Institute of Soil Research, University of Natural Resources and Life Sciences, Vienna, Austria.
J Environ Qual. 2012 Jul-Aug;41(4):990-1000. doi: 10.2134/jeq2011.0070.
Biochars are increasingly used as soil amendment and for C sequestration in soils. The influence of feedstock differences and pyrolysis temperature on biochar characteristics has been widely studied. However, there is a lack of knowledge about the formation of potentially toxic compounds that remain in the biochars after pyrolysis. We investigated biochars from three feedstocks (wheat straw, poplar wood, and spruce wood) that were slowly pyrolyzed at 400, 460, and 525°C for 5 h (straw) and 10 h (woodchips), respectively. We characterized the biochars' pH, electrical conductivity, elemental composition (by dry combustion and X-ray fluorescence), surface area (by N adsorption), water-extractable major elements, and cation exchange capacity (CEC). We further conducted differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffractometry to obtain information on the biochars' molecular characteristics and mineralogical composition. We investigated trace metal content, total polycyclic aromatic hydrocarbon (PAH) content, and PAH composition in the biochars. The highest salt (4.92 mS cm) and ash (12.7%) contents were found in straw-derived biochars. The H/C ratios of biochars with highest treatment temperature (HTT) 525°C were 0.46 to 0.40. Surface areas were low but increased (1.8-56 m g) with increasing HTT, whereas CEC decreased (162-52 mmol kg) with increasing HTT. The results of DSC and FTIR suggested a loss of labile, aliphatic compounds during pyrolysis and the formation of more recalcitrant, aromatic constituents. X-ray diffractometry patterns indicated a mineralogical restructuring of biochars with increasing HTT. Water-extractable major and trace elements varied considerably with feedstock composition, with trace elements also affected by HTT. Total PAH contents (sum of EPA 16 PAHs) were highly variable with values up to 33.7 mg kg; irrespective of feedstock type, the composition of PAHs showed increasing dominance of naphthalene with increasing HTT. The results demonstrate that biochars are highly heterogeneous materials that, depending on feedstock and HTT, may be suitable for soil application by contributing to the nutrient status and adding recalcitrant C to the soil but also potentially pose ecotoxicological challenges.
生物炭作为土壤改良剂和土壤中碳封存的应用日益广泛。人们广泛研究了原料差异和热解温度对生物炭特性的影响。然而，对于热解后仍残留在生物炭中的潜在有毒化合物的形成过程，我们的了解还很有限。我们研究了三种原料（小麦秸秆、杨树木材和云杉木材）制成的生物炭，它们分别在 400、460 和 525°C 下缓慢热解 5 小时（秸秆）和 10 小时（木屑）。我们对生物炭的 pH 值、电导率、元素组成（干燃烧和 X 射线荧光法）、比表面积（氮气吸附法）、水可提取的主要元素和阳离子交换能力（CEC）进行了表征。此外，我们还进行了差示扫描量热法（DSC）、傅里叶变换红外光谱（FTIR）和 X 射线衍射分析，以获取生物炭分子特征和矿物组成方面的信息。我们研究了生物炭中痕量金属含量、总多环芳烃（PAH）含量和 PAH 组成。在秸秆衍生的生物炭中，盐（4.92 mS cm）和灰分（12.7%）含量最高。处理温度最高（HTT）为 525°C 的生物炭的 H/C 比值为 0.46 至 0.40。比表面积较低，但随 HTT 的增加而增加（1.8-56 m g），而 CEC 随 HTT 的增加而降低（162-52 mmol kg）。DSC 和 FTIR 的结果表明，在热解过程中，不稳定的脂肪族化合物会损失，而更难降解的芳香族成分会形成。X 射线衍射图谱表明，随着 HTT 的增加，生物炭的矿物结构会发生重组。水可提取的主要和痕量元素的含量随原料组成而有很大差异，痕量元素也受 HTT 的影响。总多环芳烃（EPA16 种多环芳烃之和）含量变化很大，最高可达 33.7mg/kg；无论原料类型如何，多环芳烃的组成都表现出随着 HTT 的增加，萘的优势逐渐增加。研究结果表明，生物炭是高度不均匀的材料，根据原料和 HTT 的不同，它们可能适合通过增加土壤的养分状况和添加难降解的 C 来应用于土壤，但也可能带来生态毒理学挑战。
