Thermochemical transformation of agro-biomass into biochar: Simultaneous carbon sequestration and soil amendment

Abstract

The gradual rise in average global temperature over the last few decades is the evidence of adversities of climate change. Therefore, the research and development efforts to investigate and materialize innovative and economically viable methods to mitigate carbon emission have received unprecedented priority. One of the plausible methods to sequester carbon in a sustainable manner could be to fix carbonaceous materials on a very long-term basis by thermochemical transformation of agricultural biomass residues into biochar. It has been reported in the literature that the pyrolysis of organic materials can yield up to 50-70 % (w/w) biochar as a value-added product. Furthermore, biochar can have a carbon composition ≥60-80 %, which is equivalent to ≥2.20-2.94 ton CO2 sequestered/ton biochar. Therefore, even after a conservative estimation (e.g., 20 % liberation of carbon from the biochar after land application) of kinetics of biochar-bound carbon loss, a substantial amount of CO2 can be sequestered into soil for a very long term (≥100 s to 1,000 years or even more). On the other hand, amendment of agricultural soil with biochar has been found to enhance physicochemical as well as biological characteristics of the soil. Biochar can act as buffering agent for acidic soils; enhance water retention capacity, favorable matrix formation for beneficial microbial flora, and degradation of toxic compounds; and provide bioavailable nutrients to plants or to the beneficial microbial consortia. The present cost of commercially available biochar is 100-500 $/ton (without any carbon credit basis), which is considerably higher than other soil amendment chemicals, such as lime (50 $/ton), which is the main deterrent to its marketability. However, under one or more of the favorable conditions such as government subsidies/carbon credit gains, mass scale production (demand-supply dynamics), and data on long-term benefits correlated with techno-economics can make biochar commercially successful. This will have a substantial positive impact on mitigation of carbon emission.