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

Abstract

The high organic carbon (C org ) sequestration ability of biochar can greatly contribute to atmospheric CO 2 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 C org 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 C org sequestered over 100-year in biochar is ascribed to the lower the molar H/C org and O/ C org 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/C org ratio is 0.7 in both EBC and IBI. Besides, EBC standards also have the threshold value 0.4 of a molar O/C org 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 CO 2 -eq removed over 100-year by the biochar activity, i.e., biochar C org 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.

Net CO2 removal of rice husk biochar as soil amendment depending on energy reuse in the production stage

“…바이오차 CO 2 순격리량은 100년이상 격리되는 바이오차의 유기탄소량에서 원료바이오매스 생산, 바이오차 생산ᆞ 활용, 그리고 원료와 바이오차 제품의 운송 등에서 발생하는 온실가스 배출량을 차감한 값이다 (Zhu et al, 2022). 우 리나라에서 농림부산물 등의 폐기물 바이오매스를 원료로 하고 왕복 200 km이내 지역에 활용한다고 할 때 국제적 방 법론을 적용한 바이오차 CO 2 순격리량은 생산단계에서의 온실가스 배출량에 크게 의존한다 (Han et al, 2023).…”

“…재생에너지 100% 사용의 Fig. 2a에서 CO 2 순격리량 19천톤의 파란색을 나타내는 당진시가, 재생에너지 없이 열에너지 재사용 비율이 줄면서 차감되는 온실가스 배출량이 커져 에너지 재사용 0%의하고 독성화합물 배출에 의한 대기오염과 같은 부작용을 초래할 수 있다(Zhu et al, 2022;Han et al, 2023). 요컨대, 왕겨 바이오차는 원료 수집이 편리하여 생산 및 보급이 유리하고, 토양개량효과가 높아 농가활용에 긍정적 측면이 있으며, 분쇄와 같은 전처리가 필요하지 않아 상대적으로 에너지 소모가 적어 CO 2 순격리량을 높일 수 있다는 장점이 있다.…”

“…바이오차 생산단계에서 열에너지는 폐열회수 시스템을 통해 재사용될 수 있다. 그리고 태양열 등 재생에너지와 폐열 회수로 재사용된열에너지에 대해서는 온실가스 배출량이 0으로 산정된다(Han et al, 2023). 이를 반영한 결과, 바이 오차 톤당 온실가스 배출량은 열에너지 재사용 70, 35, 0%에서 각각 462, 779, 1089 kg CO 2 -eq ton -1 biochar로 높아졌 다 (Table2).2 Fig.…”