土壤环境污泥炭老化过程及其重金属释放的潜在生态风险评价

A new environmental issue concerning of municipal residual sludge disposal has been rising owing to a large growing number of municipal wastewater treatment plants operation with rapid urbanization in the past decade. Pyrolysis of sewage sludge seems to be a promising strategy in terms of carbon fixation, plant nutrients reuse, bio-energy recycling and heavy metals immobilization as well. It has been well documented that the heavy metals in sludge may be remained and concentrated in the sludge biochar after pyrolysis. Then there have been many studies focusing on the immobilization of heavy metals in the process of the pyrolysis. However, few reports are available concerning the stability of carbon during the mineralization of biochar after being loaded to the soil. Hence, little has been known related to the coupling variations of the stabilization of heavy metals in municipal sewage sludge biochar and the stability of the biochar when it is ageing in the soil. So the release pattern of heavy metals in the biochar and its relationship to biochar stability in soil and the related soil-water environmental influence factors cannot be clearly elucidated till now. Therefore, there is an urgent need to study on the relevance of the heavy metals release of municipal sewage sludge biochar ageing in soil and to soil-water effects. It is hoped that through the study, (1) the relationship between the biochar carbon mineralization rate and the heavy metals release behavior could be built, (2) the soil-water environmental regulation mechanisms on biochar stability and heavy metals stabilization might be uncovered, (3) the potential ecological effects on soil-water-plant environmental system would be evaluated as sewage sludge biochar loaded into soil. We hope that the outcomes of this project may break out the bottleneck in safe disposal/ use of municipal sewage sludge biochar caused by the heavy metals issue.

市政污水厂运行伴随产生的大量的剩余污泥，已经成为一个新的环境问题和挑战。污泥炭化能够实现碳的固定、植物营养成分的回收、生物质能的提取和重金属的钝化，是很有发展前景的一种污泥能源化资源化途径。炭化后污泥中的重金属绝大部分转移到了污泥炭中。目前关于热解对污泥炭中重金属的钝化研究报道较多，而对输入土壤的污泥炭的稳定性研究鲜见报道，致使污泥炭输入土壤老化过程中炭的稳定性与炭中重金属的稳定性关系研究相对不足，无法明确污泥炭土壤环境老化过程中重金属的释放规律、与炭稳定性关系及影响机制。所以，本项目拟开展“土壤环境污泥炭老化过程及其重金属释放的潜在生态风险评价”，以期建立土壤环境污泥炭老化与重金属释放之间的关系，揭示老化过程污泥炭稳定性与重金属稳定性的土水环境调控机制，评估污泥炭输入土壤对土水植物系统潜在环境风险。希望通过本项目研究为市政污泥炭的资源化安全利用提供理论指导。

随着我国经济社会的快速发展，城镇化进程不断加快，每年污水处理量不断上升，直接造成市政污泥产生量的逐年增加。大量的剩余污泥已经成为一个新的环境问题和挑战。由于污泥中含有氮磷钾等营养元素，可以作为一种良好的肥源，然而对环境有害的重金属在污水处理过程中亦大都转移到了污泥中。若污泥直接进入土壤环境，污泥中的重金属在土壤中累积将会对土-水-植物等生态系统造成潜在的风险。. 污泥热解炭化技术是很有发展前景的一种污泥能源化资源化处理路径。炭化后污泥中的重金属绝大部分转移到了污泥炭中。大量研究表明，热解能有效固定污泥中的重金属，但对输入土壤的污泥炭的稳定性研究鲜见报道，致使污泥炭输入土壤老化过程中炭的稳定性与炭中重金属的稳定性关系研究相对不足，无法明确污泥炭土壤环境老化过程中重金属的释放规律、与炭稳定性关系及影响机制。开展“土壤环境污泥炭老化过程及其重金属释放的潜在生态风险评价”研究，使污泥炭循环利用的潜在生态风险降到最低，是关系污泥炭资源化安全利用的核心问题，对推动污泥热解处理技术工程化应用，实现污泥减量化、稳定化、无害化和资源化处理具有重要意义。. 本项目通过对土壤环境污泥炭碳稳定性与重金属稳定性关系研究和污泥炭老化过程的土-水-植物系统潜在生态风险评价，基本明确了污泥炭土壤环境老化降解的动态变化及环境影响及污泥炭土壤环境老化过程中重金属的形态转化过程及环境影响，初步建立了污泥炭土壤环境老化炭稳定性与重金属稳定性之间的关系，揭示了污泥炭老化土壤理化、生物学性状的动态响应变化，评估了市政污泥炭老化的环境风险，为市政污泥的资源化安全利用提供了理论指导。