Valorisation of banana peels by hydrothermal carbonisation: Potential use of the hydrochar and liquid by-product for water purification and energy conversion

Banana peels were used as feedstock to produce a carbon dense hydrochar for the removal of toxic metals from wastewater. Compared to the biomass feedstock (41.3% mass C), the banana peel hydrochar possesses higher carbon (54–72% mass C) and lower ash contents. The carbonised banana peels treated between 150 and 300 °C (1−2h) demonstrated an excellent ability to remove Cd2+ (5–100 mg L−1), achieving 99% removal, in comparison with 75% for the raw peel. The liquid by-product generated in the carbonisation process was tested as feedstock in microbial electrochemical devices, showing significant reduction in the chemical oxygen demand levels (initially 10–25 103 mg L−1), associated with the production of electrical outputs; 81–85% reduction with microbial communities from compost, and 53–85% with anaerobic sludge. The results demonstrate the complete utilization of waste from mass cultivation of banana, providing a full-cycle solution for the pollution associated to this important crop.