Even with the use of source reduction, recycling, and combustion, there will always be waste that ultimately must be disposed of in landfills. According to the EPA's Municipal Solid Waste in the United States: 1999 Facts and Figures, landfill disposal still remains the most widely used waste management method (accounting for approximately 57.4% of the total). Many communities now face difficulties siting new landfills largely because of increased citizen and local government concerns about the potential health risks and aesthetics of situating a landfill in their neighborhoods. The EPA issued new technical standards for MSW landfills in 1991. These addressed several aspects of landfill management, including location restrictions, design and operating criteria, and groundwater monitoring. Even with national landfill standards, decreasing landfill capacity and the difficulties associated with the construction of new landfills remain significant issues.
The EPA has explored several solutions to conserving landfill capacity, including the viability of engineering materials such as plastics to be less resistant to degradation or, in other words, biodegradable. Biodegradable materials can be broken down into simpler substances (e.g., elements and compounds) by bacteria or other natural decomposers. Paper and most organic wastes such as food and leaves are biodegradable. In contrast, non-biodegradable substances cannot be broken down in the environment by natural processes. In general, degradation in landfills occurs very slowly due to modern landfill design criteria, which minimize waste exposure to sunlight, air, and moisture. In fact, even biodegradable organic materials might take decades to decompose in a landfill; carrots and cabbage have been discovered in recognizable form after several years of burial. Studies indicate that biodegradable materials may help diminish risks to wildlife and aesthetic damage (i.e., discarded six-pack beverage rings and wrappers), but will not reduce the volume or toxicity of waste nor provide a solution to decreasing landfill capacity.
In continuing efforts to conserve landfill space and reduce waste toxicity, the EPA is currently investigating the potential benefits and drawbacks associated with the use of bioreactor landfills. Bioreactor landfills are designed to transform and more quickly stabilize the decomposable organic constituents of the waste stream through the controlled injection of liquid or air to enhance microbiological degradation processes. In other words, by controlling the moisture content, bioreactor landfills facilitate microbial decomposition of waste. Recent findings show that bioreactor landfills successfully expedite the degradation process (e.g., from decades to years), offer a 15 to 30 percent gain in landfill space, and may reduce postclosure care and leachate disposal costs. In addition, the bioreactor technology significantly increases landfill gas emissions, which are captured and often used beneficially for energy recovery. Due to their complexity, however, bioreactor landfills may be more costly, and concerns have been raised regarding increased odors, liner instability, and surface seeps. Working in conjunction with state and local governments and private companies, the EPA has initiated several research and pilot projects to examine the effectiveness of this innovative technology.
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