In 2010, the Sheboygan (Wis.) Regional Wastewater Treatment Facility was one of the most energy-efficient treatment facilities in the state. Despite this, the city strived to do better, initiating its most ambitious and successful energy-production and energy-recovery project yet. This project was collaboratively developed by the city-Donohue team to dramatically improve its energy efficiency, production and recovery, letting the facility regularly produce more energy than it requires and achieve net zero energy status.

This project included two elements: anaerobic digestion improvements to increase effective digestion capacity and biogas production and 400kW of additional microturbine capacity to convert the large quantity of biogas released to heat and electricity. The city chose the innovative and energy efficient linear-motion mixers to increase biogas production. Sheboygan was the first facility in Wisconsin to use this digester mixing technology.

Before the project, biogas from the three primary digesters passed through the secondary digester to make it to the distribution system. This arrangement had become a major bottleneck impeding the beneficial use of the biogas. Modification of the biogas collection system was done so that each of the four digesters connected independently to a common header for distribution to utilization equipment.

The microturbines include paralleling switchgear that synchronizes the output with the electric utility. The power output is adjusted to match the utility power (sine waves) so they are in sync, allowing the microturbines to parallel with the utility power grid to supplement the plant’s power usage and export power to the utility grid when the generated power exceeds the plant power requirements.

With this project, Sheboygan became the first wastewater treatment facility in Wisconsin to regularly produce more electrical energy than it requires, exporting excess renewable electricity to the utility grid and becoming a net zero energy facility.

“This project is the culmination of concerted efforts to achieve net zero energy with biogas — derived electricity,” says Rick Niederstadt, PE, awards judge. “This is a monumental achievement and one that demonstrates a commitment to sustainability and the use of innovative technologies.”

Because of this project, the Sheboygan Regional Wastewater Treatment Facility is one of only few facilities in the world producing all of its electrical energy using a renewable fuel (biosolids and high-strength waste).

Unison Solutions, Inc. and Energenecs are proud to be part of the team that supplied the biogas conditioning skids and the Capstone turbines for this project.

For more information on the American Council of Engineering Companies of Wisconsin, visit www.acecwi.org.

For more information on Unison Solutions, visit www.unisonsolutions.com.