Hagemann Nikolas, Schmidt Hans-Peter, Bucheli Thomas D, Grafmüller Jannis, Vosswinkel Silvio, Herdegen Volker, Meredith William, Uguna Clement N, Snape Colin E
Environmental Analytics, Agroscope, Zurich, Switzerland.
Ithaka Institute, Arbaz, Switzerland.
PLoS One. 2025 Sep 2;20(9):e0330206. doi: 10.1371/journal.pone.0330206. eCollection 2025.
Biochar is a carbon-rich material produced via pyrolysis that is increasingly recognized for its role in carbon sequestration, particularly through its application in agriculture and materials. However, accurately predicting the long-term persistence of biochar in the environment remains challenging. While incubation trials have been widely used to assess biochar degradation, their extrapolation beyond centennial timescales is uncertain. In this study, we evaluate the consistency between three physicochemical characterization methods that are considered as proxies for biochar persistence-hydropyrolysis (HyPy), solid-state electric conductivity (SEC), and elemental analysis to obtain molar hydrogen:carbon ratios. We produced 42 biochars from straw and wood using a continuously operated pilot-scale auger reactor at temperatures ranging from 400 to 800 °C under otherwise constant pyrolysis conditions. We then systematically analyzed the elemental composition, SEC and the fraction of biochar carbon that is resistant to HyPy (BCHyPy). Hydropyrolysis eliminates all free and covalently bound non-aromatic species and all aromatic species consisting of up to seven fused rings. Our results confirm that BCHyPy content increases with pyrolysis temperature and stabilizes above 600-680 °C, reaching >90% of total carbon in high-temperature biochars. Similarly, SEC increased exponentially with pyrolysis severity, correlating strongly with BCHyPy and H/C molar ratio. The latter has so far been used to predict biochar persistence. Our findings from a controlled temperature series of biochars highlight that SEC and BCHyPy could be useful proxies for parameterizing multi-pool decay models of biochars produced in practice.
生物炭是一种通过热解产生的富含碳的材料，其在碳固存中的作用日益受到认可，特别是通过其在农业和材料领域的应用。然而，准确预测生物炭在环境中的长期持久性仍然具有挑战性。虽然培养试验已被广泛用于评估生物炭的降解，但将其外推到百年以上的时间尺度是不确定的。在本研究中，我们评估了三种物理化学表征方法之间的一致性，这些方法被视为生物炭持久性的替代指标——加氢热解（HyPy）、固态电导率（SEC）和元素分析以获得摩尔氢碳比。我们使用连续运行的中试规模螺旋式反应器，在400至800°C的温度范围内，在其他热解条件恒定的情况下，由秸秆和木材制备了42种生物炭。然后，我们系统地分析了元素组成、SEC以及生物炭中对HyPy具有抗性的碳的比例（BCHyPy）。加氢热解消除了所有游离和共价结合的非芳香族物种以及所有由最多七个稠环组成的芳香族物种。我们的结果证实，BCHyPy含量随热解温度升高而增加，并在600 - 680°C以上稳定，在高温生物炭中达到总碳的>90%。同样，SEC随热解程度呈指数增加，与BCHyPy和H/C摩尔比密切相关。后者迄今为止一直用于预测生物炭的持久性。我们从一系列温度控制的生物炭中获得的结果表明，SEC和BCHyPy可能是用于参数化实际生产的生物炭多库衰减模型的有用替代指标。
