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Research Profile

Dr. Sahadat Hossain – Creating Treasure from Trash

Landfills are usually looked-on as worthless piles of garbage, but that’s hardly the case. Many landfills are more than just places to store municipal solid waste; they’re “factories” producing a valuable asset – methane gas – that can be used as an energy source. And it’s an energy source that’s virtually free if the landfill is properly managed.

Landfill gas is generated during the natural process of bacterial decomposition of organic material. The U.S. Environmental Protection Agency designates landfills as the largest single human source of methane emissions in the U.S., accounting for 33% of all methane sources. That’s what interests Civil Engineering Assistant Professor Sahadat Hossain and why he’s beginning a project with the City of Denton to maximize the output of methane gas from the city’s landfill.

Denton currently uses this methane to power a biodiesel production plant. Other cities in Texas also capture and use landfill gas. For example, methane gas from Waco’s landfill helps to power a snack food plant. According to the EPA, there are approximately 480 landfill gas energy projects currently in operation in the United States.

A number of factors influence the quantity of gas that a municipal solid waste (MSW) landfill generates. These include the types and age of the waste buried in the landfill, the quantity and types of organic compounds in the waste, and the moisture content and temperature.

“The absence of nutrient, i.e. moisture, in the waste prolongs the decomposition, which can take as much as 50 to 100 years for complete decomposition,” said Dr. Hossain. “However, a bioreactor landfill (or Enhanced Leachate Recirculation (ELR) Landfill as defined by the Texas Commission on Environmental Quality) is operated to enhance refuse decomposition, gas production and waste stabilization.”

Dr. Hossain sees several benefits associated with the operation of landfills as bioreactors, including increased gas production, more rapid settlement, the rapid stabilization of a landfill to a more environmentally benign state, and acceleration of refuse decomposition, which may shorten the regulated post-closure monitoring period and reduce the overall cost of the landfill.

MSW landfills often require large tracts of land on or immediately beyond the urban growth areas and may occupy an area up to several hundreds of acres. For example, the City of Denton’s site occupies approximately 243 acres, 152 acres of which are designated as the actual landfill footprint.

Minimizing waste or increasing the capacity of landfills within the same area is becoming a major consideration for local and state agencies and federal regulatory bodies. Recycling efforts have somewhat reduced the amount of waste, but bioreactor processes can increase the capacity of landfills by accelerating waste decomposition, causing the waste to settle. This allows more waste to be added before the landfill reaches its allowable height, which in Texas can be up to 250 feet.

Dr. Hossain’s project will take three years to complete and is valued at almost $183,000. His research will focus on the performance monitoring of leachate recirculation systems and their effect on the landfill gas production in bioreactor or ELR landfill. He will also study the changes in physical and engineering characteristics of MSW with time and decomposition. Based on the research, a protocol will be developed to effectively implement the leachate recirculation in the landfill and monitor its performance during the landfill’s operation. The project involves both field and laboratory studies

“This is going to be the benchmark project in Texas,” he said. “The Texas Commission on Environmental Quality and Denton and other cities will be utilizing the research data for the possible implementation of leachate recirculation systems in landfills across the state.”