Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Civil Engineering


One of the primary concerns a community must consider upon adoption of a sludge disposal program is that of operating costs. The operating costs of a vacuum filtration process are relatively high due to the large amounts of chemical coagulants which are generally required to condition the sludge so that it will exhibit its best dewatering characteristics. This project was undertaken to assess the value of lime softening sludge as a conditioning agent for digested sewage sludge preceding vacuum filtration. The sludges studied were obtained from the Sioux Falls Water Treatment Plant and the Sioux Falls Wastewater Treatment Plant. Sioux Falls is presently lagooning both these sludges, but is considering the adoption of a vacuum filtration process for wastewater sludge dewatering. Very little work appears to have been done regarding the vacuum filtration of combined lime sludge and sewage sludge. Sisk (4) after interviewing a representative of the Komline-Sanderson Company, related that several municipalities throughout the United States have attempted to dewater combined sludges, but obtained unfavorable results. He also reported, as a counterpoint, that Nebraska City, Nebraska and Superior, Nebraska have obtained successful results by adding the lime softening sludge from their water treatment plants directly into the sanitary sewers. The raw combined sludge, accumulated in the primary settling tanks at the sewage treatment plant, was then vacuum filtered. Each of the two cities reported that the cost of conditioning chemicals was greatly reduced and the biochemical oxygen demand reduction of the wastewater was greatly increased in the plant. Because each sludge exhibits characteristics dependent upon the process from which it was derived, it is necessary that the sludges used in a study be defined as to their origin. Also important to this study were the amounts of sludge produced at both the water and wastewater treatment plants. The wastewater treatment plant produces a digested-primary-activated sludge which is presently being lagooned immediately adjacent to the plant. The sludge, which accumulates in the primary settling basins, flows to a sludge· thickner and is thereafter pumped to one of four anaerobic digesters. After digestion for a 26 day period, it flows to the lagoons. An average of 200,000 gallons per day (gpd) of sludge is produced with the digested sludge having a solids content of approximately two percent. Figure 1 is an aerial photograph which shows the Sioux Falls Wastewater Treatment Plant and the relatively large area required for sewage sludge lagooning. The water treatment plant partially softens Sioux Falls' water supply of 10 million gallons per day (mgd). Slaked pebble lime is added to the water in the form of a slurry, with a minimum amount of mixing. Lime sludge production amounts to approximately 144,000 gallons per day, exhibiting an average solids content of about 10 percent. The lime sludge is presently being lagooned in an area in close proximity to the wastewater treatment plant.

Library of Congress Subject Headings

Sewage disposal
Water -- Purification--Filtration




South Dakota State University