超高浓度(VHG)乙醇发酵研究进展

简要介绍了超高浓度乙醇发酵的特点及面临的困难,对VHG乙醇发酵国内外研究进展进行了综述,同时对该领域发展的前景进行了分析和展望。     

氧化还原电位控制下自絮凝酵母高浓度乙醇发酵

控制自絮凝酵母高浓度乙醇发酵过程的氧化还原电位（oxidoreduction potential, ORP）能降低环境胁迫对细胞的影响,提高乙醇生产强度和乙醇收率。实验考察了初始糖浓度为200、250、300 g·L^-1及ORP控制为-100、-150 mV和不控制的乙醇发酵情况。结果表明控制ORP的发酵过程,生物量和细胞存活率均高于不控制的系统,相应的发酵速度得到了提高,但是乙醇对糖的收率存在最优值。在实验设定初始糖浓度最高的300 g·L^-1的发酵过程中,控制ORP为-150 mV时,取得了最大的净乙醇生成量和乙醇对糖的收率。ORP控制改变了絮凝颗粒的粒径分布,运用多元线性拟合,发现ORP对絮凝的影响是正向的。ORP改变了发酵液中生物量及代谢物的浓度而间接影响了细胞的絮凝状况。     

高浓度乙醇发酵技术研究进展

高浓度乙醇发酵技术具有高设备利用率、高乙醇浓度、高细胞密度和高发酵效率等优点,能够有效提高发酵成熟醪乙醇浓度,降低生产成本,提高装置生产能力,是乙醇发酵行业及科研机构的主要研究方向之一.简述了高浓度乙醇发酵技术的原理、特点以及面临的问题,对高浓度乙醇发酵国内外研究进展进行了综述,同时对高浓度乙醇发酵的发展前景进行了展望...     

培养基优化以促进超高浓度发酵生产乙醇(英文)

An optimal medium (300 g·L-1 initial glucose) comprising 6.3 mmol·L-1 Mg2+, 5.0 mmol·L-1 Ca2+, 15.0 g·L-1 peptone and 21.5 g·L-1 yeast extract was determined by uniform design to improve very high gravity (VHG) ethanol fermentation, showing over 30% increase in final ethanol (from 13.1% to 17.1%, by volume), 29% decrease in fermentation time (from 84 to 60 h), 80% increase in biomass formation and 26% increase in glucose utilization. Experiments also revealed physiological aspects linked to the fermentation enhancements. Compared to the control, trehalose in the cells grown in optimal fermentation medium increased 17.9-, 2.8-, 1.9-, 1.8- and 1.9-fold at the fermentation time of 12, 24, 36, 48 and 60 h, respectively. Its sharp rise at the early stage of fermentation when there was a considerable osmotic stress suggested that trehalose played an important role in promoting fermentation. Meanwhile, at the identical five fermentation time, the plasma membrane ATPase activity of the cells grown in optimal medium was 2.3, 1.8, 1.6, 1.5 and 1.3 times that of the control, respectively. Their disparities in enzymatic activity became wider when the glucose levels were dramatically changed for ethanol production, suggesting this enzyme also contributed to the fermentation improvements. Thus, medium optimization for VHG ethanol fermentation was found to trigger the increased yeast trehalose accumulation and plasma membrane ATPase activity.     

气提法弱化超高浓度乙醇发酵过程中自絮凝酵母振荡行为

超高浓度(very high gravity,VHG)连续乙醇发酵过程中的振荡行为会导致发酵终点的乙醇浓度振荡和降低,是VHG连续乙醇发酵面临的主要问题。研究表明,游离酵母Saccharomyces cerevisiae 4126和自絮凝酵母BHL01在VHG连续乙醇发酵过程中,生物量、残糖、乙醇、甘油等发酵参数都呈现130～145 h的周期性振荡,且絮凝酵母发酵体系的平均乙醇浓度和乙醇生产强度都明显高于游离酵母体系。在絮凝酵母VHG连续乙醇发酵过程中利用发酵尾气气提分离乙醇,酵母细胞振荡行为被明显弱化,达到拟稳态状态,并且使发酵液中的残糖浓度控制在0.1 g·L^-1以下,平均乙醇浓度为110.87 g·L^-1,乙醇产率达到2.99 g·L^-1·h^-1。因此,本研究为弱化VHG连续乙醇发酵中的参数振荡行为提供了新的技术手段。     

超高浓度乙醇发酵培养基优化与酵母生理变化

为促进超高浓度乙醇发酵(350 g/L起始葡萄糖),采用均匀设计法优化发酵培养基成分,结果为8.2 mmol/L Mg2+,1.0 mmol/L Ca2+,30.0 g/L蛋白胨和27.1 g/L酵母浸出膏。采用该优化培养基,实验测得发酵终点乙醇体积分数为18.3%,比未优化时提高约58%,同时,菌体生长和葡萄糖转化利用等其它参数也明显提高。实验进一步探索与发酵状况改善有关的酵母生理方面的变化。结果表明,在发酵过程中生长于优化培养基的菌体的质膜ATP酶活力和胞内海藻糖含量明显高于对照组,提示二者在促进发酵中的重要作用。这是超高浓度乙醇发酵培养基优化引起酵母质膜ATP酶活力和胞内海藻糖含量变化的首次报道。     

液化温度对混合原料酒精高浓度发酵的影响

从液化温度对混合原料高浓度发酵的影响角度出发,分析了不同混合原料对液化温度的需求。通过试验表明,玉米原料采用105℃液化,而其他原料采用95℃液化,原料液化后再混合进行发酵的方式比原料混合后液化的方式发酵酒度提高7.2%。     

固定化酵母乙醇萃取发酵研究

以十二烷醇为萃取剂，对固定化酵母乙醇萃取发酵进行了研究。探讨了萃取剂对酵母细胞的毒性，以及萃取剂用量、搅拌转速、基质浓度等因素与乙醇萃取发酵的关系，并测定了萃取过程中乙醇的分配系数。为固定化酵母乙醇发酵与溶剂萃取耦合新工艺的开发研究提供了资料。     

超高浓度硝基水溶肥工艺实验研究

介绍了水溶性复肥因其速溶速效、节水省工、高效环保的优点,进行了采用硝酸钙与硫酸钾反应制取硝酸钾,加入磷酸用氨中和,再补充适量硝酸铵后制得均一养分的高深度水溶肥的实验。实验结果表明:该工艺小试条件下技术可行,生产出的19-18-19超高浓度硝基水溶性复合肥符合HG/T 4365-2012新标准。     

双酵母发酵膨化秸秆酶解液产乙醇研究

为了提高玉米秸秆的酶解率,对玉米秸秆进行膨化预处理,以乙醇质量浓度为影响值设计实验,研究时间、含氮量、温度、酵母比例四因素对发酵过程的影响。通过单因素试验及正交试验确定了双酵母发酵的最佳试验条件为48 h、含氮质量分数0.25%、33℃、酿酒酵母与毕赤酵母体积比3∶7,乙醇质量浓度可达10.2 g/L。本试验为秸秆乙醇的产业化生产提供技术依据。     

Application of full permeate recycling to very high gravity ethanol fermentation from corn

A ceramic membrane with pore size of 0.2 μm was used to percolate grain stillage of very high gravity (VHG) ethanol fermentation from corn, and the micro-filtration permeate was completely recycled for the cooking step in the next fermentation process. The concentrations of solids, sugars, total nitrogen and Na⁺ in the grain stillage and permeate reached a relative steady state after two or three batches of filtration and recycling process. There are no negative effects of by-products on VHG ethanol fermentation, and the final ethanol yield was above 15% (v/v). The conditions of filtration were examined to determine the optimum conditions for the process and included an initial flux of clean water above 550 L·m⁻²·h⁻¹ (0.1 MPa), an operating differential pressure of 0.15 MPa, an operating temperature above 70 °C, and a permeation flux greater than 136 L·m⁻²·h⁻¹. It could be concluded that full permeate recycling during ethanol production was an efficient process that resulted in less pollution and less energy consumption. Zhongyang Ding and Liang Zhang made equal contribution to this research.     

氧化度对超重力场净化硝烟效率的影响

针对两级旋转填料床强化吸收NOx过程中存在第二级效率低的问题,在两级间设立氧化塔,考察硝烟中NOx的脱除率随氧化度、超重力因子、喷淋密度、气速的影响规律。实验结果表明:NOx浓度越高,达到较高氧化度的时间越短;NOx浓度较低时,氧化度达到50%的氧化时间比较短,但要达到90%则需要较长氧化时间;不同超重力因子、喷淋密度、气速等条件下其脱除率均随氧化度的增加而增加;在较高NOx浓度和氧化度下,脱除率高于常规吸收平衡值的5%。     

Energy-saving direct ethanol production from viscosity reduction mash of sweet potato at very high gravity (VHG)

Sweet potato is an important dietary and economic material in China (accounting for 85% of global production in 2005) and Southeast Asia. The limitation of using root and tuber of sweet potato mash at high solids content is attributed to its high viscous nature. The aim of this study was to investigate the influence of different viscosity reduction factors and found optimal parameters via a surface response design. The optimal xylanase enzyme dose, pretreatment time and temperature were 1.56 AGU/g, 87.6 min and 44.1 °C, respectively. Using pretreatment sweet potato mash on the optimized condition, the final viscosity 498.1 cp and ethanol yield of 135.1 g/kg was obtained by Saccharomyces cerevisiae, which was equivalent to 90.7% of the theoretical yield.     

超重力法处理高浓度氮氧化物废气中试研究

采用超重力旋转填料床治理某厂硝化尾气,在前期研究基础上,中试试验重点考察操作参数及系统运行的稳定性。考察了进气量、液气比、超重力因子、吸收剂的浓度等因素对吸收率的影响,确定了治理氮氧化物的适宜条件。结果表明:在进气量100m3.h-1、液气比20L.m-3、超重力因子90和尿素浓度20%的条件下,单级吸收率达到了85.4%,采用两级串联吸收,连续稳定运行30天,平均吸收率达到了96%以上。     

Continuous ethanol fermentation using immobilized yeast in a fluidized bed reactor

Continuous ethanol fermentation of glucose using fluidized bed technology was studied. Saccharomyces cerevisiae were immobilized and retained on porous microcarriers. Over two-thirds of the total reactor yeast cell mass was immobilized. Ethanol productivity was examined as dilution rate was varied, keeping all other experimental parameters constant. Ethanol yield remained high at an average of 0.36 g ethanol g^?1 glucose (71% of theoretical yield) as the dilution rate was increased stepwise from 0.04 h^?1 to 0.14 h^?1. At a dilution rate of 0.15 h^?1, the ethanol yield steeply declined to 0.22 g ethanol g^?1 glucose (44% of theoretical yield). The low maximum percentage of theoretical yield is primarily due to an extended mean cell residence time, and possibly due to the inhibitory effect of a high dissolved carbon dioxide concentration, enhanced by the probable intermittent levels of low pH in the reactor. Constant ethanol production was possible at a high glucose loading rate of 840 g dm^?3 day^?1 (attained at a dilution rate of 0.14 h^?1). Although the highest average ethanol concentration (97.14 g dm^?3) occurred at the initial dilution rate of 0.04 h^?1, the peak average ethanol production rate (2.87 g (g yeast)^?1 day^?1) was reached at a greater dilution rate of 0.11 ^h-1. Thus, the optimal dilution rate was determined to be between 0.11 h^?1 and 0.14 h^?1. Ethanol inhibition on yeast cells was absent in the reactor at average bulk-liquid ethanol concentrations as high as 97.14 g dm^?3. In addition, zero-order kinetics on ethanol production and glucose utilization was evident.     

Performance analysis of an immobilized yeast packed-bed reactor for ethanol fermentation

The performance of an immobilized packed-bed bioreactor for continuous ethanol fermentation was evaluated. Immobilized yeasts were prepared by entrapment in calcium alginate gel. An axial dispersed plug flow model incorporating the effects of substrate and product inhibition on fermentation kinetics was developed. The model equations were solved by the method of orthogonal collocation and the suitability of the reactor model to predict the conversions obtained in this biocatalytic reaction system was assessed.     

Effect of various energy sources on the fermentation process of bovine colostrum

The present work consisted in evaluating the feasibility of utilizing different energy sources--corn, nixtamalized corn, sorghum and corn starch--in colostrum fermentation, by incorporating them in two different percentages, with and without the addition of acetic acid. The crude and true protein, ammonia, and dry matter content, as well as pH, total sugars, lactic acid, starches, dry matter digestibility, bacteriological count and gross energy, were studied. Results revealed that up to 10 days of fermentation, the most viable energy source was nixtamalized corn, and that the addition of acetic acid was not useful in colostrum preservation. The incorporation level of nixtamalized corn added to colostrum which rendered the best results, was that of 6.33%.     

Effect of phosphate rock sources on biological nitrogen fixation by soybean

Very little information is available concerning the effect of phosphate rock (PR) sources on biological nitrogen fixation (BNF) in legume crops. In a greenhouse study, the¹⁵N isotopic dilution technique was used to compare the effectiveness of three sources of PR (Hahotoe rock, Togo; Tilemsi rock, Mali; and Sechura rock, Peru) with that of triple superphosphate (TSP) in increasing soybean seed yield and the amounts of N fixed by the soybean crop. The acid Hartsells slit loam was limed to pH 5.2 and incubated with 8.5 mg N kg^–1 as K¹⁵NO₃ and sucrose for 2 months prior to planting. Then fertilizer P was incorporated into the soil at 12.5, 25, 50, and 100 mg P kg^–1 rates.The relative agronomic effectiveness (RAE) of the three PRs with respect to TSP (RAE = 100%) in terms of increasing seed yield was Hahotoe rock = 6.0%, Tilemsi rock = 45.9%, and Sechura rock = 75.2%; this trend followed the same trend as PR reactivity, i.e., Sechura rock > Tilemsi rock > Hahotoe rock. BNF was affected significantly by all the P treatments. Of the total N derived from the three N sources (atmosphere, N_dfa; fertilizer K¹⁵NO₃, N_dff; and soil, N_dfs), N_dfa was highest with TSP and lowest with Hahotoe rock, whereas the reverse was found with N_dfs. Among various plant parts, more N_dfa was translocated and stored in seeds than in stems + leaves and roots. The RAE values of the three PRs with respect to TSP (RAE = 100%) in terms of influencing the amount of BNF were Hahotoe rock = 3.0%, Tilemsi rock = 43.4%, and Sechura rock = 71.2%. A linear relationship was found between the amount of BNF by the whole soybean plant and the soybean seed yield.     

Simultaneous saccharification and fermentation of alkaline-pretreated corn stover to ethanol using a recombinant yeast strain

Bio-ethanol converted from cheap and abundant lignocellulosic materials is a potential renewable resource to replace depleting fossil fuels. Simultaneous saccharification and fermentation (SSF) of alkaline-pretreated corn stover for the production of ethanol was investigated using a recombinant yeast strain Saccharomyces cerevisiae ZU-10. Low cellobiase activity in Trichoderma reesei cellulase resulted in cellobiose accumulation. Supplementing the simultaneous saccharification and fermentation system with cellobiase greatly reduced feedback inhibition caused by cellobiose to the cellulase reaction, thereby increased the ethanol yield. 12 h of enzymatic prehydrolysis at 50 °C prior to simultaneous saccharification and fermentation was found to have a negative effect on the overall ethanol yield. Glucose and xylose produced from alkaline-pretreated corn stover could be co-fermented to ethanol effectively by S. cerevisiae ZU-10. An ethanol concentration of 27.8 g/L and the corresponding ethanol yield on carbohydrate in substrate of 0.350 g/g were achieved within 72 h at 33 °C with 80 g/L of substrate and enzyme loadings of 20 filter paper activity units (FPU)/g substrate and 10 cellobiase units (CBU)/g substrate. The results are meaningful in co-conversion of cellulose and hemicellulose fraction of lignocellulosic materials to fuel ethanol.     

Efficient electrochemical reduction of nitrate to nitrogen on tin cathode at very high cathodic potentials

The electrochemical reduction of nitrate on tin cathode at very high cathodic potentials was studied in 0.1 M K₂SO₄, 0.05 M KNO₃ electrolyte. A high rate of nitrate reduction (0.206 mmol min⁻¹ cm⁻²) and a high selectivity (%S) of nitrogen (92%) was obtained at −2.9 V versus Ag/AgCl. The main by-products were ammonia (8%) and nitrite (<0.02%). Small amounts of N₂O and traces of NO were also detected.As the cathodic potential increases, the %S of nitrogen increases, while that of ammonia displays a maximum at −2.2 V. The %S of nitrite decreases from 65% at −1.8 V to <0.02% at −2.4 V. The kinetic analysis indicated that the formation of nitrogen and ammonia proceeds through the intermediate nitrite.The reduction follows first order kinetics for both nitrate and nitrite at more cathodic potentials than −2.4 V, while at less negative potentials the kinetics is more complicated.The %Faradaic efficiency (%FE) of the reduction at −2.9 V was about 60% initially and decreased to 22% at 40 min.A cathodic corrosion of tin was observed, which was more intensive in the absence of nitrate. At potentials more negative than −2.4 V, small amounts of tin hydride were detected.