Why does sludge need to be dried?

what is sludge drying?
Sludge drying refers to the process of removing most of the water content from sludge through actions such as percolation or evaporation. The sludge drying methods are mainly natural evaporation and mechanical dehydration, both of which aim to further reduce the moisture content of the sludge.

Why does sludge need to be dried?
Three main worthy of sludge drying:
to removed water in the sludge, the volume of the sludge can be reduced, and the cost of sludge treatment can be reduced.
to make physical and chemical properties of the sludge are stabilized, and further degradation will not occur during sludge disposal to avoid secondary pollution.
to render sludge use for aerobic composting, incineration, resource reuse, or even landfill
Sludge drying can be divided into high temperature drying and low temperature drying. High temperature drying is to evaporate the water in the sludge by increasing the temperature of the drying sludge heat source. The low temperature drying is to use a heat source lower than the ignition point of the sludge to evaporate the water in the sludge.
However, high-temperature drying will lead to the volatilization of harmful substances in the sludge, and the stability and safety of high-temperature equipment are poor and have been phased out. Low temperature drying is to use circulating hot air (about 70 degrees) to evaporate the sludge moisture. Due to the low temperature, harmful substances will not decompose and volatilize, thus greatly improving the stability and safety of the equipment.