One Man's Trash Is Another's Power Source

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The second week of May in the city of Fargo, N.D., is called "cleanup" week, when residents are allowed to put nearly all unwanted items in front of their homes for municipal workers to collect. As one can imagine, this is a busy time for Fargo's solid waste manager, Terry Ludlum, as trucks roll in and out all day dumping refuse at the city landfill northwest of town.

Now all of that trash is being used to generate power for an industrial facility and electricity for area homes and businesses. The Division of Solid Waste has spent over $1 million for renewable energy projects at the landfill. It supplies a Cargill Inc. oilseed processing plant about three miles away with gas for its boiler and contributes power to the grid for the Cass County Electrical Cooperative with a newly installed Caterpillar generator. "Cargill had seen us flare the vapors and they were wondering if they might be able to utilize this stream in lieu of natural gas," Ludlum says. "We began piping it over there in 2001, and they've been using it to fire their boilers ever since."

Northeast of Fargo and across the Red River in Fosston, Minn., Polk County Solid Waste Manager Bill Wilson has made his operation more efficient by adding new revenue streams that can be generated by burning refuse. In the mid-1990s, Wilson, who supervised construction of the facility, applied for a state grant to retrofit the trash burner to meet new guidelines that were implemented by the U.S. EPA. Wilson and company didn't stop there. "Once we demonstrated [EPA] compliance, we went back to the state of Minnesota and asked if we could use [the leftover funds from the retrofit] for a turbine-generator project." After years of work and planning, the Polk County incinerator began running the generator in May, and will use the electricity produced to increase the facility's level of self sufficiency.

The environmental benefits of depleting the hazardous gases and vapors generated by landfills, like decreasing offensive smells that would otherwise leak into the atmosphere are obvious. However, purely from an economical standpoint, making the investment to collect the gas and combust it makes sense too. By burning methane, the landfill gas collection project in Fargo is accredited with the regional power pool and will produce almost 7.3 million kilowatt-hours (kwh) annually-that is electricity for sale.

In Polk County, the incinerator provides steam energy for several customers in the Fosston industrial park, making the mechanism of the entire enterprise more efficient, Wilson says. "Since we started in 1988, we have acquired three customers that buy the steam we produce," he says, adding that the situation makes the industrial park stronger and more sustainable. When you take all of the employees whose income is generated from this industrial park, those dollars are turned over three or four times in Fosston, which is great for a small town in northwest Minnesota, he says.

It's also a huge deal for a big city in North Dakota. "Economically, this is a new source of revenue for the city of Fargo," says City Enterprise Director Bruce Grubbs. "This is a viable resource that has to be managed." The cost of the electrical generator, as well as other equipment and maintenance, was over $1 million, but by selling the landfill gas and avoiding natural gas and electricity costs for its own facilities, the project will pay for itself in only 2� years, he says. The generator will supply the electrical load for the entire landfill-baling facility, office/shop, scale house, leachate pumps and the landfill gas collection compressors. This project also qualified for the federal Clean Renewable Energy Bonds program. These interest-free bonds were used to finance the purchase of the generator and expand the methane gas collection system. "This program allowed us to purchase the generator and other equipment for the landfill with loans we can pay back interest free," Grubbs says.

Minnkota Electric Cooperative and its subsidiary Cass County Power Cooperative were interested in purchasing power from the landfill to increase their green energy rates, Grubbs says. Electricity sales alone will generate $142,000 in revenue for the waste management division. In addition, exhaust and engine heat from the generator will be used to meet the energy needs of the campus transfer station where trash is baled prior to placement in the landfill. In addition, the Polk County incinerator provides renewable energy credits for Minnkota. "They are really committed to producing electricity from renewable resources whenever and wherever they can," Wilson says.

National Trend
What's happening in North Dakota and Minnesota are only two examples of a nationwide movement to capitalize on the energy producing power of garbage. The EPA's Landfill Methane Outreach Program, which publishes a plethora of related information online, reports that there are approximately 425 landfill gas energy projects currently in operation, or under development, in the United States. This recycled energy is used in creative ways, from heating greenhouses, producing electricity and heat in cogeneration applications, firing brick kilns, supplying a high-British thermal unit (Btu) pipeline quality gas, fueling garbage trucks, and providing fuel to chemical and automobile manufacturing plants.

Projects range from small-scale, community-driven initiatives to multimillion dollar private investments. The range of endeavors between the public and private sectors are diverse and well-distributed, says Brian Guzzone of the EPA. "Aside from incentives provided in the 2005 Energy Policy Act, as well as other federal provisions and financing arrangements, it's simply a strong market for renewable energy that is driving these endeavors," he says.

Currently, landfills are the largest source of U.S. anthropogenic, or human produced, methane emissions. Landfill methane is produced when organic materials are decomposed by bacteria under anaerobic conditions-in the absence of oxygen. Landfill gas, however, is far from pure. It is composed of methane and carbon dioxide in approximately equal concentrations, as well as smaller amounts of nonmethane volatile organic compounds, nitrogen oxide and carbon monoxide. "For every million tons of waste, there is the potential to generate about 800 kilowatts of electricity," Guzzone says. "But there are a lot of factors that can influence these calculations."

The collection and combustion of landfill gas has become a common method of reducing emissions generated by municipal waste. At some landfills, gas is combusted by flaring, at others gas is combusted for energy and heat production, as is the situation in Fargo. From a federal perspective, methane emissions are regulated under the Clean Air Act as a result of the "New Source Performance Standard and Emissions Guidelines" published by the EPA in March 1996. It is further observed that methane has a greenhouse gas potential of nearly 21 times that of carbon dioxide, and since the gas is combustible, leaks from landfills can cause spontaneous explosions to occur. Along with inundations of undesirable odors, landfills have been considered by city managers to be liabilities. "This whole project was born out of an effort to control odors," Ludlum says.

Collecting and Combusting
For these same reasons, regulating and monitoring landfill emissions has been a major focus area for the EPA. "From an air quality perspective there are many public health and safety benefits demonstrated by these projects that are depleting the methane from a landfill," Guzzone says. "The dangers are significantly diminished." Capture and use of landfill methane as fuel for electricity generation is done through the development of well fields and collection systems at the landfill. When and where electrical generation is impractical, flaring is preferred over direct venting to reduce emissions and fire hazards.

During the extraction process, landfill gas is removed through a system of PVC piping attached to vertical wells. "There is a suction on the landfill that draws the gas out and then feeds it into the generators that produce electricity," Guzzone says.

The peak generation of methane occurs at the closure of the landfill, meaning when the site stops allowing municipal waste to be dumped there. Other than that, however, Guzzone says there are no average figures or general statistics in regard to methane generation from anaerobic digestion in landfills because there are many variables that can alter production. "Every site is unique because this is a very dynamic system," Guzzone says, referring to organic material decomposing under the pressure of anaerobic digestion.

In Fargo, Grubbs says once the landfill has reached full capacity it will continue to produce gas for the next 30 years with an annual energy equivalent ranging from 285 billion to 500 billion Btu. "Everything we can do to save, recycle and produce energy is critical-we're turning what was considered a liability into an asset," Grubbs says. As little as 20 years ago generating energy from trash was the stuff of fiction and movies-mad scientists using coffee grounds to fuel time machines, for instance. Now, however, recycling waste to generate power is becoming a staple practice to protect the environment and increase the economic efficiency of municipal waste operations.

Nicholas Zeman is a Biomass Magazine staff writer. Reach him at [email protected] or (701) 746-8385.