Research progress on flocculation-based technology for the enhancement of sludge dewatering: A review

The production of municipal sludge is increasing with the development of urbanization in these years. The municipal sludge usually has a high moisture content and contains large number of organic pollutants. Inappropriate treatment methods will lead to secondary pollution. Conventional mechanical dehydration can hardly meet the moisture content requirements for subsequent disposal. Flocculation is widely used in the sludge dewaterability enhancement for its economic efficiency and reliability. This paper provides a comprehensive review of flocculation-based techniques for municipal sludge dewatering. Firstly, the advantages and disadvantages of pretreatment techniques is elaborated. Even though flocculation is widely applied in sludge dewatering, deep dehydration always faces bottleneck in area such as removing cell bound water and changing the structure of EPS, etc. when using individual flocculation. Limited understanding of mechanisms and behaviors of joint technology of flocculation and physical/chemical/biological methods, have been highlighted as knowledge gaps in sludge dewatering. Some specific cases, mechanisms of action, practical considerations, dewatering effects and economic analyses of flocculation-coupled multiple technologies for deep sludge dewatering are analyzed in detail, Finally, the limitations, challenges and outlook of flocculants applied in sludge dewatering are comprehensively discussed.