Dehydration Performance of Municipal Sludge and Its Dewatering Conditioning Methods: A Review

Municipal sludge is an inevitable byproduct during thetreatmentof wastewater, which is produced by sewage treatment plants in urbanresidential areas, and it contains pathogens, heavy metals, and otherpollutants. Municipal sludge is suitable for application in energyutilization because of its high organic content and relatively lowtoxic matter. The high moisture content of municipal sludge bringshuge difficulties to its harmless disposal and resource utilization.At present, the main method used for sludge dehydration is mechanicaldewatering. However, the mud cake produced by this method still hasa water content of up to 80%, which does not meet the current rigorousrequirements. Therefore, the development of deep dehydration technologyfor sludge is imperative. In this paper, the basic properties andstructure of sludge were summarized. As a key component of sludgeflocs, extracellular polymeric substance (EPS) has received much attentionin sludge dewatering conditioning. Meanwhile, the influencing factorsof sludge dewatering were also fully elaborated, including sludgetypes, sewage hardness, surface charge, size distribution, and sludgeviscosity. And the main methods of sludge dewatering treatment werecomprehensively included, namely, the physical method, chemical method,biological method, and combined conditioning methods. The advantagesand disadvantages of each method are mentioned, and their applicationsituations were analyzed. Furthermore, comment was provided on theconditioning mechanism, adaptability, prospects, and limitations ofthe techniques for improving sludge dewatering. This systematic reviewrelated to sludge dewatering can not only provide reference informationfor the conditioning method but also benefit the exploitation of efficientand ecofriendly sludge dewatering technology.