Electric Landfill

If you’ve been living in the Bangor area since 1975, chances are your trash has landed in the Pine Tree Landfill (PTL). Right off of I-95, the pyramid of garbage has been a hot button issue for the town of Hampden for years. People call it an eyesore and have complained about the stench. Citizens living near the site have been concerned about groundwater pollution. And these days, nearly everyone is worried about the greenhouse gases landfills produce.

But recently there has been a change in attitude at PTL.

“Where the Pine Tree Landfill used to be brought up at every town meeting, it’s now practically come off the agenda,” says Susan Lessard, who has been the town manager of Hampden for the past eight years. Why the change of tune?

For the past year, Casella Waste Systems Inc., the owner of PTL, has been running the first landfill-gas-to-energy facility in the state of Maine. Also, at the end of 2009, the landfill will be capped and closed—the first commercial landfill in the state to do so.

“Landfills were once ‘cemeteries’ for what society discarded as solid waste. What we are doing here at the Pine Tree Landfill is transforming a renewable resource into real economic and environmental benefits,” says Don Meagher, manager of planning and development for Casella.

Turning the methane released from decomposing waste into electricity isn’t a new idea. The Environmental Protection Agency (EPA) created the Landfill Methane Outreach Program (LMOP) in 1994 to reduce methane emissions from municipal solid waste landfills by turning it into electricity. This process offsets the need to use fossil fuels such as coal and natural gas as energy sources, reduces greenhouse gas emissions and pollution, and benefits the local economy.

Over the past seven years, the PTL has turned their manmade mountain of trash into what looks to be a giant birthday cake aflame with dozens of lit candles. What it really is is a collection and flare system that burns off released methane, which has no smell, and hydrogen sulfide, which produces the rotten-egg smell associated with the dump. By torching the gases emitted from the landfill, PTL has significantly reduced their greenhouse gas effect.

After the gas collection and flare system was installed, the company wanted to do more with the landfill gas. New revenue streams for renewable energy were gaining popularity. With new federal tax credits for renewable energy and new rules on carbon credits, Casella began developing the project and hired Cianbro as the general contractor to build a landfill-to-gas-energy plant, which cost $8 million.

“Five years ago it would have cost more to build the plant than we would have gotten back in revenue,” says Meagher.

How it works

How does one get electricity out of a mound of trash? It’s a relatively simple process that is monitored 24 hours a day at the PTL energy facility. First a short chemistry lesson:

Methane, a greenhouse gas that many scientists believe is a key contributor to global climate change, is created when organic material (like food scraps) decomposes without access to oxygen. Typical landfill gas is about 50% methane, 30% carbon dioxide, 19% nitrogen, and 1% oxygen. There are also trace amounts of other gases, most notably hydrogen sulfide.

Municipal solid waste landfills are the second-largest human-generated source of methane emissions in the country. The EPA estimates that a landfill-gas-to-energy project will capture and destroy roughly 60%–90% of the methane emitted from the landfill.

Currently, Casella has drilled 43 wells from the top of the landfill to the very bottom right above the liner. The wells are three feet in diameter. Into each well is placed a 12-inch-diameter perforated plastic pipe surrounded by crushed gravel for stability. The gas collected in these wells is sucked through a horizontal vacuum collection system traveling throughout the landfill. The pipes lead to the engine plant where the methane is cleaned, and used as fuel in generators. The electricity produced is distributed through Bangor Hydro’s grid and sent to homes throughout New England.

The landfill-gas-cleaning process is performed through a biological scrubber that uses bacteria originally found in the dark recesses of the Atlantic Ocean that live off of gases coming out of volcanic vents. These bacteria were harvested and adapted to be able to remove hydrogen sulfide in natural gas fields and wastewater treatment plants. Casella decided to try the bacteria at PTL to help scrub the sulfur from the landfill gas.

“If hydrogen sulfide was combusted in the engines, it would produce a corrosive effect,” Meagher says. “We decided to go with the bacteria technology even though it was somewhat experimental in a landfill gas application.”

Each of the three engines that convert the gas to electricity are 20-cylinder internal-combustion engines that operate at 1,500 horsepower. Standing in the engine room, one can actually feel the power of the engines vibrating their body—and that’s just when they’re operating at half speed.
Each engine generates one megawatt of power. An average house uses 5,000 kilowatts of power per year. One megawatt equals 1,000 kilowatts. So, in a little over an hour, one of the PTL generators creates enough energy to run a single home for a year on garbage. How’s that for efficiency?

“Hampden is leading the way,” says Lessard. “The whole thing is fascinating!”

These generators will be able to operate on methane from the landfill long after PTL has closed its doors. It’s been estimated that the landfill will release methane for the next 20 years, though the amount and quality will decrease over time. The Juniper Ridge Landfill in Old Town, also operated by Casella, is next in line for a landfill-gas- to-energy plant. Currently, Juniper Ridge is generating more methane than PTL. The amount of gas will increase over time. It’s estimated that at its peak, Juniper Ridge will generate four times as much energy as PTL and for much longer.

Money matters

The Pine Tree Landfill is recognized by Maine, Massachusetts, and Connecticut as a Class I renewal resource, which means it generates electricity without using a fossil fuel. Today, businesses that sell electricity are required by law to get a certain percentage of that electricity from a renewable source, like solar panels, windmills, hydropower, or landfill gas. Companies who aren’t able to do so have two options: pay a fine or buy credits from companies who meet the criteria—like Casella. Another revenue source for Casella is selling carbon credits. Much like renewable energy credits, carbon credits deal solely with greenhouse gases—like methane.

“Methane has a global warming potential that is 23 times more potent than carbon dioxide,” says David Burns, environmental engineering services manager for the Maine Department of Environmental Protection. “If a landfill either collects and flares their gas or produces energy from it and gets the proper verification that the gas has been destroyed, the landfill can put their credits up for sale on the market.”

Besides being good for the environment, PTL has been good for the local economy. Since 2002, PTL has paid Hampden over $7 million, most of it coming from the $1.85 per ton of waste they accept at the landfill. Pine Tree Landfill has reimbursed the property taxes of residents who live near the landfill to the tune of $837,000 and they have paid about $36,000 toward a bottled water program to these residences even though there are no impacts on drinking water from the landfill.

The extra money hasn’t been a factor in the town budget, but it has helped fund some big capital projects. Half of the money has been put into an endowment where the interest accrued has helped build a new playground, rehabilitate the pool, and purchase 280 acres of woodland that once belonged to L. L. Bean.

Because of this money Hampden hasn’t had to raise taxes to fund these special projects and they haven’t had to put the effort into borrowing money or raising it themselves. With more money to put into infrastructure, new fire trucks and police cars, buildings, and education, and a low mill rate of $15.90, it’s no wonder the population has been growing since 2002.

But what’s important to Lessard is that Casella will still have a presence at the landfill, turning waste into energy, for the next 20 years. “They have an interest that the environment remains safe because they’re still here. I see that as a positive,” she says.

And the current “Trash Queen of Maine,” Lessard, is looking forward to handing that title over to Margaret Daigle, town manager of Old Town, as they get set to start reaping the benefits of landfill gas to energy at the Juniper Ridge Landfill.

“It’s great that something good can come from something that has been a bone of contention in Hampden for so long,” Lessard says. “This is a homegrown solution to be proud of.”