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

Municipal sludge is an inevitable byproduct during the treatment of wastewater, which is produced by sewage treatment plants in urban residential areas, and it contains pathogens, heavy metals, and other pollutants. Municipal sludge is suitable for application in energy utilization because of its high organic content and relatively low toxic matter. The high moisture content of municipal sludge brings huge difficulties to its harmless disposal and resource utilization. At present, the main method used for sludge dehydration is mechanical dewatering. However, the mud cake produced by this method still has a water content of up to 80%, which does not meet the current rigorous requirements. Therefore, the development of deep dehydration technology for sludge is imperative. In this paper, the basic properties and structure of sludge were summarized. As a key component of sludge flocs, extracellular polymeric substance (EPS) has received much attention in sludge dewatering conditioning. Meanwhile, the influencing factors of sludge dewatering were also fully elaborated, including sludge types, sewage hardness, surface charge, size distribution, and sludge viscosity. And the main methods of sludge dewatering treatment were comprehensively included, namely, the physical method, chemical method, biological method, and combined conditioning methods. The advantages and disadvantages of each method are mentioned, and their application situations were analyzed. Furthermore, comment was provided on the conditioning mechanism, adaptability, prospects, and limitations of the techniques for improving sludge dewatering. This systematic review related to sludge dewatering can not only provide reference information for the conditioning method but also benefit the exploitation of efficient and ecofriendly sludge dewatering technology.