Getting More out of Landfills
By introducing air and water into solid waste, a bioreactor landfill in Florida hastens the decomposition process, extending landfill life and generating methane gas for energy
From afar, the New River Regional Landfill in Union County, Florida may look like any other landfill. Huge mounds of garbage covered with plastic sheeting jut into the air. But close inspection reveals that this is a bioreactor landfill, which uses a novel injection system to speed up the waste decomposition process from 25 to 30 years to five to 10 years.
“We were the first operating bioreactor landfill in the country,” states Darrell O’Neal, executive director of the New River Solid Waste Association. “We’ve had 17 different countries come to see our bioreactor system. One German guy said this is the most instrumented landfill in the world.”
Vertical pipes protrude from the ground under a white lined hill. Some are used for the injection of air and leachate, which consists of rainwater that percolates through the landfill and collects at the bottom liner and is pumped out of the landfill for treatment. “Those are Cells 1 and 2,” says Perry Kent, assistant director of landfill operations, pointing to the area covered by the gleaming liner. Perry has been involved with the project since its inception. “It’s been real interesting watching this thing develop.”
Although located in Union County, the landfill collects trash from surrounding Bradford, Baker, Gilchrist, and Alachua counties as well. It receives 800 to 1000 tons of municipal solid waste a day and recently was named the National Winner of SWANA Landfill Management Excellence Award. “That award shows the landfill is clean and runs efficiently,” says Ravi Kadambala, a University of Florida graduate student obtaining his Ph.D. and working as a graduate research assistant at the New River Landfill. “New River is one of the cleanest landfills in the U.S., and it is very well maintained.”
Florida will benefit from bioreactor technology by learning what can be done to extend the life of landfills and gaining a body of knowledge useful in improving the training of future engineers and landfill operators in Florida, explains Fletcher Herrald, a government analyst with the Bureau of Solid and Hazardous Waste at the Division of Waste Management with the Department of Environmental Protection. “When we started, we were trying to move the science of landfills into the 21st century by learning a safe way to treat waste and not just dump it.”
Adding Key Ingredients
Ever hear of how you can dig up a newspaper after 20 years and still read it? Bioreactor landfills are designed and operated to encourage waste decomposition by adding water or air to the landfill since garbage biodegrades more quickly when wet. “Most landfill bioreactors add only leachate,” Schert reveals. “Some supplement the leachate with well water. Very few add air.”
The New River landfill is constructed with vertical wells, an exposed geomembrane cap made of high density polyethylene, and in-situ instrumentation. It also has gas collection, air injection, leachate recirculation, and segregated leachate collection systems.
It all started in 1998, when William “Bill” Hinkley of the Florida Department of Environmental Protection (DEP) grew frustrated with the enormous growth of landfilling in Florida. Hinkley contacted Schert of the then Florida Center for Solid Waste at the University of Florida (UF) and discussed ideas for obtaining funding for a full- scale bioreactor landfill demonstration project. The project became a joint project with UF and the University of Central Florida. The Florida Legislature appropriated funding from the DEP’s Solid Waste Trust Fund for the demonstration project, and Schert, along with UF professor of environmental engineering Timothy Townsend approached O’Neal about starting a bioreactor system. “It was an opportunity to treat the landfill as we go and break down the organics in a five- to-seven year time frame,” O’Neal recalls. “From an environmental point of view, it’s a great opportunity.”
Townsend developed the overall design of the bioreactor system for the existing New River landfill and then turned it over to the landfill’s engineer of record Darabi & Associates. The firm subcontracted Jones Edmunds and Associates, a civil and environmental engineering firm with several offices in Florida, in fleshing out the details.
Ten acres of Cells 1 and 2 are dedicated to operate as an active bioreactor area. Vertical wells were drilled through waste placed there about 70 feet high. The wells were drilled to different depths using a four-inch flight auger, going as deep as 10 feet above the sand drainage layer and bottom liner system. Thermocouples were placed at the bottom of each well to measure temperature during operation. In total, the instrumented well field has 134 wells in 45 vertical injection well clusters. An air injection manifold covers about half the field.
Instrumentation measures not only temperature but also moisture and gas composition. This was set up in rows between the rows of well clusters. The gravel-packed slotted PVC cylinders contain a device for sensing moisture as well as a thermocouple and a tube for collecting gas samples. The goal was to install three sensor packs per hole, each surrounded by sand separated by clay.
A white liner was placed over the top of Cells 1 and 2 for gas collection a few months after all the wells were drilled. The gas collection pipes are connected to trenches under the liner where the biogas is collected and then pulled out of the landfill using three large rotary blowers. After going through the blowers, the gas is routed to a flare, where methane (a harmful greenhouse gas) is burned and converted into carbon dioxide (a much less potent and harmful greenhouse gas). The gas system also includes two large compressors used to inject ambient air into the waste through the wells drilled into it.
Capture the Methane
But Michael Ohlsen, biomass project manager at the Florida Energy Office in Tallahassee with the DEP for the state of Florida, points out one thing excites him about the bioreactor system: since decomposition of waste is accelerated, so is production of methane. “Landfill gas generated is about 55 percent methane.” While most landfills just burn it off, it is considered a waste to do that since it can be used in place of natural gas, and other landfills have benefited from reusing it, he says.
Ohlsen cites a biomass plant coming online near New River and could easily see them piping the gas there. “We could see a glass manufacturing company buying property next door, or any type of manufacturing facility that runs large pieces of equipment, and instead of the equipment running off natural gas, they can use the gas from the landfill.”
While the Florida Legislature and the Florida Department of Environmental Protection has funded the bioreactor project, the Hinkley Center for Solid and Hazardous Waste Management manages it. “We’ll have given about $ 6.1 million by the end of 2008,” Herrald states. “We paid for the brain power for the design and research on bioreactor technology at several sites in Florida.” These include Polk County, Highlands County, Alachua County, and New River Regional Landfill, which covers Baker, Bradford and Union counties. Almost a third of the money went to construction costs and materials at New River.
The project aims to train students in Florida’s state university system as well as landfill operators and engineers. The Hinkley Center sponsors research projects in nine universities in the state— UF, University of Central Florida, University of South Florida, Florida State University, Florida International University, Florida Atlantic University, Florida A&M University, Florida Institute of Technology, University of Miami, and University of West Florida. Several engineering firms advise the center as part of its Technical Advisory Group, including CH2MHill, Darabi & Associates, PBS&J , SCS Engineers, GeoSyntec Consultants, Environmental Control Systems, EA Engineering Science and Technology, Jones Edmunds and Associates, and S2L.
The Solid Waste Management and Resource Recovery Act of 1988 created the Hinkley Center to coordinate research, training, and service activities relating to waste management. At the time, it was called the Florida Center for Solid and Hazardous Waste Management. When Bill Hinkley passed away, the center was renamed in his honor. The University of Florida College of Engineering serves as the host institution, and the center receives mostly state money, which is used for research.
Many Players Benefit
“I handle recirculation leachate, collect gas and leachate samples, and analyze them and give it to officials at Jones Edmonton Associates,” says Kadambala, who has worked at the landfill since 2005. “I’m getting my Ph.D., so while I’m working there I’m basically helping myself too, because I’m getting a lot of research data I can publish.”
“I want us to do research on things that matter to people,” Schert says. Ongoing research at the landfill site includes the operation of gas extraction, leachate recirculation, and air injection systems. Leachate volumes and characteristics, gas quality and generation rate, settlement, instruments, and waste properties are also being monitored.
Bioreactor activities are also going on at two other landfills in Florida besides New River Regional. The Polk County Landfill is active, but the Alachua County Southwest Landfill sits closed. However, it’s taking steps to re-institute leachate recirculation under the liner cap, effectively creating a bioreactor.
With its success, members of the team that created the New River bioreactor landfill see huge potential for the technology. “Eventually,” O’Neal says, “bioreactor landfills will be the only approved landfills in the country because of the environmental threat.”
For more information on bioreactor landfills in Florida, visit www.bioreactor.org
For more information on the William W. “Bill” Hinkley Center for Solid and Hazardous Waste Management, visit www.hinkleycenter.com