Interest in biochar production from organic waste has been growing in recent years due to its broad applicability, availability, and smoother production. Biochar production techniques are being continuously modernized to improve the production rate and quality. Though numerous methods have been reported in the recent past, a systematic classification of the same is yet to be explored. Based on the advancement of the techniques being employed for biochar production and modification of conventional methods, we have categorized all major techniques of biochar production into two primary classes. In the traditional approach, ancient methods and conventional pyrolysis techniques (Slow and Fast pyrolysis) are included, whereas, in modern approaches, several advanced technologies such as Gasification, Torrefaction, Hydrothermal carbonization, Electro-modification, along with modified traditional methods (Flash pyrolysis, Vacuum pyrolysis, and Microwave pyrolysis) are comprised. Further, the systematic review was intended to evaluate various types of feedstocks (agricultural biomass, forest/woody biomass, aquatic biomass, urban waste, and paper waste) with their potential to produce biochar. It was observed that the feedstock containing high cellulose was found to be helpful in improving the overall properties of biochar, including enhanced adsorptive action and retention of nutrients.

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