【作者】 王鑫；

【导师】 冯玉杰；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2010， 博士

【摘要】 有机废水处理是能源密集型综合技术,高能耗是其主要问题之一。在世界性能源危机的环境中,传统的废水处理技术不仅导致了较高的化石能源需求,而且有机物降解和能耗造成了大量的碳排放,引发了一系列新的环境问题。微生物燃料电池(Microbial fuel cell,MFC)是21世纪环境工程领域新兴的废水处理同步能源回收技术,能在胞外产电菌的作用下将有机废物中的化学能直接转化为电能,然而目前产电机理尚不清晰。考虑到未来应用,MFC成本过高以及产电过程中的影响机制有待进一步研究。本论文围绕多元生物质在MFC中的转化规律、新型电极材料的开发和双室MFC的低成本运行规律,其目的是降低MFC技术的成本,将MFC技术推向市场化。本文首次验证了啤酒废水可以直接作为MFC底物产电。在单室空气阴极方形MFC中,以啤酒废水中的土著微生物为接种菌源,全浓度废水为底物,获得了最大功率密度为205mW·m-2(30℃)。温度影响了阴极电位,20℃下功率密度降低至170 mW·m-2,但COD去除率和库仑效率(CE)变化不大。加入50和200mmol·L-1 PBS后功率密度上升。随废水浓度的升高,CE降低而功率密度线性升高。秸秆汽爆洗液同样也可以作为阳极廉价底物产电,最大功率密度644mW·m-2。电导率的变化影响了阳极电位,使功率密度先上升而后下降。而PBS浓度升高使阴极区表面pH缓冲能力增强,提高了阴极性能。在纤维素糖化菌群(H-C)和产电菌的协同作用下,首次在MFC中实现了天然固体秸秆产电,获得了331mW·m-2的最大功率密度。将底物更换为汽爆秸秆后,最大功率密度升高至406mW·m-2。微生物群落演替分析表明,体系中可能的产电菌为Rhodopseudomonas palustris。开发出了基于低成本碳纤维布的阳极材料和Nafion/PTFE新型阴极粘结剂材料,使MFC的单位容积和单位功率成本降低70%以上。使用碳纤维布替代传统E-TEK碳布后,阳极成本降低了75%,功率输出提高了7%。未经预处理的碳纤维布产电性能较差。使用马弗炉对碳纤维布进行热处理后(450℃,30min)获得了922mW·m-2的最大功率密度,比只经过丙酮清洗的碳纤维布阳极高3%,仅比高温氨处理的碳布低7%。预处理提高MFC性能的机理是:丙酮清洗和热处理是通过去除电极表面影响电子传递的杂质,提供了更大的电化学活性表面积,促进了产电过程进行。高温氨处理后除清洁作用外,表面N/C原子个数比与热处理相比升高了近1倍(由2.9%升高至4.6%),说明氨处理过程中生成的含氮官能团(如胺基)对产电过程有促进作用。在此基础上,使用重氮盐向碳布表面连接不同含量的胺基,测试了胺基含量对产电性能的影响。在较低的胺基含量下,MFC的功率输出并无显著变化。当官能团比重上升至0.4%和0.9%后,MFC的功率密度有显著提升,最大功率密度与氨处理电极相同,阳极表面的微生物蛋白含量也与氨处理电极相近。然而过量的胺基连接量抑制了微生物的生长,降低了功率输出。开发出了廉价空气阴极Nafion-PTFE催化剂粘结剂,降低了阴极成本。发现MFC的最高功率输出随粘结剂中Nafion含量线性增加。经过25个周期运行后,Nafion为粘结剂的MFC获得的CE为20-29%,而粘结剂中加入PTFE略微降低CE至17-26%,而所有MFC最高电压输出变化不大。发现了阳极恒定+200mV(Ag/AgCl)电位加速启动,降低了MFC运行成本。启动期内恒电位系统较高的输出电流是由于阳极恒定正电位提高了底物氧化推动力造成的。启动完成后,不同方法启动的MFC性能相同。进一步的研究表明,阳极电位在-400mV至+200mV(Ag/AgCl参比)范围内,随着阳极电位升高最大输出电流升高,而最高电流获得的时间缩短。但当阳极电位进一步升高至+400mV,峰电流却降低至6.9mA。CE随阳极电位的升高而增大,低电位下(-400mV至0mV)的CE较低主要是由于氢气甲烷的产生造成的。升高阳极电位可以提高产电菌氧化底物的推动力,从而在竞争中有效抑制发酵气体生成。在较高的阳极电位下微生物生长获得的电量比例降低,生长受到抑制。构建了无曝气双室微生物碳捕获电池(MCCs),通过在阴极溶液中培养小球藻(Chlorella vulgaris)原位捕获阳极产生的CO2,同时产生O2供给阴极作为电子受体,消除了双室MFC阴极高能耗高成本的曝气过程,最大功率密度为5.6W·m-3。CV和DO测试结果表明MCC阴极反应的机理是藻类光合产氧,然后氧气被还原,周期内阳极室产生的所有气态CO2均被捕获。碳平衡计算表明MCC的碳捕获率高达94±1%,为废水的零碳排处理提供了新方法。更多还原

【Abstract】 Since organic wastewater treatment is an energy intensive technology, high energy consumption is one of main problems for wastewater treatment. Traditional wastewater treatment processes not only needed large amount of fossil energy, but also discharged CO2 into atmosphere, incurring new environmental problems. Microbial fuel cell (MFC) is a new environmental technology for wastewater treatment with simultaneous energy recovery in 21st century. In MFCs, chemical energy from organic pollutant can be directly converted into electrical energy by anodic exoelectrogenic bacteria. However, the mechanism of electron transfer in MFCs is still not clear. Considering for its future applications, high cost and the mechanisms of environmental factors affected the performance of MFCs still need to be investigated. In present thesis, research works were performed focusing on the multiple biomass conversion, development of new electrode materials and low-cost operation of MFCs. The aim is to decrease the cost of MFCs for future applications. Beer brewery wastewater was demonstrated for the first time as substrate in MFCs, and the maximum power density was 205mW·m-2 (30°C) in an air-cathode MFC using aboriginal bacteria as inoculum and full-strength wastewater as substrate. Decrease of temperature resulted in the decline of cathode potential and power density (170 mW·m-2). However, the COD removal efficiency and Coulombic efficiency (CE) were not affected by the temperature. Addition of buffer with concentrations of 50 and 200mmol·L-1 increased power densities. Power densities increased with increase of wastewater concentration, accompanied with a decrease of CE. Corn stover hydrolysate was also demonstrated to be suitable substrate for electricity generation in MFCs. The maximum power density was 644mW·m-2. Conductivity affected the anode potential, resulting in an increase of power density, followed by a decrease to 351mW·m-2. When the PBS concentration increased, power density possiblely due to high buffer capacity provided a neutral surface condition for cathode. By the bioaugmentation of exoelectrogenic bacteria and celluosic saccharificating bacteria (H-C), it was demonstrated for the first time that natural corn stover can be used for electricity generation in MFCs. The maximum power density was 331mW·m-2. Power can be increased into 406mW·m-2 when substrate was switched into steam exploded corn stover residual solids. Community analysis showed that the potential exoelectrogene in this system was Rhodopseudomonas palustris.New inexpensive anode material, carbon mesh, and Nafion/PTFE binder for cathodes can decrease both the unit volume cost and unit power cost by more than 70%, When using carbon mesh instead of E-TEK carbon cloth, the cost of anode materials reduced by 75%, and the maximum power density increased by 7%. The performance of carbon mesh without any pretreatment was low. However, after heating in furnace (450°C, 30min), the maximum power density was 3% higher than that using carbon mesh only cleaned by acetone, or 7% lower than ammonia treated carbon cloth. The mechanisms of performance enhancement after pretreatments were as follow: Acetone cleaning and heat pretreatment removed the surface contaminations that affected electron transfer, provided a larger electrochemical active area for electron transfer. Besides surface cleaning, N/C atomic ratio was one time higher after high temperature ammonia treatment than untreated samples, showing that nitrogen related functional groups (e.g. amine group) that facilitated electron transfer from bacteria to electrodes were formed. Based on the hypothesis, functionalization was performed using diazonium salt to connect amine group on the surface of carbon cloth anode. Power densities were not significantly increased when the amine group content is low. However, when the functional group content increased to 0.4% and 0.9% (w/w), the maximum power densities were similar with that obtained using ammonia treated anode, and the surface protein content were also similar. Over fictionalization inhibited bacterial growth, resulted in a decrease of power density. Novel inexpensive Nafion-PTFE mixed binders were developed to decrease the total cost of air-cathode. The maximum power densities linearly increased with percentage of Nafion in binders. The cost of binder will be decreased by 50 % with only a decrease of 25 % in power. During 25 cycles, the CEs of MFCs with Nafion binder was 20-29%, addition of PTFE into binders slightly decreased CEs to 17-26 %. No distinct change in maximum voltages was observed.The start-up time was decreased by poising anode potential at +200mV versus Ag/AgCl, which decreased the operational costs. High current generated in poised potential system was due to the high driving force of substrate oxidation. Similar performances were observed in MFCs using different start-up methods when systems were well acclimated. Further tests showed that higher anode potential over a range from -400 to +200mV resulted in a higher and earlier current peak. However, when anode potential increased further to +400mV, the peak current decreased to 6.9mA. CEs increased with anode potentials, and the low CE at low anode potentials (-400 to 0mV) were due to H2 and CH4 generation. Increasing anode potentials enhanced driving force of substrate oxidation and therefore inhibited the production of fermentation gas. The fraction of electron for bacterial growth decreased at high anode potential, indicating that the growth of bacteria was inhibited.To remove the energy consumable cathodic aeration, microbial carbon capture cells (MCCs) were constructed by growing Chlorella vulgaris in catholyte for in situ carbon capture and oxygen generation. The maximum power density was 5.6W·m-3. Cyclic voltammetry and dissolved oxygen tests showed that the cathode reaction was oxygen reduction. All the gaseous CO2 was sequestrated. Carbon balance showed that the carbon capture rate of MCC was 94±1%. MCC provided a new method for wastewater treatment with zero carbon emission.更多还原