Wausau WWTP

At a Glance
• System Configuration: 2 × C65 Grid Connect Capstone Biogas Microturbines with Unison Solutions gas conditioning
• Annual Generation: >1,000 MWh/year of clean, renewable electricity
• Thermal Output: 860,000 BTU/hr of recovered hot water for anaerobic digester heating
• Financial Impact: ~$100,000 / year in direct utility power cost reductions ($8,000–$10,000/month)
• Fuel Source: Anaerobic digester biogas
• Fleet Footprint: Commissioned in 2011; maintained and serviced by Vergent since 2020


The Challenge
Serving 40,000 residents and handling up to 9 million gallons of wastewater per day, the Wausau Wastewater Treatment Facility in Wisconsin produces high volumes of anaerobic digester gas. To protect the surrounding Wisconsin River ecosystem while managing municipal operational budgets, the city needed a reliable way to utilize its by-product biogas. The facility required an efficient distributed energy system to offset expensive utility electricity costs and supply constant thermal energy to keep its anaerobic digesters at optimal operating temperatures.


The Solution
A 130 kW Combined Heat & Power (CHP) system featuring two Capstone C65 biogas microturbines was installed alongside Unison Solutions gas conditioning equipment to convert by-product digester gas into clean power and heat.
• On-Site Renewable Power: Generates over 1,000 MWh of clean electricity annually on-site, directly offsetting $8,000 to $10,000 in monthly grid power purchases.
• Thermal Energy Recovery: Captures 860,000 BTU/hr of high-temperature exhaust heat to maintain precise digester temperatures, significantly reducing the fuel burn of facility boilers.
• Low-Maintenance Biogas Operation: Utilizes oil-free, air-bearing microturbine technology with a single moving part, minimizing mechanical wear and staff maintenance requirements on variable biogas fuel.
• Grid-Synchronized Reliability: Operates continuously in grid-connect mode to supply steady baseload power across the plant's activated sludge and solids processing operations.


The Results
• $100,000 Annual Savings: Cuts local utility expenditures by up to $10,000 per month, keeping municipal sewer utility rates low for city residents.
• Maximizes Renewable By-products: Converts methane gas into valuable electricity and heat, reducing flaring and supporting citywide sustainability benchmarks.
• Essential Fleet Asset: Managed as a key installation within Veristar's Midwest operating fleet, supported by ongoing technical service since 2020 to ensure continuous long-term uptime.
• Complements Facility Modernization: Operates seamlessly alongside recent $80 million plant upgrades, reinforcing Wausau's long-term environmental protection mission.