1. Field of the Invention
This invention concerns a chemical reactor, particularly a bioreactor in which a reactive matrix adsorbs or biochemically reacts with solutes in a liquid.
2. General Discussion of the Background
Biological reactors have been developed that use immobilized microorganisms or enzymes to degrade pollutants. Examples are found in U.S. Pat. Nos. 4,181,604; 4,416,993; 4,746,435; and 5,116,506, wherein microorganisms are grown in biofilm layers on permeable membranes. The microorganisms in the biofilm transform or degrade pollutants as polluted liquid passes through or parallel to the membranes and comes into contact with the organisms. Unfortunately, the membranes provide limited surface area on which the microorganisms can grow, and diffusional limitations into the biofilm reduce the efficiency of the reactor. Only microorganisms near a surface of the film have sufficient access to nutrients and pollutants to efficiently degrade pollutants and other biological substrates. Such reactors normally have a low biocatalyst density, and the volume of substrates that can be degraded in any given period of time is limited.
Other bioreactors have attempted to solve this problem by suspending microorganisms on small particles that are fluidized in a reactor. A higher mass transfer between the liquid and the particle surface can be achieved with such a design, but the fluidized particles distribute unevenly throughout the reactor. Uneven particle distribution leads to less than optimal utilization of the total available reaction volume in the reactor, and mass transfer limitations between the surface of the particle and the interior often occur. Very small particles also tend to flow out of the reactor as process fluid is exhausted. U.S. Pat. No. 4,833,081 attempted to improve particle retention in the matrix by incorporating, into a polyurethane foam support, small beads that contained microorganisms. The beads were suspended in the polyurethane foam to provide a fixed bioactive matrix through which a process liquid could pass. Optimum reactor volume was still not obtained, however, because diffusional limitations in the beads, and in foam containing the beads, inhibited vigorous growth of organisms within the interior of the bead. Channeling would also be likely to occur in areas of the foam with less restricted flow.
Beads that contain biological cells in U.S. Pat. No. 4,833,081 are described as having a diameter in the 50-2000 micron range. These beads are large enough that in many cases they provide diffusional barriers to the exchange of substrates and nutrients with the process liquid. The beads in that patent are also formed by an oil emulsion process that covers the bead with oil as it is formed. The bead must be washed free of the oil before it can be used in a bioreactor. Oil emulsion or interfacial polymerization processes have been thought essential to form beads of smaller than 100 microns diameter. Other processes have been found to produce even larger beads that have more serious diffusional limitations. Yet no process has been able to produce microbeads, especially with living cells, in which substantially all the beads have diameters less than 50 microns.
Another bioreactor is shown in German Patent 3 530 332, which discloses a slow moving anaerobic plugged flow type bioreactor for degrading sewage. This upflow reactor contains a series of cylindrical sponges that span the cross-section of the reactor. Slow growing microorganisms fixed on the surfaces of the sponges provide a biomass that anaerobically degrades sewage. The sponges are compressed only 0.05 meters about once per minute to dislodge small air bubbles from the surfaces of the sponges before the small bubbles coalesce to form large bubbles that disrupt reactor flow. During compression, liquid flows out of the sponges in both an upflow and downflow direction. Hence a significant portion of the liquid expelled from the sponge flows back into the sponge, which diminishes efficient transfer of reacted liquid out of the sponge.
Yet another drawback of previous reactors has been their reliance on external pumps to move liquid into and out of the reactor. The German Patent, for example, relies on a superimposed process flow through the reactor that is only periodically interfered with by compression of the sponges. Liquid will not move through the reactor in the absence of external pumps forcing a flow through the bed.
It is accordingly an object of this invention to provide an improved reactor in which the reactor itself is designed to provide a pumping force, without relying on external pumps to move liquid through the reactor.
Another object of this invention is to increase the non-laminar flow inside the reactor to more uniformly mix the new liquid with the old liquid and contact all of the reactive material in the reactor with this new solution.
Another object of the invention is to provide an improved reactor that more fully takes advantage of the available volume in the reactor to achieve biological transformations or other reactions.
Yet another object of the invention to provide an improved reactor that can more effectively perform sequential reactions, and monitor and control reaction parameters to optimize the reactions in the system.
Even yet another object is to immobilize biologically active materials in a reactive matrix without imposing significant diffusion barriers between the biologically active materials and a process liquid in the reactor.
Finally, it is an object of this invention to provide biologically efficient microbeads that can be manufactured by a simple process that does not require oil immersion.