West Bend WWTP

At a Glance
• System Configuration: 4 × C65 Capstone Biogas Microturbines
• Annual Generation: >2,000 MWh/year of clean renewable electricity
• Thermal Output: 1,720,000 BTU/hr (1.72 MMBtu/hr) of recovered hot water for digester and building heating
• Financial Impact: ~$150,000 / year in net operating cost reductions
• Fuel Source: Cleaned, conditioned anaerobic digester biogas
• Operating Mode: Grid Connect with utility power buyback synchronization
• Long-Term Service: Commissioned in 2013; serviced and maintained by Vergent since 2020


The Challenge
Treating over 5 million gallons of wastewater daily for 48,500 residents, the West Bend Wastewater Treatment Plant (WWTP) in Wisconsin experienced a surge in high-strength waste receiving, resulting in significant excess anaerobic digester gas. Rather than flaring this valuable renewable resource, the city sought to convert the waste gas into continuous electricity and heat to offset plant O&M costs. The facility required a safe, low-maintenance energy system capable of operating on variable-quality biogas while meeting strict utility interconnection standards.


The Solution
A 260 kW Combined Heat & Power (CHP) plant featuring four Capstone C65 biogas microturbines was installed alongside gas conditioning equipment (moisture removal, compression, and siloxane media filtration) and integrated with Unison Solutions and central BAS controls.
• Biogas-to-Energy Conversion: Transforms waste digester gas into over 2,000 MWh of clean electricity annually, powering treatment operations and selling excess energy back to the grid under an advantageous utility buyback agreement.
• Dual-Purpose Thermal Recovery: Captures up to 1,720,000 BTU/hr of exhaust waste heat, routing hot water directly to digester heating loops and plant service buildings to displace primary natural gas boilers.
• Low-Maintenance Reliability: Leverages microturbine technology featuring a single moving part and no oil changes, minimizing staff maintenance requirements compared to legacy reciprocating engines.
• Grid-Synchronized Performance: Operates in grid-connect mode, optimizing real-time energy dispatch and generating recurring revenue through peak-period power buyback rates.


The Results
• $150,000 Annual Savings: Significantly lowers municipal treatment plant utility overhead through combined electricity cost avoidance, natural gas displacement, and power buyback revenue.
• Maximized Digester Gas Utilization: Replaces continuous gas flaring with high-efficiency combined heat and power generation.
• Boiler Fuel Reduction: Drastically reduces natural gas consumption by utilizing free thermal energy for digester temperature regulation and building space heating.
• Proven Long-Term Operations: Serviced continuously by Vergent since 2020, ensuring sustained uptime, optimal siloxane filtration management, and ongoing equipment performance.