Enhancing biomethane production from citrus waste: An integrated approach of hydrothermal carbonization and anaerobic digestion for sustainable waste management

Abstract

This study investigates the energy recovery potential of bio-oil derived from hydrothermal carbonization (HTC) of citrus waste through anaerobic digestion (AD). The bio-oil, a complex mixture containing 30-50% of the original carbon from biomass, serves as a valuable substrate for AD. Leveraging the HTC pretreatment, the hydrolysis step in AD becomes more efficient, facilitating faster degradation rates. Anaerobic digestion of the bio-oil was conducted in a high-loading hybrid anaerobic reactor. The reactor underwent stabilization using tomato liquid fraction, followed by bio-oil feeding with an applied volumetric loading of 5 g COD/L-d under mesophilic conditions. Remarkably, COD removals exceeded 90% when utilizing the tomato fraction and surpassed 80% in the bio-oil feed. Additionally, methane yield approached theoretical levels, highlighting the effectiveness of combining HTC and AD technologies. The study demonstrates that the integration of HTC and AD offers a promising alternative for the sustainable utilization of citrus industry wastes, showcasing high removal efficiencies and methane production. This approach aligns with circular economy principles, providing a pathway for efficient waste valorization and renewable energy generation.