Carbohydrate degradation contributes to the main bioheat generation during kitchen waste biodrying process: A pilot study.

Biodrying is a promising method for processing kitchen waste (KW) with high moisture content into reusable solid recovered fuels (SRFs). During biodrying, a large amount of bioheat generated from biodegradation of biochemical components results in KW dehydration. However, the degradation rules of these components and their contribution to the bioheat in KW biodrying have not been systematically clarified. Here, a pilot experiment was performed to investigate the variations in biochemical components, hydrolase activities, and bioheat generation during three successive cycles of biodrying processes. Results showed that KW could be rapidly converted into SRFs with low calorific values of 6705-7062 kJ/kg and moisture content of 31.26%-35.21%. Analyses of hydrolase activities and mean fluorescence intensity suggested that the biodrying process pioneered the degradation of lipids and proteins in the warming stages, while carbohydrates (i.e. amylum, celluloses, etc.) underwent rapid decomposition in a large extent in the high-temperature and cooling stages. Carbohydrates with minimal difficulty in degradation, contributed 73.37%-89.92% to the total degradation mass and 59.23%-60.80% to the bioheat source during the three-cycle biodrying process. The generated bioheat was 4.32-4.56 times the amount of the theoretical heat used for water removal, indicating that internal bioheat could significantly enhance water evaporation and was sufficient for the expected water removal mass. Therefore, the evaluation of the main components to bioheat generation and its utilization efficiency makes a prominent contribution that can greatly clarify the conversion of KW biodrying into SRFs in order to efficiently promote renewable bioenergy and support the bioeconomy.