This study was conducted to demonstrate the effectiveness of a modification of lime stabilisation by the incorporation of pulverised fuel ash (PFA) for disinfection of sludge. The modified treatment is economic in terms of lime utilisation and uses another waste product, PFA, which would also require disposal. Intestinal pathogens are the most probable pathogenic organisms present in the sludge. Several species of intestinal pathogen were examined for their ability to survive in raw sludge and then subjected to disinfection. The effect of the chemical mixture was attributed to the high pH produced and maintained, as heat production in the modified process was minimal. A mixture of 60% sludge (600 g/kg): 40% CaO/PFA (44.44 g/kg / 355.56 g/kg) with the ratio CaO:PFA 1:8, was shown to be able to prevent the growth of bacterial pathogens and maintain a pH above 11.0 for at least 7 d. Although further study concerning texture and other physical properties is required, a modified sludge treatment with this relatively low proportion of lime was found to be suitable for landfill or land reclamation as far as its bacteriological disinfecting quality is concerned. (C) 1998 Elsevier Science Ltd.
