Lignocellulosic biomass to biochar: An overview on impact of production technologies on biochar yield and techno-economics

Biochar technology is getting attention globally due to its multifaceted potential in removing contaminants from wastewater, storing energy as supercapacitor, enhancing soil health, and addressing environmental challenges as a negative emission technology. The aim of this study is to review the conversion of different types of lignocellulosic biomass into biochar using various thermochemical conversion methods. The physiochemical properties of produced biochar using different characterization techniques have been reviewed. Slow pyrolysis consistently produces higher biochar yields (up to approximately 79 %) compared to fast pyrolysis, gasification, or flash carbonization, which primarily focus on generating bio-oil or syngas. Smaller biomass particles enhance heat transfer, and may lead to reduced yields due to the accelerated pyrolysis process. Lower temperatures and lignin-rich biomass promote higher solid yields, whereas higher temperatures facilitate carbonization but result in reduced biochar yield. Further, the economic viability of biochar production from large-scale industrial units and small-scale portable systems is reported as per the existing literature and the selling price of biochar produced from small scale units is found to be higher. This review suggested that the major challenges in biochar technology include but not limited to advanced harvesting techniques, improved logistics, decentralized efficient and economical biochar production units, method of biochar addition to soil etc. Future research in this technology should focus on tailoring biochar properties for specific applications, optimizing pyrolysis conditions and post-processing techniques, and exploring alternative feedstocks to enhance sustainability, efficiency, and versatility.