Chemistry: molecular biology and microbiology – Apparatus – Bioreactor
Reexamination Certificate
1999-05-26
2001-12-11
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Apparatus
Bioreactor
C435S298200, C435S180000, C210S619000, C210S150000
Reexamination Certificate
active
06329196
ABSTRACT:
The present invention relates to methods and apparatus for the enhancement of mass transfer of a fluid in a porous matrix system and, more particularly, to methods and apparatus for the controlled enhancement of mass transfer of gaseous and liquid media into and out of a biomass-containing porous support medium.
The present invention also relates to the harnessing of microorganisms in controlled processes which use oil or petroleum as a substrate and, more particularly, to methods and apparatus which enhances mass transfer of a fluid in a porous matrix system containing said microorganisms, for use in such controlled processes.
In the past, man has cultivated microorganisms in a controlled manner to take advantage of the wide range of biochemical reactions which can be mediated by their presence in a defined growth environment. One of the most well established industries in this field is the so-called “fermentation industry”, which today finds practical uses in, for example, brewing, baking and many other food and beverage processes. Since the end of the last century, man has harnessed microbes in controlled processes for the removal of pollutants from waste water and organic residues. The concept of using microorganisms for the removal of inorganic constituents from aqueous solution is also well documented and includes biosorption and luxuriant uptake. Microbes are also capable of bioconversion of some inorganic constituents, such as ammonia, via autotrophic nutrition. Also, in the field of fermentation technology, microorganisms and plant or animal cell cultures are now being extensively used to produce a wide range of chemicals and pharmaceutical products, with genetically engineered microorganisms and plant or animal cell cultures creating further interest in the biotechnology field.
Waste water and organic residue treatment processes both rely on contacting a mixed population of aerobic microorganisms with the waste water or organic residue to be treated in the presence of dissolved oxygen.
Biosorption is a general term applied to the removal of a range of constituents from solution by biological cellular material through both passive and metabolically active processes. Bioabsorption generally involves active transport across a cell membrane, whereas bioadsorption generally involves extra-cellular concentration of material at a cell surface and is not necessarily metabolically linked. Bioabsorption has been used successfully for the concentration of heavy metals from solution, including a wide range of radio-nuclides, which become concentrated in the cell. Such processes are generally aerobic and require the presence of organic growth constituents. The mechanisms used by certain microorganisms to concentrate inorganic salts across their cell membranes are of particular interest where these may be controlled to result in a net uptake of salt, with consequential decrease in the salinity of the medium which surrounds them.
Luxuriant uptake is a specific term applied to the bioabsorption by a microorganism of an essential element in quantities in excess of those normally required for metabolic processes. The prime example of luxuriant uptake is that of phosphorous removal from waste water in, for example, the so called “Bardenpho” and “Phostrip” processes.
Autotrophic nutrition by certain categories of microbes will result in the chemical transformation of inorganic constituents from one oxidation state to another, the two main examples being that of nitrification and sulphide oxidation. Such aerobic transformations of inorganic constituents may be beneficial to the final quality of water and are, thus, often practised in the treatment of waste waters or the treatment of sulphide rich gases in wet scrubbers.
The above processes, with the exception of bioadsorption and luxuriant phosphate uptake, all rely upon aerobic microbial reactions.
In the case of the production of chemicals and pharmaceutical products, the conditions of growth of the microbes or plant or animal cell cultures rely upon supply of appropriate nutrients, as well as aeration of the culture medium, in order to ensure that aerobic conditions prevail.
In all these processes, it is desirable to optimise the quantity of biomass in intimate contact with the particular medium concerned. Techniques involving biomass retention or biomass recirculation are useful, but will only be successful if it is ensured that the biomass is constantly supplied with the gases and nutrients required for growth and metabolism and, depending on the particular process involved, that the biomass is effectively supplied with a particular medium, or released products of metabolism effectively removed. There is, therefore, a desired to maximise biomass concentration per unit volume of reactive capacity, within the restraints of the mass transfer capacity of relevant gases and liquids into and out of the metabolising biomass, so as to minimize reactor size. (It should be noted that optimisation may well involve a compromise between maximising the biomass concentration per unit volume of reactor capacity and increasing the mass transfer of relevant gases and liquids into and out of the metabolising biomass. Too high a concentration of biomass per unit volume of reactive capacity, for example, could act against efficient mass transfer). Many techniques have, thus, been developed to enhance biomass retention and to improve mass transfer.
In particular, a wide range of specialist reactors have been developed for containing microorganisms or plant or animal cells during their growth and reaction periods and these vessels range in complexity from simple open vats to fluidised beds, which can be sterilised in preparation for use. Many of these reactors immobilise biomass on a porous support medium, such as open-celled foam, in order to maximise the surface area available for colonisation by the microorganisms or plant or animal cells and thereby increases the biomass density per unit volume of reactor. For example, the surface area available for colonisation by microorganisms, or plant or animal cells has been increased in packed column reactors by using a reticulated polyurethane foam as the support medium, and by either percolating the culture medium down through the bed of foam, or by causing the culture medium to flow upwards through the bed of foam. In such cases, however, control over the mass transfer of nutrients and gases to the biomass is governed only by the irrigation rate.
Another example where porous support media have been used to immobilise biomass is in rotating contact reactors aimed at maximising the surface area per unit volume, whilst maintaining a high proportion of void volume within the reactor bed. In such applications, the porous support medium, such as a substantially open-called foam, is attached to a rigid structure, usually in the form of a circular disc, which is rotated about its axis, with partial submergence in a trough of aqueous growth medium. Such a device alternately exposes the microorganisms or plant or animal cells to the nutrient medium and air in a manner that is controlled by varying the rotational speed of the device. On submergence of the porous biomass-containing matrix in the liquid phase, the interstitial spaces of the porous support medium are filled with the liquid medium to a point approaching saturation. When removed from the bulk liquid, the open pores of the medium will naturally drain their liquid contents, with a subsequent replacement of the drained void volume with air. In such a device, however, the only control exerted over the gravity induced mass transfer of liquid and gas from the porous elements is variation of rotational speed.
Other devices, in which the porous support medium is contained within a rotating drum, have also been proposed. Here, mass transfer of gas and liquid into and out of the fluid spaces in the porous support medium relies entirely upon gravitational forces and, again, the usual way of influencing mass transfer is by varying the rotational speed of the device.
I
Banks Charles Joseph
Davies Martin
Johnson William Nevil Heaton
Beisner William H.
Poff Clifford A.
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