bluuebunny/crossref_metadata_2025_split huggingface dataset:
A dynamic simulation of a two‐phase anaerobic digestion system for solid wastes
Authors: Mata‐Alvarez Joan 
Published: December 2004

AbstractIn this article, a two‐phase system for the digestion of wastes with a high solid content is simulated. The solids are charged to the hydrolyzer and then leachate recirculation is activated until biodegradation is nearly complete. Several parameters are tested, namely moisture, leachate recirculation flow rate, and hydrolyzer‐methanizer volume ratio. The results show that recirculation rate is an important parameter subject to optimization, with optimal values corresponding to hydrolyzer hydraulic retention times below 1 day. The quantity of recirculating water must be the highest possible. As a consequence, the organic load to the methanizer is reduced, making thus possible the use of a smaller methanizer volume.
Harvesting of Scenedesmus obliquus in wastewaters: Auto‐ or bioflocculation?
Authors: Lavoie Alain , de la Noüe J. 
Published: December 2004

AbstractAutoflocculation and bioflocculation are considered to be the most promising means for the economical harvesting of microalgae. We have therefore studied these phenomena with cultures of Scenedesmus obliquus produced during biological tertiary wastewater treatment. The quantity of extracellular polymers produced during ageing of the cultures proved insufficient to initiate bio‐flocculation while the concentration of Ca2+ and PO43− of the treated effluent were too low to induce autoflocculation. It has been shown, however, that the algae sediment more readily upon ageing, possibly as a result of increased ceil density. The use of density gradients made with Percoll (a colloidal solution of silica particles) allowed measurement of the true cell density and showed that this increases when cultures enter the declining growth phase. The quality of the biomass thus harvested is, however, considerably impaired, protein content decreasing from 62.7% (dry wt) during the exponential growth phase (day 5) to 14% at the end of cultures (day 21).
Operating parameters' effects on the outcome of pure and simple competition between two populations in configurations of two interconnected chemostats
Authors: Kung Cheng‐Ming , Baltzis B. C. 
Published: December 2004

AbstractIt is known from the literature that two microbial populations competing purely and simply for a common substrate in a spatially inhomogeneous environment may under certain conditions coexist in a steady state. This paper studies pure and simple competition between two microbial species in three alternate configurations of two interconnected ideal chemostats and focuses on the effects of the operating parameters‐dilution rate, substrate concentration in the feed to the vessels, recycle ratio, and volume ratio of the two vessels, splitting ratio of the external feed to the chemostats‐on the coexistence of the two competitors. It is shown that the coexistence steady state is practically feasible in the sense that it occurs in a finite domain of the operating parameters space. Theoretical and numerical results are presented, some of them in the form of operating diagrams projected on the two‐dimensional subspace. A comparison of the three possible configurations is offered.
Enzymatic function of alginate immobilized rat hepatocytes
Authors: Tompkins Ronald G. , Carter Edward A. , Carlson James D. , Yarmush Martin L. 
Published: December 2004

AbstractThe use of immobilized hepatocytes represents a promising approach for the problem of detoxification in acute hepatic failure. Hepatocyte viability and detoxification function of a number of complex enzyme systems were examined before and after immobilization in alginate droplets. Detoxification function was assessed quantitatively by measuring the kinetics of several specific detoxification systems: the cytochrome P450 system, the urea cycle, and two conjugation systems. Reaction rates for all enzyme systems were similar in immobilized and nonimmobilized cells, and were in good agreement with previously published literature values. These results indicate that transport limitations do not occur in these gels and that the intrinsic reaction rate is the limiting step. Feasibility of detoxification replacement by immobilized cells is discussed using measured reaction rates.
Thermochemical pretreatment of lignocellulose to enhance methane fermentation: II. Evaluation and application of pretreatment model
Authors: Baugh Kent D. , Levy James A. , McCarty Perry L. 
Published: December 2004

AbstractA model was developed and evaluated as a tool for predicting the formation of soluble products from staged thermochemical treatment of lignocellulosic materials under acidic conditions typical of autohydrolysis. The model was used to predict the general trend of hemi‐cellulose and cellulose hydrolysis between pH 2 and 4 and temperatures of 170–230°C, and results were compared with experimental data. When the model was evaluated for this range of temperatures and pH values, results indicated: (1) a relatively low temperature (175°C) during the first stage allows hydrolysis of the hemi‐cellulose polysaccharides without significant mono‐saccharide decomposition, (2) subsequent stages at higher temperatures (equal or greater than 200°C) are needed for significant cellulose hydrolysis, but glucose decomposition will also occur, and, (3) a pH in the range of 2–2.5 will enhance polysaccharide hydrolysis while limiting monosaccharide decomposition. The model's predictions, indicating that the formation of biodegradable products could be optimized using Pretreatments at pH 2–2.5 for the pH range evaluated, were confirmed in experiments with white fir as a representative lig nocellulose.
Photobioreactor design: Mixing, carbon utilization, and oxygen accumulation
Authors: Weissman Joseph C. , Goebel Raymond P. , Benemann John R. 
Published: December 2004

AbstractPhotobioreactor design and operation are discussed in terms of mixing, carbon utilization, and the accumulation of photosynthetically produced oxygen. The open raceway pond is the primary type of reactor considered; however small diameter (1–5 cm) horizontal glass tubular reactors are compared to ponds in several respects. These are representative of the diversity in photobioreactor design: low capital cost, open systems and high capital cost, closed systems. Two 100‐m2 raceways were operated to provide input data and to validate analytical results. With a planktonic Chlorella sp., no significant difference in productivity was noted between one pond mixed at 30 cm/s and another mixed from 1 to 30 cm/s. Thus, power consumption or CO2 outgassing limits maximal mixing velocities. Mixing power inputs measured in 100‐m2 ponds agreed fairly well with those calculated by the use of Manning's equation. A typically configured tubular reactor flowing full (1 cm diameter, 30 cm/s) consumes 10 times as much energy as a typical pond (20 cm deep flowing at 20 cm/s). Tubular reactors that flow only partially full would be limited by large hydraulic head losses to very short sections (as little as 2 m length at 30 cm/s flow) or very low flow velocities. Open ponds have greater CO2 storage capacity than tubular reactors because of their greater culture volume per square meter (100–300 L/m2 vs. 8–40 L/m2 for 1–5‐cm tubes). However, after recarbonation, open ponds tend to desorb CO2 to the atmosphere. Thus ponds must be operated at higher pH and lower alkalinity than would be possible with tubular reactors if cost of carbon is a constraint. The mass transfer coefficient, KL, for CO2 release through the surface of a 100‐m2 pond was determined to be 0.10 m/h. Oxygen buildup would be a serious problem with any enclosed reactor, especially small‐diameter tubes. At maximal rates of photosynthesis, a 1‐cm tubular reactor would accumulate 8–10 mg O2/L/min. This may result in concentrations of oxygen reaching 100 mg/L, even with very frequent gas exchange. In an open pond, dissolved oxygen rises much more slowly as a consequence of the much greater volume per unit surface area and the outgassing of oxygen to the atmosphere. The maximum concentration of dissolved oxygen is typically 25–40 mg/L. The major advantage of enclosed reactors lies in the potential for aseptic operation, a product value which justifies the expense. For most products of algal mass cultivation, open ponds are the only feasible photobioreactor design capable of meeting the economic and operating requirements of such systems, provided desirable species can be maintained.
Use of surface‐immobilized Trichoderma in batch and fed‐batch fermentations
Authors: Duff Sheldon J. B. 
Published: December 2004

AbstractNeedle‐punch polyester was shown to be an effective support material for the immobilization of Trichoderma reesei Rut C30. When used as a resident inoculum for a batch process, the immobilized Trichoderma was very stable and resulted in a reduced rate of biomass generation in the bulk liquid phase as compared to cultures inoculated with free mycelium. Fed‐batch fermentations with the immobilized Trichoderma produced ca. 80% of the activity of those using free cells; however, the activity was more stable and the crude enzyme broth produced had a greatly reduced biomass concentration.
Production of optically active 2,3‐butanediol by Bacillus polymyxa
Authors: De Mas Carles , Jansen Norman B. , Tsao George T. 
Published: December 2004

AbstractBacillus polymyxa produces (R, R)‐2,3‐butanediol from a variety of carbohydrates. Other metabolites are also produced including acetoin, acetate, lactate, and ethanol. The excretion of each metabolite was found to depend on the relative availability of oxygen to the culture. When the relative oxygen uptake rate was high, enhanced yields of acetate and acetoin were noted. At an intermediate oxygen availability, the butanediol yield was maximal. When the availability of oxygen was more restricted, higher yields of lactate and ethanol occurred. The cells appeared to regulate themselves such that energy generation is optimal subject to the constraint that the cells do not produce more reducing equivalents than can be oxidized by the electron transport system. The dependence of each product yield on the relative oxygen availability was determined, and this knowledge was used to carry out a fed‐batch fermentation that attained a final butanediol concentration of over 40 g/L in 50 h.
The relationship between fiber‐porosity and cellulose digestibility in steam‐exploded Pinus radiata
Authors: Wong Ken K. Y. , Deverell Kay F. , Mackie Keith L. , Clark Tom A. , Donaldson Lloyd A. 
Published: December 2004

AbstractSteam explosion after sulphur dioxide impregnation of wood chips is an effective method for improving the enzymatic digestibility of cellulose in the softwood Pinus radiata. Digestibility of pretreated fiber was progressively increased by altering the conditions of steam explosion. With increasing digestibility, there was an observed increase in fiber porosity as measured by the solute exclusion technique. Accessible pore volume and accessible surface area to a 5‐nm dextran probe positively correlated with both 2‐ and 24‐h digestion yields from pretreated fiber. The increase in accessibility was probably the result of hemicellulose extraction and lignin redistribution. A subsequent loss in accessibility, brought about by structural collapse or further lignin redistribution, resulted in a corresponding loss in digestibility. It appears that steam explosion increases cellulose digestibility in P. radiata by increasing fiber porosity.
Effect of cycling on the stability of plasmid‐bearing microorganisms in continuous culture
Authors: Stephens M. L. , Lyberatos G. 
Published: December 2004

AbstractThe implication of the possible existence of differences in the times required for plasmid‐bearing and non‐plasmid‐bearing microorganisms to adjust their metabolic activities to step changes in their environment is examined. This adaptability difference suggests the possibility of maintaining an engineered strain in continuous culture by transient operation. It is shown for the case where adaptability is neglected that no cycling strategy will prevent the washout of the engineered strain, but the addition to the model of a time delay in substrate utilization can result in coexistence upon cycling. Numerical simulations of cycling in feed substrate concentration are carried out to illustrate the concept Operating diagrams are also constructed to indicate the conditions under which washout of the plasmid bearing strain can be prevented.
The anion‐exchange substrate shuttle process: A new approach to two‐stage biomethanation of organic and toxic wastes
Authors: Thiele Jurgen H. , Zeikus J. Gregory 
Published: December 2004

AbstractA novel biomethanation process configuration is described which uses improved biocatalysts to enhance the productivity and stability of waste biomethanation systems. The design facilitates the maintenance of acetogenic and methanogenic bacteria under optimum substrate concentrations far above their Ks values in a two‐stage biomethanation system with closed loop reactors. Volatile fatty acid anions (VFA anions) are provided as substrates for the methanogenic stage by using an anion exchange unit coupled to the acidogenic stage. The slow growing and sensitive acetogenic and methanogenic bacteria are protected from oxygen, cationic pollutants, toxins, and microbial contamination by use of the substrate shuttle process. Due to the closed loop process configuration, washout of the ecoengineered biocatalysts is excluded. The modular system configuration allows industrial mass production of the system components. The new biomethanation process enhances both the BTU content of the gas and the methane production over state‐of‐the‐art anaerobic digestor bioreactor concepts.
Gluconic acid production by an mobilized glucose oxidase reactor with electrochemical regeneration of an artificial electron acceptor
Authors: Bourdillon Christian , Lortie Robert , Laval Jean Marc 
Published: December 2004

AbstractA reactor, using the enzymatic electrocatalysis scheme, was developed on a laboratory preparative scale for the catalytic oxidation of glucose into gluconic acid. Glucose oxidase was directly immobilized on the surface of a carbon felt electrode and a solution of glucose and benzo‐quinone passed through the electrode in order to regenerate the electron acceptor. The reactor was able to produce continuously 1.5 g gluconate/h with a catalytic current of 0.4 A. This gave a high productivity ca. 100 g/h/L reactor. A one‐dimensional model was developed which demonstrated the efficiency of coupling between enzymatic and electrochemical reactions due to the proximity of the two reaction sites. For example the catalytic current was practically independent of mass transfer parameters. The operational stability of immobilized glucose oxidase was increased 50 times at least when electroregenerated benzoquinone was used as oxidant instead of oxygen.
Biodegradation by immobilized bacteria in an airlift‐loop reactor—influence of biofilm diffusion limitation
Authors: Wagner K. , Hempel D. C. 
Published: December 2004

AbstractNaphthalene‐2‐sulfonate was degraded by submerse growing Pseudomonads in a chemostat culture. The kinetic parameters for the Monod equation, including Pirts maintenance energy, were calculated from these experiments regarding naphthalene‐2‐sulfonate as substrate and oxygene as cosubstrate. By immobilizing the bacteria on sand particles, the degradation of naphthalene‐2‐sulfonate was carried out in a specialy designed three‐phase airlift‐loop reactor in a completely fluidized state. From these experiments, the influence of biofilm diffusion limitation on reaction kinetics and criteria for stable biofilm formation on sand particles were obtained.
Experimental simulation of oxygen profiles and their influence on baker's yeast production: I. One‐fermentor system
Authors: Sweere A. P. J. , Mesters J. R. , Janse L. , Luyben K. Ch. A. M. , Kossen N. W. F. 
Published: December 2004

AbstractIn production‐scale bioreactors microorganisms are exposed to a continually changing environment. This may cause loss of viability, reduction of the yield of biomass or desired metabolites, and an increase in the formation of by‐products. In fed‐batch production of baker's yeast, profiles may occur in substrate and oxygen concentrations and in pH. This article deals with the influence of a periodically changing oxygen concentration on the growth of baker's yeast in a continuous culture. Also, influences on the production of ethanol, glycerol, acetic acid, and on the composition of the cells were investigated. It was found that relatively fast fluctuations between oxygen‐unlimited and oxygen‐limited conditions with a frequency of 1 or 2 min had a distinct influence on the biomass and metabolite production. However, RNA, protein, and carbohydrate contents measured in cells exposed to fluctuations differed little from those in cells from an oxygen‐unlimited or an oxygen‐limited culture. The respiration and fermentation capacities of cells exposed to fluctuations can be larger than the capacities of cells grown under oxygen‐unlimited conditions.
Improvements in ethanol tolerance of Kluyveromyces fragilis in jerusalem artichoke juice
Authors: Rosa M. Fernanda , Correia Isabel Sá , Novais Júlio M. 
Published: December 2004

AbstractAlcoholic fermentation of Jerusalem artichoke juice, a natural complex medium, allowed the production of 13% (v/v) ethanol utilizing an inulin‐fermenting strain of Kluyveromyces fragilis, strongly sensitive to ethanol. However, the fermentation of a simple medium with a similar concentration of fermentable sugars (235 g/L) as saccharose stopped prematurely when only 7% (v/v) ethanol had been produced. Differences in the two fermentation profiles were attributed to the significantly lower ethanol tolerance of K. fragilis IGC 2671 in the simple medium with 2% saccharose as compared with diluted J.a. juice with a similar sugar concentration, in fact, (1) in diluted J. a. juice, growth was possible up to 8% (v/v) added ethanol compared with 6% (v/v) in simple medium and (2) ethanol‐induced inhibition of the specific growth and fermentation rate as well as ethanol‐induced stimulation of the specific death rate were much more drastic in simple medium. Present results show that (1) the complex composition of the medium used for alcoholic fermentation plays a marked role in the ability of the yeast to tolerate and produce ethanol; (2) J. a. juice proved a very appropriate medium for a productive alcoholic fermentation, namely, in processes based on strains with a low ethanol resistance; and (3) to characterize and compare the ethanol tolerance of fermenting yeasts, the standardization of the medium composition must be taken in consideration.
Kinetic effects of simultaneous inhibition by substrate and product
Authors: Van Den Heuvel J. C. , Beeftink H. H. 
Published: December 2004

AbstractThe starting point for the present investigations was the finding that increasing influent concentrations from 10 to 380 mmol/L glucose decreased the attainable growth rate of an acidogenic population in continuous culture from 0.52 to 0.05 h−1 To account for this phenomenon, a new kinetic model is developed that combines substrate and product inhibition. Both effects are connected through the product yield, giving rise to a complex dependency of the growth rate on the substrate concentration. As a main feature, the maximum attainable growth rate decreases almost hyperbolically above some optimal substrate concentration in the influent. Furthermore, under certain conditions the kinetic model predicts the existence of three steady states: a high‐conversion and a low‐conversion state that are both stable and a metastable intermediate state. The latter states from the multiple‐steady‐state region are to be avoided, and eventual transitions to these states may have important consequences for the stability and the operation of such reaction systems. Substrate as well as product inhibition is reported for Propionibacterium freundenreichii and recently could be demonstrated for the above‐mentioned acidogenic population. The proposed model allows optimization of anaerobic wastewater treatment processes and is applicable also to other fermentations.
Immobilization of E. coli β‐galactosidase and its derivatives by polyacrylamide gel
Authors: Khare S. K. , Gupta M. N. 
Published: December 2004

AbstractWe have recently prepared some crosslinked derivatives of Escherichia coli β‐galactosidase by treating the enzyme with bisimidoesters. In this article, we report the results obtained when the native and these crosslinked derivatives are entrapped in polyacrylamide gel lattice. It was found that use of combination of three protective agents, viz., bovine serum albumin, cysteine, and lactose, during immobilization gave an increased yield of 190% in the case of DMA crosslinked preparation. In the case of native enzyme, the Km, pH optimum, and temperature optimum were found to remain unchanged on immobilization. The DMA crosslinked preparation entrapped in polyacrylamide in the presence of BSA, lactose, and cysteine was found to be a significantly better catalyst and hydrolyzed 47% milk lactose as compared to 31% hydrolysis by entrapped native enzyme in 6 h.
Action of Bacillus subtilis α‐amylase on native wheat starch
Authors: Colonna Paul , Buléon Alain , Lemarié Fabienne 
Published: December 2004

AbstractNative starch granules from wheat have been subjected to enzymatic depolymerization with an α‐amylase from Bacillus subtilis. Crystallites made from short‐chain amylose and residues from mild acid hydrolysis have been also tested. Electron microscopy, particle size analysis, DSC, and x‐ray diffractometry reveal that enzymatic degradation occurs granule by granule. Gel permeation chromatography shows off the macromolecular nature of the remaining material. In contrast, acid erodes simultaneously all the granules, leading to a splitting into small particles. Crystalline fractions are completely degraded by α‐amylase. These results support evidence for an active disentanglement of chains, carried out by the different subsites of α‐amylase molecules. A simple mathematical treatment is proposed to explain the results of the kinetics.
A structured mechanistic model of the kinetics of enzymatic lysis and disruption of yeast cells
Authors: Hunter J. B. , Asenjo J. A. 
Published: December 2004

AbstractA structured, mechanistic model has been built for the kinetics of yeast cell lysis by microbial cell lytic enzymes, based on an understanding of the two‐layer yeast cell wall structure and the properties of yeast‐lytic enzyme systems. The model predicts the release of protein, peptides and carbohydrates from four cell structures: the outer and inner wall layers, the cytosol and organelles or proteins present in particles; it also predicts organelle or particle lysis or solubilization and the breakdown of released proteins to peptides. Applications of the model to design and optimization of selective product release are discussed.
Defined bacterial culture development for methane generation from lactose
Authors: Yang Shang‐Tian , Tang I‐Ching , Okos Martin R. 
Published: December 2004

AbstractThe defined microbial cultures for methane generation from lactose were investigated. A mixed culture consisting of homolactic (Streptococcus lactis), homoacetic (Clostridium formicoaceticum), and acetate‐utilizing methanogenic (Methanococcus mazei) bacteria was used to convert lactose and whey permeate to methane at mesophilic temperatures (35–37°C) and a pH around 7.0. Lactose was first converted to lactic acid by S. lactis, then to acetic acid by C. formicoaceticum, and finally to methane and CO2 by M. mazei. About 5.3 mol methane were obtained from each mole of lactose consumed, and the conversion of acetate to methane was the rate‐limiting step for this mixed‐culture fermentation.