Biochar Production from Crop Residues

Our ancestors used biochar for improving soil fertility 2,500 years ago. In recent years, extensive research has been done on biochar because of its valuable properties. Biochar is a byproduct of biodegradable wastes from agricultural, municipal solid-wastes, forestry, etc. Producing biochar as a value-added product from wastes not only mitigates environmental health from greenhouse gases, volatile organic compounds, and leachates but is also used as a soil amendment, carbon sequestration, activated carbon, and so on. It is a charcoal-based material, rich in carbon sources, which is produced by thermochemical conversion of biomass into biochar in the presence or absence of air. There are different methods of producing biochar. Each method has its own advantages such as fast pyrolysis performed at 10–10,000 °C produces high content of bio-oil. Slow pyrolysis at 300–700 °C produces a larger quantity of biochar. Hydrothermal carbonization is an economically convenient method performed for biomass with high water content at 180–250 °C. The gasification method used is for syngas production such as carbon monoxide, hydrocarbons, carbon dioxide, hydrogen, methane at > 800 °C, and torrefaction performed in the presence of gas, water, or a stream environment. Production of biochar, bio-oil, and syngas differs based on the method performed and biomass characteristics. Physicochemical properties of biochar, such as surface area, porosity, cation exchange capacity, pH, are influenced by biomass property and pyrolysis temperature. The application of biochar is based upon the physicochemical properties of biochar.