【作者】 郭婉茜；

【导师】 任南琪；

【作者基本信息】 哈尔滨工业大学 ， 环境工程， 2008， 博士

【摘要】 氢气是清洁、高效、可再生能源,也是化石燃料的理想替代品之一。生物制氢具有回收能源和净化环境的双重功效。发酵法生物制氢技术产业化的关键因素是进一步提高反应器系统的产氢能力,降低生产成本。开发高效生物制氢反应器及提高反应器内的产氢微生物生物量是解决这一瓶颈因素的有效途径之一。与传统悬浮生长型反应器相比,附着生长型膨胀床反应器具有在低HRT条件下运行稳定,反应器内可保持较高生物量,传质效率高等优点。尽管如此,其在生物制氢领域的研究及应用还缺乏报道。所以,研究附着生长型膨胀床反应器的启动及运行调控,以获得较高的生物量和产氢能力,对于加速发酵法生物制氢技术的产业化进程具有重要意义。针对以上问题,本文采用3个相同设计尺寸的膨胀床反应器,系统地研究了附着型和颗粒型膨胀床的启动和运行调控及其影响因素,并对两种反应器的产氢效能进行了比较分析。对附着型膨胀床的研究发现,启动容积负荷对获得目标发酵类型至关重要。启动容积负荷为4 kgCOD/m3·d和8 kgCOD/m3·d的2个反应器分别在第32 d和第15 d实现了成功启动。启动容积负荷为8 kgCOD/m3·d的反应器形成乙醇型发酵。采用间歇试验,对反应器的接种污泥进行不同的预处理,并与不经过预处理的对照样品对比,发现多次曝气法是建立乙醇型发酵初始生态群落的有效预处理方法。多次曝气法预处理和加热预处理有效的抑制或杀灭了耗氢菌的活性,可以促进产氢。碱处理和酸处理对于微生物活性的恢复不利。碱处理可观察到甲烷,对耗氢菌的抑制不完全。群落分析结果表明,不同方法的预处理,改变了微生物的初始群落结构,是造成发酵类型及产氢能力差异的内在因素。以多次曝气法预处理的污泥为接种污泥,控制启动容积负荷为8 kgCOD/m3·d,启动附着型膨胀床,连续运行150 d,在运行容积负荷控制120 kgCOD/m3·d左右,pH平均值为4.2~4.4的条件下,反应器的平均产氢能力为0.71 L/L·h。对颗粒型膨胀床的研究表明,产氢颗粒污泥的形成是反应器成功启动的关键。以缺氧污泥混合厌氧颗粒污泥进行接种,可以快速培养出产氢颗粒污泥。容积负荷也间接影响了颗粒污泥的形成,当反应器容积负荷为36~96 kgCOD/m3·d时,颗粒污泥的粒径是随容积负荷的增加而增加的。快速缩短HRT,即加大进水流量来提高容积负荷,比保持HRT不变,提高进水COD浓度对产氢微生物快速颗粒化更加有效。通过快速缩短HRT的策略,可使颗粒污泥粒径增长加快了66.7 %。投加少量微粒载体,可促进产氢微生物颗粒化进程。应用响应曲面法中的CCD模型,对载体投加量和晶核载体的粒径对产氢微生物颗粒化的影响进行分析,发现二者对所形成的颗粒污泥的产氢速率、生物量和粒径都有影响。优化产氢的载体投加方案为:添加的载体粒径为0.68 mm,载体添加比为5.92 %时,预测产氢速率为13.47 L/d,预测生物量为15.82 g/L,预测形成的产氢颗粒污泥平均粒径为1.59 mm。随后进行的验证试验较好的证明了模型的准确性。综合对产氢微生物颗粒化的影响因素,启动颗粒型膨胀床生物制氢反应器,在启动后第20 d观察到颗粒污泥的形成。形成成熟颗粒污泥后,系统最大产氢能力达到1.07 L/L·h,污泥平均浓度高达24.1 gVSS/L。反应器中颗粒污泥的沉速随粒径的增大而增大;但在一定运行条件下,粒径增大到一定程度,沉速便不再增加。试验得到膨胀床内的产氢颗粒污泥在清水中的静沉速与粒径成二次多项式关系,可以表示为Y = 33.93x2 - 8.453x + 16.58,该式拟合程度较好,R2 = 0.998。可以较为准确的反映膨胀床中产氢颗粒污泥的粒径与沉速的关系。以葡萄糖为底物,启动和运行附着型和颗粒型膨胀床。附着型膨胀床在HRT为1.0 h,葡萄糖浓度为40 g/L时,最大产氢速率为6.54 L/L·h;颗粒型膨胀床在HRT为1.5 h,葡萄糖浓度为60 g/L时,最大产氢速率为6.85 L/L·h。而当HRT为1.0 h,葡萄糖浓度为40 g/L时,两个反应器获得的最大氢气产率分别为1.69 mol/mol-葡萄糖和1.54mol/mol-葡萄糖。两个反应器稳定运行时的平均生物量差别不大,均可达到25~29 g/L。微生物群落结构分析表明,生物膜和颗粒污泥表面群落结构复杂,细菌种类繁多,颗粒内部的菌群比较单调。生物膜和产氢颗粒污泥内形成了良好的产氢产酸微生态系统;产氢颗粒污泥外部活性要大于颗粒内部,产氢主要在颗粒污泥外部完成,颗粒污泥内部产氢细菌种类和数量较少。对于长期运行的附着型膨胀床,载体的定期补充是必须考虑的;而颗粒型反应器就不必考虑上述不足,所以基于降低运行成本和简化操作复杂性的目的,推荐选择颗粒型膨胀床作为连续流生物制氢反应器进行应用。更多还原

【Abstract】 Hydrogen is a clean, effetive and renewable energy, and is a satisfactory alternative for fossile hydrocarbon fuels in the future. Biohydrogen from waste is attactive due to energy recovery and environmental cleanup at the same time. Improving hydrogen-producing capacity and reducing the cost are the key factor to realize industrialization. One of the most effective ways is to employ high effecient reactor systems and obtain higher active biomass concentration. As compared to cell suspended growth systems, cell attached growth expanded bed system has been noted more efficient in obtaining higher biomass concentration and mass transfer in low HRT. Nevertheless, the research and application of this reactor is scarecely reported. Accordingly, deep understanding of the principles and applying techniques of the cell attached growth expanded bed hydrogen production reactor is quite necessary. The present research attempted to investigate the strategy of rapid startup and stable operation mainly on biofilm-based and granule-based expanded bed hydrogen production processes. Moreover, higher hydrogen production ability and biomass concentration are desired as well as stable operation.Aiming at solving the above problems, this thesis focused on startup and operation strategy and the factors, which affected the processes of biofilm-based and granule-based hydrogen-producing expanded bed reactors. The results showed organic loading rate (VLR) was a significant parameter in reactor control and hydrogen production, especially in fermentation types formation. When VLR was controled at 4 kgCOD/m3·d and 8 kgCOD/m3·d, the reactors achieved successful startup. Ethanol-type fermentation formed under the VLR of 8 kgCOD/m3·d.In order to enrich hydrogen production bacteria and establish better communities in mixed culture reactors, inoculation at start-up stage need pretreatment. Four pretreatment methods, this is, heat-shock, acid, alkaline and repeated-aeration pretreatment, were conducted. The heat-shock, acid and repeated-aeration pretreatment operation had effectively suppressed the methanogenic activity in the mixed culture, and the alkaline pretreatment was unsuccessful at methanogenesis repression. Different pretreatment methods could induce different fermentation types. Ethanol-type fermentation was observed by repeated-aeration pretreatment. The different pretreatment methods could affect the formation of microbial communities by the evaluation of denaturing gradient gel electrophoresis (DGGE) profiles. The results indicated that the pretreatment methods had probably led to the differences in the initial microbial communities, which were directly responsible for different fermentation types and hydrogen yields.Inoculated by repeated aeration pretreatment sludge, started at VLR of 8 kgCOD/m3·d, the biofilm-based expanded bed reactor performed well in 150 d operation, and the average hydrogen production rate was 0.71 L/L·h.Studies showed that hydrogen-producing granule formation is key factor to successful startup of granule-based expanded bed reactor. Inoculation source, the size and amount of the initial carrier, and VLR all affected microbial granulation. Mixture of anoxic sludge and anaerobic sludge was better choice for inoculation. VLR increase was favorable for granulation. It was also observed that quick decrease of HRT was effective in rapid granulation which increase of substrate concentration. The granulation period was shortened by 66.7 % using quick HRT decrease technique. Central composite design (CCD) using response surface methodology was applied to study the interactive effects of carrier size and amount on hydrogen producing bacteria granulation. The optimized results showed when granule size of 0.68 mm and inoculation ratio of 5.92 %, the predicted hydrogen production rate was 13.47 L/d, and the average biomass concentration was 15.82 g/L. According to the results of the statistical design, the verified tests were conducted in triplicate tests. The results showed that the excellent correlation between predicted and measured values verifies the model validation and existence of an optimal point.A granule-based expanded bed reactor was operated according to the optimized conditions obtained. Results showed that hydrogen-producing granule was observed at the 20 d from startup, and the maximum hydrogen production rate was 1.07 L/L·h with the average biomass concentration of 24.1 g/L. The settling velocity increased with granule size in the reactor. The granule size and the settling velocity was in an quadratic polynomial relationship, which could be expressed as Y = 33.93x2 - 8.453x + 16.58. The fitting index, R2 = 0.998, which suggested that the model was quite accurate to reflect the relationship of hydrogen producing granule size and the granule settling velocity.Glucose as substrate, startup at respectively optimized operating conditions, comparison tests were conducted to biofilm-based and granule-based expanded bed hydrogen-producing reactors. The results showed that when HRT of 1.0 h, the corresponding glucose concentration of 40 g/L, the biofilm-based expanded bed achieved maximum hydrogen production rate of 6.54 L/L·h; when HRT was 1.5 h, the corresponding glucose concentration of 60 g / L, the granule-based expanded bed reactor achieved maximum hydrogen production rate of 6.85 L/L·h. Moreover, when HRT of 1.0 h and the corresponding glucose concentration of 40 g/L, the two reactors obtained the maximum hydrogen yield of 1.69 mol/mol-glucose and 1.54 mol/mol-glucose, respectively. There was no significant difference observed in the average biomass in the two reactors. The average biomass concentration was all in a range of 25~29 g/L. The microbial communities were investigated by means of DGGE and Confocal Laser Scanning Microscope (CLSM) techniques. Results showed that the polysaccharide was unevenly distributed in the biofilm, and the concentration was less. However, in the hydrogen-producing granule, the polysaccharide was more evenly distributed with a high concentration. The microcosm was well established in the biofilm and the hydrogen-producing granule. There were more active hydrogen-producing bacteria detected in the outer section of the granule compared to the inner section, which was responsible for high effective hydrogen production.For long-term operation of the biofilm-based reactors, the regular supplement of the large amount of carrier should be taken into consideration. In contrast, the granule-based reactors would not to consider these shortcomings. As a result, based on the consideration of lower the operating costs and simplifying operational complexity, granule-based expanded bed reactor was recommended as better choice for a continuous flow reactor for large scale production of hydrogen.更多还原