土壤中生物炭的运动迁移机理及其模型研究

Land application of biochar (charcoal created by pyrolysis of biomass) is a promising practice to sequester atmospheric CO2, improve soil fertility, reduce environmental pollution, and influence the environmental behaviors of different pollutants in soils, etc. However, prior to the widespread implementation of this carbon sequestration technique, the environmental benefits and risks associated with biochar field application must be well understood. Three critical questions are proposed in the project: 1) what soil characters influence the movement of biochar particles in soils following land application, 2) how the biochar characters influence the transport of biochar particles in soils, 3)what retention mechanisms control the biochar transport in soils, and how to predict biochar transport in soils. This project intends to address the first question by investigating the effect of soil-water chemistry in terms of pH, ionic strength, etc. The second question will be solved by studying the effect of biochar properties, such as surface charge, particle size, etc. For the third question, the retention mechanisms will be analyzed firstly by using in-situ observation, then optimize the parameters of classic colloid transport models and establish the suitable mathematical models to simulate biochar transport mechanisms. The findings of this project will improve our understanding of the benefits and disadvantages associated with this novel green technique, and also will provide technical support for in-situ remediation of contaminated soil and groundwater.

目前，生物炭已被公认为是固定大气中二氧化碳的一个有效方法，覆盖农田后可增加土壤肥力、降低农用化学品对环境的危害、影响土壤中各类污染物的环境行为等。但是关于生物炭农田施肥后在土壤环境中运动迁移规律研究很少。因此本项目提出了三个关键科学问题：1）土壤哪些性质会影响生物炭在土壤介质中的运动迁移过程？2）生物炭本身的性质对运动迁移过程有什么影响？3）如何预测生物炭的沉积释放规律？针对这些问题，本项目提出以下三方面的研究内容：1）研究pH、离子强度等土壤性质对生物炭运动迁移的影响；2）研究生物炭颗粒尺寸、表面电荷等性质对生物炭运动迁移的影响；3）通过原位观察进行机理分析，根据经典胶体运动迁移和沉积释放模型,优化模型参数，建立适合描述生物炭运动迁移机理的数值模型。本项目研究成果有助于人们更好地了解这项新型环保技术利弊，同时为土壤-地下水环境系统中污染物的原位修复提供技术支撑。

生物炭作为一类新型环境功能材料，具有比表面积大、孔隙率高、表面活性基团丰富等特性，在治理农业面源污染、改善气候条件、土壤性能改良等方面备受关注，成为环境科学等学科研究的前沿热点。土壤性质和生物炭本身性质是研究生物炭在土壤环境中运动迁移规律关键影响因素。本项目以小麦秸秆和玉米秸秆为原料，在500℃厌氧条件下热解制取生物炭，研究在不同的pH、离子强度以及不同价态的盐离子条件下生物炭颗粒的沉积释放过程。在此基础上，进一步研究不同的生物炭添加量以及不同pH、离子强度的条件下，生物炭对多孔介质中镉滞留的影响。并通过对流弥散方程拟合数据结果，从理论上模拟生物炭协同镉在饱和多孔介质中的迁移过程，为我国农业生产和地下水安全战略，提供一定的技术和理论支持。