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1.
In this study, the challenge of selecting porous coordination networks (PCNs) as filler particles in mixed matrix membranes (MMMs) was examined using molecular simulations. PCNs are promising nanoporous materials in gas separations because of their tunable pore sizes, high porosities, good thermal and mechanical stabilities. Gas permeability and selectivity of 200 new MMMs composed of 20 different PCNs and 10 different polymers were calculated for CO 2/N 2 separation. We showed that selecting the appropriate PCN as filler particles in polymers results in MMMs that have high CO 2/N 2 selectivities and high CO 2 permeabilities compared with pure polymer membranes. Several PCN/polymer MMMs were identified to exceed the upper bound established for CO 2/N 2 separation. Effect of framework flexibility of PCNs on the performance of MMMs was also examined. Results showed that considering the flexibility of PCNs is important for predicting gas permeability of pure PCNs but has less significance for predicting gas permeability of PCN-filled MMMs whenever the PCN volume fraction is low. For rapid screening of PCN/polymer MMMs, flexibility of the fillers can be neglected as a reasonable approximation if the filler volume fraction is < 0.3. The methods introduced in this study will create many opportunities for selecting PCN/polymer combinations for MMMs with useful properties in CO 2 separation applications. 相似文献
2.
A system is described that combines the fermentation of cellulose to acetate, CH 4, and CO 2 by Ruminococcus albus and Methanobrevibacter smithii with the fermentation of acetate to CH 4 and CO 2 by Methanosarcina barkeri to convert cellulose to CH 4 and CO 2. A cellulose-containing medium was pumped into a co-culture of the cellulolytic R. albus and the H 2-using methanogen, Mb. smithii. The effluent was fed into a holding reservoir, adjusted to pH 4.5, and then pumped into a culture of Ms. barkeri maintained at constant volume by pumping out culture contents. Fermentation of 1% cellulose to CH 4 and CO 2 was accomplished during 132 days of operation with retention times (RTs) of the Ms. barkeri culture of 7.5–3.8 days. Rates of acetate utilization were 9.5–17.3 mmol l −1 day −1 and increased with decreasing RT. The K
s for acetate utilization was 6–8 mM. The two-stage system can be used as a model system for studying biological and physical
parameters that influence the bioconversion process. Our results suggest that manipulating the different phases of cellulose
fermentation separately can effectively balance the pH and ionic requirements of the acid-producing phase with the acid-using
phase of the overall fermentation.
Received: 7 December 1999 / Received revision: 28 April 2000 / Accepted: 19 May 2000 相似文献
3.
Summary In animal nutrition, incubation of feed samples with CO 2/HCO 3-buffered rumen fluid is used to predict the nutritional values of the feed. During fermentation, volatile fatty acids (VFAs) are produced, which release CO 2 from the buffer through their H + ions. This indirect gas production amounted to 20.8 ml gas per mmol VFA. By incubating glucose, rice starch and cellulose, the relationship between direct and indirect gas production in relation to fermentation kinetics was studied. The total amount of gas formed was found to be dependent on the composition of the fermentation end-products formed. This could be described by: ml gas = M v·mmol HAc + 2M v·mmol HB + 0.87M v·mmol Tot. VFA where HAc = acetic acid; HB = butyric acid; and M v = molar gas volume. No clear relationship was found between the rate of fermentation and total gas production. From rice starch more total gas was produced than from glucose and cellulose, which were fermented faster and slower, respectively.
Correspondence to: S. F. Spoelstra 相似文献
4.
Over the past decade, in vitro methods have been developed to study intestinal fermentation in pigs and its influence on the digestive physiology and health. In these methods, ingredients are fermented by a bacterial inoculum diluted in a mineral buffer solution. Generally, a reducing agent such as Na 2S or cysteine-HCl generates the required anaerobic environment by releasing metabolites similar to those produced when protein is fermented, possibly inducing a dysbiosis. An experiment was conducted to study the impact of two reducing agents on results yielded by such in vitro fermentation models. Protein (soybean proteins, casein) and carbohydrate (potato starch, cellulose) ingredients were fermented in vitro by bacteria isolated from fresh feces obtained from three sows in three carbonate-based incubation media differing in reducing agent: (i) Na 2S, (ii) cysteine-HCl and (iii) control with a mere saturation with CO 2 and devoid of reducing agent. The gas production during fermentation was recorded over 72 h. Short-chain fatty acids (SCFA) production after 24 and 72 h and microbial composition of the fermentation broth after 24 h were compared between ingredients and between reducing agents. The fermentation residues after 24 h were also evaluated in terms of cytotoxicity using Caco-2 cell monolayers. Results showed that the effect of the ingredient induced higher differences than the reducing agent. Among the latter, cysteine-HCl induced the strongest differences compared with the control, whereas Na 2S was similar to the control for most parameters. For all ingredients, final gas produced per g of substrate was similar ( P>0.10) for the three reducing agents whereas the maximum rate of gas production ( Rmax) was reduced ( P<0.05) when carbohydrate ingredients were fermented with cysteine-HCl in comparison to Na 2S and the control. For all ingredients, total SCFA production was similar ( P>0.10) after 24 h of fermentation with Na 2S and in the control without reducing agent. Molar ratios of branched chain-fatty acids were higher ( P<0.05) for protein (36.5% and 9.7% for casein and soybean proteins, respectively) than for carbohydrate (<4%) ingredients. Only fermentation residues of casein showed a possible cytotoxic effect regardless of the reducing agent ( P<0.05). Concerning the microbial composition of the fermentation broth, most significant differences in phyla and in genera ascribable to the reducing agent were found with potato starch and casein. In conclusion, saturating the incubation media with CO 2 seems sufficient to generate a suitable anaerobic environment for intestinal microbes and the use of a reducing agent can be omitted. 相似文献
5.
The work investigated the properties and feasibility of using bacterial cellulose membrane (BCM) as a new and environmental friendly support carrier to immobilize glutamate decarboxylase (GAD) (a unique enzyme in the conversion of γ-aminobutyric acid (GABA) production). During cultivation, the porosities of BCM decreased successively with more extended fibrils piling above one another in a criss-crossing manner thus forming condensed and spatial structure. The BCM with this ultrafine network structure was found to immobilize GAD best via covalent binding because of the highest efficiency of immobilization (87.56% of the enzyme was bonded) and a good operational stability. And the covalent binding efficiency (amount of enzyme immobilized versus lost) was closely related to the porosity or the inner network of the BCM, not to the surface area. The capacity per surface area (mg/cm 2) increased from 1.267 mg/cm 2 to 3.683 mg/cm 2 when the porosity of BCM ranged from 49% to 73.80%, while a declining trend of the loss of GAD specific activity (from 29.30%/cm 2 to 7.38%/cm 2) was observed when the porosity increased from 49.9% to 72.30%. Two non-linear regression relationships, between the porosity and loading capacity and between porosity and enzyme activity loss, were empirically modeled with the determination of coefficient R2 of 0.980 and 0.977, respectively. Finally, the established in vitro enzymatic conversion process demonstrated 6.03 g/L of GABA at 0.10 mol/L Glu, 60 min of retention time and 160 mL of suspension volume after the 1st run and a loss of 4.15% after the 4th run. The productivity of GABA was 6.03 g L ?1 h ?1, higher than that from other reported processes. 相似文献
6.
To improve the yield of cellulose production in bacteria, we investigated the stimulatory effects of six different alcohols
during fermentation of Acetobacter xylinum 186. Our study showed that after static fermentation at 30°C for 6 days, bacterial culture with 1.0% (v/v) of methanol added
in the medium produced the highest bacterial cellulose (BC) yield at 103.5 mg/100 ml, which was 21.8% higher than the control
group. Addition of 0.5% of ethylene glycol in the culture yielded 105.5 mg/100 ml BC, 24.1% higher than the control group.
Adding 0.5% of n-propanol yielded 96.4 mg/100 ml BC, 13.4% higher; 3.0% of glycerol yielded 108.3 mg/100 ml BC, 27.4% higher; 0.5% of n-butanol yielded 132.6 mg/100 ml BC, 56.0% higher; and 4.0% of mannitol in the culture yielded 125.2 mg/100 ml BC, 47.3% higher,
respectively. The rate of bacterial cellulose production increased with the growth rate of the bacteria. The stimulatory effects
of these alcohols that we observed were significant in the later stage of fermentation, which was considered to be important
for the biosynthesis of bacterial cellulose. 相似文献
7.
Life cycle assessment (LCA) of indigenous freshwater microalgae, Scenedesmus dimorphus, cultivation in open raceway pond and its conversion to biodiesel and biogas were carried out. The LCA inventory inputs for the biogas scenario was entirely based on primary data obtained from algal cultivation (in pilot scale raceway pond), harvesting, and biogas production; while only the downstream processing involved in biodiesel production namely drying, reaction and purification were based on secondary data. Overall, eight scenarios were modeled for the integrated process involving: algae-based CO2 capture and downstream processing scenarios for biodiesel and biogas along with impact assessment of nutrient addition and extent of recycling in a life cycle perspective. The LCA results indicated a huge energy deficit and net CO2 negative in terms of CO2 capture for both the biodiesel and biogas scenarios, majorly due to lower algal biomass productivity and higher energy requirements for culture mixing. The sensitivity analysis indicated that variability in the biomass productivity has predominant effect on the primary energy demand and global warming potential (GWP, kg CO2 eq.) followed by specific energy consumption for mixing algal culture. Furthermore, the LCA results indicated that biogas conversion route from microalgae was more energy efficient and sustainable than the biodiesel route. The overall findings of the study suggested that microalgae-mediated CO2 capture and conversion to biodiesel and biogas production can be energy efficient at higher biomass productivity (> 10 g m−2 day−1) and via employing energy-efficient systems for culture mixing (< 2 W m−3). 相似文献
8.
The physical parameters of cellulose such as surface area and porosity are important in the development of cellulose composites which may contain valuable additives which bind to cellulose. In this area, the use of acid hydrolyzed nano-dimensional cellulose nanowhiskers (CNWs) has attracted significant interest, yet the surface area and porosity of these materials have not been explored experimentally. The objective of this work was to characterize the surface area and porosity of CNWs from different origins (plant cotton/bacterium Gluconacetobacter xylinus) and different acid treatments (H 2SO 4/HCl) by N 2 adsorption; as well as to compare surface area and porosity of bacterial cellulose synthesized by static and agitated cultures. Our results showed that CNWs produced from H 2SO 4/HCl exhibited significantly increased surface area and porosity relative to starting material cotton fiber CF11. Micropores were generated in HCl hydrolyzed CNWs but not in H 2SO 4 hydrolyzed CNWs. Bacterial CNWs exhibited larger surface area and porosity compared to plant CNWs. Cellulose synthesized by G. xylinus ATCC 700178 from agitated cultures also exhibited less surface area and porosity than those from static cultures. 相似文献
9.
Exploration of triclosan analogs has led to novel diaryl ureas with significant potency against in vitro cultures of drug-resistant and drug-sensitive strains of the human malaria parasite Plasmodium falciparum. Compound 18 demonstrated EC 50 values of 37 and 55 nM versus in vitro cultured parasite strains and promising in vivo efficacy in a Plasmodium berghei antimalarial mouse model, with >50% survival at day 31 post-treatment when administered subcutaneously at 256 mg/kg. This series of compounds provides a chemical scaffold of novel architecture, as validated by cheminformatics analysis, to pursue antimalarial drug discovery efforts. 相似文献
10.
The production of bioethanol, biohydrogen and biogas from wheat straw was investigated within a biorefinery framework. Initially, wheat straw was hydrothermally liberated to a cellulose rich fiber fraction and a hemicellulose rich liquid fraction (hydrolysate). Enzymatic hydrolysis and subsequent fermentation of cellulose yielded 0.41 g-ethanol/g-glucose, while dark fermentation of hydrolysate produced 178.0 ml-H 2/g-sugars. The effluents from both bioethanol and biohydrogen processes were further used to produce methane with the yields of 0.324 and 0.381 m 3/kg volatile solids (VS) added, respectively. Additionally, evaluation of six different wheat straw-to-biofuel production scenaria showed that either use of wheat straw for biogas production or multi-fuel production were the energetically most efficient processes compared to production of mono-fuel such as bioethanol when fermenting C6 sugars alone. Thus, multiple biofuels production from wheat straw can increase the efficiency for material and energy and can presumably be more economical process for biomass utilization. 相似文献
11.
Atmospheric CO 2 enrichment may impact arbuscular mycorrhizae (AM) development and function, which could have subsequent effects on host plant species interactions by differentially affecting plant nutrient acquisition. However, direct evidence illustrating this scenario is limited. We examined how elevated CO 2 affects plant growth and whether mycorrhizae mediate interactions between C 4 barnyard grass ( Echinochloa crusgalli (L.) Beauv.) and C 3 upland rice ( Oryza sativa L.) in a low nutrient soil. The monocultures and combinations with or without mycorrhizal inoculation were grown at ambient (400 ± 20 μmol mol ?1) and elevated CO 2 (700 ± 20 μmol mol ?1) levels. The 15N isotope tracer was introduced to quantify the mycorrhizally mediated N acquisition of plants. Elevated CO 2 stimulated the growth of C 3 upland rice but not that of C 4 barnyard grass under monoculture. Elevated CO 2 also increased mycorrhizal colonization of C 4 barnyard grass but did not affect mycorrhizal colonization of C 3 upland rice. Mycorrhizal inoculation increased the shoot biomass ratio of C 4 barnyard grass to C 3 upland rice under both CO 2 concentrations but had a greater impact under the elevated than ambient CO 2 level. Mycorrhizae decreased relative interaction index (RII) of C 3 plants under both ambient and elevated CO 2, but mycorrhizae increased RII of C 4 plants only under elevated CO 2. Elevated CO 2 and mycorrhizal inoculation enhanced 15N and total N and P uptake of C 4 barnyard grass in mixture but had no effects on N and P acquisition of C 3 upland rice, thus altering the distribution of N and P between the species in mixture. These results implied that CO 2 stimulation of mycorrhizae and their nutrient acquisition may impact competitive interaction of C 4 barnyard grass and C 3 upland rice under future CO 2 scenarios. 相似文献
12.
Studies have been made on the temperature dependence of both the hydraulic conductivity, Lp, and the THO diffusion coefficient, ω, for a series of cellulose acetate membranes (CA) of varying porosity. A similar study was also made of a much less polar cellulose triacetate membrane (CTA). The apparent activation energies, Ea, for diffusion across CA membranes vary with porosity, being 7.8 kcal/mole for the nonporous membrane and 5.5 kcal/mole for the most porous one. Ea for diffusion across the less polar CTA membrane is smaller than Ea for the CA membrane of equivalent porosity. Classical viscous flow, in which the hydraulic conductivity is inversely related to bulk water viscosity, has been demonstrated across membranes with very small equivalent pores. Water-membrane interactions, which depend upon both chemical and geometrical factors are of particular importance in diffusion. The implication of these findings for the interpretation of water permeability experiments across biological membranes is discussed. 相似文献
13.
Physical cleaning and/or chemical cleaning have been generally used to control biofouling in the reverse osmosis (RO) process. However, conventional membrane cleaning methods to control biofouling are limited due to the generation of by-products and the potential for damage to the RO membranes. In this study, supercritical carbon dioxide (SC CO 2) treatment, an environmentally friendly technique, was introduced to control biofouling in the RO process. SC CO 2 (100 bar at 35°C) treatment was performed after biofouling was induced on a commercial RO membrane using Pseudomonas aeruginosa PA01 GFP as a model bacterial strain. P. aeruginosa PA01 GFP biofilm cells were reduced on the RO membrane by >8 log within 30 min, and the permeate flux was sufficiently recovered in a laboratory-scale RO membrane system without any significant damage to the RO membrane. These results suggest that SC CO 2 treatment is a promising alternative membrane cleaning technique for biofouling in the RO process. 相似文献
14.
The timely enumeration of cells of nanocellulose-producing bacteria is challenging due to their unique growth properties. To better understand the metabolism of the bacteria and better control the concentration of living cells during cultivation, a prompt cell counting technology is crucial and urgently required. In this work, two fluorescent dyes, the asymmetrical anthocyanidin dye SYBR Green I (SG) and propidium iodide (PI), were first combined for Komagataeibacter xylinus species to determine live/dead bacterial cells quantitatively and promptly. The number of live and dead K. xylinus cells determined using an epifluorescence microscope corresponded well to the results obtained using a fluorescence microplate reader. The R2 values were 0.9986 and 0.9920, respectively, and were similar to those obtained with the LIVE/DEAD ® BacLight TM commercial kit. SG/PI double-staining showed proper efficiency in distinguishing live/dead cells for the K. xylinus strain ( R2 = 0.9898). The technology was applied to standardize four different K. xylinus strains, and the initial cell concentration of the strains was precisely controlled (no significant difference among the strains, P> 0.05). The cellulose yield per live cell was calculated, and significant differences ( P < 0.05) were found among the four strains in the following order: DHU-ATCC-1> DHU-ZCY-1> DHU-ZGD-1> ATCC 23770. The study shows (i) the application of the SG/PI staining to standardizing inocula for bacterial cellulose production so that a more accurate comparison can be made between different strains, and (ii) the lower cost of using SG rather than the SYTO 9 of the commercially available LIVE/DEAD ® BacLight TM kit. 相似文献
15.
Summary In an effort to establish the reasons for the limitations in the final ethanol concentration of Zymomonas mobilis fermentation, the effects of CO 2 and ethanol on the fermentation were investigated using continuous and fed-batch cultivation systems. The nucleation and
stripping out of CO 2 from the fermenter using diatomaceous earth or nitrogen gas or both exhibited a profound effect on the glucose uptake rate
during the early stages of fed-batch fermentation, but did not improve final ethanol yields. The addition of ethanol together
with above mentioned experiments confirmed conclusively that ethanol inhibition is responsible for the final ethanol concentration
obtainable during Zymomonas mobilis fermentation. The final concentration lies between 90 and 110 gl −1 or approximately 12–15% (v/v) ethanol. 相似文献
16.
Controlling the concentration of dissolved oxygen is a standard feature in aerobic fermentation processes but the measurement
of dissolved CO 2 concentrations is often neglected in spite of its influence on the cellular metabolism. In this work room air and room air
supplemented with 5 and 10% carbon dioxide were used for aeration during the cultivation of the thermophilic microorganism
Bacillus caldolyticus (DSM 405) on starch to produce α-amylase (E.C. 3.2.1.1) and neutral protease (E.C. 3.4.24.27/28). The increased CO 2 concentrations resulted in a 22% raise in activity of secreted α-amylase and a 43% raise in protease activity when compared
with aeration with un-supplemented room air. There was no effect on the final biomass concentration. Furthermore, the lag-phase
of fermentation was reduced by 30%, further increasing the productivity of α-amylase production. Determinations of dissolved
CO 2 in the culture broth were conducted both in situ with a probe as well as using exhaust gas analysis and both the methods
of quantification showed good qualitative congruence. 相似文献
17.
Acetogens such as Clostridium ljungdahlii can play a crucial role reducing the human CO 2 footprint by converting industrial emissions containing CO 2, CO and H 2 into valuable products such as organic acids or alcohols. The quantitative understanding of cellular metabolism is a prerequisite to exploit the bacterial endowments and to fine-tune the cells by applying metabolic engineering tools. Studying the three gas mixtures CO 2 + H 2, CO and CO + CO 2 + H 2 (syngas) by continuously gassed batch cultivation experiments and applying flux balance analysis, we identified CO as the preferred carbon and electron source for growth and producing alcohols. However, the total yield of moles of carbon (mol-C) per electrons consumed was almost identical in all setups which underlines electron availability as the main factor influencing product formation. The Wood–Ljungdahl pathway (WLP) showed high flexibility by serving as the key NAD + provider for CO 2 + H 2, whereas this function was strongly compensated by the transhydrogenase-like Nfn complex when CO was metabolized. Availability of reduced ferredoxin (Fd red) can be considered as a key determinant of metabolic control. Oxidation of CO via carbon monoxide dehydrogenase (CODH) is the main route of Fd red formation when CO is used as substrate, whereas Fd red is mainly regenerated via the methyl branch of WLP and the Nfn complex utilizing CO 2 + H 2. Consequently, doubled growth rates, highest ATP formation rates and highest amounts of reduced products (ethanol, 2,3-butanediol) were observed when CO was the sole carbon and electron source. 相似文献
18.
Mass culture of microalgae is a potential alternative to cultivation of terrestrial crops for bioenergy production. However, microalgae require nitrogen fertiliser in quantities much higher than plants, and this has important consequences for the energy balance of these systems. The effect of nitrogen fertiliser supplied to microalgal bubble-column photobioreactor cultures was investigated using different nitrogen sources (nitrate, urea, ammonium) and culture conditions (air, 12% CO 2). In 20 L cultivations, maximum biomass productivity for Chlorella vulgaris cultivated using nitrate and urea was 0.046 and 0.053 g L −1 day −1, respectively. Maximum biomass productivity for Dunaliella tertiolecta cultivated using nitrate, urea and ammonium was 0.033, 0.038 and 0.038 g L −1 day −1, respectively. In intensive bubble-column photobioreactors using 12% CO 2, maximum productivity reached 0.60 and 0.83 g L −1 day −1 for C. vulgaris and D. tertiolecta, respectively. Recycling of nitrogen within the photobioreactor system via algal exudation of nitrogenous compounds and bacterial activity was identified as a potentially important process. The energetic penalty incurred by supply of artificial nitrogen fertilisers, phosphorus, power and CO 2 to microalgal photobioreactors was investigated, although analysis of all energy burdens from biomass production to usable energy carriers was not conducted. After subtraction of the power, nitrogen and phosphorus energy burdens, maximum net energy ratios for C. vulgaris and D. tertiolecta cultivated in bubble columns were 1.82 and 2.10. Assuming CO 2 was also required from a manufactured source, the net energy ratio decreased to 0.09 and 0.11 for C. vulgaris and D. tertiolecta, so that biomass production in this scenario was unsustainable. Although supply of nitrogen is unlikely to be the most energetically costly factor in sparged photobioreactor designs, it is still a very significant penalty. There is a need to optimise both cultivation strategies and recycling of nitrogen in order to improve performance. Data are supported by measurements including biochemical properties (lipid, protein, heating value) and bacterial number by epifluorescence microscopy. 相似文献
19.
Growth kinetics of Aspergillus niger strain A.n./61 on a solid medium containing beet pulp were examined. Solid state fermentation was carried out in laboratory microfermenter (aerated packed columns). During the experiments the CO 2 evolution, protein biosynthesis, as well as cellulose and sucrose utilization were determined. It was found that CO 2 evolution evidently increased in the logarithmic phase, together with the protein biosynthesis. Between 30–32 h of culture CO 2 evolution and protein content in product were the greatest. Subsequently, CO 2 evolution decreased. During 28 h of culture, cellulose was slightly utilized, the strain using mainly sucrose. Intense utilization of cellulose was paralleled by a drop in CO 2 evolution. 相似文献
20.
The evolution of CO 2 in a fed-batch culture of recombinant Escherichia coli containing human-like collagen (HLC) cDNA was determined with an O 2-enriched air supply (40%, v/v) in a 12.8 l fermentor; a maximum CO 2 concentration of 12.7% in the effluent gas was detected. The CO 2 pulse injection experiments showed that: (1) a 20% CO 2 pulse introduced in the batch cultivation phases inhibited cell growth but if introduced in the fed-batch cultivation phases
slightly stimulated growth; and (2) CO 2 inhibited HLC expression only in the expression phase, where the final HLC concentration decreased by 34% under a 3 h 20%
CO 2 pulse. The higher the CO 2 concentration and/or the longer the duration of the CO 2 pulse, the stronger the stimulatory or inhibitory effects.
An erratum to this article can be found at 相似文献
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