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氮是蛋白质、酶、核酸、氨氧化细菌、硝化细菌和反硝化细菌所必须的[1]。然而过量的氨氮会损害水生环境,导致水体富营养化和溶解氧(dissolved oxygen,DO)下降,最终导致鱼类和其它水生生物死亡[2-3]。MFC现在被认为是一种很有前景的技术,与其它好氧技术和厌氧技术相比,MFC具有污泥产量较低以及去除污染物同时进行能源回收等优点[4]。近些年,通过将MFC与传统的脱氮工艺相结合,从而实现污水同步脱氮产电引起人们的广泛关注[5-7]。王佳琪等[8]探讨了碳氮比对单室MFC产电及污染物去除效果的影响,然而当碳氮比为7时,MFC的脱氮功能受到严重的抑制。与单室MFC相比,双室MFC中阴极室和阳极室发生的反应相对独立,相互干扰较小。因此当MFC与传统脱氮工艺相结合时更多采用的是双室MFC,可以依据功能的不同进行灵活的配置。
生物电营养反硝化是近年来一种新兴技术,其可以用电而不是有机物作为电子供体[9-10]。2007年CLAUWAERT等[11]以乙酸盐为阳极底物,不含有机物的NO3−污水为阴极底物构建双室MFC实现阴极完全脱氮。DING等[12]探究了阴极不同接种污泥对电营养反硝化的影响,优化了接种污泥选取策略。虽然电营养反硝化MFC中NO3−/NO2−可以从阴极中获得电子,然而这些电子来自于阳极上的碳氧化。从来源上看,碳仍然是反硝化过程的主要电子供体来源。因此,电营养反硝化MFC的阳极底物通常为含氨废水而阴极底物为单一的硝酸盐废水,而实际污水往往含有有机物、NH4+-N、NO3−-N、NO2−-N等多种污染物。VIRDIS等[13]在废水中应用完全脱氮的MFC,使用1个独立的硝化反应器与1个双室MFC结合。含乙酸钠和氨氮的合成废水被连续送入MFC的阳极室,然后阳极室出水流入外部硝化反应器进行硝化反应,最后进入MFC的阴极室利用阳极传递的电子进行反硝化。然而,采用外部硝化反应器的系统设计额外增加了建设成本。VIRDIS等[14]通过控制阴极室中的曝气强度,克服了这一弱点,将同步硝化反硝化与MFC进行结合。ZHANG等[15]通过构建阴极混合生物膜MFC,在碳源充足的盛宴阶段实现同步硝化反硝化,但在碳源缺乏的饥荒阶段则需要进行停曝利用电营养反硝化进行脱氮,然而低DO虽然有利于脱氮但对产电不利。同步硝化反硝化需要精确控制DO、pH等操作条件,操作复杂。为解决反硝化菌在好氧阴极难以富集和脱氮效果差的问题,ZHANG等[16]构建阳极反硝化MFC进行脱氮,使阴极硝化产生的NO3−/NO2−通过AEM迁移到厌氧阳极室中进行反硝化。黄丽巧等[17]通过构建阴极硝化耦合阳极反硝化的双室MFC,探究了以AEM作为分隔膜的MFC(AEM-MFC)和以CEM作为分隔膜的MFC(CEM-MFC)的脱氮性能,结果表明当阴极NH4+-N投加200 mg·L−1时,AEM-MFC只需要66 h即可完全去除总氮,而相同条件下,CEM-MFC需要26 d才能达到相同的脱氮效果。虽然阳极反硝化MFC具有良好的脱氮效果,但由于AEM的阻隔作用,阳极室中的NH4+无法得到有效去除,仍需要进一步处理。
目前双室MFC的阴阳极室通常以不同成分的污水作为底物。阴极脱氮型MFC为处理同一种污水,有的增设外部硝化反应器或蠕动泵等设施从而增加了建设成本,有的对DO进行调控,通过调节曝气强度/曝气时间实现硝化与反硝化,操作复杂。而阳极脱氮型MFC阳极室与阴极室的分隔膜通常采用AEM,由于AEM对阳离子的阻隔作用,阳极室中的NH4+无法得到有效去除。因此,本研究构建了一种CEM与AEM交替排列的FC-MFC,操作简单且无需外部硝化反应器等外部设施。阳极室与阴极室之间用CEM与AEM进行交替分隔,在浓度差作用下离子进行迁移,最终实现阳极室中有机物和氨氮的同步去除。通过改变阳极室COD(P1、P2、P3和P4分别为500、700、900和1 100 mg·L−1),设置不同进水碳氮比,探究不同阳极COD对FC-MFC污染物去除及产电性能的影响。并以P4工况为例,分析FC-MFC氮去除途径。
四室微生物燃料电池同步脱氮除碳及产电性能
Simultaneous nitrogen and carbon removal and electricity generation in four-chamber microbial fuel cell
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摘要: 微生物燃料电池近年来被证实可以用来同步脱氮,然而微生物燃料电池中阴阳极室通常以不同成分的污水作为底物。为了实现废水脱氮,往往需要进行出水调配或停曝等复杂的操作。为解决上述问题,本研究构建了阴极硝化耦合阳极反硝化的四室微生物燃料电池(four chamber microbial fuel cell,FC-MFC),阳极室与阴极室之间用阳离子交换膜(cation exchange membrane,CEM)与阴离子交换膜(anion exchange membrane,AEM)进行交替分隔。在浓度差作用下离子进行定向迁移,最终实现阳极室有机物和氨氮的同步去除。探讨了阳极COD(即进水碳氮比)对FC-MFC产电及污染物去除效果的影响,并分析FC-MFC的氮去除途径。结果表明:随着阳极室COD的增加,各MFC模块的产电周期、峰值输出电压和最大功率密度随之增加,同时阳极室COD和TN的去除率也呈上升趋势,该系统对高碳氮比污水具有良好的抵抗负荷。当进水COD和NH4+-N质量浓度分别为1 100 mg·L−1和100 mg·L−1时,4个MFC模块的峰值输出电压介于526~619 mV,最大功率密度为103.47~121.00 mW·m−2,阳极室COD去除率和TN去除率分别高达94%和96%以上。氮去除途径分析结果表明,阳极室微生物吸附代谢作用、阴极室内源反硝化、阴极室通过AEM迁移至后序位阳极室进行反硝化过程分别贡献了25.96%~25.97%、0.91%~5.18%、68.87%~73.20%。Abstract: The microbial fuel cell(MFC) has been demonstrated to be a promising method for nitrogen removal. However, in traditional MFC, the anode and cathode chambers utilize distinct wastewater components as substrates, requiring intricate processes, such as effluent allocation or stopping aeration, to achieve nitrogen removal. Here, we show the concept of simultaneous nitrification and denitrification that occurs in separate anode and cathode chambers rather than in the same cathode chamber. Cathodic nitrification coupled to anode denitrification for nitrogen removal was achieved in a four-chamber microbial fuel cell(FC-MFC). This system employed cation exchange and anion exchange membranes to alternate between anode and cathode chambers. This promoted the directional migration of ions under concentration gradients, which facilitated the concurrent removal of organic matter and ammonia in the anode chamber. The impact of anode COD on MFC power generation and pollutant removal efficiency was investigated and the nitrogen removal pathway of this FC-MFC system was examined. The results showed that the power generation cycles, peak output voltages and maximum power densities of each MFC module increased with the increase of anode COD, along with the increased removal rates of COD and TN in the anode chamber. Notably, this system demonstrated an excellent resilience to high carbon-nitrogen ratio wastewater. When the influent COD and NH4+-N concentrations were 1100 mg·L−1 and 100 mg·L−1, respectively, the peak output voltages were 526~619 mV and maximum power densities were 103.47~121.00 mW·m−2 for four MFC modules, the COD and TN removal rates in the anode chamber were over 94% and 96%, respectively. Nitrogen removal pathway analysis revealed that microbial adsorption and metabolism in the anode chamber, endogenous denitrification in the cathode chamber, and the AEM-mediated denitrification process in the post-order anode chamber contributed 25.96%~25.97%, 0.91%~5.18%, and 68.87%~73.20% to nitrogen removal, respectively.
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表 1 FC-MFC和单室MFC工艺成本构成
Table 1. The cost structure of FC-MFC and single chamber MFC
部件 FC-MFC 单室MFC(4个) 材料 成本/元 材料 成本/元 框架 有机玻璃 2 400 有机玻璃 2 400 阳极 碳毡 5.94 碳毡 5.94 阴极 碳毡 5.94 碳布(20%的聚 四氟乙烯溶液和20%的Pt/C催化剂等) 147.93 曝气设施 空气泵/转子流量计 113 — — 离子交换膜 CEM/AEM 300.72 — — -
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