Biochar from agricultural residues for soil conditioning: Technological status and life cycle assessment

As a product/co-product of biomass thermochemical conversion, the yield and quality of biochar depend on its source material and the production process, so is its performance in soil conditioning. In this mini-review, various technologies, including slow pyrolysis, fast pyrolysis, torrefaction, and gasification were briefly discussed, among which slow pyrolysis and torrefaction were found to give higher biochar yield. Because the yield of biochar and the emissions in the production process play a critical role in the outcomes of its life cycle assessment, it is important to carefully choose and optimize the production technology of biochar. The life cycle benefit of biochar for soil conditioning was found generally positive, indicated by its improvement of ecosystem quality, mitigation of climate change, and reduced resource consumption. However, the variability in biochar properties makes it challenging in technology upgrading, application, and commercialization, and the lack of regulations and standardization makes biochar acceptance difficult.