Challenges and opportunities of lignocellulosic biomass for anaerobic digestion

Global annual production of lignocellulosic biomass including undervalued agricultural residues and greenhouse biomass is about 181.5 billion tonnes. This undervalued biomass has a high potential to produce biogas in anaerobic digestion (AD). Among the various pre-treatment methods, hydrothermal (HT) pre-treatment of lignocellulosic biomass is a promising approach to increase biogas production in AD. However, the high carbon to nitrogen ratio (C/N) of lignocellulosic biomass is reported to be the major limiting factor for a higher biogas yield. Hence, the synergistic integration of low C/N ratio biomass with high C/N ratio lignocellulosic biomass in an AD system appears to be a logical option to enhance biogas yield. High moisture lignocellulosic biomass HT pretreatment and biogas production in AD have the potential for renewable energy production with limited use of process energy. However, hydrothermal process temperature, AD substrate C/N ratio and its inhibitory elements are important parameters for optimum biogas production. Greenhouse biomass pretreatment in hydrothermal process can produce biochar, biogas and biofertilizer, which can be used as input heat and nutrient source for greenhouses. Finally, the operation of greenhouse in this system can manage zero waste and reduce greenhouse gas (GHG) emissions and climate change.