Solids removed in primary treatment are pumped directly to anaerobic digesters. Sludge from secondary treatment is thickened by a gravity belt drainage process and is then fed to the digesters. The digesters use anaerobic bacteria to decompose and stabilize the organic portion. Methane gas, a useful byproduct, is formed in the digestion process. Methane is used to fuel engines for power generation.
Heat also is recovered from the engines in a closed loop hot water supply system.
The system provides the heat necessary for the sludge digestion process.