生物炭的环境老化及其对污染物行为的影响

The application of biochars in the environment is beneficial in different areas, including improving soil fertility and sequestering carbon. Importantly, biochars are proven to be strong adsorbates to both heavy metals and organic pollutants, and thus could effectively retain these pollutants. The introduction of biochars in soil system could decrease the leaching as well as plant uptake of pollutants. However, after being applied in the environment, biochars may be chemically, physically or biologically altered. Importantly, biochars could interact with dissolved organic matter (DOM) or transitional metals. These processes will significantly change biochar surface properties including oxygen-containing functional groups, particular size and pore size distribution, which consequently alters the environmental functions of biochars. Therefore, the initial properties of biochar cannot be used to forecast its environmental impacts, including its effects on pollutant fate and risk. Many uncertainties exist for the applications of biochar in remediation of contaminated soils and groundwater. The property change of biochars during their aging in the environment should be carefully examined and incorporated in the assessment of environmental significance in biochar life span. This work is thus specifically designed to study the effect of biochar aging on biochar properties and pollutant behavior. Biochars were made from a number of parent biomass types and under a range of well-defined combustion conditions. Short-term intensified aging will be simulated in lab. The processes include freeze-thaw cycling, chemical oxidation, and micro-biological degradation simulating physical, chemical, and biological processes. Biochar interactions with environmental components will also result in the change of their properties as well as their environmental functions. We hypothesized that the coating of DOM on biochars resulted in the decreased biochar surface sorption sites and thus decrease sorption of pollutants. In addition, DOM may act as electron shuttle and accelerate biochar aging. The interaction between biochars and transitional metals may enable the formation of biochar-metal complexes, which may increase the stability of biochars. Biochar properties will be carefully characterized and compared before and after aging. Traditional batch sorption/desorption experiment will be used to study the interactions between various pollutants and biochars. The behavior of the adsorbed pollutants in biochar during the aging will be assessed. The primary investigator's previous work was focused on the environmental functions of biochars. All the instruments needed in this study are conveniently available. This study will establish a fundamental database for environmental risk assessment of biochar aging and provide further information to apply biochar as a potential adsorbent in the environment.

生物炭对污染物的强烈吸附是其重要的环境效应之一，但是生物炭进入环境后，必然在物理、化学、生物过程中被老化，同时，在与溶解有机质（DOM）和过渡金属元素等的相互作用中，生物炭的表面性质会发生显著改变。因此，生物炭的环境效应及其对污染物行为和风险的影响不能用生物炭的初始性质进行预测，对生物炭吸附控制污染效用和风险的理解客观上需要考虑其在环境条件下的性质变化。本研究拟以物理、化学和微生物方法模拟生物炭老化过程，探究各种环境过程对生物炭老化的影响机制，系统描述生物炭在各个过程中老化后的性质变化，重点阐释过渡金属元素与生物炭相互作用形式及其对生物炭老化的作用机制，DOM在生物炭表面覆盖及其电子穿梭能力对生物炭老化的影响；通过吸附/解吸实验研究生物炭老化对污染物环境行为的影响，并对被吸附污染物在生物炭老化过程的二次污染风险作出评估，为生物炭的环境友好应用提供理论基础。

本项目以不同生物质来源制备的生物炭为研究对象，模拟生物炭在环境中的老化，针对生物炭老化过程中表面化学性质的变化、影响生物炭老化的环境因子及老化机理等诸多问题展开研究，深入探讨老化对生物炭与污染物之间相互作用的影响，从而理解生物炭施用生命周期内的动态风险问题。. 通过冻融循环实验、NaClO氧化、过氧化氢氧化、HCI和HCI-HF酸化等物理化学老化方法模拟了不同生物质来源、不同温度制备的生物炭在自然环境中的老化过程以及影响老化的环境因子，利用元素分析、比表面积分析及傅里叶红外光谱分析等表征分析方法研究老化过程对不同稳定性生物炭的元素组成、表面形态及表面基团等的影响，理解生物炭性质和其老化过程之间的关系，从而系统认识生物炭的地球化学过程，探讨生物炭老化的环境效应。. 以萘、双酚A、磺胺甲噁唑和菲为代表性污染物，分析这几种污染物与不同材料及不同烧制温度得到的生物炭的吸附行为，比较氧化处理前后生物炭与这污染物之间相互作用的差异，进而针对生物炭氧化过程对被吸附污染物的风险作出评估。. 通过应用电子顺磁共振波谱仪和激光显微拉曼光谱仪分别测定不同裂解温度和酸处理的生物炭样品的自由基信号和化学键振动特征，以探究不同裂解温度和酸处理老化对生物炭上自由基的影响机制。结果表明，低氧条件下的裂解过程会伴随着生物炭碳层结构的缺陷形成以及C-C键的断裂，从而形成以氧为中心的自由基；另外，酸洗后自由基信号的增加率远大于碳含量的增加率，这可能归因于酸洗会使有机-无机复合体的C-O-C和COOH上的C-O键的断裂而生成新的自由基。. 以纤维素和木质素为原料于不同温度下制备生物炭，结合常规理化性质表征比较分析生物炭经NaClO氧化前后BPCAs信息的相关变化。结果表明，NaClO氧化导致生物炭1.8%~79.3%的BPCAs质量损失但各单体BPCA的百分含量并没有明显变化，证明NaClO氧化不会改变生物炭BPCAs的分布特征。B5CA/B6CA和B6CA/B4CAs比值作为辨析环境炭黑来源的特征值，氧化前后均指示相同的生物炭来源，表明BPCAs方法识别环境中生物炭来源具有高可靠性。