Water Pollution Control



 Glossary / Definitions

See Also…

Environmental Services

Historical Info

Plant History


Stage 7 - Sludge Digestion

Raw sludge withdrawn from the primary clarifiers, together with the scum off the top of the primary and final clarifiers, is pumped to the primary anaerobic digester. Here it is mixed continuously and heated to 35 degrees Celsius. This stage provides the necessary environment for anaerobic digestion of sludge, which is the decomposition of organic matter by micro organisms in the absence of air. After a digestion period of 20 days, the sludge flows to the secondary digester. Here the stabilized sludge is thickened. Liquid from the top is returned to the plant. The sludge is then transferred to storage lagoons for further thickening. The sludge is then applied to farm land as a soil conditioner and fertilizer. During the digestion process methane gas is produced. The gas is utilized to fuel boilers and provide heat for the digesters and buildings.


The two sludge digesters are sealed units and are monitored by sensors in the units. Pictured here are the piping and equipment located between the digesters.  They are needed for collecting the methane gas and transporting it from the digesters.