ABSTRACT
Sludge disinfection is necessary before its application to land mainly because of the presence of pathogenic microorganisms. Sludge disinfection minimises the risk of pathgenic contamination and ensure the safety of public health. Anaerobic and aerobic digestion does not disinfect the sludge, but greatly reduces the number of pathogenic organisms. Pasteurisation for small plants may be achieved by direct steam injection into the tank trucks that transport the sludge to the disposal site. Liquid digested sludge is normally stored in earthen lagoons. In sludge-drying beds, vapour pressure differences account for evaporation to the atmosphere. The heat required for sludge drying is generally obtained from a combustion process. The dried sludge is transported on drag conveyors to two incinerators and falls through shafts that are provided at the top of the combustion chamber, directly into a hot fluidised bed. Sludge-drying beds, if used for a sufficiently long time, may serve to fulfil the function of a heat drying process.
