A Proposal for Extending Biological Criteria Applied in Sanitary Control of Sewage Sludge Intended for Agricultural Use

A sanitary indicator has been proposed to gather informations about the presence of CFU (colony forming units) of bacteria capable of causing hemolysis of sheep blood cells, known as hemolytic bacteria, in a sewage sludge sample. A group of hemolytic, heterotrophic bacteria, which are differentiated in terms of their phenotypes and genotypes, includes many species and types. As follows from literature, these bacteria are commonly found in raw sewage sludge. Therefore, there is a methodical basis for isolation and detection of the presence of this group of potentially pathogenic bacteria, other than Salmonella, on the basis of a rapid inoculation test on a specified culture medium in sewage sludge, both prior to and following the sludge processing. After confirmation of the results obtained, the values of such an indicator could make a useful criterion extending the scope of sanitary control presently used for admitting sewage sludge for agricultural use. A qualitative test should extend the scope of sewage sludge sanitary control before allowing it to be used in agriculture, and thus reduce the risk of biological contamination of soil.