The nature of the sludge has a dual character. On the one hand, it contains a large amount of organic material and nutrients such as NPK, which could be reused. On the other hand, some pollutants retained in the sludge, makes the sludge in high moisture, and includes a lot of harmful and carcinogenic substances (pathogenic bacteria, parasite eggs, heavy metals, etc. ) that are difficult to degrade. If not treated appropriately, it will easily cause secondary pollution to groundwater and soil, directly threatening the environment and public health. obviously that the most essential in sewage treatment is sludge treatment.