Sustainable management of unavoidable biomass wastes

The growing global population is posing severe stress on the earth's carrying capacity in terms of food, water, and energy supply. Biomass is the only renewable alternative that can be used for energy, liquid fuels, and bio-based materials simultaneously, which makes it an indispensable resource in the near and mid-term future as the world is slowly shifting away from fossil fuels. Wood waste (WW), agricultural waste (AW), food waste (FW), municipal solid waste (MSW), and sewage sludge waste (SSW) are identified as unavoidable biomass wastes because they are directly linked to the food-energy-water nexus core that is essential for the existence and development of human society. Proper management of these unavoidable biomass wastes is one of the significant factors that determine a sustainable future. This review provides a holistic view of unavoidable biomass wastes treatment strategies with a focus on hydrothermal processing (HTP) because most of the unavoidable biomass wastes are intrinsically wet biomass wastes. In addition, key properties of different biomass wastes, commonly used pretreatment methods, and major best available conversion technologies are evaluated for converting biomass wastes into energy, fuels, and products. Finally, options for integrating multiple technologies for the sustainable management of biomass wastes are highlighted, providing a promising road map for future development. The current review suggests that multiple technologies integrated energy systems are the key to sustainable management of unavoidable biomass wastes.