The Possibility of Meeting Greenhouse Energy and CO<Subscript>2</Subscript> Demands Through Utilisation of Cucumber and Tomato Residues

The article examines the possibility of using residues from greenhouse cucumber and tomato cultivation as biomass for energy and CO₂ production in order to meet greenhouse needs. Methane fermentation and combustion were compared. Moreover, the legitimacy of ensiling as a storage method for biogas plant was evaluated. The tested waste was found to be an unsuitable feedstock for the production of silage due to low sugar and high protein content. Fresh waste had a higher biogas yield than silage; however, its fermentation lasted longer. Furthermore, the results showed that, in the case of fresh residues, the methane fermentation proved to be a more energy-efficient process, while air-dry biomass is a more sustainable feedstock for combustion. The energy and CO₂ balance showed that, regardless of the method used, the available quantity of waste is too small to meet the greenhouse needs.     

蝉拟青霉液体发酵条件优化

采用液体发酵蝉拟青霉,对蝉拟青霉的发酵条件进行优化,以提高蝉拟青霉胞外多糖产量及生物量。摇瓶发酵条件下,在单因素基础上设计正交实验确定各因素的最佳组合。优化后得最佳发酵培养基:蔗糖8%,牛肉膏0.75%,酵母膏0.125%,MgSO_4·7H_2O 0.3%,KH_2PO_4 0.2%,麸皮0.5%。该条件下胞外多糖产量为5.96 g/L,生物量为42 g/L,较优化前提高了1倍。采用发酵罐进行扩大培养,对分批发酵时的初糖浓度进行了优化,并分析了补料分批发酵对发酵过程的影响。发酵罐培养时最适初糖浓度为5%,此时生物量最高为38 g/L,多糖含量最高为5.5 g/L;采用补料分批发酵时,多糖产量最高为5.89 g/L,生物量最高为40 g/L,效果优于分批发酵。     

Effect of phosphate supply and aeration on poly-β-hydroxybutyrate production in Azotobacter chroococcum

The effects of phosphate supply and aeration on cell growth and PHB accumulation were investigated in Azotobacter chroococcum 23 with the aim of increasing PHB production. Phosphate limitation favoured PHB formation in Azotobacter chroococcum 23, but inhibited growth. Azotobacter chroococcum 23 cells demonstrated intensive uptake of orthophosphate during exponential growth. At the highest phosphate concentration (1·5 g/litre) and low aeration the amount of intracellular orthophosphate/g residual biomass was highest. Under conditions of fed-batch fermentation the possibility of controlling the PHB production process by the phosphate level in the cultivation medium was demonstrated. A 36 h fed-batch fermentation resulted in a biomass yield of 110 g/litre with a PHB cellular concentration of 75% dry weight, PHB content 82·5 g/litre, PHB yield Y_P/S = 0·24 g/g and process productivity 2·29 g/litre·h.     

Der Einfluß der Prozeßparameter auf die Ethanolausbeute in Batchprozessen bei Verwendung von Saccharomyces cerevisiae

The production costs of ethanol are dependent on the efficiency of the substrate-ethanol conversion to a high degree. The more the substrate used during the fermentation is converted into alcohol the better is the economy of the process. Therefore the ethanol yield Y _S^P is an important object of the process optimization. In batch fermentation processes the most essential influence factors are the initial biomass concentration X₀, the initial substrate concentration S₀, the temperature T, and the pH-value. A model reflecting the complex relationships between these influence factors and the ethanol yield could be obtained by regression. It allows an exact valuation of these optimum process parameters which are necessary for realizing high ethanol yields in the batch fermentation. For the strain Saccharomyces cerevisiae Sc 5 used in this research was found an ethanol yield maximum Y_S^P = 0˙5384 at the parameters X₀ = 64.61 g/l S₀ = 82.91 g/l T = 36.45°C pH = 6.54.     

Application of Supercritical Fluid Extraction in Biotechnology

ABSTRACT

In the present paper recent investigations on the applications of supercritical fluid extraction (SCE) from post fermentation biomass or in situ extraction of inhibitory fermentation products as a promising method for increasing the yield of extraction have been reviewed. Although supercritical CO₂ (SC-CO₂) is unfriendly, or even toxic, for some living cells and precludes direct fermentation in dense CO₂, it does not rule out other useful applications for in situ extraction of inhibitory fermentation products and fractional extraction of biomass constituents. This technique is a highly desirable method for fractional extraction of biomass constituents, and intracellular metabolites due to the potential of system modification by physical parameters and addition of co-solvents to selectively extract compounds of different polarity, volatility and hydrophilicity without any contamination.     

A thermodynamic analysis of electron production during syngas fermentation

Currently, syngas fermentation is being developed as one option towards the production of biofuels from biomass. This process utilizes the acetyl-CoA (Wood-Ljungdahl) metabolic pathway. Along the pathway, CO and CO₂ are used as carbon sources. Electrons required for the metabolic process are generated from H₂ and/or from CO. This study showed that electron production from CO is always more thermodynamically favorable compared to electron production from H₂ and this finding is independent of pH, ionic strength, gas partial pressure, and electron carrier pairs. Additionally, electron production from H₂ may be thermodynamically unfavorable in some experimental conditions. Thus, it is unlikely that H₂ can be utilized for electron production in favor of CO when both species are present. Therefore, CO conversion efficiency will be sacrificed during syngas fermentation since some of the CO will provide electrons at the expense of product and cell mass formation.     

Co‐hydrolysis of lignocellulosic biomass for microbial lipid accumulation

The herbaceous perennial energy crops miscanthus, giant reed, and switchgrass, along with the annual crop residue corn stover, were evaluated for their bioconversion potential. A co‐hydrolysis process, which applied dilute acid pretreatment, directly followed by enzymatic saccharification without detoxification and liquid–solid separation between these two steps was implemented to convert lignocellulose into monomeric sugars (glucose and xylose). A factorial experiment in a randomized block design was employed to optimize the co‐hydrolysis process. Under the optimal reaction conditions, corn stover exhibited the greatest total sugar yield (glucose + xylose) at 0.545 g g^?1 dry biomass at 83.3% of the theoretical yield, followed by switch grass (0.44 g g^?1 dry biomass, 65.8% of theoretical yield), giant reed (0.355 g g^?1 dry biomass, 64.7% of theoretical yield), and miscanthus (0.349 g g^?1 dry biomass, 58.1% of theoretical yield). The influence of combined severity factor on the susceptibility of pretreated substrates to enzymatic hydrolysis was clearly discernible, showing that co‐hydrolysis is a technically feasible approach to release sugars from lignocellulosic biomass. The oleaginous fungus Mortierella isabellina was selected and applied to the co‐hydrolysate mediums to accumulate fungal lipids due to its capability of utilizing both C5 and C6 sugars. Fungal cultivations grown on the co‐hydrolysates exhibited comparable cell mass and lipid production to the synthetic medium with pure glucose and xylose. These results elucidated that combining fungal fermentation and co‐hydrolysis to accumulate lipids could have the potential to enhance the utilization efficiency of lignocellulosic biomass for advanced biofuels production. Biotechnol. Bioeng. 2013; 110: 1039–1049. © 2012 Wiley Periodicals, Inc.     

A mathematical approach for the estimation of biomass production rate in solid state fermentation

The oxygen uptake rate (OUR) was studied in a solid state fermentation process of dried citrus peel with the strain Aspergillus niger QH-2 in order to obtain the growth estimation of the microorganism in the system. The relationship between OUR, the maintenance coefficient (m) and the yield for oxygen consumption Y_O2 allows the estimation of the biomass rate if we consider that both parameters are not constants in some periods of the process. It was estimated that in the first 24th the strain has an specific growth rate of 0.174 h^?1 with values for Y_O2 and m in the order of 2.84 g-cell/g-oxygen and 0.006 g-oxygen/g-cell ·h respectively.     

Solid-state fermentation for production of griseofulvin on rice bran using Penicillium griseofulvum

Griseofulvin is a secondary metabolite produced from fungal species that have morphology suitable for solid-state fermentation (SSF). Reports on production of griseofulvin by SSF are scarce. The present work investigates SSF for griseofulvin production, optimization of its process parameters vis-à-vis the conventional submerged fermentation and its downstream processing from the same. Rice bran adjusted to an initial moisture content (IMC) of 50% (v/w) inoculated with 1 mL of a suspension of 10(6) spores/mL under agitation at 250 rpm containing the modified Czapek-Dox medium and additional 0.1% choline chloride as a precursor gave a yield of griseofulvin in 9 days that was comparable to submerged fermentation after 28 days. The yield of griseofulvin (microg/g dry biomass) was comparable in SSF and submerged fermentation. The biomass was estimated by estimation of chitin. Discussions on the effect of each parameter in SSF have also been included.     

Indirect method for quantification of cellular biomass in a solidscontaining medium used as pre-culture for cellulase production

A process that combines the advantages of solid state fermentation (SSF) and submerged fermentation (SmF) could increase the efficiency of cellulase production required in the cellulosic ethanol industry. Due to the difficulty of measuring cellular biomass in the presence of solids, we developed a novel methodology for indirect quantification of biomass during production of the preculture for a combined fermentation process. Cultivation of Aspergillus niger was initiated as SSF using sugar cane bagasse as a solid substrate. Experiments were conducted in the absence of bagasse to determine growth kinetic parameters. Changes in glucose and biomass concentrations were measured. and the data were used for simulation employing a simple unstructured model. Parameters were estimated by applying a combination of Simulated Annealing (SA) and Levenberg-Marquardt (LM) algorithms to search for minimization of the error between model estimates and experimental data. Growth kinetics followed the Contois model, with a maximum specific growth rate (μ_max) of 0.042/h, a yield coefficient for biomass formation (Y_x/s) of 0.30 g/g and a death constant (k_D) of 0.005/h.These parameters were used to simulate cellular growth in the solids-containing medium. The proposed model accurately described the experimental data and succeeded in simulating the cell concentration profile. The selected pre-culture conditions (24 h as SSF followed by 48 h as SmF) were applied for cellulase production using the combined fermentation process and resulted in an endoglucanase activity (1,052 ± 34 U/L) greater than that obtained using the conventional SmF procedure (824 ± 44 U/L). Besides the standardization of pre-culture conditions, this methodology could be very useful in systems where direct measurement of cell mass is not possible.     

棘孢曲霉固态发酵柚皮产柚苷酶的条件优化

【目的】以柚皮为原料,优化棘孢曲霉利用柑橘加工副产物固态发酵柚苷酶的条件。【方法】采用高效液相色谱法检测酶活力,通过单因素试验考察固水比、装样量、接种量、温度对柚苷酶发酵的影响,用正交试验优化发酵条件。【结果】单因素试验结果的显著性分析表明培养基的固水比、装样量和培养温度对柚苷酶产量有显著性影响,而接种量影响不显著;经正交试验确定的优化条件是：固水比1:1 (质量体积比),装样量5 g/250 mL三角瓶,温度为30 °C,接种1 mL孢子悬浮液,发酵8 d。在此优化条件下,柚苷酶酶活力为8.19 IU/g干物质,比初始培养基产柚苷酶活力提高7.38倍。【结论】通过对固水比、装样量和发酵温度进行优化,大幅度提高了棘孢曲霉固态发酵柑橘加工副产物的柚苷酶产量,为柚苷酶的生产提供了一种高产发酵工艺。     

Estimation of fermentation biomass concentration by measuring oxygen uptake off-line with an oxygen electrode

Summary An indirect method for biomass determination was developed for aerobic cultivation in media containing solid substrates. This method involved off-line estimation of oxygen uptake with an oxygen electrode using a calibration factor and was applied to penicillin fermentation with Penicillium chrysogenum. The volumetric oxygen uptake rate was independent of the amount of sample sealed in the measuring cell. Storage of the sample for a period up to 2.5 h also had no influence on the rate of O₂ uptake. The specific O₂ uptake rate at 70 to 75 h fermentation time was used as the calibration factor to calculate the respiration-active part of the biomass. Specific penicillin V formation rates related to net dry weight, respiration-active biomass (X _A )and RNA content were compared. Only the penicillin V production rate related to X _A showed a similar behaviour as the penicillin V production rate related to RNA content. For this reason, it is assumed that X _A ,like RNA content, is more closely related to the metabolic state of the cells than the net dry weight. This method, therefore, provides a more suitable reference parameter for fermentation control than the generally used net dry weight.Offprint requests to: D. Siegmund     

Modelling of concentration profiles in tower fermenter. The influence of the axial dispersion coefficient

The production of CO₂ in tower fermenters which can cause back mixing, and thereby reducing the efficiency of such fermenters has been modelled with respect to fermentation. It is confirmed that the effect is significant. The effect of variations in the kinetic parameters, the maximum specific growth rate and the biomass yield coefficient was found to be insignificant. A good correlation between experimental and calculated data was obtained.     

Lactic acid production with Lactobacillus casei ssp. rhamnosus NBIMCC 1013: Modeling and optimization of the nutrient medium

The medium needed to perform a fermentation process with viable cells of Lactobacillus casei ssp. rhamnosus NBIMCC 1013 for the production of lactic acid was modeled and optimized. On the basis of single‐factor experiments and statistical analysis, the significant factors affecting the fermentation process, i.e. the concentration of carbon source, concentrations of both yeast and meat extracts, and the range of variability of these components were determined. Modeling and optimization of the medium contents were performed using central composite design. The composition of the medium used for the production of lactic acid (g/L) was as follows: glucose 69.8, meat extract 17.07, yeast extract 10.9, CH₃COONa 10, K₂HPO₄ 0.25, KH₂PO₄ 0.25, MgSO₄·7H₂O 0.05, and FeSO₄ 0.05. The maximum specific growth rate of the lactic acid bacteria (μ=0.51 h⁻¹) and other kinetic parameters were determined during cultivation in a laboratory bioreactor using the logistic equation and the Luedeking–Piret model. The obtained medium allows the production of lactic acid under optimum conditions, at high specific sugar assimilation rates and high lactic acid accumulation rates. The positive results of the paper are the new nutrient medium for lactic acid production and the process kinetic model, enabling scaling up and switching to a continuous process.     

Short-term effect of acetate and ethanol on methane formation in biogas sludge

Biochemical processes in biogas plants are still not fully understood. Especially, the identification of possible bottlenecks in the complex fermentation processes during biogas production might provide potential to increase the performance of biogas plants. To shed light on the question which group of organism constitutes the limiting factor in the anaerobic breakdown of organic material, biogas sludge from different mesophilic biogas plants was examined under various conditions. Therefore, biogas sludge was incubated and analyzed in anaerobic serum flasks under an atmosphere of N₂/CO₂. The batch reactors mirrored the conditions and the performance of the full-scale biogas plants and were suitable test systems for a period of 24 h. Methane production rates were compared after supplementation with substrates for syntrophic bacteria, such as butyrate, propionate, or ethanol, as well as with acetate and H₂+CO₂ as substrates for methanogenic archaea. Methane formation rates increased significantly by 35 to 126 % when sludge from different biogas plants was supplemented with acetate or ethanol. The stability of important process parameters such as concentration of volatile fatty acids and pH indicate that ethanol and acetate increase biogas formation without affecting normally occurring fermentation processes. In contrast to ethanol or acetate, other fermentation products such as propionate, butyrate, or H₂ did not result in increased methane formation rates. These results provide evidence that aceticlastic methanogenesis and ethanol-oxidizing syntrophic bacteria are not the limiting factor during biogas formation, respectively, and that biogas plant optimization is possible with special focus on methanogenesis from acetate.     

Canopy warming caused photosynthetic acclimation and reduced seed yield in maize grown at ambient and elevated [CO2]

Rising atmospheric CO₂ concentration ([CO₂]) and attendant increases in growing season temperature are expected to be the most important global change factors impacting production agriculture. Although maize is the most highly produced crop worldwide, few studies have evaluated the interactive effects of elevated [CO₂] and temperature on its photosynthetic physiology, agronomic traits or biomass, and seed yield under open field conditions. This study investigates the effects of rising [CO₂] and warmer temperature, independently and in combination, on maize grown in the field throughout a full growing season. Free‐air CO₂ enrichment (FACE) technology was used to target atmospheric [CO₂] to 200 μmol mol^?1 above ambient [CO₂] and infrared heaters to target a plant canopy increase of 3.5 °C, with actual season mean heating of ~2.7 °C, mimicking conditions predicted by the second half of this century. Photosynthetic gas‐exchange parameters, leaf nitrogen and carbon content, leaf water potential components, and developmental measurements were collected throughout the season, and biomass and yield were measured at the end of the growing season. As predicted for a C₄ plant, elevated [CO₂] did not stimulate photosynthesis, biomass, or yield. Canopy warming caused a large shift in aboveground allocation by stimulating season‐long vegetative biomass and decreasing reproductive biomass accumulation at both CO₂ concentrations, resulting in decreased harvest index. Warming caused a reduction in photosynthesis due to down‐regulation of photosynthetic biochemical parameters and the decrease in the electron transport rate. The reduction in seed yield with warming was driven by reduced photosynthetic capacity and by a shift in aboveground carbon allocation away from reproduction. This field study portends that future warming will reduce yield in maize, and this will not be mitigated by higher atmospheric [CO₂] unless appropriate adaptation traits can be introduced into future cultivars.     

Optimization of a Propionibacterium acidipropionici continuous culture utilizing sucrose

To produce propionic acid and vitamin B₁₂ from sucrose, the strain Propionibacterium acidipropionici NRRL B3569 was selected by screening a number of Propionibacterium strains. The nutrient composition and the fermentation conditions for this strain were optimized in continuous culture. The investigations show that within a concentration range of 30–170 g l^–1 of sucrose in the fermentation medium, no significant substrate inhibition occurred. For the production of propionic acid and vitamin B₁₂, concentrations of 1.5 mg FeSO₄·7H₂O g^–1 dry biomass, 0.75 mg cobalt ions g^–1 dry biomass, 0.3 mg 5,6-dimethylbenzimidazole g^–1 dry biomass, and 12 g yeast extract 1^–1 were necessary additions to the sources of nitrogen, phosphate, and magnesium ions. The extra addition of up to 2.8 g betaine g^–1 dry biomass significantly increases the production of vitamin B₁₂. In the optimization of the pH value, temperature, and aeration, it was established that the conditions for propionic acid production and vitamin B₁₂ production are different. Whereas the optimal production of propionic acid took place under completely anaerobic conditions with a pH value of 6.5 and a temperature of 37°C, optimal vitamin B₁₂ production required a temperature of 40°C and aerobic conditions (0.5 vvm aeration at 100 rpm) with a pH value of 6.5.     

Paradigmatic status of an endo- and exoglucanase and its effect on crystalline cellulose degradation

Background

Presently, different studies are conducted related to the topic of biomass potential to generate through anaerobic fermentation process alternative fuels supposed to support the existing fossil fuel resources, which are more and more needed, in quantity, but also in quality of so called green energy. The present study focuses on depicting an optional way of capitalizing agricultural biomass residues using anaerobic fermentation in order to obtain biogas with satisfactory characteristics.. The research is based on wheat bran and a mix of damaged ground grains substrates for biogas production.

Results

The information and conclusions delivered offer results covering the general characteristics of biomass used , the process parameters with direct impact over the biogas production (temperature regime, pH values) and the daily biogas production for each batch relative to the used material.

Conclusions

All conclusions are based on processing of monitoring process results , with accent on temperature and pH influence on the daily biogas production for the two batches. The main conclusion underlines the fact that the mixture batch produces a larger quantity of biogas, using approximately the same process conditions and input, in comparison to alone analyzed probes, indicating thus a higher potential for the biogas production than the wheat bran substrate. Adrian Eugen Cioabla, Ioana Ionel, Gabriela-Alina Dumitrel and Francisc Popescu contributed equally to this work     

Improvement of fermentative hydrogen production: various approaches

Fermentation of biomass or carbohydrate-based substrates presents a promising route of biological hydrogen production compared with photosynthetic or chemical routes. Pure substrates, including glucose, starch and cellulose, as well as different organic waste materials can be used for hydrogen fermentation. Among a large number of microbial species, strict anaerobes and facultative anaerobic chemoheterotrophs, such as clostridia and enteric bacteria, are efficient producers of hydrogen. Despite having a higher evolution rate of hydrogen, the yield of hydrogen [mol H₂ (mol substrate^–1)] from fermentative processes is lower than that achieved using other methods; thus, the process is not economically viable in its present form. The pathways and experimental evidence cited in the literature reveal that a maximum of four mol of hydrogen can be obtained from substrates such as glucose. Modifications of the fermentation process, by redirection of metabolic pathways, gas sparging and maintaining a low partial pressure of hydrogen to make the reaction thermodynamically favorable, efficient product removal, optimum bioreactor design and integrating fermentative process with that of photosynthesis, are some of the ways that have been attempted to improve hydrogen productivity. This review briefly describes recent advances in these approaches towards improvement of hydrogen yield by fermentation.