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Gas in landfill could save Grand Forks on power bill

For the Grand Forks landfill, that old cliche about one man's trash being another's treasure could literally be true when the facility closes in October.

For the Grand Forks landfill, that old cliche about one man's trash being another's treasure could literally be true when the facility closes in October.

A preliminary report the city commissioned says the landfill could contain enough natural gas to power a 2-megawatt generator for 20 years, enough to power the sewage plant and the garbage baling facility.

At present electricity rates, a $3.5 million investment in power generation could pay for itself in six years, said the report, conducted by UND's Energy and Environmental Research Center.

For the remaining 14 years, the city can reap more or less free energy from 40 years' worth of garbage.

Public works director Todd Feland said he's cautious about the 20-year figure because it's based on "formulaic assumptions," meaning researchers assumed that a certain amount of garbage would generate a certain amount of gas.

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"I think we have enough information to go to a feasibility study, but there're too many unknowns to make a big investment," he said. When the City Council's public service committee meets today, he'll recommend more samples be taken, he said.

How it works

When garbage decomposes, it releases, among other things, methane, the main ingredient in natural gas. Technically, this kind of gas is called "biogas" to distinguish it from real natural gas, which comes out of the ground.

Methane is both a good thing and a bad thing. It's a bad thing because it's a potent greenhouse gas, 21 times better at warming the atmosphere than carbon dioxide. By law, the city has to get rid of it somehow, the cheapest way being to just flare it off.

Properly treated, landfill gas is a good thing because it can either heat a building or run a generator. It's a time-tested technology that's only gotten better with time as new power generation technology becomes available.

The city of Fargo, for example, tapped its landfill in 2002 and sent the gas to the nearby Cargill plant in a deal that benefits both. The company saw a lower natural gas bill and the city got money for the gas. It is expected to break even this year.

Grand Forks' landfill also is conveniently located near a plant, in this case the city's sewage plant, a little more than a third of a mile north. The garbage baling facility, which will stay open when the landfill closes, is slightly closer.

Researchers estimated the value of the natural gas at about $1 million a year, based on present natural gas and electricity rates.

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The fine print

Whether the $3.5 million is a wise investment or not, though, depends on several factors.

The one that concerns Feland the most is how much gas there is. Ironically, the EERC study said that there is less gas than there might have been because the city diverted a lot of harmless garbage, such as yard waste, to the inert landfill nearby. This extended the life of the main landfill but reduced the amount of gas.

Another factor is the purity of the gas. The key contaminant is a compound called "siloxane" that leaves a difficult-to-remove residue when burnt. Over time, the residue damages machinery, such as power generators.

Water vapor can reduce the potency of the gas.

Purification equipment could cost in the neighborhood of $750,000, accounting for a fifth of the total cost. But, without it, the gas would damage gas turbines or internal combustion engines used as generators.

Feland said the city could skimp on equipment if it used the gas only for heating but heating needs are pretty minimal presently.

In the next few years, though, the sewage plant is scheduled for an upgrade and one of the options is a composting facility, which uses bacteria and heat to break down sewage.

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Reach Tran at (701) 780-1248; (800) 477-6572, ext. 248; or send e-mail to ttran@gfherald.com .

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