Thermogravimetry as a technique for establishing the stabilization progress of sludge from wastewater treatment plants

Stabilization processes are key to the reliable performance of any wastewater treatment plant. However, a simple, yet reliable and widely acceptable analytical tool to evaluate the degree of stability reached during sewage sludge treatment remains to be found. Mesophilic aerobic digestion has been carried out on laboratory scale in aerated reactors using non-stabilized sludges from three different wastewater treatment plants. Temperature programmed combustion tests were carried out to investigate the stabilization degree of samples throughout the lab treatment. Differential thermal analysis (DTA) has shown that energy release during sludge combustion shifts to higher temperatures as stabilization advances. The integration of the DTA curve gives an area which is proportional to the energy released so it has been possible to quantify this shift by representing the percentage of the cumulative area at each temperature along each sample combustion. Although the initial composition of the sludge should be considered in each particular case, this preliminary study shows that thermogravimetry may offer a means of ascertaining whether an acceptable degree of stability has been reached by aerobic digestion.