Sludge is an inevitable product of sewage treatment plants and sewage treatment. When sludge without proper treatment and disposal enters the environment, it directly brings secondary pollution to water bodies and the atmosphere, which not only reduces the effective treatment capacity of the sewage treatment system, but also poses a serious threat to the ecological environment and human activities.
Along with the process of treating sewage in wastewater treatment plants, a large amount of sludge is produced. The amount of sludge is about 0.3% to 0.5% of the treated water volume (water content of about 97%). Of the total construction cost of a wastewater treatment plant, about 20% to 50%, or even 70%, is spent on sludge treatment. Therefore, sludge treatment is an important part of the wastewater treatment system and must be given full attention. Sludge contains a large amount of harmful and toxic substances such as parasite eggs and heavy metals; useful substances such as plant nutrients, organic matter and water. The purpose of sludge treatment is to reduce, stabilize, render harmless, and utilize the sludge in an integrated manner. The unit processes usually used are: thickening, stabilization, sludge conditioning, and dewatering.
