【作者】 郭毅萍；

【导师】 樊耀亭；

【作者基本信息】 郑州大学 ， 无机化学， 2010， 博士

【摘要】 在环境和能源问题亟待解决的当今世界,利用废弃生物质发酵制氢越来越凸显出其战略性意义。本研究围绕纤维素类生物质发酵制氢的工业化目的,主要以纤维素类生物质的高效经济降解和发酵制氢效率的提高两方面为手段,对生物质厌氧发酵制氢工艺进行了成本及效率优化,并利用物理或化学等研究方法对其工艺机理进行了深入分析。具体内容如下：1.生物质发酵制氢过程基本参数的考察。通过对天然产氢菌源利用生物质发酵制氢过程中的主要生态因子的考察,确定了生物质厌氧发酵制氢的最佳参数。实验以牛粪堆肥作为天然产氢菌源,以经过生物法糖化预处理的玉米作为制氢底物,发现底物适当的生物预处理对发酵制氢有良好的促进作用,并且生物发酵制氢的最佳初始pH值条件随底物预处理程度的不同而变化：底物的糖化预处理越充分,适合厌氧发酵制氢的最佳初始pH值越低。当经过预处理的玉米中还原糖含量为51.2±3.6%,淀粉含量为32.4±2.8%,糖化率为61.1±3.9%时,在初始pH值为7.0的产氢体系中得到最大累积产氢量270.5 mL/g TVS。然后在底物的最佳糖化预处理条件下,利用响应面方法中的中心组合实验设计考察了底物浓度和初始pH值对生物发酵制氢的影响,发现底物浓度和初始pH值及其交互作用都是对厌氧发酵产氢潜能影响显著的因素,而对产氢速率影响显著的因素只有底物的浓度。通过对实验数据的回归分析,得到在底物浓度为10g/L以及初始pH值为6.0时,体系有最大厌氧发酵产氢潜能340mL/g TVS以及产氢速率11.5mL/h TVS。对最佳条件下生物发酵制氢过程中相关生态因子的考察发现,在系统高效产氢阶段体系的pH值为5.12-4.79,氧化还原电位(ORP)维持在-521mV到-458mV之间,发酵液态末端产物以丁酸为主,占末端产物总量的49.4%-55.7%。2.超声波处理天然产氢菌源消化污泥对生物发酵制氢的影响。该研究利用超声波处理消化污泥从而提高其生物制氢效果,考察了超声波处理消化污泥的最适条件及作用机理,确定了超声波处理方法对生物厌氧发酵制氢的积极作用。实验发现超声波对天然菌源消化污泥生物发酵制氢效果的影响程度与反应体系中底物的性质有关：越难以被降解利用的底物,超声波对其生物发酵制氢效果的促进作用越明显。由于本实验的主要目的是考察超声波对产氢菌源消化污泥的作用对生物制氢的影响,因此为了去除底物的干扰,选择易被微生物利用的蔗糖为产氢底物。实验利用Box-Wilson中心组合实验设计(CCD)分析优化了超声波功率和处理时间对生物厌氧发酵制氢的影响。回归分析数据表明超声波处理时间对消化污泥生物发酵产氢速率提升程度的影响最为显著,在处理消化污泥的超声波功率为130w/L及处理时间为10s时,厌氧发酵产氢效率是未用超声波处理的消化污泥产氢速率的1.34倍。对经过超声波处理的消化污泥在厌氧发酵制氢过程中的主要末端产物挥发性脂肪酸(VFAs)和还原糖的检测结果发现超声波处理没有改变生物制氢的发酵途径和发酵性质。并且将超声波同时作用于含有消化污泥和底物的产氢混合溶液时能使产氢速率提高1.48倍,单独作用于底物蔗糖时导致产氢速率提高1.17倍。同时发现超声波作用使消化污泥中可溶性COD的量显著增加,分析出超声波的作用机理是在不损坏消化污泥中微生物细胞的前提下将其中的有机大分子分解成小的颗粒,同时去除消化污泥中表面松弛、无活性组织的部分,使其包含的细胞间物质直接与反应态相接触。3.构建了纤维素粗酶固态降解玉米秸杆生物发酵制氢系统。将纤维素酶的制备与纤维素氢气的生产联合起来,通过纤维素酶从廉价生物质中的固态发酵制备、纤维素粗酶对玉米秸秆的生物降解、然后用于厌氧发酵制氢的方式,有效地降低了秸秆生物发酵制氢的成本。实验首先考察了利用绿色木霉Trichoderma viride固态发酵制备纤维素酶的环境因素,结果显示当固态发酵含水量为55%,接种量为15%,装瓶量为10g时,纤维素酶在250ml的三角瓶中发酵4天后得到最大纤维素酶滤纸酶活。然后利用Plackett-Burman设计实验筛选出固态发酵培养基组分中影响纤维素酶活性的三个主要因素,即硫酸镁浓度,玉米麸添加量和磷酸二氢钾浓度,用最陡爬坡路径使这三因素的浓度逼近最大响应区域,最后用Box-Behnken设计实验通过回归分析确定了三个主要因素对纤维素酶滤纸酶活的最大响应质量浓度分别为：硫酸镁0.20%,玉米麸9.0%,磷酸二氢钾0.61%,此时得到的最大滤纸酶活为8.9IU/gds,对比培养基优化前提高了37%。在利用制备的纤维素粗酶固态发酵降解秸秆的实验中,考察了纤维素粗酶剂量与秸秆糖化效果的关系,结果表明上述制备的纤维素酶对秸秆中的半纤维素有明显的降解作用,对秸秆中的纤维素有一定的降解作用,而对秸秆中的木质素几乎没有作用,说明所制备的纤维素粗酶中主要含有对半纤维素降解作用明显的酶系。当1g秸秆中加入1IU单位的纤维素粗酶,在40度恒温下固态厌氧发酵3天时,可以达到最佳的秸秆糖化效果。最后用经过纤维素粗酶处理过的秸秆厌氧发酵制备氢气,在反应体系初始pH值为6.5,牛粪堆肥浓度为100g/L,处理过的秸秆浓度20g/L以及厌氧发酵产氢时间为53h时得到最大累积产氢量122mL H2/g-TVS,此氢产量是未处理秸秆氢产量的45倍。更多还原

【Abstract】 It is well known that most contries will be on the verge of fossil fuels crisis in a few decades time. And the carbon emissions from the use of fossil fuels have led to global climate changes, environmental degradation as well as health problems. It is urgent to develop non-polluting and renewable energy source. Bio-hydrogen production from renewable organic wastes by anaerobic fermentation represents an important area because it accomplishes the dual goals of waste reduction and energy production. Furthermore, dark biohydrogen fermentation requires less inputs of electricity or energy compared to other hydrogen producing processes such as photosynthetic fermentation. Cellulose as the primary product of photosynthesis in terrestrial environments could be a vast renewable resource for bio-hydrogen production. However, from current situation, the reduction in cellulase production cost and the enhancement of the hydrogen producing bacteria activity are two burning keys to the industrialization of bio-hydrogen production from cellulosic biomass. In ordr to efficiently produce bio-hydrogen from cellulosic biomass, strategies were adopted to optimize the parameters in the bio-hydrogen producton process, and related mechanisms were also studied by physical or chemical methods in this paper. The main contents and results are following:1. The optimization and investigation of the basic parameters in bio-hydrogen production from biomass by anaerobic fermentation. The focus of this study was evaluating the performance and optimal operating conditions of bio-hydrogen from biomass in mixed culture.The seed of hydrogen producing bacteria was harvested from dairy manure compost. Results showed the bio-pretreatment of hydrogen producing substrate using one solid microbe additives greatly enhanced the bio-hydrogen production, and the optimal initial pH value changed along with the different saccharification hydrolysis efficiency of the substrate. The higher the saccharification efficiency was, the lower the optimal initial pH value. When the reducing sugar content in the pretreated substrate was 51.2±3.6%, starch content was 32.4±2.8% and saccharification efficiency was 61.1±3.9%, the cumulative hydrogen yield of 270.5 mL/g TVS was obtained at initial pH value of 7.0. And then statistically analysis based central composite experimental designs were applied to optimize the key process parameters of substrate concentration and initial pH valus for bio-hydrogen production from pretreated cron by dairy manure compost. Experimental results showed both of the two keys had individual and interactive significant influences on bio-hydrogen production yield, but just the substrate concentration had the significant influence on bio-hydrogen production rate. According to the regression analysis, the maximum bio-hydrogen production potential 340mL/g TVSand bio-hydrogen production rate 11.5mL/h TVS were obtained when substrate concentration was lOg/L and initial pH value was 6.0. The detection of main parameters showed in the optimal bio-hydrogen producing period the operational pH range was 5.12-4.79, the oxidation-reduciton potential maintained from-521mV to-458mV, and the main by-product in VFAs was butyrate, which occupied 49.4%-55.7% of liquid by-products.2. Effect of ultrasonic treatment of digestion sludge on bio-hydrogen production by anaerobic fermentation. The utilization of ultrasonic treatment on digestion sludge to enhance microbial activity for bio-hydrogen production was investigated. The objectives of this research were finding out the function of ultrasonic treatment on digestion sludge and making out ultrasonic mechanism on digestion sludge in bio-hydrogen producing process.Experimental results showed the effect of ultrasonic treatment of digestion sludge on bio-hydrogen production was related with the character of the hydrogen producing substrate, when the substrate was more difficult to be utilized, the enhancement effect of ultrasonic treatment of digestion sludge on bio-hydrogen production was more significant. Because the main aim in this study was to evaluate the effect of ultrasonic treatment of digestion sludge on bio-hydrogen production, the actions of hydrogen producing substrate should be avoided, so sucrose was chose as the hydrogen producing substrate, which was easier to be exploited by hydrogen producing bactiria. A Box-Wilson Central Composite Design (CCD) as an effective tool in batch tests was used to optimize the two independent variables of ultrasonic time and ultrasonic power. Regression analysis showed the liner term of ultrasonic exposure time (X1) and its square term as well as the interactive term of the two variables X1 X2 had a significant effect on the ratio of r values with the low P values of less than 0.1, and the liner term of ultrasonic exposure time had the strongest effect on the ratio. The optimal conditions of ultrasonic power and exposure time were 130w/L and 10s, respectively, while the predicted value of the ratio of hydrogen production rate obtained was 1.34. Total volatile fatty acids (VFAs) and three main by-products as well as carbohydrates changes in bio-hydrogen production processes between the ultrasonic treatment digestion sludge and the one without ultrasonic treatment were measured. Results implied the utilization of ultrasound to treat digestion sludge did not denature the biodegradation paths for bio-hydrogen production. Hydrogen production rate ratio of 1.48 appeared when ultrasonic treatment was applied directly on both substrates and digestion sludge at the same time, and the ratio of 1.17 was observed when ultrasound was just executed on substrates. Results also showed ultrasonic treatment of digestion sludge could greatly increased the soluble CODs concentration of digestion sludge. So the mechanism of ultrasonic treatment of digestion sludge on bio-hydrogen production was assisted in decentralizing the biological floc and disrupting large organic particles into smaller-size particles but not killing the microorganisms. Meanwhile, ultrasound disassembled the flaccid surface of digestion sludge and released the intercellular materials to the aqueous phase.3. A two-phase process combined cellulase production and bio-hydrogen production from cornstalk was constructed. Strategies were adopted to cost-efficiently produce cellulose-hydrogen by anaerobic fermentation in this study. First, cellulase used for hydrolyzing cellulose was prepared by solid-state fermentation (SSF) on cheap biomass from Trichoderma viride. Second, the crude cellulase was applied to cellulose-hydrogen process directly.When cellulase was produced, several cultural conditions for cellulase production on cheap biomass such as moisture content, inoculum size and culture time in solid-state fermentation were studied. According to the experimental results, the maximum cellulase activity was obtained at moisture content of 55%, fermentation substrates of lOg in 250mL flask, inoculums size of 15% and culture time of 4 days. And then the components of solid-state medium were optimized using statistical methods to further improve cellulase capability. Plackett-Burman experimental design was adopted to find out the important components in medium, which were MgSO4, corn bran and KH2PO4. Path of the steepest ascent was employed to find proper direction of the three changing variables. The significant independent variables of MgSO4, corn bran and KH2PO4 were further explored using Box-Behnken design. Regression results showed the maximum predicted value of FPA obtained was 8.9 IU/gds, when the optimal variables values were MgSO4 of 0.20 %, corn bran of 9.0% and KH2PO4 of 0.61%, respectively. The FPA values of cellulase increased 37% compared to the one before the optimization of medium compoents. When the cellulase was applied in cellulose-hydrogen production from cornstalk wastes, the effects of the dosage of the crude cellulose on the components of the corn stalk wastes and saccharification efficiency were tried at 40℃in anaerobic condition for 3 days. Cellulose, hemicellulose, and lignin as main components were analyzed before and after hydrolytic pretreatment of cornstalk wastes. Results implied that the enhanced soluble saccharides mostly came from the biodegration of hemi-cellulose and the crude cellulase had significant effect on hemi-cellulose than on cellulose and lignin. The dosage of 1IU/g cornstalk wastes was obtained as the proper proportion for cornstalk wastes hydrolysis by this crude cellulase. Bio-hydrogen production was carried out using hydrolytic cornstalk wastes as substrates and dairy manure compost as seed by anaerobic fermentation. The maximum cumulative hydrogen yield 122mL H2/g-TVS was obtained at initial pH 6.5, dairy manure compost concentration of 100g/l, substrate concentration of 20g/l and culture time 53h. This valure was about 45-fold than that from raw cornstalk wastes.更多还原