The solids removed in the primary clarifiers, and that portion of the solids removed in the secondary clarifiers that is not needed for seeding, are pumped to sludge thickening tanks prior to treatment in the anaerobic digesters. Provisions have also been made for septage disposal at the plant, which, over the course of a year s time, accepts the septic tank contents from approximately 3,500 homes. Sludge from these thickening tanks is transferred each day to the primary sludge digestion tanks where biological processes reduce the organic material in the sludge about 50 percent. This operation is similar to that of a septic tank. But unlike a septic tank, a digester is heated to 97 degrees F and constantly mixed to encourage continuous decomposition of organics.
Sludge pumps During the solids digestion process, methane gas is produced by microbial action.
Rather than releasing this gas, it is collected and stored within the domes of the secondary digesters and used to fuel the boilers which maintain the primary digesters constant temperature. Methane gas generated in excess of the needs of the heat exchanger is utilized as a supplemental energy source for heating the Operations building. Sludge from the primary digesters is transferred each day to the secondary digesters, which function as settling tanks to concentrate the material. It is then pumped to the Operations building for de-watering, which further concentrates the sludge.