Use of thermogravimetry for single characterisation of samples of the composting process from sewage sludge

Pyrolysis and combustion of different samples from a sewage sludge composting tunnel plant were studied by thermogravimetry. Two series of samples were analyzed: initially, 8 samples were taken at 8 different points from different stages of the process; later, 5 samples from different points at the end of the composting tunnel were taken. The experiments were carried out at 10 °C/min, in N2 atmosphere and N2:O2 4:1 atmosphere. The results were discussed to analyze the heterogeneity of the samples. In addition, the compositions of the samples taken for the analysis were deduced using the decomposition kinetics as correlation of weight loss vs. time. The fractions considered were sewage sludge, straw and sawdust. The compositions deduced were compared with the toxicity concentration of dioxins, in order to analyze the possible variations of toxicity determined.

► TG, DTG and kinetics have been useful for analyzing the uniformity.
► The determination of dioxin concentration in compost samples is not easy.
► There is a great variation of dioxin concentration in similar samples.