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微生物燃料电池(microbial fuel cell, MFC)可通过微生物作用将有机废物的化学能转化为电能,实现能源结构的优化。产电微生物附着在阳极上并催化有机物产生质子和电子,电子经过阳极电极和外部电路到达阴极,质子通过离子交换膜从阳极室传输至阴极室,质子、电子和电子受体三者在阴极室结合,形成电流回路,从而实现废水处理的同时回收电能[1-2]。然而,由于反应器存在建设成本较高和功率密度相对较低的问题,MFC的扩大化应用受到限制[3-4]。电极成本占反应器建造成本的50%以上[5-6]。而且,MFC的整体性能在很大程度上取决于电极的性能[7]。MFC中生物电化学的核心过程是复杂的底物可以在电极上进行生物催化氧化[8]。电极材料的选择对电极性能具有显著影响。电活性细菌的附着、生物膜的形成和电子从生物膜到电极材料的转移速率均会受到电极材料的表面性能、电子传递类型和电阻的影响[9]。
传统电极材料主要包括碳毡(carbon felt, CF)[10]、碳布(carbon cloth, CC)[11]以及活性炭(activated carbon, AC)[12]等碳基材料。但是,这些碳基材料的原料资源受限且制造成本较高。生物炭是废弃生物质热解的副产品,具有负碳平衡[13-14]。废弃生物质是一种具有高附加值的潜在电极材料,可以用于超级电容器的电极材料[15]。生物炭也可以作为MFC的电极材料用以传输能量[16-17]。大多废弃生物质具有天然的大孔结构,经过高温碳化后,其表面粗糙度会增加。与平面结构相比,这一特征有利于微生物的附着生长、生物膜的形成和电极表面上电活性的增加[18]。BATAILLOU等[17]以雪松木作为电极原料,经过高温热解后用于MFC阳极,结果表明,在900 ℃下热解的生物炭电极的输出功率是传统CF电极的5倍。我国是农业大国,玉米作物分布在大部分农业区,而玉米秸秆作为副产物,未得到充分合理的利用。在MFC中采用秸秆生物炭作为电极,不仅可以实现秸秆废弃物的再利用,还可以解决秸秆废弃物处理的环境和经济问题。
硫化物和硝酸盐是废水中常见的有害物质,其主要来自于工业废水和农业污染等。有研究表明,MFC同步脱硫除氮会提高MFC产电效率,增加污染物去除率。蔡靖等[19]构建了双室MFC同步脱氮除硫,污染物去除率和产电性能表现优异,硝态氮去除率可达96.5%,硫化物去除率达99.64%,最大电流密度达457.20 mA·m−2。关于MFC同步脱硫反硝化的大部分研究都是在阳极同步进行脱硫和反硝化,阴极配以强氧化性化学物质,但MFC电化学反应和反硝化过程都需要电子,不可避免地要产生竞争,使MFC总体产电性能和基质去除能力下降,而且阴极的强氧化性物质也会造成二次污染。
基于以上研究结果,本研究以玉米秸秆作为电极原料,通过碳化控制手段制备了生物炭作为MFC电极,阳极室内以S2−为电子供体,阴极室内以NO3−为电子受体,构建了同步脱硫反硝化MFC。以CF作为参照电极,考察了玉米秸秆生物炭电极MFC在电化学性能、电能输出和污染物去除等方面的性能,探究了硫氮比等条件对生物脱硫反硝化以及产电效能的影响。
玉米秸秆生物炭电极用于微生物燃料电池脱硫反硝化性能
Desulfurization and denitrification performance of corn straw biochar electrode for microbial fuel cell
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摘要: 研究了玉米秸秆生物炭作为微生物燃料电池电极的性能。阳极以S2−为单一电子供体,阴极以NO3−为电子受体,以碳毡为对照电极,考察玉米秸秆生物炭电极用于生物燃料电池同步脱硫反硝化的电化学性能、产电性能以及污染物去除能力,分析了不同硫氮质量浓度比对生物炭电极微生物燃料电池脱氮除硫效率以及输出电能的影响。结果表明,玉米秸秆生物炭电极微生物燃料电池实现了更高的交换电流密度(22.42×10−3 A·cm−2)和更低的电荷转移电阻(4.24 Ω)。与碳毡电极相比,玉米秸秆生物炭电极微生物燃料电池最大输出电压和最大功率密度分别提升了18.91%和16.67%。当硫氮比为5:4时,反应器脱硫反硝化和产电能力最佳。阳极室S2−出水质量浓度由120 mg·L−1降至1.08 mg·L−1,去除率为99.1%,其中76.52%转化为SO42−-S,阴极室NO3−-N去除率为94.5%。此时反应器输出电压和功率密度也达到最大值,分别为450.68 mV和1.03 W·m−2。Abstract: In this study, the performance of corn straw biochar as the electrode of microbial fuel cell was investigated. The anode and cathode were configured with S2− as the exclusive electron donor, and with NO3− as the electron acceptor, respectively, and carbon felt was employed as the reference electrode to assess the electrochemical performance, power generation capability, and pollutant removal capacity of the corn stalk biochar electrodes in the simultaneous desulfurization-denitrification microbial fuel cells. Furthermore, the influences of different sulfur-to-nitrogen concentration ratios on the denitrification and desulfurization efficiency and the electrical energy output of the biochar electrode microbial fuel cells were explored. The experimental results show that the corn straw biochar microbial fuel cell achieved higher exchange current density (22.42×10−3 A·cm−2) and lower charge transfer resistance (4.24 Ω). Compared with carbon felt electrode, the maximum output voltage and power density of microbial fuel cell with corn straw biochar electrode increased by 18.91% and 16.67%, respectively. When the ratio of sulfur to nitrogen was 5:4, the best desulfurization, denitrification and electricity generation capacity occurred for the reactor. The effluent concentration of S2− in anode chamber decreased from 120 mg·L−1 to 1.08 mg·L−1, and the removal rate was 99.1%, of which 76.52% converted to SO42−-S, and the removal rate of NO3−-N in cathode chamber was 94.5%. At this time, the output voltage and power density of the reactor reached the maximum values, which were 450.68 mV and 1.03 W·m−2, respectively.
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Key words:
- microbial fuel cell /
- biochar /
- desulphurization and denitrification /
- electrocatalysis
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表 1 Tafel曲线计算结果
Table 1. The calculation results of Tafel curve
电极 线性拟合方程 R2 i0/(A·cm−2) CF y= 1.518 1x − 2.300 9 0.998 7 5.01×10−3 CS y =0.751 7x − 1.649 4 0.994 9 22.42×10−3 表 2 不同硫氮比下MFC产电性能
Table 2. Electricity generation performance of MFCs at different sulfur-nitrogen ratios
硫氮比 最大输出
电压/mV最大功率
密度/(W·m2)库伦
效率/%5:2 409.84 0.84 14.36 5:4 450.68 1.03 19.57 5:6 446.85 0.94 18.21 5:8 420.13 0.89 14.36 -
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