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Sheboygan Wastewater Plant

When it was time to upgrade the outdated boiler used to heat anaerobic digesters at the City of Sheboygan’s wastewater treatment plant in 2003, the facility’s superintendent wanted to solve two problems at once.

The Sheboygan Regional Wastewater Treatment Plant, which treats up to 15 million gallons of water each day, had more methane biogas, a by-product of the anaerobic-digestion process, than it knew what to do with.

At the time, methane gas produced onsite in the anaerobic (without oxygen) digestion process had two purposes: to fuel boilers that heat the anaerobic digesters and to fuel an old 500-horsepower Caterpillar engine that drove an in uent pump capable of pumping 11,800 gallons of water per minute. However, more than 25 percent of the methane biogas was considered waste and just ared at the plant site. Unfortunately, ared methane gas has a greenhouse-gas impact on the atmosphere 21 times greater than carbon dioxide.

At the same time, the City wanted to reduce ever rising electricity costs.

“We wanted something that made sense for the bottom line and the environment,” said Dale Doerr, the plant’s superintendent. “We wanted to get the latest, most ef cient system available.”

Search for solution begins

The process got underway in 2003 when the City completed a study in conjunction with the local utility – Alliant Energy – and Focus on Energy, a state-wide program that offers grants for energy-saving

At a glance


Sheboygan, Wisconsin, USA


December 2005


Methane gas from an anaerobic digester


• 10 Capstone C30 MicroTurbinesTM, fueled by waste methane gas from the wastewater plant, generate up to 300 kW of electrical power (2,300 megawatts per year).

• Capstone Heat Recovery Modules installed on each turbine capture each microturbine’s exhaust heat, which is re-used to maintain the digester’s 95-degree temperature and heat buildings.

• Gas-cleaning system removes moisture and siloxanes from raw methane gas.

Out-of-the-Box Agreement

• Alliant Energy-Wisconsin Power & Light purchased the 10 Capstone microturbines, paid for electrical connections from the wastewater plant to the electrical grid, purchased a gas-cleaning system and a gas-compression system.

• The City of Sheboygan purchases all electricity the microturbines produce, installed heat-recovery modules and provides the methane fuel for the microturbines.


• The wastewater plant’s electricity bill has not changed in ve years, despite utility rates up 105 percent on average.

• In 2007, the system produced, 1,681 MW of electricity valued at $121,000, and 61,000 therms of biogas valued at nearly $57,000.

• In 2007, the wastewater treatment plant sold 2,076 Renewable Energy Credits for $6,540 because of green energy the Capstone microturbines produced.

The Sheboygan Wastewater Treatment Plant has 10 low-emission Capstone microturbines that use methane gas created by solid waste to generate onsite electricity and heat, cutting the plants electric and natural gas bills by 40 percent and earning renewable energy and emissions credits.

Image | Sheboygan Wastewater Plant

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