The next sustainable revolution in solid waste management: bioreactor landfills
Ram N. Tewari
Director, Solid Waste Operations Division
Broward County, Florida
Member, APWA Solid Waste Management Committee
Solid waste management is a critical indicator of the society's overall quality of life. A recent study by the American Society of Civil Engineers (ASCE)—"2003 Progress Report for America's Infrastructure"—painted a bleak picture of the nation's twelve infrastructure categories. However, the solid waste category fared relatively well in this study. It earned the top grade of "C+" repeating its ASCE's 2001 grade. Although this is encouraging news, there are a lot more reasons for solid waste professionals to try harder to improve their performance.
In the United States, we generated about 232 million tons (or 4.5 pounds per person per day) of municipal solid waste (MSW) in 2000, as compared to 195 million tons in 1990. Though our population in the United States represents only six percent of the world's population, we are currently producing 50 percent of the world's MSW. It is forecasted that these numbers will continue to increase. In 2006, the population of the United States is expected to be about 288 million; by 2020, about 323 million; and by 2050, the estimated U.S. population will be 394 million. This significant increase in population will result in a lot of solid waste being generated in the future. How do we face this challenge and manage the increasing cost of solid wastes effectively (e.g., providing a higher level of service at a lower cost)? We can do this by being creative, exploring innovative technologies, regional cooperation, and establishing public/private partnerships.
The United States Environmental Protection Agency (USEPA) has the following integrated hierarchy of MSW management: recycling (reuse, including source reduction and composting); waste-to-energy (and other recovery systems); and disposal (landfilling). Though landfilling is the last resort, it remains one of the primary methods of disposing of MSW and continues to be the disposal method of choice. Almost two-thirds of the U.S. MSW is currently being sent to the landfills. Currently, these landfills must meet the requirements of the Resource Conservation and Recovery Act (RCRA), Subtitle D, the Clean Water Act, the Clean Air Act, and numerous other federal, state, and local regulations.
Sanitary landfilling in the United States has made monumental strides in the last 25 years, moving from open dumps with little or no control to state-of-the-art facilities. Still, it is hard to be a good guy in the landfill business because the public often does not appreciate the intricacies of the landfill operations. We have to operate the landfills efficiently because they are going to be with us forever. Landfills will remain in demand because of lower unit cost, stalled growth in the waste-to-energy area, and limited potential growth in recycling. Social factors such as continued population growth, rising per capita MSW generation due to higher standards of living, low probability of zero waste, and the difficulty of siting new landfills due to the Not-In-My-Back-Yard (NIMBY) mindset will also create an inescapable need for landfills. It is incumbent upon us, the public works professionals, to operate landfills more efficiently and to explore innovative technologies and concepts that are sustainable, economically feasible, and environmentally sound. These objectives can be met by one very promising approach: the bioreactor landfill processing of MSW.
A bioreactor landfill is defined by the USEPA as a MSW landfill, or a portion thereof, where any liquid other than leachate is added in a controlled fashion to the waste mass. Rapid waste stabilization is the principal goal of the bioreactor landfill. Under this model, landfills become facilities where the waste is contained and actively digested by adding liquids to reach a moisture content of at least 40 percent by weight to accelerate biodegradation of the waste.
Also, the Solid Waste Association of North America (SWANA) has defined a bioreactor landfill as "any permitted Subtitle D landfill or landfill cell where liquid or air is injected in a controlled fashion into the waste mass in order to accelerate or enhance biostabilization of the waste."
This process is in contrast to a traditional landfill (dry tomb) that simply preserves layers of compacted garbage in as dry a condition as possible, to minimize the leachate which then biodegrades within its limits and timeframes. The bioreactor landfill uses liquid (either leachate or from an external source) as an additional component to the waste mix. This liquid intensifies the natural process of microbial waste decomposition. There are various strategies for addition of moisture (e.g., leachate recirculation, spray application and percolation ponds) to create a favorable environment for decomposition.
There are three types of bioreactor operational processes which can be used: aerobic, anaerobic, and hybrid or facultative. In an aerobic bioreactor, air (oxygen) is added to promote aerobic activity and accelerate waste stabilization of the landfill. This is the same process that decomposes organic matter in a compost system. In an anaerobic bioreactor landfill, moisture is added in the form of recirculated leachate and other liquids to obtain optimum moisture levels. Biodegradation occurs in the absence of oxygen (anaerobically) and produces gas. A hybrid or facultative landfill accelerates waste degradation by employing a sequential aerobic-anaerobic treatment to rapidly decompose organics in the upper sections and collect gas from lower sections. The rate of stabilization progressively decreases from aerobic to anaerobic operations (aerobic>hybrid>anaerobic).
The following are substantial potential benefits to operating a bioreactor landfill:
Another plus to the bioreactor technology is the fact that it can reduce long-term care requirements for monitoring gas migration and cover maintenance while minimizing the time required for profitable energy production through gas recovery. And bioreactor landfills can lower the cost of operations. Several potential cost and operational benefits of bioreactor technology support the case to explore this technology more fully.
There are about 20 full-scale demonstration projects under construction, in startup, or in early stages of operation. USEPA is continuing its State-of-the-Practice Bioreactor Landfill Study. Hopefully, these projects will provide an understanding of regulatory, environmental, technical and operational issues. The bioreactor landfill has the potential to be one of the environmentally and economically sound and responsible solutions to our increasing MSW disposal needs. Be a visionary by embracing this cutting-edge technology.
Ram Tewari can be reached at (954) 577-2394 or at email@example.com.