Processing Solid Waste Material
In addition to treating the wastewater, our sewage plant also processes the residual solid-waste material. These solids are placed in a 'digester' or large holding tank. This tank acts like a stomach and using bacteria digests the solid material in a process known as anaerobic digestion. During the process, methane is recaptured and used to run large diesel engines at the plant.
A picture of the one of our sewage treatment plant's 'duel fuel' diesel engines is below and to the right. This engine runs on both natural gas and methane diesel engine gas that is recaptured in the plant's digester.
Sustainability involves 3 parts: planet, profit, and people. Treating wastewater is very energy intensive, so capturing and using the methane is very sustainable. It benefits the planet because the methane gas is not released into the atmosphere. And it benefits the profit and bottom line because less energy has to be purchased to operate the facility.
The Madison-Chatham Joint Sewage Treatment Plant underwent a $3 million upgrade, in 2010, which will included improvements to the digesters. The digesters, which handle hundreds of thousands of gallons of waste at a time, were cleaned and a new mixing system designed to increase the production of methane gas was installed. Because the upgrade will make the facility more energy self-sufficient, it was designated as a "green" project.
For More Information
Visit the following Wikipedia page to learn more about anaerobic digestion.