Reduction of Fecal Streptococcus and Salmonella by selected treatment methods for sludge and organic waste

The increasing utilization of waste water sludge and source-separated organic household waste in agriculture has brought the quality aspects into focus; among others the hygienic aspects. In this study, the reducting effect on Fecal Streptococcus (FS) and Salmonella of different methods for stabilization and methods for further treatment of sludge and organic waste has been investigated. The most common methods for stabilization, i.e. aerobic and anaerobic stabilization, only reduce the indicator organisms by approximately 1 logarithmic decade. Methods for further treatment of sludge and organic waste have shown reductions of microorganisms allowing for unrestricted utilization in agriculture, meeting the product control: FS below 100/g and no Salmonella detected. The effect of storage of sludge at summer and winter temperatures respectively has been investigated. At temperatures (around 20 degrees C) significant reductions of Salmonella were found, while the die out at low temperatures (below 10 degrees C) was limited. FS was not reduced systematically during storage, and therefore, FS is not usable as indicator organism for the hygienic properties of sludge during storage. (C) 1997 IAWQ. Published by Elsevier Science Ltd.