Combined Heat & Power Improvements

The  Downers Grove Sanitary District hired Baxter & Woodman to implement energy efficiency and electrical generation improvements at the District’s 11 MGD Wastewater Treatment Center (WWTC) to achieve the ultimate goal of energy neutrality.

As a step toward this goal, the District pursued a combined heat and power (CHP) improvements project to generate energy from digester gas, along with construction of several energy efficiency improvements. While the District generated sufficient digester gas for heating various facility processes, the digester gas production from sludge alone was not enough to make energy generation a cost effective pursuit. Multiple site, space, and hydraulic constraints were present due to the maturity of the WWTC facilities.

Baxter & Woodman and the District developed a road map to energy neutrality, including increasing digester gas production by co-digestion with fats, oils, and greases, constructing two 280 kW CHP units, and further reducing energy usage. Baxter & Woodman worked with the District to implement a grease receiving program to accept restaurant grease to boost digester gas production.  The additional gas produced supports digester gas cleaning and energy generation equipment.

The District has seen its digester gas production double due to the hauled restaurant grease.

In Summer 2013, Baxter and Woodman completed design of a 280 kW engine generator capable of heat recovery. The engine will operate on treated digester gas and will provide energy to offset approximately 50% of the WWTC energy consumption. The thermal energy recovered by the CHP unit will be used in the digestion process to heat sludge, effectively eliminating the need for purchased natural gas.