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榨菜加工过程中产生的废水含高浓度有机物(以COD计为300~2 000 mg·L−1)、高盐度(以NaCl计为15~25 g·L−1)与高氨氮(200~300 mg·L−1)[1-2]。此类废水以及其他高盐废水需高效处理后才能排放,否则将对土壤和水体环境造成极大的威胁[3]。厌氧和好氧技术通常被联合用于高盐废水治理[4-6]。然而,综合处理过程不但消耗了大量能量、易造成二次污染,而且常常不能同时达到氮和碳的排放标准[7]。值得注意的是,生物电化学系统(biological electrochemical system,BES)是一种可持续且具有成本效益的技术,已证明具有良好脱氮能力[8-10]。BES在处理C/N为0的含氮废水时,依然有着较高的硝酸盐去除率[11]。
就功能而言,混合生物阴极 MFC可实现BES中不同形式氮的转化与去除[11]。用厌氧泥与好氧泥依次混合接种MFC阴极的方式可实现良好的TN去除率(89.8%~97.6%)[12]。最近有研究[13]表明,混合生物阴极 MFC在处理榨菜废水时实现了完全脱氮,并提出脱氮机理包括盛宴阶段、饥荒阶段和稳定阶段共3个阶段的理论。
在盛宴阶段、饥荒阶段与稳定阶段发生的主反应分别为异养硝化/好氧反硝化反应、自养硝化与电营养反硝化[13]。异养硝化/好氧反硝化菌可利用基底中的有机物作为电子供体,将不同形态的氮转化成N2[14]。异养硝化菌在碳源充足的条件下,将含氮的化合物氧化成
${\rm{NO}}_2^ - $ 、${\rm{NO}}_3^ - $ ,且大部分能在曝气的条件下将硝态氮还原成氮气,实现好氧反硝化[15]。相较于传统脱氮工艺,异养硝化/好氧反硝化可在同一个反应器中进行,且具有更高的氨氮去除效率[16]。异养硝化反应所产生的氨氮可作为异养硝化/好氧反硝化菌的反应物,从而实现同步硝化和反硝化效果[17]。目前,被报道出的异养硝化/好氧反硝化菌(属)有Paracoccus、Thauera、unclassified_f__Rhodobacteraceae、Flavobacterium、Arcobacter、Halomonas[18-19]。电营养反硝化是一种有潜力的脱氮新技术[13]。电营养反硝化一般机理为:阴极生物膜上存在一类电活性自养脱氮微生物,可直接利用电子,将阴极底物中的
${\rm{NO}}_3^ - $ 与${\rm{NO}}_2^ - $ 还原成N2。在生物电极脱氮过程中,电营养反硝化可减少传统反硝化反应对有机物的依赖[20]。目前已报道参与电营养反硝化的潜在菌(属)有Thauera、Acholeplasm、tappia indica、Xanthobacter、Azoarcus、Pseudomonas stutzer[11,15,21]。混合生物阴极 MFC稳定阶段周期较长,主要原因为稳定阶段的电营养反硝化速率缓慢[13]。因此,探究电营养反硝化速率的影响因素,已成为混合膜 MFC走向实践应用所面临的一个关键。目前,关于生物电极脱氮电子传递机制的研究尚少。根据已有的研究,推测的传递方式可能为直接接触方式、电子中介体方式。电营养反硝化菌可以分泌电子介体,且外源电子介体可有效提高生物电极脱氮的效率[21]。非膜结合细胞色素蛋白、Rnf复合体、红素氧还蛋白、氢化酶与甲酸脱氢酶可能参与生物电极脱氮中电子的直接传递[22]。电子传递链的两端分别为阴极电子和硝酸盐,因此,电流强度对双室混合膜 MFC 的电营养反硝化具有直接影响,但关于这方面的研究目前鲜有报道。
为优化混合生物阴极MFC处理高盐榨菜废水时的脱氮效果,本研究通过改变外电阻,设置了4组不同峰值电流强度(S1、S2、S3、S4分别为(0.24±0.03)、(0.37±0.03)、(0.55±0.11)、(0.5±0.2) mA)的实验,探讨了不同电流强度对高盐双室混合膜 MFC脱氮的影响,并分析了对应的产电特性和微生物群落,优化了反应器运行的最佳工况条件,为后续双室混合膜 MFC处理高盐废水研究提供思路与解决方法。
电流强度对高盐废水混合生物阴极MFC脱氮及产电的影响
Effect of current intensity on nitrogen removal and electricity generation in hybrid biocathode MFC for high-salinity wastewater treatment
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摘要: 构建了双室混合生物阴极微生物燃料电池(microbial fuel cell,MFC)处理高盐榨菜废水,探讨了不同电流强度对混合膜 MFC 脱氮的影响,并分析了产电特性及微生物群落特征。结果表明,高电流通量可缩短双室混合膜MFC的完全脱氮周期,且主要缩短的是稳定期周期。相对于其他3个实验组,电流强度最大的S3实验组硝酸盐平均去除速率((5.72±0.10) mg·(L·d)−1)与硝酸盐最高去除速率((8.45±0.15) mg·(L·d)−1)均最大,且实现总氮100%去除的时间最短(19 d),稳定期硝酸盐去除速率k (6.122 5 mg·(L·d)−1)最大,这说明增大电流强度可促进混合膜MFC 电营养反硝化。电营养反硝化菌可直接利用电子进行反硝化反应,而较大的电子通量给阴极电活性自养脱氮微生物提供了丰富的生命燃料。在产电方面,曝气阶段开路电压(S1、S2、S3、S4分别为750、729、721、699 mV)随外加电阻的增大而增大,最大功率密度相差却并不显著(1.09、0.94、1.04、1.02 W·m−3);停止曝气阶段,阴极室电子受体的减少,导致MFC产电性能普遍下降,外电阻最大的S1实验组开路电压(746 mV)与最大功率密度(0.77 W·m−3)为最高。高通量测序结果表明,承担电营养反硝化功能的菌群可能为norank_f_Hydrogenophaga,Azoarcus。以上研究结果可为后续双室混合膜 MFC处理高盐废水提供技术参考。Abstract: A dual-chamber hybrid biocathode microbial fuel cell (MFC) was constructed to treat high-salinity mustard wastewater, the effect of different currents intensities on nitrogen removal of the hybrid biocathode MFC was discussed, and the electricity generation characteristics and microbial communities were analyzed. The result shows that high current intensity can shorten complete nitrogen removal cycle of the dual-chamber hybrid biocathode MFC, mainly shorten the stable phase cycle. Compared with other three groups, both the average removal rate of nitrate (5.72±0.10) mg·(L·d)−1 and the highest nitrate removal rate (8.45±0.15) mg·(L·d)−1 of the S3 experimental group with the highest current intensity were the largest, the complete removal cycle of total nitrogen (19 d) was the least, and the nitrate removal rate (6.122 5 mg·(L·d)−1) in the stable phase of S3 was the largest, indicating that the increase of current intensity was beneficial to the electrotrophic denitrification of the hybrid biocathode MFC. The electrotrophic denitrification bacteria could directly use electrons to conduct the denitrification reaction, and large electron flux provided abundant fuel for the cathodic electrophilic autotrophic denitrifying microorganisms. In terms of electricity production, the open circuit voltage (S1: 750 mV, S2: 729 mV, S3: 721 mV, S4: 699 mV) during the aeration phase increased with the increase of the external resistance, but the difference of the maximum power density was slight (1.09, 0.94, 1.04, 1.02 W·m−3). When the aeration phase stopped, the electron acceptors in cathode chamber decreased, which led to the general decrease of the electricity generation of MFC, both the open circuit voltage (746 mV) and the maximum power density (0.77 W·m−3) of the S1 group with the largest external resistance were the highest. Finally, high-throughput sequencing showed that the bacteria with electrotrophic denitrification function may be Hydrogenophaga, Azoarcus. This research provides ideas and solutions for the subsequent research on the treatment of high-salinity wastewater with dual-chamber hybrid biocathode MFC.
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表 1 阳极阴极启动水质
Table 1. Water quality of anode and cathode start-up
电极 DO/(mg·L−1) pH 盐度/(g·L−1) COD/(mg·L−1) /(mg·L−1)${\rm{NH}}_4^ + $ TN/(mg·L−1) 来源 阳极 0 7~8 15~16 2 000 20 20~30 混合污水 阴极 0.5 7~8 15~16 1 500 220~300 220~350 榨菜废水 表 2 4组工况在3个阶段的周期和氮去除率
Table 2. Cycle and nitrogen removal rate at three stages under four working conditions
工况 盛宴期 饥荒期 稳定期 周期/d -N去除率/%$ {{\rm{NH}}_4^ +} $ TN去除率/% 周期/d -N去除率/%$ {{\rm{NH}}_4^ +} $ TN去除率/% 周期/d TN去除率/% k/(mg·(L·d)−1) R2 S1 2±1 58.91 59.11 10±1 41.09 21.45 17±1 19.43 −3.618 0 0.995 2 S2 2±1 63.30 62.93 9±1 36.70 15.55 12±1 21.52 −5.593 8 0.997 6 S3 2±1 67.61 67.55 8±1 32.39 17.09 7±1 15.36 −6.122 5 0.997 0 S4 2±1 58.18 58.14 14±1 41.82 15.43 30±1 26.43 −2.771 3 0.997 1 表 3 4组工况的产电特性
Table 3. Power generation characteristics of four working conditions
阶段 外阻值/
Ω开路电压/
mV最大功率密度/
(W·m−3)内部电阻/
ΩS1a 1 000 750 1.09 257 S2a 500 729 0.94 252 S3a 100 721 1.04 243 S4a 20 699 1.02 202 S1b 1 000 746 0.77 1 054 S2b 500 597 0.41 885 S3b 100 462 0.29 795 S4b 20 412 0.21 675 -
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