Valorization of sugarcane leaves and co-digestion with microalgal biomass to produce biofuels and value-added products under the circular economy and zero-waste concepts

This study investigates the production of biofuels and value-added products by co-digesting sugarcane leaves and microalgal biomass, aligning with circular economy and zero-waste principles. Hydraulic retention time (HRT) on continuous hydrogen production in a continuous stirred tank reactor was investigated. An optimal HRT of 12 h maximizes hydrogen production rate (3,983 mL-H₂/L·d) and yield (99.6 mL-H₂/g-VS). Microbial analysis using 16S rRNA amplicon sequencing on the Illumina platform indicates diverse communities, prominently featuring Streptococcus (43.4 %) and Clostridium (31.3 %) genera. The process efficiently utilizes residual components—acidified slurry, hydrogenic effluent, and solid residue—for methane and hydrogen generation, yielding up to 22.2 kJ/g-VS in total energy. The solid residue from hydrogen production exhibits composting properties and serves to produce vermicompost and densified refuse-derived fuel. This approach exemplifies the adept utilization of raw materials within a circular economy and zero-waste framework, yielding no waste throughout the entire process.