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 melting of sewage sludge, above 1200°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 University of Putra Malaysia, this part highlights the changes in the microstructure of domestic sewage sludge when subjected to different meltingprocedures; heating temperature, cooling rate, and holding time. The heating temperatures ranged between 1250°C–550°C, and the rate of cooling was between 2.5°C–10°C per minute. Using XRD analyses, itwas found that the melted slags were amorphous despite the different melting procedures applied. The SEM microphotographs indicated that some crystallization had occurred under the melting procedures; 1350°C with a cooling rate of 5°C per minute and a holding time of 45 minutes, 1400°C with a cooling rate of 2.5°C per minute and holding time of 45 minutes, and 1400°C with a cooling rate of 5°C per minute and without holding time.