Review of Carbon Fixation Evaluation and Emission Reduction Effectiveness for Biochar in China

As the world's largest energy consumer (i.e., 24% of the world) and one of the largest biomass resource reserve countries (i.e., total reserves of 73.42 x 10(8) t a(-1)), for China, using biomass to prepare for biochar and store it in soil to realize the carbon sequestration and emission reduction is of great significance. This paper explores the physical-chemical properties of biochar and finds out its reason-manifestation-influencing factors for carbon sequestration reduction. A series of life cycle assessment calculation methods were introduced to biochar from China's four main biomasses (i.e., crop straw, firewood and forest trees, livestock manure, and urban organic waste). According to the evaluation of carbon sequestration function and emission reduction benefit, the greenhouse gas emission reduction (i.e., CO2e, where CO2e is CO2 equivalent) is 4.51 x 10(8), 2.66 x 10(8), 4.18 x 10(8), and 3.01 x 10(8) t of CO2e for raw materials, respectively. The total potential of biochar to mitigate greenhouse gas emissions is 14.36 x 10(8) t of CO2e, which is equivalent to 15.23% of China's total greenhouse gas emissions. Through economic analysis of farmers and pyrolysis plants, it can be concluded that, when the carbon trading price is 300 CNY t(-1) of CO2e, it will result in an economic gap of 21.3 x 10(10) CNY a(-1), which requires a certain subsidy from the government. For crop stalks, firewood, woods, and livestock manure biomass resources are 7200, 7000, and 2500 CNY hm(-2) a(-1), respectively. If the carbon trading price can be increased to 600 CNY t(-1) of CO2e, both the farmers and the pyrolysis plant will have huge economic benefits. Finally, the existing bottlenecks of the technology are analyzed; the corresponding prospects are put forward; and the existing biomass utilization balance issues are discussed.