Thermal and adsorption study of the spent mushroom substrate and its hydrochar

Abstract

Mushroom cultivation and consumption have been steadily increasing in recent decades, however, after mushroom cultivation, a large amount of by-products, known as spent mushroom substrate (SMS), are left behind in open dumps where about 5 kg of SMS are generated for every kilogram of mushroom (Agaricus bisporus). Around 51 million tons of SMS are produced in the world every year. Hydrothermal carbonization (HTC) is a promising technology for the conversion of SMS into a rich carbon product, hydrochar. The hydrochar was synthesized in a hydrothermal reactor at a temperature of 180 °C for a reaction time of 1 h. The characterization of the SMS and its chars was done by FTIR, SEM, and TGA analysis. The FTIR analysis showed that aromatic and oxygen-rich functional groups are dominant on the hydrochar surface. It was noticed that the hydrochar had more visible pores compared to the SMS. The porous structure and oxygen functional groups of hydrochar probably influenced the improvement of adsorption performance, since the adsorption capacity of SMS for Cd2+ ions was 28 mg L-1, while for hydrochar it was 92 mg L-1. On the other hand, the thermal kinetic analysis has shown that hydrothermally treatment upgrades the combustion behavior of hydrochar. The kinetic parameters were determined by Kissinger and Ozawa methods. The hydrochar had notably lower activation energy compared to the SMS, which means that this hydrochar requires a smaller amount of energy to start combustion. The preliminary results show that HTC effectively transforms SMS into alternative solid biofuel and eco-friendly sorbent.