Enhancement of System and Environmental Performance of High Solids Anaerobic Digestion of Lignocellulosic Banana Waste by Biochar Addition

Banana waste, a lignocellulosic waste material, is generated in large quantities around the world. High Solids Anaerobic Digestion (HS-AD) of lignocellulosic waste can recover energy and reduce its environmental impacts. However, high carbon/nitrogen ratios and low water content in HS-AD can potentially cause system acidification and/or failure. This study investigated the addition of biochar to enhance the performance of HS-AD of mixed banana waste (peel, stem, and leaf). Biochemical methane potential assays with varying biochar dosages (2.5-30%) showed that 10% biochar addition increased methane yields by 7% compared with unamended controls. Semi-continuous HS-AD studies, without and with 10% biochar addition, were conducted at varying solids retention times (42, 35, and 28 days) for long-term performance evaluation. Biochar addition reduced volatile fatty acid accumulation, improved system stability, and increased methane production by 20-47%. The nutrient content of digestate from HS-AD of banana waste indicated its potential use as a bio-fertilizer. Life cycle assessment results showed that biochar addition to HS-AD resulted in greater environmental benefits in most categories compared with the unamended control, including eutrophication, ecotoxicity, and fossil fuel depletion when biochar was available within a radius of 8830 km.