the AWT facility from the local utility grid and repower the facility entirely with renewable electricity from the WTE facility. Backup diesel power was already available at the AWT plant to provide full operating capacity for periods when the WTE facility may not be available.

Commencing in the summer of 2009, the AWT facility was placed entirely on the WTE electrical system and has been consuming up to 2 MW of electricity per hour. This synergistic relationship allows the solid waste and water services departments to share in two ways. The solid waste department currently sells the remaining power to the local electric utility for a little less than 6 cents per kilowatt-hour, whereas the AWT was formerly purchasing electricity from the local electric utility for approximately 9 cents per kilowatt-hour under a commercial tariff rate. The 3 cents per kilowatt-hour difference is shared between the two Hillsborough County departments, resulting in a mutual benefit, which ultimately is returned to the local solid waste and wastewater rate payers in the form of reduced utility fees.

In response to this initial successful synergistic project, Hillsborough County has recently decided to expand the internal use of its renewable electricity by using up to an additional 5 MW of electric power for other essential services managed on its municipal campus, including a water treatment facility, water pump station, animal services facility, jail, and county administration offices.

Public Works Benefits
The potential cost savings that can be realized by the internal use of renewable energy produced from a modern WTE facility can be significant, depending upon the cost of electric power purchased from the local grid and the price at which utilities are willing to pay for renewable energy. These savings can be shared internally within the domain of public works to the benefit of rate payers for both solid waste and water resources.

The integration of WTE and water resources is a golden opportunity to maximize the benefits and services to the local community while minimizing the costs of these services. To borrow the phrase of Buckminster Fuller, one of the world’s most prolific inventors and visionaries, this represents the opportunity to optimize both utility systems and “do more with less!”

The year 2020 is just around the corner, and now is the time for this generation to leave its legacy by initiating the planning process for an integrated WTE and WTP campus to meet the needs of the next generation.

We live in an increasingly “environmentally tuned in” society; more of us are aware of and have an opinion on environmental issues. Topics such as sustainability and climate change surround us daily.

With modern technology, we have the means, as individuals, to broadcast our opinions to a large audience. As technology continues to facilitate our broadcast, our individual audience grows, and so too does our influence.

This growing number of external influences will need to be managed in order to successfully plan for and implement solid waste landfill programs.

Public consultation and engagement will increasingly demand attention before beginning a project. The long-held business cliche of “beg forgiveness later” will no longer be acceptable to regulators. “Ask permission now” will be the key to success.

Is a technical, engineering-based solid waste industry ready to accommodate nontechnical opinions?

It goes without saying that we’ll continue to see shifts in “where” we communicate – newspaper, radio, television, the Internet, etc. It’s challenging to predict how these media will affect us next week, let alone 10 or 15 years from now. We have no choice but to be flexible and adapt to them at their pace. So long as we’re strategically planning for communication, we will have no problem accommodating their maneuverings.