District shows off biogas-to-energy system

District shows off biogas-to-energy system

DANVILLE — What's not to like about using sewage to generate heat and electricity while also reducing gas emissions into the atmosphere?

That's the question engineer Tom Stone asked during an open house Thursday at the Danville Sanitary District, where new technology is doing just that — harnessing the naturally occurring methane gas from the plant's waste stream and using it to generate heat and electricity that lowers the plant's utility costs and reduces the methane that's released into the air.

Basically, it's turning waste into energy.

"This is a sustainable, renewable form of energy and this is what the public expects. This project is a reason to smile," said Stone, who thanked the more than 40 guests for coming and joked that the plant doesn't often get visitors for some reason.

The Danville Sanitary District hosted the open house at its treatment plant on Grape Creek Road south of Danville to give local officials and others a chance to see the biogas-to-energy system that's become operational at the plant in the last several months and is one of only a few at wastewater treatment plants in Illinois and one of only about 300 across the nation.

Todd Lee, director of the Danville Sanitary District, said public and private sectors are being challenged to do more with less. But with that challenge comes opportunities, he said, and the biogas-to-energy project is the result of an opportunity, which started about four years ago when Stone and district staff began researching whether the concept would work at the sanitary district's treatment plant.

Stone said at the time there were fewer than 100 of these systems at wastewater treatment plants nationwide, but Lee and sanitary district staff and the district's board bought into the concept and went ahead with the project that's expected to save the district $225 a day in electricity costs and $80 a day in natural gas costs.

The total cost of the project was $750,000 with most of the engineering done in-house. Factoring in a $200,000 grant from the Illinois Department of Commerce and Economic Opportunity through the Office of Research Services at the UI in Chicago, the system should pay for itself in five years.

The process starts with the sludge that comes into the treatment facility from residences and businesses. The waste is pumped into anaerobic digesters, which create gas as a byproduct called digester gas. It's primarily methane gas, which previously was flared off into the atmosphere.

But now a gas-conditioning system cools the digester gas and removes the moisture and siloxanes, which mostly come from the industrial waste stream and must be removed or they will foul up the co-generation engine. That's where the conditioned methane gas is used to produce as much as 150 kilowatt-hours of electricity. That electricity goes directly into the plant's motor control centers. The engine also produces heated water for building heat and heat for the anaerobic digesters, because the anaerobic bacteria produce the maximum amount of gas at a temperature of 96 to 97 degrees.

Stone said the anaerobic bacteria don't need oxygen and love to eat the sludge.

"They are all happy and make gas, just like some of us," he said, joking.

The average Illinois residence consumes 9,480 kwh per year, and the biogas-to-energy system produces that amount of electricity in just three days, or enough electricity to power more than 120 Illinois residences per year.

Henry Kurth, associate director of the Energy Resources Center at UI Chicago, said this type of system is an ideal focus for wastewater treatment plants. He said the Danville plant should be recognized not just for this project, but for its goal to use even less energy in the future.

Stone said the ultimate goal is to transform the treatment plant into a net-zero energy consumption facility.

"We really believe we can operate this plant 'off the grid,'" he said.

Toward that end, the district will be moving forward next year with an energy conservation system that will cut the plant's overall energy use, and there are also plans to expand the biogas-to-energy system.

"Other plants have made it to net zero, and that's our goal," Stone said.

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