Effects of high temperature melting on the porosity and microstructure of slags from domestic sewage sludge

Sewage treatment plant sludges continue to pose great problems in terms of volume, odour and method of disposal. Thermal treatment of sewage sludge is considered as an attractive method in reducing sludge volume, which at the same time produces reusable by-products. Studies on high temperature melti ng of sewage sludge, above 1200 degrees C, show promising results where by stable and inert by-products are produced. This paper presents a part of a big project on thermal treatment of sewage sludge, carried out in Universit y of Putra Malaysia, this part highlights the changes in the microstructure of domestic sewage sludge when subjected to different melting procedures; heating temperature, cooling rate, and holding time. The heating temperatur es ranged between 1250 degrees C-1550 degrees C, and the rate of cooling wa s between 2.5 degrees C-10 degrees C per minute. Using XRD analyses, it was found that the melted slags were amorphous despite the different melting p rocedures applied. The SEM microphotographs indicated that some crystalliza tion had occurred under the melting procedures; 1350 degrees C with a cooli ng rate of 5 degrees C per minute and a holding time of 45 minutes, 1400 de grees C with a cooling rate of 2.5 degrees C per minute and holding time of 45 minutes, and 1400 degrees C with a cooling rate of 5 degrees C per minu te and without holding time.