典型稀土对厌氧发酵过程微生物的作用机制及其释放规律研究

In recent years, the extensive mining of ionic rare earth mines has posed a serious threat to the surrounding soil, aquatic environment and human health. Currently, the remediation of rare earth tailings is mainly based on phytoremediation in view of the infertile soil which contains high percentages of sand and rare earth elements. A large amount of biomass rich in rare earth metals will be produced during the phytoremediation process, and anaerobic fermentation technology can transform the generated biomass into biogas, which is a very promising way to recovery energy from plant residues of phytoremediation. However, some rare earth elements may be released into the anaerobic fermentation system, which may affect the stability of the fermentation system. So far, the inhibition/promotion relationship and its functional mechanism of rare earth elements on anaerobic fermentation process are still missing. Therefore, this project intends to study the inhibition/promotion effect of rare earth elements on anaerobic fermentation and microbial communities. Besides, the mechanism of rare earth elements on anaerobic fermentation process will be studied in terms of metabolic process, the change of cell structure and the activity of key enzymes. Furthermore, the releasing and accumulation law of rare earth elements during the anaerobic fermentation of Dicranopteris dichotomarare will also be investigated. The outputs of the proposed research would improve our understanding on the convert of phytoremediation plant residues of rare earth tailings into biogas.

近年来，离子型稀土矿的粗放开采对周边土壤、水生态环境及居民的健康带来严重威胁。鉴于稀土尾矿区土壤砂化贫瘠、稀土元素含量高的双重特征，对稀土尾矿的修复目前以植物修复为主。利用超富集植物修复稀土尾矿是一个长期的过程，期间会产生出大量富含稀土金属的生物质。厌氧发酵技术能够将生物质转化为生物燃气，是非常具有潜力的修复植物资源化技术。但是，富含稀土元素的生物质原料在厌氧发酵过程中，会释放稀土元素进入厌氧发酵系统，可能会影响发酵系统的稳定性。然而，截至目前，很少有研究报道稀土元素对厌氧发酵过程的抑/促关系及其机制。因此，本项目拟研究稀土元素对厌氧发酵产气及微生物群落的抑/促效应，从微生物的代谢过程、细胞结构和关键酶活性变化等角度，解析稀土元素对厌氧发酵过程微生物的作用机理，并对富稀土芒萁厌氧发酵过程中稀土元素的释放累积规律进行研究，以期为稀土尾矿修复植物的甲烷化利用奠定理论基础。

随着我国稀土资源的不断开采，待修复的稀土尾矿区面积数量增加。稀土尾矿的主要问题是土壤沙化和有机质缺失，因此利用植物进行生态修复是较好的方式。修复过程中富稀土植物残体可以进行厌氧资源化利用，但稀土元素进入厌氧发酵系统可能会对厌氧发酵过程和发酵剩余物利用产生影响。本项目研究发现在稀土超富集植物芒萁厌氧发酵过程中，镧离子对产甲烷过程具有低促高抑的效应，但相比促进作用，抑制作用更加明显。微生物群落分析发现，高浓度La(Ⅲ)条件下主要优势细菌中缺少能够水解纤维素的梭菌属微生物（Clostridium III、Clostridium XlVa等），从而影响纤维素产甲烷过程。在此基础上，研究了木质纤维素水解产酸特性和镧离子对模型底物产酸/产甲烷过程微生物群落影响。纤维素对碱性发酵较敏感，碱性发酵时水解产酸能力下降；木聚糖pH适应范围较广，碱性发酵时具有高效的优势微生物（Amphibacillus）进行水解产酸； La(Ⅲ)对木质纤维素厌氧发酵的抑制主要作用在纤维素水解产酸过程，木聚糖水解抑制相对较弱，而对葡萄糖产甲烷过程和产甲烷菌群则无明显影响。为考察发酵剩余物安全性，研究了超富集植物芒萁和能源植物皇竹草在厌氧发酵过程中稀土元素的迁移规律。稀酸和水热预处理稀土溶出较高，而碱预处理过程稀土溶出较少；发酵过程中稀土金属主要残留在固体的沼渣中，溶出至沼液中的稀土金属比例较低，沼液经评估后可作为沼肥施用。项目部分成果数据已指导江西定南稀土尾矿区生态能源农场示范工程建设，对于推动稀土尾矿修复具有积极意义。