RECOVERY OF MATERIAL

The present invention relates to the separation or recovery from a liquid of a material which can exist in the form of agglomerates or which can be immobilised on a support (although not necessarily both). A particular example of material with which the present invention is concerned is biological material, e.g. icrobial or plant or animal cells.

Biological material (e.g. microbial cells) is frequently immobilised on a support of high internal voidage and grown in a liquid nutrient medium to yield useful products which are either excreted into the liquid medium or retained within the cells. In either case, it is ultimately necessary to effect a separation of the biological material from the liquid so that the product can be obtained. Similarly, it is also possible to culture cells in the form of agglomerates and similar considerations apply as for the separation of the agglomerated material from the liquid to obtain the product.

It is an object of the present invention to provide a method for effecting such separations.

According to the present invention there is provided a method of recovering material from a liquid, the material being in the form of agglomerates or being immobilised on a support wherein the liquid is held in a vessel having at least one outlet aperture of a size less than said agglomerates or supports, removing the liquid causing the material to be de-agglomerated or deimmobilised, and then causing the material to pass through said aperture.

Typically, the apertures will have a cross-sectional size of 0.5 to 10mm.

Preferably the bulk of the liquid is removed from the vessel before the material is de-agglomerated or de-immobilised.

The invention is applicable particularly to the separation or biological material (e.g. cells) immobilised on a resilient or other deformable support material, e.g. plastics foam of substantial (e.g. 97%) internal voidage.

Alternatively the biological material may be provided in the form of floe which is of a size larger than the exit aperture or apertures but which is 'destroyed' e.g. by the application of pressure, so that the biological material may pass through the outlet or outlets.

The de-agglomeration or de-immobilisation is preferably effected by means of pressure, e.g. by- means of a pressure wave applied to the material (such as by the pulsing of a piston in the vessel in which the material is obtained) or by the actual pressing of the material. It is also possible to use other external forces for effecting de-agglomeration or de-immobilisation, e.g. ultra-sonics or chemical means. In all cases, the material is reduced to a size such that it can pass through the outlet aperture or apertures, preferably with the assistance of pressure although in certain cases it is possible to rely simply on gravity.

The method of the invention may be used for recovery of biological material from the vessel in which a fermentation reaction is effected so that fermentation and separation may be effected sequentially in the same vessel. This is particularly advantageous where it is desired to maintain sterile conditions. It is however also possible simply to supply the biological material in

the liquid for immobilisation on supports within the vessel so that a separation from the liquid may then be effected.

Examples of biological material which may be immobilised on a resilient support of high internal voidage and which may be separated therefrom by the method of the invention are given in Table 1 together with uses of such materials.

Table 1

Organism Application

Mixed culture (aerobic) Waste treatment

Mixed culture (anaerobic) Methane, Lactic Acid

Yeast (various strains) Ethanol, cells, beer

Acetobacter Acetic acid

Aspergillus Citric acid, fungal enzymes

Trichoderma Reseii Cellulase

Capsicum sp. (plant cell) Capsaicin

Humulus (plant cell) Hop flavours

Streptomyces sp. Antibiotics

Although specific reference has been made to use of the invention for separating biological material, the invention may also be used for the separation of any fine particulate solids (e.g. inorganic material) from a liquid, provided that these solids may be agglomerated or immobilised on a support.

The invention will be further described by way of example only with reference to the accompanying drawing, in which:

Fig. 1 is a diagrammatic illustration of one embodiment of the invention.

The apparatus illustrated in Fig. 1 comprises a fermentation reactor 1, in which the biological material may be produced as a pure or mixed culture.

incorporating an upper piston 2 and a lower ρiάce 3 having apertures 3a. Piston 2 comprises two s ac d sealing rings 2a to ensure a gas/liquid tight seal as well as stability of the piston. Valves 4-8 are associated with the apparatus as shown, as is a recyling pump 9.

The fermentation reaction will be effected with biological material which is, or becomes, immobilised on a resilient plastics foam material of, for example, 97% void volume. Such materials are well established as supports for biological fermentation reactions (see for example U.K.-A-2 006 181) and for the present example process will be used as supports having a size greater than that of the apertures in plate 3, typically 6-30mm characteristic length.

Prior to the commencement of the fermentation reaction, the supports are introduced into the vessel 1. Nutrient liquid and an inoculum for a particular biological reaction are also added (via valve 4). During fermentation the supports become colonised by the biological material. Where satisfactory immobilisation of the micro-organism to the support does not occur naturally, this can be achieved by the addition of suitable immobilisation agents (e.g. polysaccharides, polyacrylamides or other charged species. Alternatively it may be necessary to modify the surface of the supports (e.g. by ion beam etching) in order to achieve the necessary level of immobilisation. It is also possible to introduce a mixture of two or more biological materials into a vessel containing the supports together with a selective affinity material so that only a selected one of the materials is immobilised on the supports.

During batch fermentation, valves 4 and 6-8 are closed whereas valve 5 may be open so that pump 9 may

be operated to allow recirculation of liquid (drained through plate 3) back to the top of reactor 1 to promote mixing. Alternatively, if the process is operated continuously, valves 4, 6 and 7 will be opened to a controlled extent to provide a continuous throughflow while the valve 5 may also be open so that pump 9 may be operated to allow recirculation of liquid (drained through plate 3) back to the top of reactor 1 to promote mixing. The system may also be reconfigured to allow upflow rather than downflow of liquid.

The particular conditions for the fermentation reaction, e.g. time, temperature, concentration of nutrient liquid are well known and are therefore not discussed further.

At the end of fermentation the separation step is commenced by opening valves 4, 5, 6 and 7. Liquid in reactor 1 therefore drains through plate 3 and passes into an effluent line, as clearly illustrated. Displacement air (or other gas) is able to enter the vessel via valve 4.

Since the "particles" of sponge material (on which the biological material is now supported) are of larger size than the apertures in plate 3, they remain in the reactor 1. Additionally, the draining of the liquid through plate 3 involves little or no shear in the liquid, which means that the biological material is not dislodged from the support. Removal of interstitial liquid can be effected at this stage by moving piston 2 to "squeeze" the foam 'particles' gently.

As the next step of separation, valves 5 and 7 are closed and valve 8 is opened. Piston 2 is now moved downwardly through reactor 1 (e.g. by means of air pressure supplied along line la or by mechanical

means) and compresses the foam particles between itself and the apertured plate 3. This compreεsive force causes the biological material to be dislodged from the 'particles'. The dislodged material passes through plate 3 and exits via valves 6 and 8 into a product line from which it is collected for further processing as required.

The reactor 1 may be prepared for a further fermentation reaction by closing valves 6 and 8 and withdrawing piston 2. The withdrawal of piston 2 allows the foam particles to resile to their original dimensions and can be used to refill the vessel 1 with fresh nutrient liquid and inoculant via valves 4 and 5. The fermentation reaction may thus be recommenced.

In a modified method of de-immobilising - the biological material from the supports, piston 2 may be pulsed - (without necessarily contacting the support) upwardly and downwardly with valve 6 being open. As the piston is raised, high velocity liquid and/or air is drawn back into vessel 1 and 'scours' the supports causing the biological material to be dislodged. When piston 2 is moved down, liquid is forced out of vessel 1 and causes the biological material to be ^' passed through plate 3. The piston may, for example, move through 60 cycles/ in or so.

Although Fig. 1 shows the use of a pneumatically operated piston, it is of course possible to use mechanical actuation.

In a modification of the invention the abovedescribed apparatus may be operated as a trickle-bed reactor in which, during the fermentation reaction, nutrient liquid is allowed to trickle through a bed of the particles and the effluent liquid is allowed to drain through valve 6.

Periodically biological material is recovered by compressing the particles by means of piston 2, as described above.

To illustrate the invention a test vessel similar to that shown in Fig. 1 was used to grow yeast cells immobilised on reticulated foam supports (6mm cubes) of high internal voidage. The base of the vessel had a diameter of about 2.5 cm and had about 30 holes each with a diameter of about 1.6 mm. The biological material was then recovered by firstly draining liquid from vessel 1, then effecting de-immobilisation of ^" the biological material and passing this biological material (now in the form of a slurry) through the apertured plate. The results were as shown in Table 2.

Table 2: Production and recovery of yeast cells ^'

Yeast strain A B C D

(g/i ⁾ (g/i ⁾ (g/i) (g/D

NCYC 1119 35.8 114 0.05 341 NCYC 1183 35.6 62.5 0.18 159 A = Concentration of yeast cells in vessel 1 (i.e. total mass of cells/total vol of reactor) B = Concentration of yeast cells initially inside foam support particles (i.e. total mass of cells/total volume of foam supports) C = Concentration of yeast cells in effluent stream

(i.e. liquid drained) D = Concentration of yeast cells in slurry after recovery * - All concentrations are on a dry weight basis.

Although not specifically indicated in Table 2, the resilient foam supports (still with immobilised material) were squeezed gently after draining of the

'bulk' liquid to remove interstitial liquid prior co the de-immobilisation of the biological material.

The figures under column 'D' (as compared to those under A and B clearly demonstrate the increase in concentration of the yeast cells after separation in accordance with the invention.

As a further illustration of the invention cells were grown in liquid nutrient medium prior to being recirculated through the vessel in order to effect immobilisation _* This was followed by a separation step as described above and demonstrates the use of the invention as a separation (recovery) only device.

Yeast strain A C

⁽ g/i ) ⁽ g/i ⁾

NCYC 1183 29 . 0 48 . 4 NCYC 1183 9 .5 33 .7 NCYC 1183 14 . 0 32 .4 NCYC 1183 3 .3 13 .5

A - Concentration of yeast cells in vessel 1 D - Concentration of yeast cells after recovery * - All concentrations are on a dry weight basis.