February 26, 2001

As Landfills Fill Up, NC State Researchers Work to Find Alternatives

With landfills filling up and closing in North Carolina and communities resisting the locating of new landfills in their area, the need for solid waste management planning is taking on new emphasis. The Wake County landfill will close in 2004, for example, but an alternative site has not yet been established. Open space is becoming scarce in Wake County at a time when the population is growing, resulting in more trash than ever. According to the North Carolina Office of State Planning, Wake County’s population has increased from 426,311 in 1990 to 592,218 in 1999. That’s nearly 166,000 more people generating garbage. In addition, a 1999 U.S. Environmental Protection Agency estimate places 55 percent of our solid waste in landfills.

North Carolina State University researchers Dr. Morton A. Barlaz, professor and associate head of civil engineering; Dr. S. Ranji Ranjithan, associate professor of civil engineering; and Dr. E. Downey Brill, professor of civil engineering and head of the department, along with their colleagues from Research Triangle Institute, want to help communities identify solid waste management alternatives that consider both recycling and composting and their associated impacts on the environment. Their approach to the study of trash management involves the application of a technique called life cycle analysis – a process by which both energy consumed (or produced) and emissions to the environment are calculated.

This research group looks at the overall effects, including advantages and disadvantages, of alternatives for integrated solid waste management – from collection of waste, recyclables and yard waste, to recycling and composting, to waste combustion and disposal in landfills. According to Barlaz, there are many tradeoffs in solid waste management among the cost, the amount of waste recycled and pollutant emissions. His research team wanted to develop an easy way to evaluate these tradeoffs.

Barlaz and his colleagues have created a comprehensive, yet flexible, approach to exploring and studying alternative solutions that are tailored for each community, enabling consideration of costs and environmental benefits of alternative solid waste management plans. This approach is implemented within a prototype software system. According to Ranjithan, "Via the many graphical interfaces available within the system, a user can input site-specific information, or information specific to a given county or community, regarding their costs, population densities, composition and generation rate, and evaluate what might be cost-effective and environmentally friendly alternatives to managing solid waste for that community."

The NC State research group recently developed a hypothetical but realistic case study to see how the model would work when applied to individual communities. The researchers studied different levels of recycling and showed how, in many instances, recycling can reduce emissions of greenhouses gases while also reducing society’s dependence on landfills.

Barlaz pointed out that when the methane gas produced in landfills is recovered for energy, the landfill actually produces more energy than it consumes, thus reducing both the consumption of fossil fuels and the air emissions associated with power production. Methane is recovered from the northern Wake County landfill and from 10 to 15 percent of landfills across the U.S. This procedure has a couple of advantages. First, the gas is not emitted to the atmosphere and therefore doesn’t become part of the pollution problem. Second, captured methane can be used instead of "virgin" fossil fuels, and the landfill becomes a net energy producer.

Making decisions that are both cost-effective and environmentally friendly is difficult, but this research could help the process. "Using the hypothetical case study, we’ve demonstrated how to identify a range of solid waste management alternatives including the least-cost solution that meets a 25 percent recycling target, and the least-cost solution that does not exceed a certain amount of greenhouse gas emissions, for example," said Ranjithan. "You can explore and identify solutions that meet the requirements you specify. I think the model has a lot of potential to help communities throughout North Carolina."

-- rudd --

Technical Contact: Dr. Morton A. Barlaz, 919-515-7676, barlaz@unity.ncsu.edu
Media Contact: Linda E. Rudd, 919-515-3848, linda_rudd@ncsu.edu

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