以活性污泥等生物技术为主的传统城市污水处理处置技术，难以满足可持续发展、生态文明的需要，在21世纪的今天，污水处理行业面临技术变革。传统工艺虽然可以有效的实现污染物控制这一目标，但在资源回收等方面存在一定的短板。因此，本论文针对低浓度城市污水中的氮元素，展开以流动电极电容去离子（Flow electrode capacitive deionization，FCDI）技术为主的氮素资源化回收相关研究，从理念和实践上进行探索与创新，为城市污水资源化处理提供新的思路。针对流动电极与传统固定电极性质差异的主要原因，建立静态/半流动/流动静态模式下的FCDI反应器，通过半流动模式在流动电极与静态电极之间建立联系，探究电极流动性对反应器性能的影响。实验表明电极液更新体积越大，电极吸附能力恢复量越大，且体系能耗越低；采用流动模式后，反应器吸附速率约提升3倍，能耗降低到4.5±0.2 J/mg Na水平，从宏观上解释了电极流动性的重要作用，为流动电极FCDI技术氨氮回收奠定了理论基础。考虑到城市污水的水质特征，采用FCDI反应器进行氨氮去除，基础运行条件的优化十分重要。实验发现1.2 V的工作电压、两溶液相同且较大的流速、1.5 wt%的导电介质含量，均能提升反应器性能，且pH值为4时，反应器性能最优，在实际操作中，中性条件下也可取得较理想的处理效果；对于初始浓度为20 mg N/L的低浓度溶液，富集液中的氨氮浓度可达到322.06 mg N/L。进一步考察流动电极中浓差对氨氮回收性能的影响。初始富集倍数越大，反应器性能越差，当初始富集倍数小于10时，反应可维持在高效区间；当富集倍数大于100时，吸附过程几乎不再进行；进一步分析离子跨膜迁移机制，说明在较高的富集倍数下，由高浓度差引起的离子反向跨膜迁移，是导致反应器性能恶化、氨氮吸附受阻的主要原因。最后，为实现氨氮同步去除与回收利用，构建一体化FCDI反应器，并引入具有离子选择性的功能性膜材料。一体化FCDI反应器实验证明，选择性膜的使用，能将氨氮选择性系数提升2倍左右，产物硫酸铵纯度可从50%提升至85%以上水平。此外，本文所搭建的一体化FCDI反应器，形成类似膜堆的构型，可实现处理规模的扩大，为反应器处理规模的扩大提供了一条可行的技术路线。
The traditional urban sewage treatment technology based on activated sludge and other biotechnology is difficult to meet the pursuit of sustainable development and ecological civilization. In the 21st century, the municipal wastewater treatment industry is facing technological changes. Although the traditional process can effectively achieve the goal of pollutant control, there are certain shortcomings in resource recovery and other aspects. Therefore, this paper conducts research on nitrogen recovery from low-strength municipal wastewater by flow electrode capacitive deionization (FCDI) technology. The exploration and innovation provide technical support and a theoretical basis for municipal wastewater treatment.To reveal the intrinsic differences between static and flow electrode capacitive deionization, static/semi-flow/flow mode FCDI reactor was established. Semi-flow mode was a connection between the static and the flow mode. A higher volume of fresh carbon slurry accounted for higher adsorption capacity as well as lower energy consumption. The timely regeneration of the FCDI electrode slurry enhanced the salt adsorption rate (3-fold) and reduced the specific energy consumption (4.5 ± 0.2 J/mg) for the deionization condition of this study. Therefore, this research provides insights into the fundamental understanding of the FCDI technology.Considering the characteristic of municipal wastewater, the basic operating conditions were optimized. Results indicated that the working voltage of 1.2 V, the same and larger flow rate, and the content of the conductive additive of 1.5 wt% can improve the performance for ammonia removal. The experiment also found that a pH value of 4 is optimal, but in actual operation, neutral conditions are also fine. When the initial concentration was 20 mg N/L, the finial ammonia concentration in the brine can achieve 322.06 mg N/L. Ather that, the effect of concentration gradients was investigated. Results indicated that compared to concentration factors (CFs), the effect of AC contents on the deionization process was almost neglectable. To achieve efficient ammonia removal and enrichment, initial CF below 10 and refreshment of flow-electrode when CF exceeded 100 were recommended. The poor system performance under high initial CF was caused by the concentration polarization as well as the ion back diffusion. To achieve ammonia recovery and utilization, a stacked-FCDI cell was constructed. What’s more, M-CEM, a monovalent ion selective membrane was introduced to removal ammonia selectively. When M-CEM was employed, the selectivity towards ammonia increased by almost 2 times, and the purity of the product (ammonium sulfate) increased from 50% to more than 85%. This study indicated that the novel design and efficient operation of the stacked FCDI reactor is an alternative way for ammonia recovery and generation as value-added products, as well as a possible approach to scaling up.
