改性碳纳米材料钝化堆肥重金属过程吸附解吸动力机制与钝化材料环境释放效应-以草坪用地为例

Municipal solid waste (MSW) and sewage sludge (SS) compost contain valuable plant nutrients and organic matter that can improve soil fertility and crop yield. Land application of MSW and SS compost is an effective waste disposal technique. However, However, MSW and SS compost often contains potentially toxic elements that can cause soil contamination, phytotoxicity and undesirable residues in plant and animal products. In order to avoid food chain, MSW and sewage sludge compost has often been utilized in green land (for example lawn), leading to heavy metal pollution in urban soil. Additionally, carbon-based nano-materials have great specific surface area and the structure of rich pores. After modification, carbon-based nano-materials have a lot of oxygen functional groups in surface with a strong adsorption of heavy metals. Therefore, by adding two modified carbon-based nano-materials- graphene and carbon black in compost and planting turfgrass in compost-amended soil, the objective of this research is going to investigate the kinetic mechanism of heavy metal adsorption and the effect of environmental release. Microscopic analytical technologies and culture experiments are applied to investigate compost heavy metal migration in soil-plant system, the kinetic mechanism of adsorption/desorption of heavy metals from available to residual state, the responses of soil properties, soil enzymes and ecological indicators of soil taxa to carbon-based nano-materials. The results of this study will provide scientific basis for safe application of compost products as well as heavy metal remediation.

垃圾堆肥与污泥堆肥含有大量的有机质和植物营养元素，土地利用是实现其资源化利用的有效方式。但堆肥中还含有重金属，为了避开食物链，两种堆肥被广泛用于绿化用地（如草坪）。堆肥的土地利用，成为加剧土壤重金属污染的重要因素之一。另外，碳纳米材料具有极大的比表面积和丰富的孔结构，经改性处理后表面含有大量的含氧功能团，对重金属具有较强的吸附性，在重金属污染治理方面应用前景广阔。鉴于此，将两种纳米碳材料-石墨烯和纳米碳黑改性后添加到堆肥中，通过草坪建植，研究改性纳米碳材料对堆肥重金属的吸附动力学机制及其环境释放效应，主要包括：堆肥重金属在土壤-植物体系迁移的空间变异行为；堆肥重金属有效态与残渣态转化的吸附解吸平衡动力学机制；土壤性质、土壤酶、土壤生态指示生物类群响应特征，以达到认识改性纳米碳材料钝化堆肥重金属的机理及其环境释放效应的目的。研究最终为各类含重金属堆肥的安全利用及重金属钝化修复提供科学依据。

堆肥中重金属是限制其应用的主要因素之一，要解决堆肥安全利用的问题，就需要对其进行修复。石墨烯与纳米碳黑经改性后会增加其亲水性，将对堆肥重金属的钝化起到有效的作用。以氧化石墨烯、石墨烯、碳纳米管及各类改性纳米碳黑对堆肥重金属进行有效钝化，才能使堆肥安全应用于草坪基质。鉴于此，课题重点展开了碳纳米材料钝化堆肥重金属在草坪建植体系土壤—植物中迁移定位特征；钝化堆肥重金属有效态与残渣态的吸附解吸动力学机制及碳纳米材料等环境释放对草坪建植体系土壤系统的生态效应等研究。. 取得的主要研究进展与重要结果为：碳纳米材料对Pb、Cr、Cu的固定效果较好，其中对Cu的固定效果最佳，释放率仅是对照的26.79~55.36%。在单离子体系中氧化石墨烯对Cd和Pb、碳纳米管对Cu的吸附容量大；Cd、Pb、Cu最大吸附量分别是299.34、250.77、414.61mg•g-1。添加碳纳米材料会明显降低草坪基质中可培养细菌总数和多样性，氧化石墨烯处理下降较多；细菌优势种由假黄单胞菌属变为芽孢杆菌属。碳纳米材料对真菌菌落的组成也会产生影响，如碳纳米材料处理木霉属所占比例更高，成为优势种；而放线菌数量显著降低。基质添加碳纳米材料能显著增加了线虫个体数量，使群落优势属发生变化。添加碳纳米材料食细菌性线虫和植物寄生性线虫的数量增多，尤以氧化石墨烯增加为最多，但捕食-杂食性土壤线虫在添加碳纳米材料后会消失了，使线虫类群组成完整性下降。碳纳米材料显著降低了线虫的丰富度，以氧化石墨烯处理为最低。添加石墨烯、氧化石墨烯和碳纳米管后，基质小型节肢动物个体数量增多，尤其以氧化石墨烯和碳纳米管处理效果更为明显。氧化石墨烯显著提高了捕食性、植食性和食真菌营养类群的个体数量。添加碳纳米材料后，蚯蚓体内SOD、POD和CAT酶活性除个别处理外，均呈降低趋势。研究结论不仅对突破堆肥利用的限制瓶颈做了积极有益的探索，也为各类含重金属类堆肥安全利用、重金属钝化修复、碳纳米材料环境释放等理论的认识具有重要意义。