Biochar production, activation and adsorptive applications: a review

Rising global population and urbanization are major causes of waste generation, energy demand and carbon emissions. The atmospheric CO2 concentration has increased of 44% from 284 ppm in 1850 to 409 ppm in 2018. In 2017, the world energy consumption was 582 quadrillion British thermal units (qBtu), including 495 qBtu of fossil fuels and 87 qBtu of renewable and nuclear energy sources. Therefore, there is a need for new energies and methods of carbon sequestration, for instance by recycling biomass into biochar. Here, we review the thermochemical valorization of waste biomass by pyrolysis, gasification, torrefaction and carbonization to produce biochar with promising and environmental applications. We detail parameters that control biochar yields, quality and composition. Physical and chemical routes of biochar activation are also described. We focus on the utilization of biochar as soil amendment and for the adsorption of pollutants from wastewater. We conclude by a discussion on the techno-economic and lifecycle assessment of biochar production technologies.