Improvement of biohydrogen production by Enterobacter cloacae IIT-BT 08 under regulated pH

The present study investigates the effect of pH and intermediate products formation on biological hydrogen production using Enterobacter cloacae IIT-BT 08. Initial pH was found to have a profound effect on hydrogen production potential, while regulating the pH 6.5 throughout the fermentation was found to increase the cumulative hydrogen production rate and yield significantly. Modified Gompertz equation was used to fit the cumulative hydrogen production curves to obtain the hydrogen production potential P, the hydrogen production rate R and lag phase λ. At regulated pH 6.5, higher H(2) yield (3.1molH(2)mol(-1) glucose), specific hydrogen production potential (798.1mL/g) and specific rate of H(2) production (72.1mLL(-1)h(-1)g(-1)) were obtained. The volatile fatty acid profile showed butyrate, ethanol and acetate as the major end metabolites of fermentation under the operating pH conditions tested; however, their pattern of distribution was pH dependent. At the optimum pH of 6.5, the acetate to butyrate ratio (A/B ratio) was found to be higher than that at any other pH. The study also investigates the effect of sodium ions on biohydrogen production potential. It was also found that sodium ion concentration up to 250mM enhanced the hydrogen production potential; however, any further increase in the metal ion concentration had an inhibitory effect.     

溶氧及pH对产朊假丝酵母分批发酵生产谷胱甘肽的影响

在7 L发酵罐中研究了溶氧和pH对产朊假丝酵母分批发酵生产谷胱甘肽的影响。结果表明,当葡萄糖浓度为30 g/L且通气量控制在5 L/min时,搅拌转速达到300 r/min即可满足细胞生长和谷胱甘肽合成对溶解氧的需求。不同pH控制方式对谷胱甘肽分批发酵的影响有较大差异。不控制pH时,细胞干重和谷胱甘肽产量比控制pH为55的发酵分别低27%和95%,且有50%的谷胱甘肽向胞外渗漏。研究了将pH控制在4.0、4.5、5.0、5.5、6.0和6.5的谷胱甘肽分批发酵过程,发现在pH 5.5时谷胱甘肽总产量最高。用前期研究建立的动力学模型模拟了不同pH (4.0～6.5)下的分批发酵过程,并从动力学角度解释了pH对细胞生长和谷胱甘肽合成的影响。     

Hydrogen production by Rhodobacter sphaeroides strain O.U.001 using spent media of Enterobacter cloacae strain DM11

Combined dark and photo-fermentation was carried out to study the feasibility of biological hydrogen production. In dark fermentation, hydrogen was produced by Enterobacter cloacae strain DM11 using glucose as substrate. This was followed by a photo-fermentation process. Here, the spent medium from the dark process (containing unconverted metabolites, mainly acetic acid etc.) underwent photo-fermentation by Rhodobacter sphaeroides strain O.U.001 in a column photo-bioreactor. This combination could achieve higher yields of hydrogen by complete utilization of the chemical energy stored in the substrate. Dark fermentation was studied in terms of several process parameters, such as initial substrate concentration, initial pH of the medium and temperature, to establish favorable conditions for maximum hydrogen production. Also, the effects of the threshold concentration of acetic acid, light intensity and the presence of additional nitrogen sources in the spent effluent on the amount of hydrogen produced during photo-fermentation were investigated. The light conversion efficiency of hydrogen was found to be inversely proportional to the incident light intensity. In a batch system, the yield of hydrogen in the dark fermentation was about 1.86 mol H₂ mol⁻¹ glucose; and the yield in the photo-fermentation was about 1.5–1.72 mol H₂ mol⁻¹ acetic acid. The overall yield of hydrogen in the combined process, considering glucose as the preliminary substrate, was found to be higher than that in a single process.     

产氢菌Enterobacter sp.和Clostridium sp.的分离鉴定及产氢特性

在高温水体中分离得到2株具有较高产氢活性的微生物菌株Z-16和C-32。根据两菌株的16SrDNA序列分析,初步鉴定菌株Z-16为Enterobactersp.,菌株C-32为Clostridiumsp.。研究了起始pH值、反应温度、碳源等对菌株放氢活性的影响。菌株Z-16的最适产氢条件为:反应系统起始pH7·0,反应温度35℃,以蔗糖为产氢底物。在最适条件下,菌株Z-16的氢转化率为2·68molH2/mol蔗糖。菌株C-32的最适产氢条件为:反应系统起始pH8·0,反应温度35℃,以麦芽糖为产氢底物。在最适条件下,菌株C-32的氢转化率为2·71molH2/mol麦芽糖。以葡萄糖为碳源时,菌株Z-16和菌株C-32的氢转化率分别为2·35和2·48molH2/mol葡萄糖。     

Optimization of culture conditions for hydrogen production by Ethanoligenens harbinense B49 using response surface methodology

The design of an optimum and cost-efficient medium for high-level production of hydrogen by Ethanoligenens harbinense B49 was attempted by using response surface methodology (RSM). Based on the Plackett-Burman design, Fe(2+) and Mg(2+) were selected as the most critical nutrient salts. Subsequently, the optimum combination of the selected factors and the sole carbon source glucose were investigated by the Box-Behnken design. Results showed that the maximum hydrogen yield of 2.21 mol/mol glucose was predicted when the concentrations of glucose, Fe(2+) and Mg(2+) were 14.57 g/L, 177.28 mg/L and 691.98 mg/L, respectively. The results were further verified by triplicate experiments. The batch reactors were operated under an optimized condition of the respective glucose, Fe(2+) and Mg(2+) concentration of 14.5 g/L, 180 mg/L and 690 mg/L, the initial pH of 6.0 and experimental temperature of 35+/-1(o)C. Without further pH adjustment, the maximum hydrogen yield of 2.20 mol/mol glucose was obtained based on the optimized medium with further verified the practicability of this optimum strategy.     

初始底物浓度及pH对丁酸梭菌T4发酵木糖产氢的影响

本研究采用间歇培养方式对丁酸梭菌T4发酵木糖进行产氢研究,考察初始pH和初始底物浓度对其产氢特性的影响。结果表明,菌株T4在初始pH5.0～8.5及初始底物浓度5～40g/L时均可以产氢,其累积产氢量和最大比产氢速率随着pH及底物浓度的增加均呈现先增加后减少的趋势。在pH6.5和底物浓度20g/L时,比产氢速率和累积产氢量达到最大,分别为4.26L/L和18.86mmol-H2/hg-DCW,而后随着pH或者底物浓度的增加二者均呈现减少的趋势;在pH6.5和底物浓度15g/L时,得到最大值比产氢量为2.17mol/mol-木糖。而在不同的pH下,发酵产生的液态产物主要是乙酸和丁酸,其中在pH小于6.0时,有少量的丙酸生成,而在pH大于6.0时,则有乙醇生成。     

Microbial hydrogen production with Bacillus coagulans IIT-BT S1 isolated from anaerobic sewage sludge

Bacillus coagulans strain IIT-BT S1 isolated from anaerobically digested activated sewage sludge was investigated for its ability to produce H(2) from glucose-based medium under the influence of different environmental parameters. At mid-exponential phase of cell growth, H(2) production initiated and reached maximum production rate in the stationary phase. The maximal H(2) yield (2.28 mol H(2)/molglucose) was recorded at an initial glucose concentration of 2% (w/v), pH 6.5, temperature 37 degrees C, inoculum volume of 10% (v/v) and inoculum age of 14 h. Cell growth rate and rate of hydrogen production decreased when glucose concentration was elevated above 2% w/v, indicating substrate inhibition. The ability of the organism to utilize various carbon sources for H(2) fermentation was also determined.     

Effect of ammonia concentration on fermentative hydrogen production by mixed cultures

The effect of ammonia concentration ranging from 0 to 10 g N/L on fermentative hydrogen production by mixed cultures was investigated in batch tests using glucose as substrate at 35 degrees C and initial pH 7.0. The experimental results showed that during the fermentative hydrogen production, the substrate degradation efficiency increased with increasing ammonia concentration from 0 to 0.01 g N/L. The hydrogen production potential, hydrogen yield and average hydrogen production rate increased with increasing ammonia concentration from 0 to 0.1g N/L. The maximum hydrogen production potential of 291.4 mL, maximum hydrogen yield of 298.8 mL/g glucose and maximum average hydrogen production rate of 8.5 mL/h were all obtained at the ammonia concentration of 0.1g N/L.     

Increase in Silk Production by the Silkworm,Bombyx morì L., due to Oral Administration of a Juvenile Hormone Analog

(R)-1,3-butanediol ((R)-1,3-BD) is an important substrate for the synthesis of industrial chemicals. Despite its large demand, a bioprocess for the efficient production of 1,3-BD from renewable resources has not been developed. We previously reported the construction of recombinant Escherichia coli that could efficiently produce (R)-1,3-BD from glucose. In this study, the fermentation conditions were optimized to further improve 1,3-BD production by the recombinant strain. A batch fermentation was performed with an optimized overall oxygen transfer coefficient (82.3?h^?1) and pH (5.5); the 1,3-BD concentration reached 98.5?mM after 36?h with high-yield (0.444?mol (mol glucose)^?1) and a high maximum production rate (3.63?mM?h^?1). In addition, a fed-batch fermentation enabled the recombinant strain to produce 174.8?mM 1,3-BD after 96?h cultivation with a yield of 0.372?mol (mol glucose)^?1, a maximum production rate of 3.90?mM?h^?1, and a 98.6% enantiomeric excess (% ee) of (R)-1,3-BD.     

玉米芯发酵法生物制氢

在批式培养试验中, 以牛粪堆肥为天然产氢菌源, 玉米芯为底物, 通过厌氧发酵生产氢气。系统考察了底物预处理条件、初始pH值和底物浓度对玉米芯产氢能力的影响。在初始pH 8.0, 1.0%盐酸预处理底物30 min, 底物浓度10 g/L的最佳产氢条件下, 玉米芯最大产氢能力〔每克TVS（总挥发性固体物）产氢量〕和最大产氢速率（每克TVS每小时产氢量）分别为107.9 mL /g、4.20 mL/g·h-1。玉米芯经酸预处理后半纤维素含量由42.2%下降至3.0%, 而酸预处理的玉米芯产氢前后纤维素、半纤维素和木质素含量只有少量变化。产氢菌主要用酸预处理产生的可溶性糖产氢, 故底物的酸预处理对玉米芯的发酵产氢非常重要。用傅里叶变换红外光谱(FTIR)分析显示酸预处理和产氢过程中玉米芯的特征峰发生变化, 酸预处理过程降解了底物纤维素的无定形区和半纤维素, 产氢微生物对纤维素的结晶区有破坏作用。     

玉米芯发酵法生物制氢

在批式培养试验中, 以牛粪堆肥为天然产氢菌源, 玉米芯为底物, 通过厌氧发酵生产氢气。系统考察了底物预处理条件、初始pH值和底物浓度对玉米芯产氢能力的影响。在初始pH 8.0, 1.0%盐酸预处理底物30 min, 底物浓度10 g/L的最佳产氢条件下, 玉米芯最大产氢能力〔每克TVS（总挥发性固体物）产氢量〕和最大产氢速率（每克TVS每小时产氢量）分别为107.9 mL /g、4.20 mL/g·h-1。玉米芯经酸预处理后半纤维素含量由42.2%下降至3.0%, 而酸预处理的玉米芯产氢前后纤维素、半纤维素和木质素含量只有少量变化。产氢菌主要用酸预处理产生的可溶性糖产氢, 故底物的酸预处理对玉米芯的发酵产氢非常重要。用傅里叶变换红外光谱(FTIR)分析显示酸预处理和产氢过程中玉米芯的特征峰发生变化, 酸预处理过程降解了底物纤维素的无定形区和半纤维素, 产氢微生物对纤维素的结晶区有破坏作用。     

Production of acetic acid by Acetogenium kivui

Summary The formation of acetic acid by the thermophilic nonsporeforming homoacetogenic bacterium Acetogenium kivui was studied under various conditions. In pH-controlled batch fermentation at pH 6.4 this bacterium was able to produce up to 625 mM of acetic acid from glucose within 50–60 h. The value of _max obtained was about 0.17 h^-1, the yield was about 2.55 mol of acetic acid per mol of glucose utilized. In continuous fermentation both substrate concentration and dilution rate (D) influenced the yield of acetate and the stationary concentration: a glucose concentration of 67 mM at D=0.09 h^-1 resulted in 2.82 mol acetate/mol glucose and 190 mM acetate at a production rate of 17.1 mM/1 h. When the dilution rate was increased the production rate reached a maximal value of 43.2 mM/1 h at D=0.32 h^-1. At a glucose concentration of 195 mM the dependence of yield upon dilution rate followed a similar pattern and an acetate concentration of 420 mM could be obtained. Enzymatic studies indicate that in A. kivui pyruvate ferredoxin-oxidoreductase and acetate kinase are inhibited at acetate concentrations higher than 800 mM. Based on these results a fed-batch fermentation was developed, which allowed to produce more than 700 mM acetic acid within 40–50 h.Dedicated to Prof. Dr. H. J. Rehm on the occasion of his 60th birthday     

Ethanol fermentation in an immobilized cell reactor using Saccharomyces cerevisiae

Fermentation of sugar by Saccharomyces cerevisiae, for production of ethanol in an immobilized cell reactor (ICR) was successfully carried out to improve the performance of the fermentation process. The fermentation set-up was comprised of a column packed with beads of immobilized cells. The immobilization of S. cerevisiae was simply performed by the enriched cells cultured media harvested at exponential growth phase. The fixed cell loaded ICR was carried out at initial stage of operation and the cell was entrapped by calcium alginate. The production of ethanol was steady after 24 h of operation. The concentration of ethanol was affected by the media flow rates and residence time distribution from 2 to 7 h. In addition, batch fermentation was carried out with 50 g/l glucose concentration. Subsequently, the ethanol productions and the reactor productivities of batch fermentation and immobilized cells were compared. In batch fermentation, sugar consumption and ethanol production obtained were 99.6% and 12.5% v/v after 27 h while in the ICR, 88.2% and 16.7% v/v were obtained with 6 h retention time. Nearly 5% ethanol production was achieved with high glucose concentration (150 g/l) at 6 h retention time. A yield of 38% was obtained with 150 g/l glucose. The yield was improved approximately 27% on ICR and a 24 h fermentation time was reduced to 7 h. The cell growth rate was based on the Monod rate equation. The kinetic constants (K(s) and mu(m)) of batch fermentation were 2.3 g/l and 0.35 g/lh, respectively. The maximum yield of biomass on substrate (Y(X-S)) and the maximum yield of product on substrate (Y(P-S)) in batch fermentations were 50.8% and 31.2% respectively. Productivity of the ICR were 1.3, 2.3, and 2.8 g/lh for 25, 35, 50 g/l of glucose concentration, respectively. The productivity of ethanol in batch fermentation with 50 g/l glucose was calculated as 0.29 g/lh. Maximum production of ethanol in ICR when compared to batch reactor has shown to increase approximately 10-fold. The performance of the two reactors was compared and a respective rate model was proposed. The present research has shown that high sugar concentration (150 g/l) in the ICR column was successfully converted to ethanol. The achieved results in ICR with high substrate concentration are promising for scale up operation. The proposed model can be used to design a lager scale ICR column for production of high ethanol concentration.     

玉米秸秆水解液发酵联产氢气与2,3-丁二醇的初步研究

选用实验室自行筛选的Klebsiella pneumoniae ECU-15,进行了玉米秸秆水解液发酵联产氢气和2,3-丁二醇的初步研究。结果表明:以葡萄糖为碳源时,两目标产物随培养条件的改变呈现相同的变化趋势,且最佳发酵温度为37℃,最佳pH为6.0,最佳初始糖浓度为30 g/L;不同比例葡萄糖/木糖为混合碳源时,均能实现氢气和2,3-丁二醇的联产过程,但随着木糖含量的增加,细胞产量、氢气产量和2,3-丁二醇的产量都有所下降,并且木糖的存在会降低葡萄糖的消耗速率;实验最后以玉米秸秆水解液和同比例模拟合成培养基为底物,初步探明了该菌株利用水解液发酵联产氢气和2,3-丁二醇的可行性,最终氢气产量为0.65 v/v,产氢得率为0.43 mol/mol sugar;2,3-丁二醇产量为5.05 g/L,得率为0.82 mol/mol sugar。     

厌氧细菌Acetanaerobacterium elongatum从葡萄糖的产氢特性研究

为了了解影响厌氧发酵产氢细菌Acetanaerobacterium elongatumZ7产氢效率的因素,采用生理学方法对其进行了研究。结果表明:乙醇型发酵菌A.elongatumZ7的最适产氢温度为37℃,最适产氢的起始pH为8.0。该菌发酵葡萄糖和阿拉伯糖产氢的能力较强,氢气产率分别为1.55mol H2/mol葡萄糖和1.50mol H2/mol阿拉伯糖。酵母粉是菌株Z7生长和产氢所必须的生长因子;pH影响菌株的生长和葡萄糖利用率;氢压则影响电子流的分配,从而改变代谢产物乙酸和乙醇的比例;当产氢菌与甲烷菌共培养以维持发酵体系低的氢压时,可使氢的理论产量提高约4倍;培养基中乙酸钠浓度>60mmol/L明显抑制产氢。另外,一个只利用蛋白类物质的细菌能够促进菌株Z7对葡萄糖的利用,进而提供氢产量,为生物制氢的工业化生产提供理论参考。     

温度对谷胱甘肽分批发酵的影响及动力学模型

研究了24～32℃范围内产朊假丝酵母生产谷胱甘肽的分批发酵过程,发现较高温度对细胞生长有促进作用,而较低温度则更有利于谷胱甘肽产量的提高。应用改进的Logistic和LuedekingPiret方程分别对细胞生长动力学和谷胱甘肽合成动力学进行了模拟,得到不同温度下各种动力学参数。在此基础上,进一步研究了温度同细胞生长动力学参数之间的内在联系,得到谷胱甘肽分批发酵过程中细胞浓度的变化同温度以及底物浓度之间的一般关系式：dX-dt＝［0.0224(T+1.7)］2X(1-X/X_max)1+S｛8.26×10.6×exp［-31477/R/(T+273)］｝。验证实验结果表明,该模型具有很好的适用性。     

Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost

Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost was reported for the first time. Batch tests were carried out to analyze influences of several environmental factors on biohydrogen production from wheat straw wastes. The performance of biohydrogen production using the raw wheat straw and HCl pretreated wheat straw was then compared in batch fermentation tests. The maximum cumulative hydrogen yield of 68.1 ml H2/g TVS was observed at 126.5 h, the value is about 136-fold as compared with that of raw wheat straw wastes. The maximum hydrogen production rate of 10.14 ml H2/g TVS h was obtained by a modified Gompertz equation. The hydrogen content in the biogas was 52.0% and there was no significant methane observed in this study. In addition, biodegradation characteristics of the substrate were also discussed. The experimental results showed that the pretreatment of the substrate plays a key role in the conversion of the wheat straw wastes into biohydrogen by the composts generating hydrogen.     

Optimization of bio-hydrogen production from biodiesel wastes by Klebsiella pneumoniae

Biodiesel wastes containing glycerol were utilized by Klebsiella pneumoniae DSM 2026 to produce hydrogen. The optimization of medium components was performed using both Plackett-Burman and uniform design methods. Using the Plackett-Burman design, glycerol, yeast extract, NH(4)Cl, KCl and CaCl2 were found to be the most important components, which were further investigated by uniform design and second-order polynomial stepwise regression analysis. The optimized medium containing 20.4 g.L(-1) glycerol, 5.7 g.L(-1) KCl, 13.8 g.L(-1) NH(4)Cl, 1.5 g.L(-1) CaCl(2) and 3.0 g.L(-1) yeast extract resulted in 5.0-fold increased level of hydrogen (57.6 mL/50 mL medium) production compared to initial level (11.6 mL/50 mL medium) after 24 h of fermentation The optimization of fermentation condition (pH, temperature and inoculum) was also conducted. When the strain grew in the optimized medium under optimal fermentation condition in a 5-L stirred tank bioreactor for batch production, hydrogen yield and production reached 0.53 mol/mol and 117.8 mmol/L, respectively. The maximum hydrogen evolution rate was 17.8 mmol/(L.h). Furthermore, 1,3-propanediol (6.7 g.L(-1)) was also obtained from the liquid medium as a by-product.     

Optimisation of media and cultivation conditions for L(+)(S)-lactic acid production by Lactobacillus casei NRRL B-441

Process variables and concentration of carbon in media were optimised for lactic acid production by Lactobacillus casei NRRL B-441. Lactic acid yield was inversely proportional to initial glucose concentration within the experimental area (80-160 g l(-1)). The highest lactic acid concentration in batch fermentation, 118.6 g l(-1), was obtained with 160 g 1(-1) glucose. The maximum volumetric productivity, 4.4 g 1(-1) h(-1) at 15 h, was achieved at an initial glucose concentration of 100 g l(-1). Similar lactic acid concentrations were reached with a fedbatch approach using growing cells, in which case the fermentation time was much shorter. Statistical experimental design and response surface methodology were used for optimising the process variables. The temperature and pH optima for lactic acid production were 35 degrees C, pH 6.3. Malt sprout extract supplemented with yeast extract (4 g l(-1)) appeared to be an economical alternative to yeast extract alone (22 g l(-1)) although the fermentation time was a little longer. The results demonstrated both the separation of the growth and lactic acid production phases and lactic acid production by non-growing cells without any nutrient supplements. Resting L. casei cells converted 120 g l(-1) glucose to lactic acid with 100% yield and a maximum volumetric productivity of 3.5 g l(-1) h(-1).     

Influence of Ni(2+) concentration on biohydrogen production

In this paper, the effect of Ni(2+) concentration ranging from 0 to 50mg/L on fermentative hydrogen production by mixed cultures was investigated in batch test. The results showed that at 35 degrees C and initial pH 7.0, Ni(2+) was able to enhance the hydrogen production rate with increasing Ni(2+) concentration from 0 to 0.2mg/L, and enhance the hydrogen production potential and hydrogen yield with increasing Ni(2+) concentration from 0 to 0.1mg/L. The maximum hydrogen production potential of 288.6mL and the maximum hydrogen yield of 296.1mL/g glucose were obtained at the Ni(2+) concentration of 0.1mg/L. In all tests, the major soluble metabolites produced by mixed cultures were ethanol, acetic acid and butyric acid, without propionic acid. Ni(2+) had little effect on the substrate degradation efficiency with increasing concentration from 0 to 50mg/L. Ni(2+) was able to enhance the biomass production yield with increasing Ni(2+) concentration from 0 to 0.1mg/L. The maximum biomass production yield of 232.5mg/g glucose was obtained at the Ni(2+) concentration of 0.1mg/L. In all tests, the final pH after fermentative hydrogen production was lower than the initial pH.