生物炭内源污染物的产生及其生态风险研究

Biochars have many advantages including soil remediation, carbon sequestration and greenhouse gas control, and have attracted a great deal of research attention. However, some researchers also observed possible negative impacts of biochars from the aspects of soil amendments, microbiologic population, crop yield, sequestering carbon and mitigation agent of the greenhouse effect. In addition, biochars might contain some chemicals (such as heavy metals, polycyclic aromatic hydrocarbons (PAHs), crystalline silica, dioxin, phenolic compounds and phytotoxin), which have been proven to be toxic. From this point of view, we need understand generation mechanisms and ecological risks of endogenous contaminants in biochars. The negative impacts of these chemicals in biochars need to be comprehensively and carefully assessed before the massive product and application of biochars. Our previous studies indicated that environmentally persistent free radicals were generated in biochars, and the intensities of these free radicals were dependent on the raw material and preparation method (different temperature and holding time). After washed by deionized water, the generation of hydroxyl radicals in water was decreased, and the toxic impacts were partially inhibited. It is thus possible that the toxic chemicals could be removed with proper method and thus ensure the safe application of biochars. In this proposed study, biochars will be prepared using different types of raw materials (rice straws, corn stalks, tobacco stalks, pine sawdust, activated sludge, biosolids in Erhai lake, cellulose, hemi-cellulose (subbed by xylan) and lignin (alkali) ) and methods (200 ℃, 350 ℃, 500 ℃, 650 ℃ and 800 ℃ holding for 1 hour, 2 hours and 4 hours in furnace). The endogenous contaminants in biochars will be analyzed using different chemical extraction reagents (deionized water, acid, alkali and organic reagents) to identify their speciations. We will then study the generation mechanisms of endogenous contaminants (type, form and concentration) being generated from raw materials as affected by preparation method. This work is specifically designed to study the micro and macro environmental effects of biochars. But laboratory and field research will be conducted to investigate the impacts of endogenous chemicals to typical crop, soil microorganism and aquatic organism. The chemical structure change of the biomass in relation to endogenous chemical generation will be highlighted. Eventually, we will propose effective solutions to control or remove these potentially toxic chemicals. This study will establish a fundamental database for the safe application of biochars, and the results will provide essential theoretical support for the sustainable use and development of biochars technique.

生物炭具有多方面的应用潜力，一些研究者检测到生物炭中多种化学物质，表现了对其可能的负面效应的担忧。但是，还没有相关研究对生物炭内源污染物的产生类型和机制进行系统的探讨，成为生物炭大规模应用的障碍。本研究拟对生物炭内源污染物的产生及其生态风险进行全面的考察，采用不同类型的原材料和方法制备生物炭，结合水、酸、碱和有机试剂浸提生物炭内源污染物，研究原材料、制备方法对生物炭内源污染物（类型、形态和浓度）产生的影响；重点探讨生物炭烧制过程中的化学结构如何变化，内源有机化合物如何产生，内源金属（特别是重金属）形态如何变化；通过讨论生物炭浸提前后其内源污染物在实验室和田间对典型农作物、土壤微生物和水生生物等产生的微观和宏观的环境风险，理解生物炭内源污染物产生可能环境风险的核心机制，进而提出行之有效的解决方案。本研究是生物炭大规模生产使用的必经之路，将为生物炭技术的可持续发展提供保障。