Seasonal variations in the microbial population density present in biological sludge

Sludge produced during the treatment of wastewater is being used as fertili zer in several Gulf countries. The Water and Sewage Authority of Saudi Arab ia has targeted the reuse of the total amount of sludge in the future. Howe ver, these sludges should be properly treated before reuse as they contain a large number of pathogens and parasites. Little information is available on the microbial characteristics of sludge produced in wastewater treatment plants operating in this region. Variations in the population densities me asured by Standard Plate Count, total coliform, fecal coliform, coliphage, and Clostridium perfringens present in the sludge, were monitored during a one year study at Al-Khobar wastewater treatment plant so that the effect o f seasonal variations on the tate of these five indicator microorganisms co uld be investigated. This paper covers an evaluation of the fate of indicat or microorganisms in the drying sludge. Insight gained in this study will b e helpful in establishing guidelines for the use of sludge as fertilizer fo r agriculture purposes.