Showing papers on "Bioreactor published in 2004"

Microfluidic PDMS (Polydimethylsiloxane) Bioreactor for Large‐Scale Culture of Hepatocytes

Abstract: Microfluidics could provide suitable environments for cell culture because of the larger surface-to-volume ratio and fluidic behavior similar to the environments in vivo. Such microfluidic environments are now used to investigate cell-to-cell interactions and behaviors in vitro, emulating situations observed in vivo, for example, microscale blood vessels modeled by microfluidic channels. These emulated situations cannot be realized by conventional technologies. In our previous works, microfluidic channels composed of two PDMS (poly(dimethylsiloxane)) layers were successfully used for Hep G2 cell culture. To achieve physiologically meaningful functions in vitro, a culture with a larger number of cells and higher density must be performed. This will require bioreactors with larger surface areas for cell attachment and sufficient amounts of oxygen and nutrition supply. For those purposes, we fabricated a bioreactor by stacking 10 PDMS layers together, i.e., four cell culture chambers, and a chamber dedicated to the oxygen supply inserted in the middle of the 10-stacked layers. The oxygen supply chamber is separated from the microfluidic channels for the culture medium perfusion by thin 300-μm PDMS walls. The high gas permeability of PDMS allows oxygen supply to the microfluidic channels through the thin walls. On the basis of the measurement of glucose consumption and albumin production, it is shown that cellular activity exhibits a gradual increase and saturation throughout the culture. We clearly observed that in the case of the microfluidic bioreactor for large-scale cultures, the oxygen chamber is indispensable to achieve longer and healthy cultures. In the present bioreactor, the cell density was found to be about 3–4 × 107 cells/cm3, which is in the same order of magnitude as the conventional macroscale bioreactors. Consequently, by stacking single culture chambers and oxygen chambers in between, we could have a scalable method to realize the microfluidic bioreactor for large-scale cultures.

Continuous Production of Butanol by Clostridium acetobutylicum Immobilized in a Fibrous Bed Bioreactor

Abstract: We explored the influence of dilution rate and pH in continuous cultures of Clostridium acetobutylicum. A 200-mL fibrous bed bioreactor was used to produce high cell density and butyrate concentrations at pH 5.4 and 35°C. By feeding glucose and butyrate as a cosubstrate, the fermentation was maintained in the solventogenesis phase, and the optimal butanol productivity of 4.6 g/(L h) and a yield of 0.42 g/g were obtained at a dilution rate of 0.9 h-1 and pH 4.3. Compared to the conventional acetone-butanol-ethanol fermentation, the new fermentation process greatly improved butanol yield, making butanol production from corn an attractive alternative to ethanol fermentation.

Anaerobic hydrogen production with an efficient carrier-induced granular sludge bed bioreactor.

Abstract: A novel bioreactor containing self-flocculated anaerobic granular sludge was developed for high-performance hydrogen production from sucrose-based synthetic wastewater. The reactor achieved an optimal volumetric hydrogen production rate of ∼7.3 L/h/L (7,150 mmol/d/L) and a maximal hydrogen yield of 3.03 mol H2/mol sucrose when it was operated at a hydraulic retention time (HRT) of 0.5 h with an influent sucrose concentration of 20 g COD/L. The gas-phase hydrogen content and substrate conversion also exceeded 40 and 90%, respectively, under optimal conditions. Packing of a small quantity of carrier matrices on the bottom of the upflow reactor significantly stimulated sludge granulation that can be accomplished within 100 h. Among the four carriers examined, spherical activated carbon was the most effective inducer for granular sludge formation. The carrier-induced granular sludge bed (CIGSB) bioreactor was started up with a low HRT of 4–8 h (corresponding to an organic loading rate of 2.5–5 g COD/h/L) and enabled stable operations at an extremely low HRT (up to 0.5 h) without washout of biomass. The granular sludge was rapidly formed in CIGSB supported with activated carbon and reached a maximal concentration of 26 g/L at HRT = 0.5 h. The ability to maintain high biomass concentration at low HRT (i.e., high organic loading rate) highlights the key factor for the remarkable hydrogen production efficiency of the CIGSB processes. © 2004 Wiley Periodicals, Inc.

Start-up of autotrophic nitrogen removal reactors via sequential biocatalyst addition

Abstract: A procedure for start-up of oxygen-limited autotrophic nitrification-denitrification (OLAND) in a lab-scale rotating biological contactor (RBC) is presented. In this one-step process, NH4+ is directly converted to N-2 without the need for an organic carbon source. The approach is based on a sequential addition of two types of easily available biocatalyst to the reactor during start-up: aerobic nitrifying and anaerobic, granular methanogenic sludge. The first is added as a source of aerobic ammonia-oxidizing bacteria (AAOB), the second as a possible source of planctomycetes including anaerobic ammonia-oxidizing bacteria (AnAOB). The initial nitrifying biofilm serves as a matrix for anaerobic cell incorporation. By subsequently imposing oxygen limitation, one can create an optimal environment for autotrophic N removal. In this way, N removal of about 250 mg of N L-1 d(-1) was achieved after 100 d treating a synthetic NH4+-rich wastewater. By gradually imposing higher loads on the reactor, the N elimination could be increased to about 1.8 g of N L-1 d(-1) at 250 d. The resulting microbial community was compared with that of the inocula using general bacterial and AAOB- and planctomycete-specific PCR primers. Subsequently, the RBC reactor was shown to treat a sludge digestor effluent under suboptimal and strongly varying conditions. The RBC biocatalyst was also submitted to complete absence of oxygen in a fixed-film bioreactor (FFBR) and proved able to remove NH4+ with NO2- as electron acceptor (maximal 434 mg of NH4+-N (g of VSS)(-1) d(-1) on day 136). DGGE and real-time PCR analysis demonstrated that the RBC biofilm was dominated by members of the genus Nitrosomonas and close relatives of Kuenenia stuttgartiensis, a known AnAOB. The latter was enriched during FFBR operation, but AAOB were still present and the ratio planctomycetes/AAOB rRNA gene copies was about 4.3 after 136 d of reactor operation. Whether this relates to an active role of AAOB in the anoxic N removal process remains to be solved.

Industrial Wastewater Treatment in a Membrane Bioreactor: A Review

Abstract: This paper provides a detailed literature review of wastewater treatment in a membrane bioreactor process (MBR) with special focus on industrial wastewater treatment. MBR systems are compared with conventional wastewater treatment systems. The characteristics of the bioreactor treatment process (biomass concentration and floc size, organic and mass loading rates, etc.) are examined. The membrane separation of microorganisms from the treated wastewater is discussed in detail. Problems of membrane fouling and membrane washing and regeneration, linked to activated sludge characteristics, are examined. © 2004 American Institute of Chemical Engineers Environ Prog, 23: 59–68, 2004

Modeling and simulation of oxygen-limited partial nitritation in a membrane-assisted bioreactor (MBR).

Abstract: Combination of a partial nitritation process and an anaerobic ammonium oxidation process for the treatment of sludge reject water has some general cost-efficient advantages compared to nitrification-denitrification. The integrated process features two-stage autotrophic conversion of ammonium via nitrite to dinitrogen gas with lower demand for oxygen and no external carbon requirement. A nitrifying membrane-assisted bioreactor (MBR) for the treatment of sludge reject water was operated under continuous aeration at low dissolved oxygen (DO) concentrations with the purpose of generating nitrite accumulation. Microfiltration was applied to allow a high sludge retention time (SRT), resulting in a stable partial nitritation process. During start-up of the MBR, oxygen-limited conditions were induced by increasing the ammonium loading rate and decreasing the oxygen transfer. At a loading rate of 0.9 kg N m(-3) d(-1) and an oxygen concentration below 0.1 mg DO L(-1), conversion to nitrite was close to 50% of the incoming ammonium, thereby yielding an optimal effluent within the stoichiometric requirements for subsequent anaerobic ammonium oxidation. A mathematical model for ammonium oxidation to nitrite and nitrite oxidation to nitrate was developed to describe the oxygen-limited partial nitritation process within the MBR. The model was calibrated with in situ determinations of kinetic parameters for microbial growth, reflecting the intrinsic characteristics of the ammonium oxidizing growth system at limited oxygen availability and high sludge age. The oxygen transfer coefficient (K(L)a) and the ammonium-loading rate were shown to be the appropriate operational variables to describe the experimental data accurately. The validated model was used for further steady state simulation under different operational conditions of hydraulic retention time (HRT), K(L)a, temperature and SRT, with the intention to support optimized process design. Simulation results indicated that stable nitrite production from sludge reject water was feasible with this process even at a relatively low temperature of 20 degrees C with HRT down to 0.25 days.

Bacterial diversity and function of aerobic granules engineered in a sequencing batch reactor for phenol degradation.

Abstract: Phenol is a major pollutant in industrial wastewater, and its removal is of obvious interest. Biological treatment of phenol is generally preferred to physical or chemical treatment methods because of lower costs and the possibility of complete mineralization. However, conventional biological treatment systems such as the activated sludge process are known to be sensitive to high phenol loading rates and fluctuations in phenol loading due to substrate inhibition from phenol toxicity (44). These substrate inhibition difficulties can be overcome by strategies such as cell immobilization to protect microbial cells against phenol toxicity (24). Aerobic granulation is a recently reported form of cell immobilization technology that is attracting considerable research attention (27, 38). Aerobic granules are self-immobilized aggregates of microorganisms formed in engineered systems such as sequencing batch reactors (SBRs). Unlike activated sludge flocs, microbial granules have a well-defined appearance and are still visible as separate entities after settling (9). Granulation facilitates the accumulation of high amounts of active biomass and the effective separation of this biomass from the wastewater liquor. Early studies of aerobic granulation involved the use of benign substrates such as glucose and acetate (38, 39). Several recent studies reported the successful cultivation of aerobic granules using toxic phenol as a substrate and examined the effect of phenol loading on granule structure, activity, and metabolism (13, 14). While the microbial diversities of glucose-fed aerobic granules and phenol-degrading activated sludge have been reasonably well described (39, 43, 44), a gap in our understanding of the microbial communities residing in phenol-degrading aerobic granules still exists. Aerobic granules can be viewed as a special form of biofilm but without carriers for biofilm attachment. Growth environments for biofilm communities are different from those for planktonic communities, and microbial communities in attached biofilms have been shown to be highly distinct from the suspended biomass, even within a single reactor system (4, 8). Recent studies stress the importance of gaining an understanding of the functions of microbial communities, as population diversity alone may not be adequate in maintaining ecosystem stability. Recognizing the diversity and the links within the key functional groups in a given system can lead to better ways to model diversity and function as well as to improve process stability (3, 12, 16). In this study, culture-independent and culture-dependent methods were used in combination to study the microbial community of phenol-degrading aerobic granules and to isolate, characterize, and identify ecologically relevant microorganisms. One of the isolates demonstrated a strong ability to degrade phenol and maintained a dominant presence within the granule community. A second isolate showed a weak ability to degrade phenol but was exceptional in its ability to autoaggregate. Based on these observations, a functional model of the microbial community in the aerobic granules was proposed. This work is expected to be useful in understanding the ecology and function of aerobic granules and in developing optimal control and management strategies for aerobic granulation systems.

Photosynthetically oxygenated salicylate biodegradation in a continuous stirred tank photobioreactor.

Abstract: A consortium consisting of a Chlorella sorokiniana strain and a Ralstonia basilensis strain was able to carry out sodium salicylate biodegradation in a continuous stirred tank reactor (CSTR) using exclusively photosynthetic oxygenation. Salicylate biodegradation depended on algal activity, which itself was a function of microalgal concentration, light intensity, and temperature. Biomass recirculation improved the photobioreactor performance by up to 44% but the results showed the existence of an optimal biomass concentration above which dark respiration started to occur and the process efficiency started to decline. The salicylate removal efficiency increased by a factor of 3 when illumination was increased from 50 - 300 muE/M-2 (.)s. In addition, the removal rate of sodium salicylate was shown to be temperature-dependent, increasing from 14 to 27 mg/l(.)h when the temperature was raised from 26.5 to 31.5degreesC. Under optimized conditions (300 muE/m(2) (.)s, 30degreesC, 1 g sodium salicylate/l in the feed and biomass recirculation) sodium salicylate was removed at a maximum constant rate of 87 mg/l.h, corresponding to an estimated oxygenation capacity of 77 mg O-2/l(.)h (based on a BOD value of 0.88 g O-2/g sodium salicylate for the tested bacterium), which is in the range of the oxygen transfer capacity of large-scale mechanical surface aerators. Thus, although higher degradation rates were attained in the control reactor, the photobioreactor is a cost-efficient process which reduces the cost of aeration and prevents volatilization problems associated with the degradation of toxic volatile organic compounds under aerobic conditions. (C) 2004 Wiley Periodicals, Inc. (Less)

Effect of Organic Loading Rate on Aerobic Granulation. II: Characteristics of Aerobic Granules

Abstract: Four sequential aerobic sludge blanket reactors, Reactors R1, R2, R3, and R4, were operated at organic loading rates (OLRs) of 1, 2, 4, and 8kg chemical oxygen demand (COD)/m3day, respectively. Aer...

Perfusion process for producing erythropoietin

Abstract: The invention relates to a process for producing erythropoietin (EPO) in which eukaryotic cells, which are suitable for expressing EPO, are adapted to SMIF7 medium in a suitable bioreactor, the resulting cells are transferred to a larger bioreactor and further expanded with SMIF7 medium and, while constantly bleeding and constantly perfusing, the expressed EPO is isolated from the larger bioreactor and purified.

Effect of Low Oxygen Tension on Tissue-Engineered Cartilage Construct Development in the Concentric Cylinder Bioreactor

Abstract: Cartilage is exposed to low oxygen tension in vivo, suggesting culture in a low-oxygen environment as a strategy to enhance matrix deposition in tissue-engineered cartilage in vitro. To assess the effects of oxygen tension on cartilage matrix accumulation, porous polylactic acid constructs were dynamically seeded in a concentric cylinder bioreactor with bovine chondrocytes and cultured for 3 weeks at either 20 or 5% oxygen tension. Robust chondrocyte proliferation and matrix deposition were achieved. After 22 days in culture, constructs from bioreactors operated at either 20 or 5% oxygen saturation had similar chondrocyte densities and collagen content. During the first 12 days of culture, the matrix glycosaminoglycan (GAG) deposition rate was 19.5 × 10-9 mg/cell per day at 5% oxygen tension and 65% greater than the matrix GAG deposition rate at 20% oxygen tension. After 22 days of bioreactor culture, constructs at 5% oxygen contained 4.5 ± 0.3 mg of GAG per construct, nearly double the 2.5 ± 0.2 mg of GA...

Effect of oxygen tension on adult articular chondrocytes in microcarrier bioreactor culture.

Abstract: Tissue-engineering approaches for cartilage repair hold promise for the treatment of cartilage defects. Various methods to prevent or reduce dedifferentiation during chondrocyte expansion are currently under investigation. In the present study we evaluated the effect of oxygen on chondrocyte proliferation, as oxygen has received increased attention as a possible regulator of chondrocyte differentiation and its effect during expansion is uncertain. Therefore, the effect of three oxygen tensions (4, 10.5, and 21%) was investigated in a bioreactor microcarrier culture, which allows precise control of the oxygen tension in the liquid phase. During culture cells acquired a round shape on microcarriers. No differences in proliferation rate of chondrocytes were observed within the range of oxygen tensions evaluated. Cells exhibited predominantly anaerobic metabolism and, per mole of glucose, approximately 2 mol of lactate was produced independent of oxygen tension. Cellular oxygen consumption was comparable for all bioreactor cultures. Nevertheless, specific consumption rates were relatively high (2-4 x 10(-17) mol. cell(-1). s(-1)), in comparison with chondrocytes in cartilage (0.8-2.2 x 10(-18) mol. cell(-1)). Subsequent cartilaginous tissue formation in pellets was not affected as qualitatively assessed by safranin-O staining. At the oxygen concentrations evaluated, no effect of oxygen tension was observed on proliferation, oxygen consumption, and yield of lactate on glucose administration. For future investigations of chondrocytes and oxygen, the bioreactor system, which allows precise control and monitoring of oxygen tension, holds promise.