Showing papers on "Bioreactor published in 1998"

Substrate gradient formation in the large-scale bioreactor lowers cell yield and increases by-product formation

Abstract: A heterogeneous micro-environment was identified in a 12 m3 bioreactor with a height-to-diameter ratio of 2.5. The reactor was aerated by a ring sparger and stirred by three Rushton turbines. E. coli cells were cultivated in minimal medium to a cell density in the order of 30 g/l. Samples of glucose, the growth limiting component fed to the process, were taken at three levels in the bioreactor (top/middle/bottom). These showed that glucose concentration declined away from the feedpoint. The gradients depended on the mixing characteristics of the feedpoint, and concentrations of up to 400 times the mean value were found when feed was added to a relatively stagnant mixing zone. This resulted in up to 20% lower biomass yield compared to the bench scale. Gradients also affected the by-product formation, resulting in acetate formation in the large-scale bioreactor. IPTG induction of a recombinant protein was shown to influence important cell parameters and considerably increased the yield of carbon dioxide per glucose added, indicating an increased maintenance. The product formation rate was, however, not notably affected by the scale-up.

Biological production of products from waste gases

Abstract: A method and apparatus are designed for converting waste gases from industrial processes such as oil refining, and carbon black, coke, ammonia, and methanol production, into useful products. The method includes introducing the waste gases into a bioreactor where they are fermented to various products, such as organic acids, alcohols, hydrogen, single cell protein, and salts of organic acids by anaerobic bacteria within the bioreactor. These valuable end products are then recovered, separated and purified.

Production of Soluble Microbial Products (SMP) in an Anaerobic Baffled Reactor: Composition, Biodegradability, and the Effect of Process Parameters

Abstract: The composition and biodegradability of effluents from biological treatment plants is of increasing interest due to tightening effluent standards. One of the main constituents of effluents are soluble microbial products (SMPs) produced in the reactor during metabolism and endogenous decay. The objective of this preliminary work was to examine the influence of operating parameters such as temperature, hydraulic retention time (HRT), and organic loading rate (OLR) on the production of SMPs in a compartmentalised anaerobic baffled reactor (ABR) fed a simple sucrose-nutrients substrate. In addition, in order to gain greater insight into the SMPs produced, the composition and anaerobic biodegradability of various molecular weight fractions were analysed. It was found that decreasing operating temperature resulted in slight increases in SMP production, a decreased rate of degradation, and hence increases in effluent SMPs. In addition, decreasing HRTs, and increasing OLRs, also resulted in increased effluent SMP...

Acetate production from whey lactose using co-immobilized cells of homolactic and homoacetic bacteria in a fibrous-bed bioreactor

Abstract: Acetate was produced from whey lactose in batch and fed-batch fermentations using co-immobilized cells of Clostridium formicoaceticum and Lactococcus lactis. The cells were immobilized in a spirally wound fibrous sheet packed in a 0.45-L column reactor, with liquid circulated through a 5-L stirred-tank fermentor. Industrial-grade nitrogen sources, including corn steep liquor, casein hydrolysate, and yeast hydrolysate, were studied as inexpensive nutrient supplements to whey permeate and acid whey. Supplementation with either 2.5% (v/v) corn steep liquor or 1.5 g/L casein hydrolysate was adequate for the cocultured fermentation. The overall acetic acid yield from lactose was 0.9 g/g, and the productivity was 0.25 g/(L h). Both lactate and acetate at high concentrations inhibited the homoacetic fermentation. To overcome these inhibitions, fed-batch fermentations were used to keep lactate concentration low and to adapt cells to high-concentration acetate. The final acetate concentration obtained in the fed-batch fermentation was 75 g/L, which was the highest acetate concentration ever produced by C. formicoaceticum. Even at this high acetate concentration, the overall productivity was 0.18 g/(L h) based on the total medium volume and 1.23 g/(L h) based on the fibrous-bed reactor volume. The cells isolated from the fibrous-bed bioreactor at the end of this study were more tolerant to acetic acid than the original culture used to seed the bioreactor, indicating that adaptation and natural selection of acetate-tolerant strains occurred. This cocultured fermentation process could be used to produce a low-cost acetate deicer from whey permeate and acid whey.

Bacterial Community Dynamics during Start-Up of a Trickle-Bed Bioreactor Degrading Aromatic Compounds

Abstract: This study was performed with a laboratory-scale fixed-bed bioreactor degrading a mixture of aromatic compounds (Solvesso100). The starter culture for the bioreactor was prepared in a fermentor with a wastewater sample of a care painting facility as the inoculum and Solvesso100 as the sole carbon source. The bacterial community dynamics in the fermentor and the bioreactor were examined by a conventional isolation procedure and in situ hybridization with fluorescently labeled rRNA-targeted oligonucleotides. Two significant shifts in the bacterial community structure could be demonstrated. The original inoculum from the wastewater of the car factory was rich in proteobacteria of the alpha and beta subclasses, while the final fermentor enrichment was dominated by bacteria closely related to Pseudomonas putida or Pseudomonas mendocina, which both belong to the gamma subclass of the class Proteobacteria. A second significant shift was observed when the fermentor culture was transferred as inoculum to the trickle-bed bioreactor. The community structure in the bioreactor gradually returned to a higher complexity, with the dominance of beta and alpha subclass proteobacteria, whereas the gamma subclass proteobacteria sharply declined. Obviously, the preceded pollutant adaptant did not lead to a significant enrichment of bacteria that finally dominated in the trickle-bed bioreactor. In the course of experiments, three new 16S as well as 23S rRNA-targeted probes for beta subclass proteobacteria were designed, probe SUBU1237 for the genera Burkholderia and Sutterella, probe ALBO34a for the genera Alcaligenes and Bordetella, and probe Bcv13b for Burkholderia cepacia and Burkholderia vietnamiensis. Bacteria hybridizing with the probe Bcv13b represented the main Solvesso100-degrading population in the reactor.

Biological Treatment of TNT-Contaminated Soil. 2. Biologically Induced Immobilization of the Contaminants and Full-Scale Application

Abstract: Anaerobic treatment of originally contaminated soil from a former ammunition plant was carried out in a laboratory slurry reactor. While fermenting glucose to ethanol, acetate, and propionate, the anaerobic bacteria completely reduced the nitro groups of 2,4,6-trinitrotoluene (TNT) and aminodinitrotoluenes, which led to a complete and irreversible binding of the reduced products to the soil. 2,4-Dinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine were also reduced in the soil slurry and were no longer detectable after the anaerobic treatment. To mineralize the fermentation products, a subsequent aerobic treatment was necessary to complete the bioremediation process. This bioremediation process was tested in a technical scale at Hessisch Lichtenau−Hirschhagen, Germany. A sludge reactor (Terranox system) was filled with 18 m3 of contaminated soil (main contaminants were TNT, 2,4-dinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine) and 10 m3 of water. The anaerobic stage was carried out by periodi...

Characterization of Hematopoietic Cell Expansion, Oxygen Uptake, and Glycolysis in a Controlled, Stirred-Tank Bioreactor System

Abstract: Cultures of umbilical cord blood and mobilized peripheral blood mononuclear cells were carried out in a stirred bioreactor with pH and dissolved oxygen control. Expansion of total cells and colony-forming units granulocyte-macrophage was greatly enhanced by the use of a cell-dilution feeding protocol (as compared to a cell-retention feeding protocol). The specific oxygen consumption rate (qO2) for these cultures ranged from 1.7 x 10(-8) to 1.2 x 10(-7) micromol/(cell.h). The maximum in qO2 for each culture closely corresponded with the maximum percentage of progenitor or colony-forming cells (CFCs) present in the culture. The maximum qO2 values are slightly less than those reported for hybridomas, while the lowest qO2 values are somewhat greater than those reported for mature granulocytes. Examination of the ratio of lactate production to oxygen consumption in these cultures suggests that post-progenitor cells of the granulomonocytic lineage obtain a greater portion of their energy from glycolysis than do CFCs. The different metabolic profiles of CFCs and more mature cells suggest that monitoring the uptake or production of oxygen, lactate, and other metabolites will allow estimation of the content of several cell types in culture.

Anaerobic sequencing batch reactor treatment of dilute wastewater at psychrophilic temperatures

Abstract: Anaerobic treatment of dilute wastewater was studied using three laboratory-scale anaerobic sequencing batch reactors (ASBRs), each with an active volume of 6 L. The reactors were fed a synthetic substrate made from nonfat dry milk supplemented with nutrients and trace metals. The chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD 5 ) of the feed were 600 mg/L and 285 mg/L, respectively. Steady-state performance data were collected over a time period of 2 years at reactor temperatures of 5, 7.5, 10, 12.5, 15, 17.5, 20, and 25°C. Hydraulic retention times (HRTs) were maintained at 24, 16, 12, 8, and 6 hours. Steady-state process kinetics and removal efficiencies were evaluated for the various conditions. Results showed that the ASBR process was capable of achieving more than 90% soluble COD (SCOD) and BOD 5 removal at temperatures of 20°C and 25°C at all HRTs. At a temperature of 5°C and a 6-hour HRT, SCOD and BOD 5 removals were 62% and 75%, respectively. At intermediate temperatures ranging from 5 to 25°C and HRTs between 24 and 6 hours, removal of soluble organic matter ranged from 62 to 90% for COD and from 75 to 90% for BOD 5 . In all cases, solids retention times were high enough to maintain good performance. Substrate removal rates and half-saturation coefficients were also determined at all temperatures. The temperature correction coefficient was determined to be 1.08 in the temperature range of 7.5 to 25°C. It is concluded that the ASBR has unique characteristics that enable efficient removal of organics during treatment of dilute wastewaters at low temperatures.

Biodegradation of Atrazine Under Denitrifying Conditions

Abstract: Anaerobic biodegradation of atrazine by the bacterial isolate M91-3 was characterized with respect to mineralization, metabolite formation, and denitrification. The ability of the isolate to enhance atrazine biodegradation in anaerobic sediment slurries was also investigated. The organism utilized atrazine as its sole source of carbon and nitrogen under anoxic conditions in fixed-film (glass beads) batch column systems. Results of HPLC and TLC radiochromatography suggested that anaerobic biotransformation of atrazine by microbial isolate M91-3 involved hydroxyatrazine formation. Ring cleavage was demonstrated by 14CO2 evolution. Denitrification was confirmed by detection of 15N2 in headspace samples of K15NO3-amended anaerobic liquid cultures. In aquatic sediments, mineralization of uniformly ring-labeled [14C]atrazine occurred in both M91-3-inoculated and uninoculated sediment. Inoculation of sediments with M91-3 did not significantly enhance anaerobic mineralization of atrazine as compared to uninoculated sediment, which suggests the presence of indigenous organisms capable of anaerobic atrazine biodegradation. Results of this study suggest that the use of M91-3 in a fixed-film bioreactor may have applications in the anaerobic removal of atrazine and nitrate from aqueous media.

Acetic acid production from fructose by clostridium formicoaceticum immobilized in a fibrous-Bed bioreactor

Abstract: The fermentation kinetics of acetic acid production from fructose by Clostridium formicoaceticum was studied at pH 7.6 and 37 degreesC. Recycle batch, fed-batch, and continuous fermentations using immobilized cells in a fibrous-bed bioreactor were studied for their potential application in producing acetic acid from fructose, a fermentable sugar commonly found in corn steep liquor and many other food processing wastes. For the immobilized cell fermentation, acetic acid yield from fructose was approximately 1.0 g/g, with a final acetate concentration of approximately 78 g/L and the overall reactor productivity (based on the fibrous bed bioreactor volume) of approximately 0.95 g/(L.h) in the fed-batch fermentation. For a similar fed-batch fermentation with free cells, acetic acid yield was approximately 0.9 g/g, the highest final acetate concentration was approximately 46 g/L, and the overall productivity was approximately 0.12 g/(L.h). In the continuous fermentation with immobilized cells, the reactor productivity decreased from 3.2 to 1. 3 g/(L.h) as retention time increased from 16 to 72 h to reach 100% conversion. Compared to free-cell fermentations, the superior performance of the fibrous-bed bioreactor can be attributed to the high density (>30 g/L) of viable cells immobilized in the fibrous bed. The fermentation product, acetic acid, was found to be a noncompetitive inhibitor to the cells. However, the immobilized cells had a higher maximum production rate (pmax) and a higher value for the inhibition rate constant (Kp) than those for the free cells, suggesting that the immobilized cells in the fibrous-bed bioreactor were less sensitive to acetic acid inhibition than the free cells. This improvement in kinetic behaviors for immobilized cells confirms that the fibrous-bed bioreactor can be used as an effective tool for adapting and screening for acetate-tolerant strains.

Efficient production of L-(+)-lactic acid using mycelial cotton-like flocs of Rhizopus oryzae in an air-lift bioreactor.

Abstract: L-(+)-Lactic acid production was enhanced in a culture of Rhizopus oryzae by induction of a mycelial flocs morphology. By conventional culture the morphology of R. oryzae is that of a pellet-like cake; however, when mineral support and poly(ethylene oxide) are added to the culture, the morphology of R. oryzae takes on a cotton-like appearance. The formation of these cotton-like mycelial flocs was induced by the addition of 5 ppm poly(ethylene oxide) into a 12-14 h culture containing 3 g/L of the mineral support before the formation of the conventional pellet morphology. The cotton-like flocs were also formed in cultures grown in an air-lift bioreactor. This morphology allowed effective mass transfer inside the flocs and effective fluidity of culture broth in an air-lift bioreactor. L-(+)-Lactic acid concentration produced by mycelial flocs in an air-lift bioreactor, with the support and poly(ethylene oxide), was 104.6 g/L with a yield of 0.87 using 120 g/L of glucose as the substrate; for this culture without both, the concentration was 43.2 g/L. These results demonstrate that cotton-like mycelial flocs are the optimal morphology for use in the air-lift bioreactor culture of R. oryzae.

Metabolic transformations and characterisation of the sludge community in an enhanced biological phosphorus removal system

Abstract: Enhanced biological phosphorus removal was performed in a continuous laboratory-scale two-reactor system with sludge recirculation over a 75-day period. Influent wastewater was a synthetic medium based on acetate, and the sludge age was kept at 12 days. The adapted sludge stored poly-β-hydroxyalkanoic acids (PHA) in the anaerobic reactor with a conversion ratio of 1.45 PHA/acetic acid (based on chemical O2 demand: COD/COD) and gave ratio of a phosphate-P release to acetic acid uptake of 0.51 P/CH3COOH (w/w). Fractionation of anaerobic and aerobic sludges showed that the main part of phosphorus taken up, was eluted in the trichloroacetic acid fraction indicating that it was polyphosphate. A total of 60% of the phosphorus in the aerobic sludge was solubilized in the trichloroacetic acid fraction, whereas this fraction accounted for only 32% of the phosphorus in the anaerobic sludge. Only 4% of the total phosphorus in the aerobic sludge and 2% in the anaerobic sludge was found in the EDTA fraction, indicating low amounts of metal-bound phosphates. Isolation on acetate-based agar medium showed that Acinetobacter strains were present in the sludge. However, a more complete analysis of the bacterial community of the sludge was obtained by creating a clone library based on the 16S rRNA gene. A total of 51 partial clone sequences were phylogenetically evaluated. The predominating group was found in the high-(G+C) (mol%) gram-positive bacterial subphylum (31% of the sequenced clones), while the gamma proteobacteria only constituted 9.8% of the clones.

Using a membrane bioreactor to reclaim wastewater

Abstract: A pilot-scale membrane bioreactor sufficiently purified simulated municipal wastewater for indirect recharge to groundwater or nonpotable uses. Throughout more than 500 days of steady-state operation, total organic carbon concentrations of <1.1 mg/L and chemical oxygen demand of <3.5 mg/L were consistently achieved. No suspended solids were detected in the effluent during this period. The treated water was fully nitrified, resulting in low ammonia and organic nitrogen concentrations but high nitrate concentrations. Cyclic oxic-anoxic operation of an additional denitrification process would be necessary to meet potable water reuse standards. Phosphorus was fully used in the bioreactor for biological growth. Heterotrophic bacteria and MS-2 viruses were completely retained by the membrane system, reducing the extent of final disinfection required.

Hg2+ Removal by Genetically Engineered Escherichia coli in a Hollow Fiber Bioreactor

Abstract: Escherichia coli cells engineered to express an Hg2+ transport system and metallothionein accumulated Hg2+ effectively over a concentration range of 0.2-4 mg/L in batch systems. Bioaccumulation was selective against other metal ions and resistant to changes in ambient conditions such as pH, ionic strength, and the presence of common metal chelators or complexing agents (Chen, S.-L.; Wilson, D. B. Appl. Environ. Microbiol. 1997, 63, 2442-2445; Biodegradation 1997, 8, 97-103). Here we report the characterization of the bioaccumulation system based on its kinetics and an isotherm. Bioaccumulation was rapid and followed Michaelis-Menten kinetics. A hollow fiber bioreactor was constructed to retain the genetically engineered cells. The bioreactor was capable of removing and recovering Hg2+ effectively at low concentrations, reducing a 2 mg/L solution to about 5 microgram/L. A mathematical equation that quantitatively described Hg2+ removal by the bioreactor provides a basis for the optimization and extrapolation of the bioreactor. The genetically engineered E. colicells and the bioreactor system have excellent properties for bioremediation of Hg2+-contaminated environments.

A membrane bioreactor for biotransformations of hydrophobic molecules

Abstract: The Membrane Bioreactor for Biotransformations (MBB) is based on the aqueous/organic two-phase system, and uses a tubular silicone rubber membrane to separate the two liquid phases. This avoids the key problem associated with direct contact two-phase processes, specifically, product emulsification. The baker's yeast mediated reduction of geraniol to citronellol was used as a model biotransformation to demonstrate MBB operation. Values for the overall mass transfer coefficient were determined for geraniol, (2.0 x 10(-5) ms-1), and for citronellol, (2.1 x 10(-5) ms-1) diffusion across the silicone rubber membrane. Using these values, and the specific activity of the biocatalyst (5 nmols-1g biomass-1), a suitable membrane surface area: biomass ratio was determined as 2.4 x 10(-3) m2g biomass-1. The bioreactor was operated at this surface area: biomass ratio and achieved a product accumulation rate 90-95% that of a conventional direct contact two-phase system. The slight reduction in product accumulation rate was shown not to be due to mass transfer limitations with respect to reactant delivery or product extraction. Copyright 1998 John Wiley & Sons, Inc.

Influence of dissolved oxygen on the nitrification kinetics in a circulating bed biofilm reactor

Abstract: The influence of dissolved oxygen concentration on the nitrification kinetics was studied in the circulating bed reactor (CBR). The study was partly performed at laboratory scale with synthetic water, and partly at pilot scale with secondary effluent as feed water. The nitrifi- cation kinetics of the laboratory CBR as a function of the oxygen concentration can be described according to the half order and zero order rate equations of the diffusion- reaction model applied to porous catalysts. When oxygen was the rate limiting substrate, the nitrification rate was close to a half order function of the oxygen concentration. The average oxygen diffusion coefficient estimated by fit- ting the diffusion-reaction model to the experimental re- sults was around 66% of the respective value in water. The experimental results showed that either the ammonia or the oxygen concentration could be limiting for the nit- rification kinetics. The latter occurred for an oxygen to ammonia concentration ratio below 1.5-2 gO 2 /gN-NH a for both laboratory and pilot scale reactors. The volu- metric oxygen mass transfer coefficient (kLa) determined in the laboratory scale reactor was 0.017 s )1 for a super- ficial air velocity of 0.02 m s )1 , and the one determined in the pilot scale reactor was 0.040 s )1 for a superficial air velocity of 0.031 m s )1 . The kLa for the pilot scale reactor did not change significantly after biofilm development, compared to the value measured without biofilm. List of symbols a m 2 m )3 specific mass transfer surface area of the gas bubbles CL;O2 mgO 2 l ˇ1 actual dissolved oxygen

Microbial degradation of hydrocarbons in soil during aerobic/anaerobic changes and under purely aerobic conditions

Abstract: Microbial hydrocarbon degradation in soil was studied during periodical aerobic/anaerobic switching and under purely aerobic conditions by using a pilot-scale plant with diesel-fuel-contaminated sand. The system worked according to the percolation principle with controlled circulation of process water and aeration. Periodical switching between 4 h of aerobic and 2 h of anaerobic conditions was achieved by repeated saturation of the soil with water. Whatever the cultivation mode, less than 50% of the diesel was degraded after 650 h because the hydrocarbons were adsorbed. Contrary to expectations, aerobic/anaerobic changes neither accelerated the rate of degradation nor reduced the residual hydrocarbon content of the soil. Obviously the pollutant degradation rate was determined mainly by transport phenomena and less by the efficiency of microbial metabolism. The total mass of oxygen consumed and carbon dioxide produced was greater under aerobic/anaerobic changing than under aerobic conditions, although the mass of hydrocarbons degraded was nearly the same. As shown by an overall balance of microbial growth and by a carbon balance, the growth yield coefficient was smaller during aerobic/anaerobic changes than under aerobic conditions.

Biocatalytic membrane reactors

Abstract: Biocatalytic membrane reactors are biohybrid artificial systems where a biochemical conversion is combined with a membrane separation process. The term may indicate either that the membrane itself is biocatalytic, that is participates directly in the reaction forming the reactor's core system, or that a bioconversion step is combined with a catalytically inert membrane operation. In the latter case, the term “membrane bioreactor” is more appropriate. With reference to the more general term “membrane reactors”, membrane bioreactors are distinguished by the fact that the chemical conversion is catalyzed by chemical catalysts of biological origin, such as enzymes and cells, instead of ordinary chemical catalysts. Membrane science and chemical and biochemical engineering contribute to the development of these systems by designing compact, flexible, and efficient apparatuses, in which conversion and product separation from the reaction site occur simultaneously, thus enhancing yield according to Le Chatelier's principle. Biocatalytic membrane reactors allow to carry out concentration and separation without the use of heat; they permit innovative formulation strategies; the equipments need less space, are flexible and easy to scale-up (they are enabling technologies and respond well to the process intensification strategy); operating costs are low; energy consumed is low; products and coproducts are of high quality (which is very important for by-product valorization, waste prevention, and minimization). Due to the abilities of both, membrane processes and biocatalysts, to work with high selectivity and without additives, biocatalytic membrane reactors are particularly suitable for processing in the food and beverage, biotechnological, biomedical, and pharmaceutical fields, as well as in wastewater treatment. In this work, their basic aspects and main applications in topics of current industrial interest are be discussed. Keywords: biocatalytic membrane; membrane bioreactor; immobilized biocatalyst kinetics; membrane; biocatalyst; submerged membrane bioreactor; enantioselective bioconversion; membrane bioseparation