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微生物燃料电池(microbial fuel cells,MFC)是一种以微生物作为催化剂将有机物中的化学能转化为电能的技术,主要由阴极、阳极、分隔材料和外电路等4个部分组成,阳极区的有机物降解后产电细菌将电子通过外电路传递至阴极,产生的质子扩散至整个阴极区域,质子与电子在阴极与电子受体发生反应,产生电流[1-2]。人工湿地(constructed wetlands, CWs)以其底部厌氧、表层好氧/缺氧特征,具备微生物燃料电池的发生条件。这使得微生物燃料电池和人工湿地耦合技术(microbial fuel cells-constructed wetlands, MFC-CWs)在去除污染物的同时也具备产电功能[3-4]。从目前研究成果来看,MFC-CWs 虽有电流输出,但产电密度较低,污染物降解能力也未得到实质性的提升[5]。YADAV等[6]构建的MFC-CWs 产电量为15.73 mW·m−2。FANG等[7]发现的MFC-CWs 最高产电量为852 mW·m−2。TURKER等[8]得出的MFC-CWs 最高产电量为15.1 mW·m−2。
尽管碳纳米复合材料在发电效率的研究方面取得了一些重要的成果,但碳纳米复合材料的进一步应用仍面临一些挑战,特别是电极材料昂贵和能量产率低[1]。在此情况下,目前的研究开始变换思路,将电子外输转为电子的原位利用,将人工湿地的产电能力转化为加快污染物降解的源动力,以电子的内部消耗来换取净化性能的极大提升。针对如何利用电子的传递和消纳进行生物电能向净化性能转化这一核心问题,RAMIREZ-VARGAS等[9]通过具有导电能力的碳质填料的填充,将人工湿地演变为一种短路状态的微生物燃料电池。碳质填料作为电子传导通道,在无需外置电路情况下,构建出电子产出-传导-消纳的原位利用路径,在电位梯度驱动下,使得有机污染物作为电子供体得以被高效降解。导电填料人工湿地中污染物去除负荷能提高10倍,且污染物去除率较常规人工湿地有显著提高[10]。
然而,目前国内外利用导电填料填充人工湿地产生原位电场来提高去除率的研究尚处于起步阶段,反应器规模通常较小,工程应用中的人工湿地构建深度通常在60 cm以上,在此条件下,导电填料的电阻比实验装置中电阻有显著提升,加上导电填料种类的有限,自发电场能否产生,污染物净化效率能不能提高,均有待于进一步研究。鉴于此,本研究在对不同饱和状态下碳质填料的电阻率进行测定的基础上,构建了与实际工程等深的人工湿地实验装置,以探索碳质填料的导电特征及其对人工湿地污染物净化效果的影响;同时,优化水力停留时间和有机负荷对系统产电性能的影响,以期为碳质填料人工湿地的应用提供参考。
碳质填料的导电特征及其对人工湿地净化效能的提升
Electro-conductivity of carbonaceous materials and their improvement in the purifying performance of the constructed wetland
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摘要: 探讨了具有导电性的碳质填料填充对人工湿地电场形成及有机物去除的影响。筛选出电阻率较低且稳定的焦炭(0.8~2.5 Ω·m)及常规填料石英砂,分别构建了人工湿地系统,在水力停留时间分别为6、12、18、24和30 h,进水COD分别为100、300和500 mg·L−1的条件下,对比了系统自然电场变化特征、有机物降解效果及其受不同水力负荷及有机负荷的影响情况。结果表明:焦炭人工湿地最大电势差(EPs)达到605~780 mV,显著高于石英砂湿地系统(275~334 mV);在高水力负荷及高有机负荷条件下,焦炭人工湿地对COD的去除率比石英砂湿地高出16%~21%。对自然电位沿程分布聚类分析的结果表明,焦炭系统中具有较好的氧化还原分区,从而有利于有机物及硝酸盐的降解,但对总磷和氨氮的去除影响不大。Abstract: In this study, the effect of electro-conductive substrate on the electric field formations and organic removals in the constructed wetlands was investigated. Coke with low resistivity (0.8~2.5 Ω·m) and stability and conventional filler quartz sand were screened out to establish constructed wetland system (electro-conductive material coke constructed wetland: EC-CW, quartz sand constructed wetland: QS-CW), respectively. The effects of hydraulic retention times (6, 12, 18, 24 and 30 h) and influent COD (100, 300 and 500 mg·L−1) on the spontaneous electric field variation and organics degradation were studied. The results showed that the maximum electric potential difference (EPs) in EC-CW was 605~780 mV, and significantly higher than that in QS-CW (275~334 mV). COD removal rate by EC-CW was 16%~21% higher than that by QS-CW at high hydraulic and organic loadings. Cluster analysis of EPs distribution along the depth showed that there were better oxidation-reduction zones in the EC-CW than QS-CW, which was benefit for the degradation of organics and nitrates, and no significant improvement for TP and
${\rm{NH}}_4^ + $ -N removal. -
表 1 不同基质填料在饱和及非饱和条件下电阻率
Table 1. Resistivity of different substrates under saturated and unsaturated conditions
填料 电阻率/(Ω·m) 自然干燥 纯水饱和 纯水不饱和 生活污水饱和 生活污水不饱和 活性炭 31.7±5.70b 4.80±0.700a 2.40±0.600b 5.70±0.500a 4.30±0.400b 无烟煤 45.8±1.90a 4.80±0.300a 15.7±1.30a 5.10±0.300a 16.2±2.00a 焦炭 2.50±0.100c 2.10±0.100b 0.800±0.200b 2.50±0.400b 1.50±0.200c 注:n=3,表中相同字母表示没有显著差异,不同字母表示具有显著差异(P<0.05)。 -
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