【作者】 赵亚；

【导师】 刘志军；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2011， 博士

【摘要】 能源枯竭和环境污染是21世纪人类面临的两大难题,开发可再生的绿色能源,构建新的能源体系对实现人类可持续发展的目标具有战略性意义。生物制氢技术具有反应条件温和(常温常压)、节能环保和利用可再生生物废弃物资源等优点,因此备受关注。本文研究生物发酵制氢技术,以一氧化碳(CO)作为发酵底物,利用纯菌种Carboxydothermus hydrogenformans作菌源,分别在间歇进料和连续进料的培养条件下,通过厌氧发酵反应产生氢气(H2)。对菌株的发酵制氢机理、生长特性、底物消耗速率以及CO抑制浓度等因素进行深入研究,并考察在中空纤维膜反应器(HFMBR)内进行连续操作条件下,不同操作参数对产氢性能的影响。论文的主要内容如下：1. C.hydrogenformans菌能够以CO作为生长碳源和代谢能源,在厌氧环境中发酵制氢,通过CO脱氢酶(CODH)将底物中的H+还原为H2,同时将CO氧化为二氧化碳(CO2)。C.hydrogenformans菌发酵反应的氢气比生产速率(SHPR)和氢气得率(yield)均较高,Yield能达到96%。此外,该菌株能以丙酮酸盐作为碳源代谢发酵制氢,主要代谢产物为挥发性脂肪酸(VFA)和乙醇,但氢气Yield仅有17%；通过SEM和EDS等手段对菌群进行分析,发现其聚结培养基中的Ca和P等无机物质形成了晶体羟基磷灰石(Ca5 (PO4) 3OH)2.利用正交实验确定C.hydrogenformans生长培养基的最优组分配比,得出了P043,HCO3-,Ca2+和Mg2+四个离子浓度对各个实验目标的影响主次顺序以及最优化浓度,最终优化的溶液组成分别为PO43=1 mM, HCO3-=5 mM, Ca2+=0.1 mM和Mg2+=0.5 mM。最优化的营养液组成能够减少菌群中无机物质的积累,并保持菌株的最佳生物活性,得到了较高的SHPR和Yield。3.研究了C.hydrogenform ance发酵制氢的反应动力学,得到菌株的衰减系数和微生物比生长速率分别为0.022h-1和0.017h-1。在菌株初始浓度为5mg-VSS/L和8 mg-VSS/L时,分别得到最大Yield为97%和和最大SHPR为3.0mol/g-VSS.d。通过研究食微比(F/M)对SHPR的影响,对CO发酵制氢过程中的气液传质规律进行分析,得出了最佳的F/M为6.3mol-CO/g-VSS,即为了避免CO传质阻力对SHPR的影响,溶液上方空间的气相CO浓度应保持在176 g-CO(gas)/g-VSS以上(1atm,70℃,100 r/min)。此外,在CO的抑制动力学实验基础上,绘制了C.hydrogenformans发酵制氢的抑制动力学曲线,得出CO抑制浓度为0.55mmol/L。利用Monod扩展方程,建立CO抑制动力学模型,通过非线性拟合方法,得出最大底物消耗速率、底物抑制浓度和半饱和常数等反应动力学模型参数。4.本文结合了生物制氢和膜生物反应器两项内容,对膜生物反应制氢新技术进行研究,证实了HFMBR中利用CO气体连续高效发酵制氢的可行性。以提高反应器中产氢速率(HPR)和CO转化率(η)为目的,考察了操作压力(PCO)、CO进料载荷(Qg)、液相循环流量(Ql)和温度(T)对反应器制氢性能的影响。研究表明,通过气体渗透而产生的Qg是Pco的函数,在Qg为0.22mol/d和1.15mol/d时,分别得到反应器内最高η为97.6%和最大HPR为0.46mol/d。提高Ql,可以改善CO与H2O间的气液传质效果,进而提高反应器内的HPR。当Ql增大到1500ml/min时,得到最高气液传质系数为1.72h-1,但生物膜表面剪切力过大,造成了部分生物膜脱落,影响反应器制氢性能的稳定性。降低反应温度可以提高CO在液相中的溶解度,提高气液传质速率,但反应温度的降低抑制了菌株的最佳生物活性,从而限制了反应器内的生物制氢能力。HMBR系统长周期运行的稳定性较好,连续运行4个月,未发现膜污染问题；微生物挂膜能力强,纤维膜上固定的微生物细胞在反应器中的比例为84.5±1.6%,而且生物膜有机活性成分也较高,VSS/SS保持在86+5.9%。通过EDS分析得知,菌群中不再含有富含Ca和P的无机晶体,进一步验证了正交实验对培养基成分优化的有效性。膜生物反应器中的最高氢气比生产速率最高能达到0.85 mol/g-VSS.d,与传统反应器中最高的氢气比生产速率0.47 mol/g-VSS.d相比,提高了0.8倍。本文对厌氧嗜热菌C.hydrogenformans的发酵制氢反应进行理论研究、实验测试分析和模型计算,得出不同操作参数对HFMBR内传质和制氢效果的影响及过程强化途径,为膜反应器制氢新技术的理论研究和应用奠定了基础。更多还原

【Abstract】 Energy exhaustion and environmental pollution are the most two important issues in 21st centrury. Developping clean fuel energy and constructing new energy system have strategic importance to realize the target of the human sustainable development. Biohydrogen production has been paid more and more attention because it could be produced at ambient temperature and pressure, as well as its environmental friendly and low energy costing due to the source of renewable biological waste.This research is aimed to study biohydrogen production technology using CO as the carbon source and pure culture of Carboxydothermus hydrogenformans as the fermentative bacteria. Anaerobic fermentation for biohydrogen production experiments are carried out in batch and continuous feeding conditions, respetively. The biohydrogen producing mechanism, biomass growing charateristics, substrate consumption and CO inhibition has been studied. Operating parameters of anerobic fermentation are determined in a hollow fiber membrane bioreactor (HFMBR) for continuous biohydrogen prodcution. The main content of the study and the results are as follows:1 C.hydrogenformans is known to use CO as the sole source of carbon and energy to produce biohydrogen under anaerobic fermentation, in which CO is oxidized to CO2, while H+ is reduced to H2. High specific hydrogen production rate (SHPR) is obtained, as well as the high hydrogen yield (Yield) of 96%. Also C.hydrogenformans can use pyruvate as the carbon source to grow and produce hydrogen, however, low Yield of 17% is observed, most of the fementative productions are volatile fatty acids (VFA) and ethanol. The characteristic that C.hydrogenforans can gather Ca and P from the medium to form the crystal of hydroxyapatite is found though the SEM and EDS analysis.2 Orthogonal experimental design are performed to optimize the medium composition, the influence order and optimal concentration of PO43, HCO3-, Ca2+ and Mg2+are observed as 1 mM,5 mM,0.1 mM and 0.5 mM, respectively. The final optimized medium culture could not only avoid the formation of inorganic crystal in the biofilm but also keep the best SHPR and Yield.3 The reaction kinetics of anaerobic fermentation for biohydrogen production has been assessed, the biomass decay efficiency and maximal growth rate are calculated as 0.022 h-1 and 0.017 h-1, respectively. The best Yield (97%) and SHPR (3.0 mol/g-VSS.d) are obtained at initial biomass densities (Xo) of 5 mg-VSS/L and 8 mg-VSS/L. The mass transfer is studied and the optimal feed/microorganism (F/M) is observed at 6.3 mol-CO/g-VSS, that is to say the CO substrate in the head space should be over 176 g-CO(gas)/g-VSS(1 atm,70℃,100 r/min). Also the kinectic courve is plotted by the CO conversion rate as function of different CO concentration in the medium, CO inhibited concentration 0.55 mmol/L is observed. Also a nonlinear regression has been applied to fit Monod extended equation to estimate the maximal specific rates of substrate depletion, critical concentration of the inhibitory substrate and half-saturation constant.4 In this thesis, biohydroen fermentation technique and membrane bioreactor are united; a new biohydrogen production method is proposed—biohydrogen production from membrane bioreactors. The feasibility of continuous anaerobic fermentation for hydrogen production using CO in a HFMBR is improved. The objective of the reactor is to improve hydrogen producing rate (HPR) and CO conversion efficient (η) by evaluating the effects of paramenters of CO partrial pressure PCO, CO loading Qg, liquid recirculation rate Q1 and temperature T on the hydrogen producing ability in the reactor. The results indicates that Qg is function of PCO; the bestηof 97.6% and HPR of 0.46 mol/d are observed at Qg=0.22 mol/L and 1.15 mol/L, respectively. While increasing Q1 can increase CO-H2O mass transfer which improves the HPR in the reactor. The highest mass transfer coefficient of 1.72 h-1 is obtained at Q1=1500 ml/min. However, the latter augmentation of liquid recirculation coincides a drop of the immobilized C. hydrogenoformans, which is probably due to a severe alteration of the biofilm. Also, T is decreased to improve the mass transfer; however the biological activity of biomass is inhibited at lower T which limited the hydrogen producing ability in the reactor. The HFMBR has a long term working stability of 4 months, no membrane fouling is observed; 84.5±1.6% of the microorganism is cultivated and fixed on the hollow fiber as the biofilm, also high organic active ingredients is observed in the biofilm with a VSS/SS of 86±5.9%. EDS analysis is conducted in the biofilm, no crystals that containing Ca and P are observed any more, which indicates the validity of the optimized medium by orthogonal experimental design. The best SHPR 0.85 mol/g-VSS.d in the HFMR is 0.8 times higher than the best SHPR traditional bioreactors for hydrogen production of 0.57.The theoretical research, experimental analysis and model calculation are proceeded in this study, also experiments are carried out based on improving mass transfer and increasing biohydrogen producing ability by evaluating operating parameters in the reactor, which establishs theory study and practical application for the method of biohydrogen production in the membrane bioreactors.更多还原