Plug-flow Bioreactor Research Articles

Continuous bacteriocin production with high cell density bioreactors

The production of divercin, a bacteriocin active against Listeria, by whole cells of Carnobacterium divergens V41 was investigated by three means: continuous cultivation with free cells; with cells immobilized in calciumalginate beads packed in a plug-flow bioreactor, and with a membrane bioreactor. The productivity and bacteriocin concentrations of the systems were compared. Immobilized cells presented the best performances with more than 10 5 AU l −1 h −1 which can be compared to the 2.8 × 10 3 AU l −1 h −1 of the batch system. The membrane bioreactor failed to be efficient for low transmission of the bacteriocin through the membranes tested.

Removal of AOC in biological water treatment processes: A kinetic modeling approach

In this paper, a steady-state biofilm model is applied for modeling substrate removal by plug-flow bioreactors in biological water treatment. The model is used with assimilable organic carbon (AOC) data from a previous pilot scale study to estimate the essential physical and kinetic parameters required for designing biological water treatment processes. The successful fitting of the model to the data demonstrates the applicability of this modeling approach for water treatment and that AOC can be used as at least a surrogate for the overall biodegradable organic matter. The model is used to obtain process insights. It is shown that there is an approximately linear relationship between substrate removal and influent concentration. For a plug-flow packed bed bioreactor, a quantity designated as the dimensionless empty bed contact time, X∗, is defined. The slope of the linear relationship, representing the approximate percentage removal of the substrate, is shown to be mainly determined by X∗. Percentage removal increases convexly with increasing X∗, however beyond a certain value of X∗, further increases achieve little improvement. Other dimensionless parameters affect the convexity of the curve.

Improved Catalytic Performance of a 2-Haloacid Dehalogenase from Azotobacter sp. by Ion-Exchange Immobilisation

The stability and catalytic efficacy of the L-2-haloacid dehalogenase isolated from Azotobacter sp. RC26 were studied after immobilisation on a DEAE-Sephacel solid matrix. While the optimum temperature for the soluble dehalogenase falls in the range of 30–40°C, the activity of the immobilised enzyme shows a four-fold increase at 60°C. Immobilisation on a plug-flow bioreactor extends the range of usable substrate concentration. The improved catalytic characteristics after immobilisation of the haloacid dehalogenase may be relevant for its possible utilization in biotechnological applications ranging from waste treatment to synthesis of steroiso-mers.

Measurement of streamwater biodegradable dissolved organic carbon with a plug-flow bioreactor

Plug-flow biofilm reactors were colonized by microorganisms indigenous to streamwater and used to measure concentrations of biodegradable dissolved organic carbon (DOC) in streamwater. We performed experiments to determine the influence of physical, chemical, and biological factors on the operation of the bioreactors. Colonization required several months and the biological removal of DOC within the reactors was influenced by hydraulic residence time, dissolved organic carbon concentration, and water temperature. The large microbial biomass within a bioreactor buffered bioreactor performance from changes in chemical and physical parameters.

Immobilisation of the D-2-haloacid dehalogenase fromPseudomonas putida strain AJ1/23

A variety of procedures were used to immobilise D-2-haloacid dehalogenase. Natural polymer supports were insufficiently robust to withstand degradation by high concentrations of 2-chloropropionate. The best results were obtained with enzyme covalently attached to controlled-pore glass via a diazo linkage. The immobilisation procedure was optimised with respect to enzyme loading, pH, temperature and the presence of substrate during attachment. Immobilisation significantly modified the kinetics of the enzyme, in particular improving its temperature stability and ability to withstand mildly alkaline conditions where it is most active. The performance of the immobilised preparation in batch and plug-flow bioreactors was assessed. Biocatalyst half-life in plug-flow reactors was better than in batch bioreactors whereas effectiveness factors, although concentration dependent in the batch reactor, were similar at least with 200 mM D,L-2-CPA as substrate.

Conception and characterization of a continuous plug flow bioreactor

This report describes the design and use of a new type of Continuous Plug Flow Reactor (CPFR). The reactor comprises a continuous glass tube (diameter of 19 mm) arranged into a spiral (0.4 m external diameter) consisting of five loops, which rotate around an axle. The CPFR has advantages over other reactors in that continuous fermentation is possible without dilution of the culture and biomass or metabolite yield is increased. In addition temperature and water activity may be adjusted to a different optimum level for each physiological stage of the cultivated microorganism.

Pilot-Scale Demonstration of a Two-Stage Methanotrophic Bioreactor for Biodegradation of Trichloroethylene in Groundwater

A two-stage methanotrophic bioreactor system was developed for remediation of water contaminated with TCE and other chlorinated, volatile, aliphatic hydrocarbons. The first stage of the reactor was a suspended-growth culture vessel using a bubbleless methane-transfer device. The second stage was a plug-flow bioreactor supplied with contaminated groundwater and cell suspension from the culture vessel. The test objectives were to determine the applicability of microbial culture conditions reported in the literature for continuous, pilot-scale TCE treatment; the technical feasibility of plug-flow bioreactor design for treatment of TCE; and the projected economic competitiveness of the technology considering the cost of methane for growth of methanotrophs. The methanotrophic organism used in the study was Methylosinus trichosporium OB3b. Information on system operation was obtained in bench tests prior to conducting the pilot tests. In bench- and pilot-scale tests, variability in the degree of TCE degradation and difficulty in maintaining the microbial culture activity led to short periods of satisfactory biotreatment. Further development of the microbial culture system will be required for long-term operation. During transient periods of high TCE degradation activity, the bioreactor concept proved feasible by exhibiting both a high degree of TCE biodegradation (typically about 90% at influent TCE concentrations of 0.5-4 ppm) and a close approximation to first-order reactor kinetics throughout the length of the reactor. Actual methane usage in the pilot-scale reactor resulted in projected methane costs of $0.33 per 1000 gallons of water treated. This cost theoretically would be reduced by system modifications. The theoretical minimum methane cost was approximately $0.05 per 1000 gallons.

Enzymically-enhanced extraction of uranium from biologically leached solutions

Many wastes contain heavy metals which are toxic and refractory: further problems arise in the production and discharge of waste radionuclides which have additional radiotoxic effects on the biosphere. Currently the problem may be tackled in four ways: (i) direct chemical methods; (ii) electrochemical treatments; (iii) ion exchange and biosorption methods; (iv) intracellular sequestration by growing microbial cells. A hybrid approach exploits the advantages of processes (iii) and (iv) with the disadvantages of neither. In this context, a biotechnological process for removing and recovering heavy metals from aqueous solutions has been evaluated at low pH. Metal uptake relies upon the in situ cumulative deposition of insoluble metal phosphate tightly bound to the cell surface of Citrobacter N14. Localized high loading of phosphate is contributed via a phosphatase-catalysed hydrolysis of an organic phosphate ‘donor’ molecule added to the metal solution with precipitation of metals (M) as cell-bound MHPO 4 . The present work reports on the potential of this immobilized microbial biomass for uranium recovery from the dilute uranium acid drainage of ENUSA mine in the Ciudad Rodrigo district of Spain. A range of supports (organic and inorganic) and immobilization methods for Citrobacter cells have been screened. Finally, biofilm and entrapped cells on polyurethane foam and cells covalently immobilized on silanized and glutaraldehyde coated Al 2O 3 Raschig rings were chosen, characterized and evaluated for stability and suitability for large scale use. The physico-chemical monitoring and chemical composition of naturally bioleached waters from ENUSA mine were evaluated and improved methods for flow injection analysis (FIA) of uranium and inorganic phosphate were developed. Optimization studies of the operational conditions and performance of a plug flow bioreactor of immobilized Citrobacter for uranium removal at 30°C gave the following conclusions: (1) a working pH of 4·5 in the absence of any metal complexing agent (citrate) has been established, (2) a [glycerol 2-phosphate]/[ UO 2 2+] ratio of 39 is necessary for an optimum uranium removal; (3) at a flow rate of 50 ml/h (residence time of 1·4 h) the efficiency of removal was 50%.

Conception and characterization of a continuous plug flow bioreactor

Conception and characterization of a continuous plug flow bioreactor

Development of a single‐pass ceramic matrix bioreactor for large‐scale mammalian cell culture

A single-pass, plug-flow bioreactor has been developed in which oxygen is supplied to entrapped hybridoma cells via silicone tubes threaded through the square channels of a macroporous ceramic monolith. Oxygen diffuses from the gas phase, through the silicone tubing, across the open square channel, and into the pores of the ceramic wall where it is consumed by entrapped cells. Advantages of such a reactor include higher product yields, protection of cells from detrimental hydrodynamic effects, no internal moving parts to compromise asepsis, and simplicity of operation. A prototype bioreactor was constructed and operated over a range of residence times. A side-by-side experimental comparison with a conventional recycle bioreactor was performed by inoculating both bioreactors with cells from the same stock culture and feeding medium from the same reservoir. Final antibody titers were 80% higher in the single-pass bioreactor at a residence time of 200 minutes compared with those of the recycle bioreactor at a residence time of 800 minutes. A theoretical analysis of oxygen transport in this bioreactor is developed to highlight important design criteria and operating strategies for scale-up.