Sodium salt enhanced self-sustaining smouldering performance of food waste: Key role of sodium and its redistribution

Abstract

Smouldering combustion is a promising way for food waste disposal. NaCl is the primary Na salt food additive. It can act as a catalyst to enhance smouldering performance. However, its detailed effects are still unknown. This study investigates the effect of NaCl on performance parameters during food waste smouldering. It primarily focuses on the catalysis performance and redistribution of Na in various products. Results show that the catalytic action of 5 % NaCl reaches saturation, with the overall decomposition ratio, average peak temperature and average front velocity of 97.8 %, 823 °C and 0.343 cm/min, respectively. After smouldering, most of Na (mainly NaCl) is retained in sand (63 %) and residue (18.1 %). Part of the released Na in the lower layer feedstock can be captured by the upper feedstock, causing the self-sustaining layer to have the highest Na concentration amongst layers. The presence of Na exerts an inhibitory effect on the graphitisation degree of smouldered char but has a negligible effect on pore structure. Recycling Na-containing spent sand is feasible for the efficient smouldering of food waste without a catalyst, and two cycles can still realise the complete decomposition of combustible components in food waste. The results of this study can guide the smouldering disposal of food waste with various contents of Na-containing additives, as well as the development of sand recycling.