Hydrothermal conversion of Chinese cabbage residue for sustainable agriculture: Influence of process parameters on hydrochar and hydrolysate

Abstract

The demands on novel and sustainable techniques for vegetable waste (VW) valorization continues to increase during the past few decades due to the growing waste production under the flourishing vegetable industries. In this study, Chinese cabbage residues were hydrothermal carbonization (HTC) at 180, 200, 220 and 240 °C for 2 to 6 h to explore the impacts of process parameters on the characteristics of hydrochars and hydrolysates and their feasibility in sustainable agriculture. Results indicated that hydrothermal temperature had a greater impact on cabbage residue hydrolysis than the residence time. With the rising reaction severity, hydrochars became more alkaline with higher amount of ash and carbon (C), while the pH and dissolved organic nitrogen (DON) and NH4+-N in the hydrolysate were gradually reduced. The thermogravimetric analysis (TG-DTG) indicated that organic constitutions in the feedstock went through incomplete decomposition. Although the recalcitrance index (R50) steadily increased through HTC (0.37–0.46), hydrochars were unstable and would not applicable for carbon sequestration. Furthermore, hydrochars and hydrolysate would be optimal media for plants seedling and growth for the abundant nutrients and dissolved organic compounds but reduced phytotoxicity. In conclusion, these results showed that HTC is highly applicable for vegetable waste management for sustainable agriculture.