Significant quantities of urban sludge generated by wastewater treatment plants pose serious eco-toxicological and environmental issues. Urban sludge collected at different stages of wastewater treatment is generally composed of non-biodegradable organic matter, micro-organisms, and mineral matter in the form of aluminum hydroxide, silica hydroxide, iron hydroxide, and calcium hydroxide. The most common uses of sewage sludge treatment are agriculture and landfill. However, they cause problems related to pollution and recovery of energy and nutrients from sewage sludge, which makes its usage as fertilizer doubtful. Therefore, thermal treatment methods handle these problems through energy recovery and pollutant destruction. In this context, we studied the urban sludge characteristics using X-ray diffraction (XRD), X-ray fluorescence (XRF), and thermal analysis. The results obtained showed that the studied samples contain different mineral fractions of 31% silica (SiO₂), 21.4% aluminum oxide (Al₂O₃), and 14.7% iron species, which make urban sludge promising in building materials. Through the heat treatment of raw and limed urban sludge, we observed a complex decomposition process, and the calculated activation energy using the isoconversional method proposed by Friedman showed a significant variation of over 10%, confirming the intricate nature of the sludge. Our findings underscore the need for a comprehensive approach to sludge management, optimizing its potential use and reducing the environmental impact.

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