A Review on International Carbon Credit Certification Methodologies for Biochar as a Soil Amendment

Abstract

The high organic carbon (Corg) sequestration ability of biochar can greatly contribute to atmospheric CO2 removal for global C neutrality. These climate-positive services of biochar are traded as C credits on international C trading platforms through reliable methodologies. Here, we reviewed the international biochar C credit certification methodologies and quality standards to build foundations for biochar C credit trading in Korea. The quality of biochar includes the quantity of Corg sequestered over 100 years, the content of toxic contaminants below their threshold values, and the biochar properties related to soil fertility, as described by European Biochar Certificate (EBC) and International Biochar Initiative (IBI) certification guidelines. The higher amount of Corg sequestered over 100-year in biochar is ascribed to the lower the molar H/Corg and O/Corg ratios, resulting from pyrolysis of feedstock at a high temperature over 350°C. For assuring the permanence of biochar, the threshold value of molar H/Corg ratio is 0.7 in both EBC and IBI. Besides, EBC standards also have the threshold value 0.4 of a molar O/Corg ratio for all biomass and require a pyrolysis condition of exceeding 500°C for 3 min at minimum for animal-derived biomass. Quality-certified biochar can be used for C credits. Biochar C credit is the amount of net CO2-eq removed over 100-year by the biochar activity, i.e., biochar Corg sequestered over 100-year minus greenhouse gas (GHG) emissions over the biochar life cycle. The three voluntary C credit trade platforms with their own biochar methodologies are Puro.earth with life cycle assessment, Carbonfuture with C-sink certification, and Verra with UNFCCC Clean development mechanism (CDM) methodology. All three methodologies present standards for permissible biomass for feedstock, energy efficiency and by-product treatment for production, permissible matrices and tracking system for end use, and the third-party verrification. On a regional basis in Korea, where biochar feedstock is mainly biogenic waste, GHG emissions during biochar lifetime mainly depend on the production stage. In pyrolysis facilities that meet EBC and Verra's high-tech standards, GHG emissions during the production stage could be assumed to be very low. However, low-tech facilities with high GHG emissions during biochar production could deteriorate biochar C credits. Therefore, securing biochar C credits could be achieved through the modernization of pyrolysis facilities. Besides, it is essential to establish a process-oriented measurement, reporting, and verification systems, to ensure scientific reliability of biochar C credit certification.Calculation methods for biochar carbon (C) credits called CORC, C-sink, and VCU used in voluntary C credit trade platforms, Puro.earth, Carbonfuture, and Verra, respectively. C credit trade platform C credit calculation methods (tCO2eq) Comments Puro.earth • CORC = Estored - Ebiomass - Eproduction - Euse • Estored = Qbiochar × Corg × FpTH,Ts × 44/12 • Qbiochar is the amount of biochar produced over the reporting period; Corg is the organic C content of the biochar produced; FpTH,Ts = c + m × H/Corg is the permanence factor of biochar organic C over a given time horizon TH in a given soil at temperature Ts, where the coefficients c and m are a function of TH and Ts • Estored: CO2sequestered over 100 years • Ebiomass, Eproduction,Euse: Life cycle GHG during each stage Carbonfuture • C-sink is determined by integrating C-sink potential, greenhouse gas emissions (GHG) during C-sink tracking after leaving factory gate, and C remaining % after 100 y in applied matrix • C-sink potential = Corg content of biochar - GHG during biomass sourcing - GHG during production - Safety margin • Safety margin = 10% of the total GHG emission of biomass sourcing and production • EBC C-sink standard requires that the biochar may only be used in specific ways Verra Overall equation • VCU = ERPS,y - PEAS,y - LEy, in year y • ERPS,y = GHG emission removals at production; PEAS,y = GHG emissions at application; LEy = Total leakage emissions, primarily attributed to transport emissions • ERPS,y = ∑((∑CCt,k,y × 44/12) - (∑PEPS,t,p,y)) • CCt,k,y = Organic carbon content, sequestered over 100 years, on a dry weight basis for biochar type t used for application type k; PEPS,t,p,y = Project GHG for production of biochar type t at production facility p may arise from pretreatment like drying wet waste, thermodynamic conversion, or use of external energy • GHG reduction at the sourcing stage is zero following a conservative scenario • GHG by transport must be accounted for only if the distance is more than 200 km in round trip High tech. production • Thermodynamic conversion emissions are zero and renewable energy use reduces GHG Low tech. production • Thermodynamic conversion includes CH4 emissions, which can be obtained using estimation equation • GHG for the pretreatment and use of external energy can be obtained using CDM Tool 05 (UNFCCC, 2008a) and CDM Tool 03 (UNFCCC, 2008b)

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