Thermal behaviour of the oversize fraction produced after decentralized co- composting of used diapers and household wet biodegradable waste

In the present study, thermal behaviour of the oversize fraction (> 4 mm size) which was recovered after co-composting of the used diapers (UD) and household wet biodegradable waste (HWBW), was investigated by performing lab-scale combustion experiments. During the co-composting runs, the UD share in the mixture was 0–20%. The oversize fractions were subjected to thermogravimetric analysis (TGA) in oxidative environment (air flow rate = 100 mL/min) under varying heating rates (10–55 °C/min). The temperature of the samples was raised up to 950 °C. The experimental data was analysed using non-isothermal isoconversional model free Kissinger–Akahira–Sunose (KAS) to determine the kinetic constants. The average activation energy for combustion of the oversize fractions was 58.01–107.7 kJ/mol whereas the average order of reaction was 0.11–0.23. Generally, the presence of undecomposed combustible portion of diaper in the oversize fraction could have reduced activation energy. The lower calorific value (LCV) of the oversize fractions ranged between 12.36 MJ/kg and 13.35 MJ/kg. The TGA coupled with mass spectroscopy (MS), Fourier transform infrared spectroscopy (FTIR), and 3-D FTIR spectrum results showed gaseous emissions (such as CO₂, C₂H₆, C₃H₈, NO₂, and CH₄) during combustion of the oversize fractions. The results suggest that the oversize waste fraction may replace some amount of non-renewable fuels. The future study should plan for pilot-scale co-combustion trials for the oversize fractions.