【作者】 侯彬；

【导师】 胡勇有；

【作者基本信息】 华南理工大学 ， 环境工程， 2012， 博士

【摘要】 纺织品生产中,大量使用偶氮染料。在纺织品着色过程中,部分偶氮染料脱落进入水体,产生了偶氮染料废水。偶氮染料废水的排放不仅会影响环境美观,而且它自身及其转化产物还会对水体产生生物毒性,有致癌作用,威胁人体健康。目前处理偶氮染料废水主要有物理法、化学法和生物法。物理和化学方法处理成本高,反应条件苛刻,且可能产生二次污染。相比之下,廉价、高效和环境友好的生物法更为人们所接受。一般只有厌氧处理才能实现微生物对偶氮染料的有效脱色。微生物燃料电池(MFC)是一种新型的同步废水处理与产电的技术,其厌氧阳极为微生物脱色偶氮染料提供了可能,有望成为一种全新概念的处理偶氮染料废水与产电的技术。本研究以刚果红为模型偶氮染料,采用MFC技术同步脱色刚果红与产电,考察了关键因素对MFC同步脱色刚果红与产电的影响,探明了MFC同步脱色与产电的相互作用机制以及电子传递机理,优化了MFC同步脱色刚果红和产电性能。得到如下主要结果与结论:构建了空气阴极—单室MFC,探讨了分隔膜种类、阳极生物膜生长以及驯化过程对MFC性能的影响和作用机制。实验结果表明,采用截留分子量为1K的超滤膜(UFM-1K)的MFC产生的功率密度最大,可以达到324 mW/m2,并且与微滤膜(MFM)相比,可以明显提高MFC的库伦效率。UFM-10K对刚果红的脱色速度最快(4.77 mg/L h),接下来分别是MFM(3.61 mg/L h),UFM-5K(2.38 mg/L h),UFM-1K(2.02 mg/L h)和质子交换膜(PEM)(1.72 mg/L h)。综合产电与刚果红脱色以及成本三个方面考量,UFM-1K是最佳选择,可替代空气阴极—单室MFC的PEM,提高MFC同步脱色刚果红与产电的性能。生物膜在阳极的生长可以加速阳极表面电化学反应速率,增强阳极的电化学活性,从而提高MFC的产电功率输出。在阳极生物膜生长1 d和5 d后,MFC的最大功率密度分别为8.6 mW/m2和33.4 mW/m2,而当阳极生物膜生长成熟后(30 d),MFC的最大功率密度可以达到297 mW/m2。通过改变共基质添加顺序考察了驯化过程对MFC同步脱色刚果红与产电的影响。研究发现驯化过程对MFC产电性能影响较大,而对脱色基本没有影响。16S rRNA测序结果显示驯化过程会对阳极生物膜微生物多样性产生影响。在好氧生物阴极MFC同步脱色刚果红与产电的研究中,MFC以UFM-1K作为分隔膜可以维持阴、阳极pH值、Na+浓度和磷酸盐浓度在一个相对稳定的水平,且产电和脱色刚果红性能都略高于以PEM作为分隔膜的MFC。另外,生物阴极MFC的最大功率密度(122 mW/m2)是非生物阴极MFC最大功率密度(24 mW/m2)的5倍。生物阴极MFC能够在30 h内完成90%的刚果红脱色,而非生物阴极MFC则需要大约50 h以上才能达到相同脱色率。表明与非生物阴极MFC相比,生物阴极MFC不仅可以提高MFC产电性能,而且能够加速刚果红在阳极的脱色。但是生物阴极MFC的启动周期较长。探索了阳极关键工况条件(包括:阳极悬浮污泥、阳极面积、共基质浓度、刚果红浓度、外接电阻和添加电子介体)对生物阴极MFC同步脱色刚果红与产电性能的影响。结果表明,对刚果红脱色和产电起主导作用的是阳极生物膜微生物,阳极悬浮污泥可在一定程度上加速MFC刚果红脱色,提高MFC的产电功率输出。刚果红脱色速率随着阳极面积的增大而加快,而MFC最大功率密度却呈现出一个先升高后降低的变化趋势。说明阳极面积并非越大越好,选择合适的阳极面积,既能提高性能又能有效利用资源节约成本。共基质(葡萄糖)浓度过低会显著降低MFC脱色刚果红和产电的性能,适宜的共基质浓度为300 mg COD/L。增大刚果红浓度将降低MFC对刚果红的脱色速率。浓度低于900 mg/L的刚果红不会对MFC产电产生明显影响。继续增大刚果红浓度,MFC产电性能则明显降低,最大稳定电压逐渐减小。但在更换了新的不含刚果红的阳极溶液后,MFC的最大稳定电压能够恢复至无染料时的水平。故刚果红浓度以不高于900 mg/L为宜。与高外接电阻相比,低外接电阻下MFC电子产生和传递速率要快,刚果红的脱色速率要高。电子介体在阳极中有利于促进刚果红脱色,而对MFC产电性能没有明显影响。好氧生物阴极MFC的阳极表面生物膜致密,且生物膜微生物以链状形式生长。阴极关键工况条件(包括:阴极悬浮污泥、阴极曝气量和添加铁锰混合液)对生物阴极MFC同步脱色刚果红与产电性能的影响研究表明,阴极悬浮污泥可以在一定程度上提高MFC的产电性能,但是对刚果红脱色基本没有作用。当阴极曝气量低于100 mL/min时,MFC最大稳定电压随着阴极曝气量的增大而升高。当阴极曝气量高于100 mL/min后,MFC最大稳定电压开始下降。与此同时,刚果红脱色速率随着阴极曝气量的增大而持续降低。表明在基于同步脱色刚果红与产电的好氧生物阴极MFC中,阴极曝气量有一个最佳值(100 mL/min),过度曝气不仅不会提高生物阴极MFC脱色刚果红和产电性能,相反还会产生抑制作用。阴极未添加铁锰混合液的MFC阴极生物膜致密,生物膜微生物以链状形式生长。阴极添加铁锰混合液的MFC阴极生物膜稀疏,并且在生物膜微生物表面包裹了许多呈多孔絮状的铁锰氧化物,表明添加的铁锰离子参与了阴极的电化学反应。因此,启动初期在阴极添加铁锰混合液能够显著缩短MFC的启动周期,并且将MFC的最大周期电压和最大功率密度分别提高了40%和74%,不过对刚果红脱色性能没有影响。采用变性梯度凝胶电泳(DGGE)和16S rRNA的指纹序列分析等分子生物学技术分析了基于同步脱色刚果红与产电的好氧生物阴极MFC阴、阳极微生物多样性。结果表明,阳极生物膜微生物以具有发酵能力的Bacteroidetes为主,并且存在大量的产甲烷菌和自养反硝化细菌。另外还检测到了隶属于δ-Proteobacteria的能够脱色刚果红的硫还原菌。不论阴极是否添加铁锰混合液启动,阴极生物膜微生物也均以Bacteroidetes为主。与未添加铁锰混合液启动的MFC相比,阴极添加铁锰混合液启动的MFC阴极生物膜催生出新的菌种,分别是锰氧化菌Leptothrix discophora和自养反硝化菌Uncultured Chlorobi bacterium。刚果红在MFC阳极的脱色同时存在两条脱色途径。在其中一种途径中,刚果红得到4个来自葡萄糖氧化产生的电子,这4个电子平均分配给刚果红的两个偶氮键,使得两个偶氮键同时被还原成为氮氮单键;在另外一种途径中,刚果红将得来的4个电子全部用于其中一个偶氮键,使得该偶氮键直接断裂。对二氨基联苯是刚果红脱色的主要产物,而且不能被阳极微生物进一步分解矿化,会在MFC阳极溶液中积累。阳极脱色微生物与产电微生物是一种竞争的生存关系。刚果红的脱色会在一定程度上抑制MFC的产电性能,然而MFC中阳极的存在却能够提高刚果红的脱色速率。MFC的启动是对阴、阳极微生物的一个筛选和富集的过程,直接影响到MFC的性能。在启动阶段可以通过调控影响微生物代谢途径的主要因素,实现目标微生物(耐受性强的产电微生物和高效脱色微生物)的富集。在MFC运行过程,阴、阳极工况条件的同时调控,可以优化MFC同步脱色刚果红和产电性能。更多还原

【Abstract】 Azo dyes represent the largest class of dyes applied in textile processing. In textile dyebaths, the degree of fixation of dyes to fabrics is never complete, resulting in dye-containing effluents. The removal of dyes from these effluents is desired, not only for aesthetic reasons, but also because many azo dyes and their breakdown products are toxic to aquatic life and mutagenic to humans. Different physical, chemical and biological techniques can be applied to remove dyes from wastewater. Each technique has its technical and economical limitations. Most physicochemical dye removal methods have drawbacks because they are expensive, have limited versatility, are greatly interfered by other wastewater constituents, and/or generate waste products that must be handled. Alternatively, biological treatment may present a relatively inexpensive and environment-friendly way to remove dyes from wastewater. Generally, high rate bacterial azo dyes decolorization is usually achieved under anaerobic condition. Microbial fuel cell (MFC) is a promising environmental technology for simultaneous wastewater treatment and energy recovery in 21st century. The anaerobic anode chamber of the MFC could be employed for high rate bacterial azo dyes decolorization. MFCs may offer a new technique in enhancing azo dye decolorization while simultaneously recovering electricity in practical applications.In this study, the effect of key operation parameters on the performance of the MFC for simultaneous Congo red decolorization and electricity generation was investigated. In addition, the interaction of Congo red decolorization with electricity generation and the charge transfer mechanism were explored and the performance of the MFC was optimized. The major conclusions are given below:The effects of membrane type, biofilm growth and enrichment procedure on the performance of an air-cathode single-chamber MFC used for simultaneous Congo red decolorization and power generation were firstly investigated. Batch test results showed that the MFC using an ultrafiltration membrane (UFM) with molecular cutoff weight of 1K (UFM-1K) produced the highest power density of 324 mW/m2 coupled with an enhanced coulombic efficiency compared to microfiltration membrane (MFM). The MFC with UMF-10K achieved the fastest decolorization rate (4.77 mg/L h), followed by MFM (3.61 mg/L h), UFM-5K (2.38 mg/L h), UFM-1K (2.02 mg/L h) and Proton exchange membrane (PEM) (1.72 mg/L h). Based on the consideration of both cost and performance, UFM-1K was the best one. Biofilm growth greatly reduced the anode polarization impedance and facilitated the kinetics of the electrochemical reactions so as to enhance extracellular electron transfer from bacteria to anode electrode and increase the power generation. Higher power density of 297 mW/m2 was observed on day 30 (a maturate bioflim) compared with the power density of 33.4 mW/m2 and 8.9 mW/m2 on day 5 and day 1, respectively. Two different enrichment procedures in which glucose and Congo red were added into the MFCs sequentially or simultaneously were tested. The results showed that the enrichment procedures have a negligible effect on the dye decolorization, but significantly affected the electricity generation. 16S rRNA sequencing analysis demonstrated a phylogenetic diversity in the communities of the anode biofilm and showed clear differences between the anode-attached populations in the MFCs with a different enrichment procedure.In the study of biocathode MFC used for simultaneous Congo red decolorization and electricity generation, the pH value and the concentration of Na+ and phosphate could be maintained in a relative stable level in both anode and cathode chamber by using UFM-1K as the separator. The performance of the MFC coupled with UFM-1K was a little better than that of the MFC coupled with PEM in terms of Congo red decolorization and electricity generation. A 400% increase in maximum power density was observed in a biocathode MFC as compared with the abiotic cathode MFC. The biocathode MFC completed 90% of Congo red decolorization within 30 h while the abiotic cathode MFC required 50 h to achieve the same decolorization efficiency. These results demonstrated that the biocathode MFC could increase the electricity generation and accelerate the Congo red decolorization. However, startup period of biocathode MFC was much longer than that of the abiotic cathode MFC.Effect of the anode operation parameters (including suspended sludge in the anode, anode surface area, concentration of the co-substrate, concentration of Congo red, resistor and adding electron redox mediator) on performance of the biocathode MFC for simultaneous Congo red decolorization and electricity generation was investigated. Batch test results showed that the suspended sludge in the anode could accelerate Congo red decolorization and increase electricity output. The Congo red decolorization increased with the anode surface area increased. However, the power density of the MFC increased firstly and then decreased. Thus, an appropriated anode surface area should be selected. The low concentration of the co-substrate (glucose) could significantly decrease the performance of the MFC in terms Congo red decolorization and electricity generation. The optimum concentration of co-substrate was 300 mg COD/L. The increased concentration of Congo red could decrease the decolorization rate. Electricity generation was not significantly affected by Congo red at 900 mg/L, while higher concentrations inhibited electricity generation due to accumulation of decolorization products. However, voltage can be recovered to the original level after replacement with anodic medium without Congo red. Thus, the preferable concentration of Congo red was not higher than 900 mg/L. Low resistor was more helpful for Congo red decolorization as compared with high resistor. The electron redox mediator in the anode was more favorable for accelerating Congo red decolorization. A thick and dense biofilm was obtained on the anode of a biocathode MFC and many spherical microorganisms on the anode surface formed chain-like colonies.Effect of the cathode operation parameters (including suspended sludge in the cathode, cathode aeration rate and adding Fe-Mn mixed solution) on performance of the biocathode MFC for simultaneous Congo red decolorization and electricity generation was also investigated. The suspended sludge in the cathode could improve the performance of the MFC in electricity generation, but had a negligible effect on the Congo red decolorization. The maximum voltage increased as the aeration rate was increased up to 100 ml/min. At the aeration rate of 200 ml /min, the maximum voltage was lower than that at 100 ml /min. In the meantime, Congo red decolorization rate decreased with the increasing of the cathode aeration rate. These results showed that excessive aeration was not favorable in a biocathode MFC used for simultaneous Congo red decolorization and electricity generation. A thick and dense biofilm was obtained on the cathode in the MFC without Fe-Mn mixed solution and many spherical microorganisms on the cathode surface formed chain-like colonies. However, a sparse biofilm was observed on the cathode in the MFC with Fe-Mn mixed solution and SEM images revealed that the microorganisms were wrapped by a lot of porous iron and manganese oxides, indicating that Fe2+ and Mn2+ were involed in the cathode reaction. Therefore, addition of the Fe-Mn mixed solution to the biocathode resulted in a significant decrease in startup period accompanied by a 40% increase in maximum voltage output from 0.25 V to 0.35 V and a 74% increase in maximum power density from 122 mW/m2 to 212 mW/m2,but had no effect on the Congo red decolorization.Denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene analysis were performed to explore the bacterial diversity in the anode and cathode of a aerobic biocathode MFC. The results revealed that the microbial communities in the anode biofilm of the aerobic biocathode MFC were dominate by fermentative Bacteroidetes and a lot of methanogenic bacteria and autotrophic denitrifying bacteria were obtained simultaneously. In addition, the observed sulfate-reducing bacteria which belonged to the phylumδ-Proteobacteria were responsible for the Congo red decolorization. There are some unique bacterial species in the cathode of the MFC with Fe-Mn mixed solution compared to that in the cathode of the MFC without Fe-Mn mixed solution, mainly including of Leptothrix discophora and Uncultured Chlorobi bacterium-like species.Congo red was decolorized in the MFC through two different pathways simultaneously. In one pathway, 4 electrons were assigned averagely to the two azo linkages in the Congo red at the same time. In another pathway, all of the 4 electrons were given to one of the azo linkages for complete cleavage. Benzidine was identified as the main decolorization products and can not be further mineralized in the anode.The reduction of Congo red would consume some electrons produced from co-substrate degradation, thus there is a competition between decolorizing microorganisms and electricity-producing bacteria. Congo red decolorization would inhibit electricity output whereas the presence of the anode in the MFC could accelerate the decolorization rate of Congo red.The target microorganisms, such as electricity-producing bacteria with high tolerability and highly efficient decolorization bacteria, could be obtained by regulating the factors which could affect the metabolism pathway of the microorganisms during the startup period of MFC. The performance of the MFC used for Congo red decolorization and electricity generation could be optimized by regulating the working conditions of the anode and the cathode simultaneously.更多还原