Oxygen In Bioreactor Research Articles

Investigating the ability of sulfur oxidizing strains in biodesulfurisation of sulfide-containing streams, screening the most capable strain and determining the optimum condition for elemental sulfur recovery from sulfide using response surface method

Beside numerous chemical methods, biological methods were developed to remove sulfide from streams using Sulfur Oxidizing Bacteria (SOB). Because of the wide variety of such bacteria and deep difference in their capability, the ability of seven well-known SOBs were investigated. According to the results T. versutus and T. aerophilum were selected as capable bacteria for further experiments. The valuable product of sulfide oxidation is elemental sulfur, the production of sulfur in the culture medium was considered as the basis for selecting the appropriate bacteria. Evaluations of bacteria showed that T. aerophilum was not able to produce elemental sulfur and only produced sulfate as its final product. However, by creating oxygen restriction conditions, sulfur production is observed for T. versutus. Therefore, the continuation of experiments on the optimization of sulfur production in the culture medium of T. versutus was investigated. Due to the fact that the amount of dissolved oxygen in bioreactor can be controlled by changing the stirrer speed, the stirrer speed was considered as one of the parameters. In these experiments, sulfide ion concentration and initial agitator speed were considered as variables and sulfur production as a response. Experiments were designed using Design Expert software and RSM method. The results of optimization experiments showed that the concentration of 10000 mg/L of sulfide and the stirrer speed of 130 rpm led to the production of elemental sulfur of 1600 mg/L. Therefore, 40% of the incoming sulfide is converted to sulfur.

Advanced treatment of dye wastewater using a novel integrative Fenton-like/MnO2-filled upward flow biological filter bed system equipped with modified ceramsite

The deposal of residual hydrogen peroxide (H2O2) in Fenton-like system and the requirement of oxygen in bioreactor are essential parts for the treatment of integrative Fenton-like/bioreactor. A novel low-cost integrative Fenton-like and MnO2-filled upward flow biological filter bed (Fenton-like/MBFB) equipped with the modified ceramsite was constructed to evaluate the main properties and catalytic activity of modified ceramsite, and the optimal conditions of integrative system and compare integrative and traditional systems. In this study, the Fenton-like reactor with modified ceramsite had higher catalytic ability whose Acid Orange 7 (AO7) degradation efficiency reached to 79.3% due to large surface area and high porosity, compared with that with raw ceramsite (44.3%). Furthermore, total utilization efficiency of H2O2 in integrative system (from 32.41% to 53.51%) and removal efficiencies of COD and AO7 were remarkably improved, which would effectively decrease the waste of H2O2 and the setting of regulation pool and aeration tank. Thus, the integrative system can save 0.51 CNY/m3 in construction cost and 0.21 CNY/m3 in operating cost. The average COD removal efficiency, AO7 degradation efficiency and effluent DO concentration were achieved to 64.8%, 79.5% and 9.3 mg/L respectively in integrative system were achieved in integrative system during sixty successive runs. Also, the potential degradation pathway of contaminants was also proposed according to the OH-enhanced at Fenton-like reactor due to catalyst and adsorption of modified ceramsite and the removal of microorganisms and modified ceramsite for contaminants at MBFB. This study demonstrated the feasibility of integrative Fenton-like/MBFB filled with modified ceramsite for simultaneously decreasing operational cost and complexity and enhancing removal efficiency, thus provided a one-step alternative for refractory dye wastewater.

Efficacy of medium chain-length polyhydroxyalkanoate biosynthesis from different biochemical pathways under oxygen-limited conditions using Pseudomonas putida LS46

Biosynthesis of medium chain length polyhydroxyalkanoates (mcl-PHAs) requires oxygen, but little is known of how mcl-PHA production is impacted in low dissolved oxygen (DO) environments, particularly when synthesized from monomers obtained via a de novo pathway. Growth and mcl-PHA synthesis characteristics under microaerophilic bioreactor conditions were observed in Pseudomonas putida LS46 when grown on carbon substrates requiring a de novo pathway, to varying extent, for mcl-PHA synthesis. Negligible PHA accumulated from glucose, acetic acid, or valeric acid under oxygen limitation (DO ≤ 0.15 mg L−1), while final mcl-PHA content reached 19.5% of cell dry mass (CDM) from hexanoic acid. The C6 content of the polymer obtained under low DO was 10% higher than in a DO excess (NH4-limited) control experiment, with less of the C10 monomers indicative of de novo synthesis. In all cases, the carbon-to-PHA yield was poor (< 0.1 C-mol C-mol−1). We conclude that, as opposed to utilizing β-oxidation intermediates, de novo biosynthesis of mcl-PHA using P. putida LS46 is not favorable in microaerophilic environments. In addition to scale-up implications, this work also suggests that lowering the bioreactor oxygen transfer rate can decrease the contribution of monomers incorporated using de novo synthesis for carbon feedstocks with mixed composition.

The role of dissolved oxygen content as a modulator of microbial polyhydroxyalkanoate synthesis.

Polyhydroxyalkanoates (PHAs) are a diverse class of bio-polymers synthesized by bacteria, usually during imbalanced growth conditions. Optimizing PHA productivity is highly dependent on the bioreactor oxygen transfer rate (OTR), which is an important consideration for process performance and economics, particularly with increasing scale. Relatively few in-depth studies are available regarding the effect of OTR and dissolved oxygen content (DOC) on PHA formation, synthesis rates, composition, and characteristics. This review examines past research studies on the effect of low DOC environments on production of short-chain length (scl-) PHAs, synthesized by both pure and mixed cultures, in order to identify opportunities and gaps concerning the effect of DOC on production of medium-chain length (mcl-) PHAs, an area that has not been studied in detail. The literature indicates that production of scl-PHA (a reductive process) acts as an electron sink allowing cells to maintain balanced redox state at low DOC. Conversely, production of mcl-PHA via fatty acid de novo synthesis (also a reductive process) does not occur to any significant extent in low DOC environments, while mcl-PHA synthesis from fatty acids (an oxidative process) can be promoted in low DOC environments. The monomer composition, molecular mass, as well as physical and thermal properties of the polymer can change in response to OTR, but further research in this area is required for both scl- and mcl-PHAs. Process design and management of bioreactor OTR in PHA production might therefore be directed by the final application of the polymer rather than cost considerations.

Microaerophilic environments improve the productivity of medium chain length polyhydroxyalkanoate biosynthesis from fatty acids in Pseudomonas putida LS46

Medium chain length polyhydroxyalkanoate (mcl-PHA, a commercially desirable biopolymer) synthesis from fatty acids is an oxidative process. Growth and mcl-PHA synthesis were studied in Pseudomonas putida LS46 when subjected to a spectrum of oxygen transfer rates, which were intended to simulate dissolved oxygen (DO) gradients likely to be encountered during process scale-up. It was found that maintaining DO at 1–5% (of air saturation at 30 °C) initiated significant mcl-PHA synthesis and concurrent growth at <0.5 μmax was also observed. Further reductions in DO resulted in nearly negligible growth, but improved biopolymer synthesis. When the volumetric oxygen mass transfer coefficient (kLa) was reduced to 38 h−1, DO was below detectable limits and both the biopolymer content (57.3 ± 3.8% CDM) and yield (0.62 ± 0.06 g mcl-PHA g octanoic acid−1) reached the maximum observed values. Under these conditions, the maximum rate of polymer synthesis was also observed (227.9 ± 9.8 mg PHA g residual cell mass−1 h−1), and this value was higher than that which could be achieved using nitrogen limitation. Further reductions in oxygen transfer rate did not improve productivity, and PHA synthesis completely ceased when aeration was replaced with N2 gassing. These results suggest that manipulation of the bioreactor oxygen transfer rate during the PHA accumulation phase could be a strategy used to improve overall productivity during a fed batch or continuous feed process.

Distribution and mass transfer of dissolved oxygen in a multi-habitat membrane bioreactor

This work investigated the DO distribution and the factors influencing the mass transfer of DO in a multi-habitat membrane bioreactor. Through the continuous measurements of an on-line automatic system, the timely DO values at different zones in the bioreactor were obtained, which gave a detailed description to the distribution of oxygen within the bioreactor. The results indicated that the growth of biomass had an important influence on the distribution of oxygen. As the extension of operational time, the volumetric oxygen mass transfer coefficient (kLa) was generally decreased. With the difference in DO values, a complex environment combining anoxic and oxic state was produced within a single bioreactor, which provided a fundamental guarantee for the total removal of TN. Aeration rate, the concentration and apparent viscosity of MLSS have different influences on kLa, but adjusting the viscosity is a feasible method to improve the mass transfer of oxygen in the bioreactor.

The Research of Solar Film Reactor Technology Designing

In view of the Membrane Bio-Reactor(MBR)'s common energy consumption and higher operating costs in domestic and overseas, we designed a solar MBR process, the design process is using solar energy to directly carry out the thermal conversion, and complete membrane bioreactor Oxygen demand and membrane pressure process of the work process without motor,blower or water pump. The reactor can make the energy consumption and operation cost greatly reduced, and the operating costs can be reduced by 56% to 78%.

Evaluation of oxygen transfer rates in stirred‐tank bioreactors for clinical manufacturing

Several methods are available for determining the volumetric oxygen transfer coefficient in bioreactors, though their application in industrial bioprocess has been limited. To be practically useful, mass transfer measurements made in nonfermenting systems must be consistent with observed microbial respiration rates. This report details a procedure for quantifying the relationship between agitation frequency and oxygen transfer rate that was applied in stirred-tank bioreactors used for clinical biologics manufacturing. The intrinsic delay in dissolved oxygen (DO) measurement was evaluated by shifting the bioreactor pressure and fitting a first-order mathematical model to the DO response. The dynamic method was coupled with the DO lag results to determine the oxygen transfer rate in Water for Injection (WFI) and a complete culture medium. A range of agitation frequencies was investigated at a fixed air sparge flow rate, replicating operating conditions used in Pichia pastoris fermentation. Oxygen transfer rates determined by this method were in excellent agreement with off-gas calculations from cultivation of the organism (P = 0.1). Fermentation of Escherichia coli at different operating parameters also produced respiration rates that agreed with the corresponding dynamic method results in WFI (P = 0.02). The consistency of the dynamic method results with the off-gas data suggests that compensation for the delay in DO measurement can be combined with dynamic gassing to provide a practical, viable model of bioreactor oxygen transfer under conditions of microbial fermentation.

Optical imaging in microfluidic bioreactors enables oxygen monitoring for continuous cell culture

For the first time, a fluorescence lifetime calibration method for an oxygen-sensitive dye ruthenium tris(2,2'-dipyridyl) dichloride hexahydrate (RTDP) is applied to image oxygen levels in poly(dimethyl siloxane) (PDMS) bioreactors containing living C2C12 mouse myoblasts. PDMS microsystems are broadly used in bioengineering applications due to their biocompatibility and ease of handling. For these systems, oxygen concentrations are of significance and are likely to play an important role in cell behavior and gene expression. Fluorescence lifetime imaging microscopy (FLIM) bases image contrast on fluorophore excited state lifetimes, which reflect local biochemistry. Unique attributes of the widefield, time-domain FLIM system include tunable excitation (337.1 to 960 nm), large temporal dynamic range (> or =600 ps), high spatial resolution (1.4 microm), calibrated detection (0 to 300+/-8 microM of oxygen), and rapid data acquisition and processing times (10 s). Oxygen levels decrease with increasing cell densities and are consistent with model outcomes obtained by simulating bioreactor oxygen diffusion and cell proliferation. In single bioreactor loops, FLIM detects spatial heterogeneity in oxygen levels with variations as high as 20%. The fluorescence lifetime-based imaging approach we describe avoids intensity-based artifacts (including photobleaching and concentration variations) and provides a technique with high spatial discrimination for oxygen monitoring in continuous cell culture systems.

Induction in the antioxidative systems and lipid peroxidation in suspension culture roots of Panax ginseng induced by oxygen in bioreactors

Roots of mountain ginseng ( Panax ginseng) were exposed to various levels of oxygen (O 2) (30, 40 and 50%) for 15, 30 and 45 days in 5 L (working volume 4 L) airlift bioreactors. Ginsenoside accumulation and dry weight was enhanced up to 40% O 2; but thereafter declined ginsenoside and dry weight of the roots by increasing level of O 2. Gradual increase in H 2O 2 content and lipoxygenase activity (LOX), resulting in cellular damage and oxidative stress as indicated by increased malondialdehyde (MDA) content after 30 and 45 days at all O 2 levels was shown. Increased levels of O 2 (above ambient) resulted in increases in non-protein thiol (NP-SH) and cysteine content. Higher activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), catalase (CAT), guaiacol peroxidase (G-POD), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S transferase (GST) activities indicated that antioxidant enzymes played an important role in protecting the roots from O 2 up to 45 days, except at 50% O 2 where GR, GST and GPx decreased compared to the control. However, after 45 days, SOD activity decreased significantly compared to the control in the O 2-treated roots. This reflects the sensitivity of enzymes to O 2 toxicity. In stress related experiment, roots showed increased synthesis of ginsenosides when 25 and 50 μM H 2O 2 was applied. However, higher dose and increasing treatment inhibited ginsenoside synthesis. The results indicate that plant roots could grow and protect themselves from O 2 stress by coordinated induction of various antioxidant enzymes and metabolite contents. These results suggest that O 2 supplementation is useful for ginsenoside accumulation using 5-L bioreactors.

Precise control of dissolved oxygen in bioreactors – a model-based geometric algorithm

In this paper, we develop a Model-Based Geometric Control Algorithm (MGA) for controlling the dissolved oxygen concentration in fermentation processes. The algorithm is developed on a generic system description which encompasses a wide range of models commonly used to describe bioprocesses. Consequently, the algorithm we have derived will apply to any process whose model fits the generic description. The algorithm uses information contained in the shape (geometry) of the profile of the state variables as they evolve in time to adapt to process variations. There are two components in the algorithm, an estimator and a controller, whose functions complement each other. The estimator component of the algorithm predicts the states and the parameters of the system one time step ahead. Since the estimator is deadbeat, the algorithm converges in a finite number of steps. The control component of the algorithm uses the states predicted by the estimator and executes a control action so that predicted error falls below a desired level. Simulations for comparing the performance of the IMC, PI and MGA controllers are presented. The MGA was implemented on-line to control the dissolved oxygen in an aminoglycoside antibiotic production process by a Streptomyces and the results of its performance are also presented.

Oxygen delivery to and use by primary porcine hepatocytes in the HepatAssist 2000 system for extracorporeal treatment of patients in end-stage liver failure.

A system for the extracorporeal treatment of end-stage liver failure patients has been developed and is now in clinical studies. This HepatAssist 2000 system consists of perfusing the plasma of the patient through a hollow-fiber bioreactor containing primary porcine hepatocytes. The goal of the system is to assist the patient while the liver regenerates or a suitable liver is found for transplantation. During the development of this system in the laboratory, an experimental protocol has been developed to simulate patient treatments. The protocol substitutes donor calf serum for patient plasma, but is otherwise similar to clinical conditions. The protocol uses a blood gas analyzer to monitor dissolved oxygen and carbon dioxide tensions at the entrance to and exit from the bioreactor. Samples are withdrawn using a standard 1-ml syringe and analyzed off-line immediately. The blood gas measurements have been used to verify that the oxygenator, placed immediately prior to the bioreactor in the plasma circuit, is properly sized to allow complete equilibration with feed gas and to maintain a physiologic level of carbon dioxide. The measurements were also used to calculate overall bioreactor oxygen consumption rates under various conditions. In one set of studies, composition of the feed gas to the oxygenator was varied from 20% to 70% oxygen, while maintaining 5% carbon dioxide and balance nitrogen. Rates of oxygen consumption and liver cell function (metabolism of diazepam) were unchanged, and no signs of oxygen toxicity were observed. In another set of studies, oxygen consumption increased linearly with number of hepatocytes used in the clinically used range of 5-10 billion hepatocytes, whether all hepatocytes were placed in one device or split between two devices operating in series or in parallel. In a third set of studies, oxygen consumption was a weak function of flowrate through the bioreactor but was highest at the clinically used recirculation rate of 400 ml/min. These data indicate that blood gas meters--readily available in hospital clinical laboratories--can be used to assist in the design of extracorporeal cell therapies, to monitor the effectiveness of system components, and to assess the effects of system modifications. These same measurements can be made noninvasively in the clinical setting to monitor oxygen consumption rates during patient treatment.

Phase fluorometric sterilizable optical oxygen sensor

We report here on a low-cost, optical oxygen sensor as an attractive alternative to the widely used amperometric Clark-type oxygen electrode for measuring dissolved oxygen tensions in cell cultures and bioreactor. Our sensor is based on the defferential quenching of the fluorescence lifetime of chromophore in response to the partial pressure of oxygen. This is measured as a phase shift in fluorescence emission from the chromophore due to oxygen quenching when excited by an intensity modulated beam of light. In this article we demonstrate the advantages of lifetime-based optical methods over both intensity based optical methods and amperometric electrodes. Our sensor is particularly suitable for measuring dissolved oxygen in bioreactors. It is autoclavable, is free of maintenance requirements, and solvents the problems of long-term stability, calibration drifts, and reliable measurement of low oxygen tensions in dense microbial cultures that limit the utility of Clark-type elcectordes. (c) 1994 John Wiley & Sons, Inc.

A novel technique based on 85Kr for quantification of gas—liquid mass transfer in bioreactors

A promising technique for quantification of the mass transfer coefficient k la for oxygen in bioreactors is described. The method is based on injection of the volatile, inert 85Kr isotope into the medium followed by measurement of the radioactivity in the gas leaving the head space. The measured response is interpreted using a simple model for the gas flow through the bioreactor. The method is compared with two other methods: (1) a dynamic method based on N 2 and (2) the classical sulphite method. The isotope method compares well with the dynamic method and, from the comparison with the sulphite method, it is concluded that the sulphite method gives an overestimation of k la which can not be explained solely by reduced coalescence due to the electrolyte. The extra effect is probably due to chemical reaction in the liquid film. The isotope method has been used to study the influence of the medium composition on the oxygen mass transfer. A major advantage of the 85Kr method is that it can be applied during real process conditions as illustrated in an experiment with growth of Aspergillus oryzae.

A microbial culture with oxygen‐sensitive product distribution as a potential tool for characterizing bioreactor oxygen transport

The dissolved oxygen (DO) level has been shown to have a profound effect on the product distribution of a Bacillus subtilis culture, with acetoin being excreted with DO above 100 parts per billion (ppb) and butanediol below 100 ppb. The product concentration ratio changed rapidly in the 80-90 ppb range. Switching from one oxygen level to another caused one already accumulated product to be converted to the other in a reversible manner. Rates of change of 0.5-1 g/L h enabled detection within 10 min. Detection sensitivity is enhanced because the ratio of two concentrations can be measured. Remarkably sensitive to mixing rates, the culture responded to changes in stirring speed during experiments in which the dissolved oxygen was controlled at a constant level with a novel control system. Thus, the culture is capable of detecting dead zones in relatively well-mixed reactors and oxygen gradients in column and tubular reactors. High-viscosity effects can also be investigated since the culture grows well in xanthan gum solutions. Preliminary kinetic model development indicates that a useful model for simulating reactor mixing and transport effects can be developed to aid in the planning of experiments.