Landfill Turns into Green Energy Source

By Pamela Bond

North Texas Daily

Aug. 31, 2005

Each person creates 4.4 pounds of trash a day, on average. Multiply that by the 300 million people living in America, and that’s a lot of garbage. It’s no wonder landfill space is problem – a problem that Denton hopes to avoid.

The City of Denton plans to implement a new method in its landfill within the next two years– one that uses a liquid to help it decompose faster than the traditional “dry” landfills.

The new landfill will utilize a bioreactor method. Bioreactors break down solid wastes using organic substances, Dr. Sam Atkinson, of the biology department, said.

More specifically, Denton’s landfill will use an anabolic bioreactor, meaning liquid will serve as the catalyst.

“In the landfill, there are a lot of microorganisms present in the waste, and we simply add water and nutrients to allow them to grow faster and therefore consume more,” Vance Kemler, Denton solid waste director, said.

The liquid is called leachate. In anabolic bioreactor landfills leachate is recycled throughout the waste, speeding the process by which microorganisms decompose it. Methane gas emissions are produced as a by-product.

While the current landfill produces methane gas, among others, the new landfill will emit much more – a concern for some environmental groups like the Environmental Protection Agency.

“We’re currently using the methane in a boiler, where it’s heated and used for energy,” Kemler said. “With the new landfill, the rest can either be sold here in town for energy use or we can buy a generator and use the methane to produce energy.”

The extra gas for energy uses is one of the landfill’s benefits, Kemler said. Also, the landfill will decompose and stabilize more quickly, making more space available.

However, there is an added cost, in the beginning, to run the landfill.

“The initial capital cost is 10 percent higher, but it is offset by the extra space we’ll have as a result,” Kemler said. “In the end it will be about the same.”

The Environmental Protection Agency is currently studying three test cases on bioreactor landfills, and therefore has not taken a permanent stance on the issue. However, at a bioreactor conference in February 2003, the Agency came to a preliminary conclusion that when gas emissions are safely collected, bioreactor landfills are safe for the environment. They prevent liquids from contaminating groundwater with two layers of lining. Also, minimizing the landfill space prolongs its life, and therefore avoids some of the long-term risks, according to the Agency’s reports.

“It’s a really good way of running a landfill,” Fred Doran, senior environmental engineer and project manager for R. W. Beck in Minneapolis, Min., said. “It stabilizes the waste more quickly. It allows you to take advantage of landfill gases. It reduces environmental risks because the leachate is more stabilized. And from a geological standpoint it’s a much better alternative because there’s less erosion when closing a landfill.”

Currently, there are 70 other bioreactor landfills in the United States. Denton’s Municipal Landfill will be the first of its kind in Texas, once the bioreactor method is completed.