Sludge from wastewater treatment plants

Three principal categories of sludge can be identified: (i) primary, from mechanical and preliminary treatments, (ii) secondary/activated, from biological treatments, and (iii) tertiary/chemical, from final physical-chemical treatments. Sustainable procedures for sludge management require the reduction of the amount of sludge to the minimum compatible with the final destination, and the production of good quality sludge, thus reducing the impact on the environment and favouring the application of reuse options instead of disposal ones. The selection of the optimal processing sequence requires the knowledge of chemical, biological and physical characteristics of sludge, so their determination under standardized conditions is a necessary tool to obtain reliable and comparable results. Standardized procedures for sludge characterization are also necessary to support the development of realistic and enforceable regulations. This chapter reports the amount of sludge produced in treatment plants and discusses the parameters to evaluate, with reference to the main practices for sludge management