Sewage Sludge Sanitation Treatments, Uncertainties And Risks, Legislative Requirements

Pathogenic organisms present in urban wastewater are, in a great measure, removed in treatment plants by primary sedimentation - free bacteria and those associated with various host cells adhere to the solid particles and settle with them, being accumulated in primary sludge. Further, biological treatment provides inactivation or destruction of pathogenic species, by conditions in aeration basins and interspecific relationships among microorganisms, as competition and predation. Also, part of the pathogenic organisms adhere to sludge flocks and are eliminated with excess activated sludge. Various sludge treatment methods have been developed and have led to satisfactory results in terms of sanitation and migration control of biological contaminants into the environment. Although wastewater treatment processes provide a strong control of the epidemic outbreaks, a complete elimination of all pathogenic organisms cannot be assured by conventional treatments applied to wastewater and the resulting sludge. Regarding the pathogen load, current national and European legislation does not provide a list of indicator organisms for pathogen loads and limits required for the safe usage of sludge in agriculture, however countries in the European Community have expressed their concern regarding the transfer of pathogens by using sludge as a fertilizer and recommended new amendments for Directive 86/278 /EEC, including clear specifications on the appropriate treatment of sludge, in order to protect human and environment health. Therefore, it becomes necessary to signalize the areas of uncertainty concerning the risk of transmitting pathogens in the process of sludge recycling and the importance of updating the legislative provisions, in light of technical and scientific progress.