Enhanced technology based for sewage sludge deep dewatering: A critical review

•Sludge enhanced dewatering technologies are comprehensively reviewed.•Mechanisms of different sludge enhanced dewatering technologies are discussed.•Process adaptability of different sludge conditioning methods are analysed.•Sludge electro-dewatering and its coupled processes are discussed.•Sludge enhanced dewatering technology and its coupled processes are prospected. Sludge is an inevitable by product of sewage treatment, and it includes pathogens, heavy metals, organic pollutants and other toxic substances. The components of sludge are complex and variable with extracellular polymeric substances (EPS) being one. EPS are highly hydrophilic and compressible, and make sludge dewatering difficult. Therefore, the development of efficient sludge-dewatering technology is an important means of mitigating rapid sludge growth. At present, the main methods used for sludge deep-dewatering technology are chemical preconditioning with high-pressure filtration and electrical mechanical dewatering. The selection of chemical preconditioning directly determines the final efficiency of the sludge-dewatering process. In this paper, we conduct a comprehensive review of the problems related to sludge dewatering and systematically summarise the impact of different chemical conditioning technologies on the efficiency of sludge dewatering. Furthermore, the characteristics of different enhanced dewatering technologies are evaluated and analysed for their adaptability and final disposal methods. We believe that this review can clarify the chemical conditioner mechanism to improve sludge dewatering, provide reference debugging information for the sludge-dewatering process and promote the development of efficient and environmentally friendly sludge-dewatering technology.