Biochar from biomass waste as a renewable carbon material for climate change mitigation in reducing greenhouse gas emissions—a review

Biomass waste generation is increasing enormously and biomass burning emits greenhouse gas emissions causing severe effects on the environment and health of the population. It contains high organic and carbon content which can be reused/diverted for useful products (like Biochar) that facilitate climate change mitigation. Biochar, a renewable carbon, is gaining importance and it opens up an area of research to explore on the properties and stability of biochar, its wide applications, impacts on soil characteristics, techno-economic details, carbon and nitrogen interactions of biochar-soil matrix, and emission control. This review addresses opportunities of biomass wastes for biochar production, various thermo-chemical reactions for preparation and its basics/mechanisms, properties of biochar and hydrochar, and gaps/operational challenges, and summarizes wide applications of biochar in soil improvement, climate change mitigation, energy production, waste management, and environmental remediation. The effect of physico-chemical parameters (temperature, heating rate, chemical composition, etc.) on the biochar production will help in valorizing this industry. The optimized process conditions involved in low temperature (torrefaction, microwave-assisted pyrolysis, hydrothermal carbonization), pyrolysis (Fast, Slow, Flash), gasification, and combustion processes for biochar, syngas, and bio-oil production are to be explored. The critical review on the biochar addition influence on CO2, CH4, and N2O emissions in various soil types and carbon sequestration is done here. The modification and activation of biochar are recently attractive due to their role in improving biochar quality and for expanding its applications. Limitations and future status of biochar production from biomass waste are highlighted. Biochar will be a promising solution as an alternative to fossil fuels, waste management, bioenergy, and combat climate change.