随着全球能源危机加剧和碳中和任务的提出，“污水再生处理-资源化”的模式成为未来城市污水处理的新愿景。传统的污水脱氮工艺以破坏性脱氮为特征，难以有效实现氮资源的回收。在众多新兴的氮回收技术中，电容去离子（Capacitive Deionization，CDI）技术具有突出的节能优势，但对氨氮的去除性能不佳。而流动电极电容去离子（Flow electrode capacitive deionization，FCDI）作为CDI技术的新兴衍生技术，基于可流动再生的电极液，有效提升了离子去除性能。本论文以城市污水中的氨氮回收为目标，以FCDI体系为基础开展了氨氮的强化去除研究，并引入普鲁士蓝类似物材料作为电极材料，突破了FCDI技术缺乏选择性的瓶颈，为城市污水的氮回收提供了技术支持。本研究取得的主要成果如下：首先，优化FCDI体系的运行参数与模式，以获得最适合氨氮去除的FCDI运行条件。通过提高操作电压、进水流速和初始进水浓度，FCDI的氨氮去除率可提高至82.5%，吸附量达6.0 mg/g，氨氮去除性能较传统的CDI/MCDI体系有了显著提升；但共存离子Ca2+、Mg2+对氨具有明显的竞争吸附，当进水中NH4+、Ca2+、Mg2+的浓度分别为20 mg/L、100 mg/L、100 mg/L时，FCDI的氨氮去除率下降至48.8%，体系的耗电量大幅增加，因此，FCDI对氨的去除选择性需要进一步提高。为提高FCDI对氨的选择性去除，进一步合成新的CuHCF@3DNC复合电极材料。引入对氨氮具有选择性去除能力的CuHCF材料，并将其嵌入至3DNC的骨架中合成CuHCF@3DNC，能够克服低导电性、结构不稳定的缺陷，更充分地发挥化学性能；CuHCF@3DNC的导电性和比电容均得到了提升，传荷电阻降至0.97 Ω，比电容值提高了85.4%；同时对不同的阳离子也表现出不同的氧化还原特征，具备选择性吸附的潜力。最后，以CuHCF@3DNC为流动电极，构建非对称的复合电极FCDI体系，显著提高了FCDI体系的离子去除能力并强化了对氨氮的去除。复合电极FCDI体系表现出对进水中NH4+优先的去除能力，并对NH4+的去除具有最高的选择性，在应对实际城市污水的氨氮去除时，复合电极FCDI体系可将出水中NH4+浓度降至5 mg/L以下，实现污水的达标排放和高纯度氨氮的富集。
With the depletion of energy and challenges toward carbon neutrality, the concept of "wastewater treatment and regeneration-resource recovery" has become a new vision for future municipal wastewater treatment. During traditional wastewater treatment prosess, ammonia is converted to gaseous nitrogen, which has no contribution to nitrogen recovery. Among many emerging nitrogen recovery technologies, capacitive deionization (CDI) technology has advantage in energy-saving, while there are deficiencies in the removal performance of ammonia nitrogen. The flow-electrode capacitive deionization (FCDI) technology effectively improves the ion removal performance, based on the flow electrode that can be continuously regenerated. Aiming at the recovery of ammonia from municipal wastewater, this paper carried out research on ammonia removal based on FCDI system. In addition, the introduction of prussian blue analog materials as electrode broke through the bottleneck of lack of ammonia selectivity in FCDI system. This research provides new inspiration and technical support for the conceptual transformation of municipal wastewater treatment. The main results of this research are as follows:First, the operating conditions of FCDI were optimized for better removal performance of ammonia. By increasing the applied voltage, the influent flow rate and the initial ammonia concentration, the removal rate of ammonia can be increased to 82.5%, with the adsorption capacity reach to 6.0 mg/g. Compared with the traditional CDI/MCDI system, the ammonia removal performance of FCDI has been significantly improved. However, the coexisting ions, Ca2+ and Mg2+, have a significant adsorption competition with ammonia, leading to lower removal rate of ammonia (48.8%) and much higher energy consumption of FCDI system. Therefore, the removal selectivity toward ammonia of FCDI needs to be further improved.To improve FCDI’s removal selectivity toward ammonia, a new CuHCF@3DNC electrode material was synthesized. The CuHCF material which can selectively removal ammonia was introduced and embedded in the carbon framework of 3DNC. This enables CuHCF to overcome the defects of low conductivity and structural instability, contributing to exploiting the chemical properties of CuHCF. The conductivity and specific capacitance of CuHCF@3DNC have been improved, the charge transfer resistance is reduced to 0.97 Ω, and the specific capacitance value is increased by 85.4%. Besides, CuHCF@3DNC showed different redox reaction characteristics for different cations, obtaining the potential for selective removal of ammonia.Finally, an asymmetric composite FCDI system was constructed with CuHCF@3DNC as the flow electrode, which significantly improved the ion removal capacity of the FCDI system and enhanced the removal of ammonia by the FCDI system. The composite electrode FCDI system shows the preferential removal ability of NH4+. During the continuous treatment of actual municipal wastewater by composite FCDI system, the water quality of effluent can meet the Standard A of Class 1 for WWTPs discharge in China. In addition, the enrichment of ammonia by CuHCF@3DNC electrode provides significant opportunity for the recovery of ammonia.
