Since the amount of sludge produced in sewage treatment is as high as 0.3%-0.5% of the treated water（calculated by the 97% moisture content）

the reduction

recycle and safe treatment of sludge are urgent. In the process of sludge treatment and disposal

sludge dewatering is the key step. However

the moisture content of sludge is still high after the current dewatering process

and thus it is critical to find a more efficient sludge dewatering technology. By summarizing common factors controlling sludge dewatering（including the hardness and conductivity of water

compressibility and blockage of filter cake

pH values

types

treatment systems

storage conditions

pumping and mixing of sludge） and common pretreatment technologies（including cracking

chemical flocculation

chemical

biological

hydrothermal and combined conditioning technologies） of sludge dewatering

not only does this research lay a theoretical foundation for further understanding sludge dewatering

but also provide technical guidance for industrial application. Moreover

it is pointed out that the effective control on sludge permeability

floc strength and size are important breakthroughs to promote sludge dewatering

and the prospect of further research of high-efficiency flocculant and a variety of combined conditioning technology are also put forward.