NZ219155A - Process for the cultivation of microorganisms involving subjecting the microorganisms to a pulsed electric field - Google Patents

Description

i ^ f Priority Dj:e(s): • n. -;> S Curr^iw.o C,"':ciflcu'!cn Fi'cd: .<r........ c,or.r„ C',:M:ye>o, O^I>Jq0K ; 2. 6, k ?R. ;,?38 /33/ 21915 ^r °MARm7",h \ "■ % V-j".-P ;' V "" foaajify Pa t ents Form No. 5 t ') PATENTS ACT 1953 COMPLETE SPECIFICATION No.:219155 Date:3 February 1987 PROCESS FOR METABOLISM AND/OR GROWTH INCREASING TREATMENT OF MICRO-ORGANISMS AND DEVICE FOR IMPLEMENTING THE PROCESS I, HEINZ DOEVENSPECK of Sigurdstrasse 1, 4950 Minden, Federal Republic of Germany, a citizen of the Federal Republic of Germany, hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: 2 219155 The invention concerns a process for metabolism and/or growth increasing treatment of micro-organisms.

It is well known that electric fields have an effect on micro-organisms (bacteria, fungi). Specifically, when bacteria are subjected to electric fields whose patterns over time can be described as pulse shaped, it has been shown that field intensities of 6-20 kV/cm have an especially marked lethal effect on the bacteria (see for example Hulsheger et al: Radiation and Environmental Biophysics (1981) 20: 53-65 and loc. cit. (1980) 18:281-2 88 ) .

In many cases, however, it is not desired to kill the micro-organisms, but on the contrary actually to cultivate them. For example, if one wishes to clarify sewage by means of microbial processes it is specifically a matter of cultivating the micro-organisms which metabolize the substances to be broken down. To achieve this it is a well known procedure to add certain substances, to sewage in order, for example, to make available nitrifying bacteria which are required for the metabolism of the sewage. Furthermore, the procedures are carried out as far as possible at temperatures at which the micro-organisms have the highest possible metabolism and multiplication rates. However, in many cases this is not sufficient to keep the desired process in operation in an ^economically efficient manner.

Proceeding on the basis of the above state of the art, y/the objective of the present invention is to demonstrate a - o - (Followed by Page 37v) process for the metabolism and/or growth increasing treatment of micro-organisms which is inexpensive, simple and effective to carry out.

Accordingly, this invention provides a process for the cultivation of micro-organisms, the process comprising subjecting the micro-organisms to an electric field which is applied in discrete pulses, the voltage waveform of each pulse being substantially that of a discharging capacitor and the electric field having a maximum intensity within the range 100 V/cm to 3.5 kV/cm. Surprisingly, it has been found that in contrast to the use of high field intensities, the use of low field intensities is associated with an increase in the growth of the micro-organisms. This increase in growth can be shown particularly in terms of their metabolic rates.

It is particularly advantageous to carry out the process when one increases the field intensity to the maximum within 1 ms at the most, and allows it to diminish exponentially. This pulse shape, if a charged capacitor is connected via a switch to a load resistance via which the capacitor then discharges, has proved to be particularly effective.

It is advantageous to have the field intensity "increase to the maximum value within 100 us , preferably within 50 p-s . It is also relevant that the increase (within certain limits) should proceed as steeply as possible. The decrease (following an e function) is advantageously allowed to take place within 10-100 ps .

The process is particularly effective where the field intensity is restricted in its maximum value to up to 0.1 - 1 kV/cm, but particularly to 0.2 - 0.5 kV/cm. 219 15 5 3A - (Followed by Page 4) Practically, there are no lower limitations to field intensity (minimum field intensity). The lower the field intensity, the longer the micro-organisms have to be subjected to the electrical field. In order to make the process of the present invention economical, however, it will be inevitably necessary to try and work with field intensities as high as possible.

Maximum field intensity nevertheless must not exceed the limits as defined as otherwise the micro-organisms would be destroyed. In the present invention the micro-organisms are treated such that they are not, or at least not in any considerable numbers, destroyed. This means that only the maximum field intensity to be used is of significance for the process according to the present invention.

A maximum field intensity is given for the present invention as a range between lOOV/cm to 3.5kV/cm so as to cover the treatment of various types (families) of microorganisms having different tolerances in respect of field intensities. / 219 15 i i t > Furthermore, it is especially advantageous if the field intensity direction alternates in relation to the direction of flow of the liquid to be treated. This is indicated particularly in the context of large systems with several electrode groups connected in series, where to change the direction of field intensity several sets of electrodes are connected in series. Alternatively the change of the field intensity direction can also take place by means of the pole reversal of the (pulse) generator, so that the successive pulses have different field intensity directions. This is indicated ( particularly for small systems.

I Alternatively the field intensity direction can be j kept constant, i.e. one can operate with direct current pulses. Because the discharges are solely pulse-shaped, the electrolysis effect in this context can essentially be 'w! disregarded. Thermal effects, because of the small amount of energy conveyed into the liquid, can also essentially be disregarded In a preferred embodiment of the process the electric pulses are applied at repetition rates which are low in comparison with the pulse durations. That is to say, one has pauses between individual electric pulses. It is particularly advantageous in this context to have Tepetition rates of between 5 and 15 Hz. it is advantageous that the electric pulses be applied p-' -ovonly in pulse groups, hence not in a continuous pulse .i ^ 0 /14/? j c»;,t ra i n, and that pauses be made between such pulse groups. // : *; , w- dtirA i .f ., t s<4# 219 15 Surprisingly, it has actually proved to be the case that such pauses do not in fact lead to any decrease in the effect of the electric pulses, but rather to an increase in the effect. It is advantageous to select pulse groups and pause intervals between the pulse groups as shorter than 30 min in each case, and preferably shorter than 15 mi n .

An especially preferred application for the procedure is the microbial generation of methane gas or biogas (manure gas), or the treatment of sewage in anaerobica11y operated reactions. Along with the abovementioned growth increasing or metabolism enhancing effects of the electric pulses, it has surprisingly proved to be the case that when one operates according to the process pursuant to the invention the production of volatile sulphur compounds is drastically reduced. Indeed, generally normal biogas contains a considerable proportion of hydrogen sulphide or other volatile sulphur compounds, which first have to be removed from the gas before the further use of the gas, e.g. in gas engines, is possible. When the process according to the invention is applied to the production of biogas such sulphur compounds are only detectable - when they can be detected at all - in drastically reduced concentration levels in the gas produced, so that the gas can be produced not only in increased quantities (due to the use of the process according to the invention), but also in a significantly more easily used quality, i.e. in a better quality than was previously the case. Even in 3 OMAR 1987$ 219 15 5 instances where the process according to the invention runs other than with its optimal parameters (pulse amplitude, pulse duration, pulse frequency, etc), there is still a significant improvement in the production of biogas as regards efficiency as a result of the use of the procedure, since the said harmful substances only occur in the gas in reduced quantities.

A further significant possibility for the use of the process according to the invention is the microbiological production of enzymes or other non-gaseous products.

Appropriate for the implementation of the procedure is a device with at least one reactor with inlet and outlet line, this device having at least one pair of capacitor electrodes which are arranged in such a manner that at least some of the contents of the reactor are located at least temporarily between the electrodes. These electrode ) plates are connected with a pulse generator circuit for supply with an electrical voltage. In this context is is possible to arrange the electrodes in the reactor enclosure in such a way that the entire contents of the "w' reactor are always between the plates. Preferably, however, the electrodes are arranged in an enclosure which is separate in terms of flow in such a way that flow connection exists between the space between the electrodes and the inside of the reactor via ducting means. The contents of the reactor are hence passed through the space between the electrodes, so that only a fraction of the ^\\\ t *, reactor contents are constantly between the plates. vj y f\ n tnn~, --! v; i987;J,; •V:.: V £>3^ 21 y i d o The main portion of the reactor volume is therefore essentially field-free* although naturally spreadage of the fields generated between the electrode plates into the inside of the reactor is possible (or probable), both via the fluid connection between the electrodes and the inside of the reactor and via the electromagnetic connection.

Circulation in such systems may be created by appropriate arrangement of the ducts (inlet and outlet) between the reactor and the electrode enclosure, but it is preferable that a circulating pump be placed in one of the ducts .

In one advantageous example of the embodiment of the device according to the invention several electrodes are arranged in series (in terms of flow), so that the liquid (with mi cro-organisms ) drawn through the area travels across a longer space between the electrodes, and hence spends a longer time between the electrodes. With such an arrangement the electrodes may be connected in parallel, so as to generate the same voltage patterns between all electron pairs, but may also be connected in series if different voltage patterns are to be generated between the electrode pairs.

It is advantageous to have the electrodes arranged in the enclosure so as to form a labyrinth, through which the JLtguid flows. In this way one obtains a particularly i i compact enclosure which nonetheless ensures a longer duration of the treatment of the liquid passed through the area. 21 9 1 5 t o 3 O W ft n t ,A?;C87r In a further preferred embodiment of the invention the electrodes are arranged coaxially to one another. This embodiment leads to a compact enclosure with particularly good flow conditions which only has a small number of static zones (in flow terms) at which solids could build up.

In another preferred embodiment of the invention the electrodes have gaps in them and are so arranged in the enclosure with respect to one another that the liquid flows through them essentially perpendicularly to their surface. With an appropriate arrangement of the apertures in the enclosure it is possible in this case also to create a flow pattern which is essentially free of static zones or surfaces on which material might accumulate.

It is advantageous to have the feed into and discharge from the reactor pass via a common electrode passage.

This is particularly the case where the temperature of the reactor contents is different from the temperature of the liquid conveyed to it. Indeed where this is the case it promotes the metabolism of the microbes if the newly conveyed substrate is pre-heated essentially to the reactor temperature so that the micro-organisms do not suffer any temperature shock. Where one wishes for example, to keep thermophilic microbes in the reactor, i.e. microbes which operate in temperature ranges up to 70 or 80°C (with high metabolic rates), it is particularly advantageous if an electrode passage is introduced between the inlet and the outlet line. 2191 It is further of great advantage if degerminating devices are incorporated in the inlet and the outlet line. A degerminating devices in the feed has the effect that the contents of the reactor can be "injected" only with those micro-organisms which one actually wishes to have in the reactor, while alien micro-organisms conveyed by the sewage are killed. As regards the micro-organisms which pass from the outlet line into other plant downstream, it is also advantageous to keep these away from the downstream plant.

In a particularly preferred embodiment of the device according to the invention the degerminating device is incorporated in the electrode passage: the electrode passage here consists - similar to the device for increasing growth - of capacitor plates which are connected to a pulse generating device. In this case, however, the pulses were such a strong selection (as regards their maximum field intensity) that the lethal effect mentioned at the beginning of this document occurs.

In a preferred embodiment of the invention the j V generator circuit has a power unit and at least one storage capacitor, along with at least one reversing switch which is connected in circuit with the power unit and storage capacitor and with the electrodes, in such a manner that in a first switch position the storage " r-_l"'Twtn capS'tjfu tor is charged by the power unit and in a second jf? ^switch position it is discharged via the electrodes. This //'!.» .V. 1 n y i* 3 "Liielalt i vely simple circuit is however very effective, since 0MA& iOqt ' " s?o/ ,/the;/pulses a :'J1 21 9 1 ore conveyed to the micro-organisms in the optimal form. Admittedly, one can operate the reversing switch mechanically, but it is particularly advantageous if one has this reversing switch operated electrically. Examples of such a reversing switch would be ignitrons, thyristors, transistors etc. These electrically operated switches are advantageously connected with a control oscillator. The device is particularly simple where the reversing switch consists of two on/off switch elements, with the first switch element arranged between the storage capacitor and the power unit, and the second switch element arranged between the capacitor and electrodes; the device is operated in such a manner that initially the second switch (connection between storage capacitor and electrodes) is disconnected, whereas the first switch element is connected, so that the capacitor is charged by the power unit. As soon as the capacitor is charged the first switch is opened so that the capacitor is now left "hanging in the air". The second switch is then closed, thus connecting the capacitor to the electrodes. In this way one obtains precisely defined on and off switching pa t ter ns.

It is advantageous if the control oscillator has a pulse generator whose output pulses can be periodically blocked by control means of a generator. The output pu'Tsejs of the pulse generator give rise to the switching i procejss between charging and discharging of the storage "lc,'apac i tor; during the time for which the output pulses • -I fffom, the pulse generator are blocked from the (further) 219 151 OMAR 1987Sji / generator the capacitor plates are no longer connected to the capac i tor.

Other preferred embodiments of the invention can be seen from the embodiment examples described below, which will be explained in more detail with reference to the Figures. These show the following: Fig. 1 a theoretical arrangement for the implementation of the process according to the i nven t ion; Fig. 2 a first preferred embodiment of the electrode device in longitudinal section; Fig. 3 the electrode device according to Fig. 2 with two sets of electrodes; Fig. 4 a second preferred embodiment of the electrode device in longitudinal section; Fig. 5 a third preferred form of embodiment of the electrode device in longitudinal section; Fig. 6 the electrode device according to Fig. 5 with bipolar electrodes; Fig. 7 a preferred embodiment of an electrode passage in longitudinal section; Fig. 8 the electrode passage according to Fig. 7 with two sets of electrodes in series; Fig. 9 a first (theoretical) circuit for the implementation of the process according to J the invention; and 1 Fig. 10 a second diagrammatical representation which essentially shows the functions seen in Fig. 6. 219 15 5 As can be seen from Fig. 1, the reactor 10 has a reactor enclosure for the implementation of the process according to the invention; in this enclosure there is (in customary fashion) an agitator 11. There are also heating means 14 connected with the inside of the reactor, which can for example be fed from a gas burner running on biogas, the biogas being taken from the inside of the reactor out of a gas outlet line 16 from the reactor 10.

The reactor 10 has an inlet line 12 (with valve) and an outlet line 13. Inlet and outlet lines 12/13 are led in counter-current through a heat exchanger 30.

The reactor 10 also has on its floor a circulation draining line 17 which leads into the suction inlet of a circulation pump 15. The pressure outlet of the circulation pump 15 leads into the inlet of an electrode device 20, described in more detail below. The outlet of the electrode device 20 is connected via a circulation return line 18 with the top cover of the reactor 10. In this way it is ensured, when the agitator 11 and the circulation pump 15 are operating, that the contents of the reactor are conveyed in a regular manner (over time) through the electrode device 20.

Fig. 2 shows a preferred embodiment of the electrode device 20. In the figure the enclosure 21 of the -electrode device 20 is made of a conductive material. In the enclosure 21 there are, horizontally arranged, two ^■insulating electrode supports 24 with gaps 25. In the •3 0 !''1ARi987v$ 1 ® c t rode supports 24 are held a central electrode 232 anc* \ a medial electrode 22] ; the gaps 25 are arranged in such a way that they connect the spaces between the outside wall of the enclosure 21 and the medial electrode 22] and between the medial electrode 2 2 j and the central electrode 232 with circulation draining line 17 and the circulation return line 18 of the device 20. In terms of the flow the two coaxial spaces are in this arrangement in parallel connection, while from the electrical point of view there are two electrodes connected in parallel, since the central electrode 232 *s electrically connected with the enclosure 21 which is formed by the distal electrode 23j, while the electrode 22] forms the counter-electrode for both the electrodes formed in this way. This pair of electrodes is connected with a generator 40, which is described in more detail below.

Fig. 3 shows an electrode device 20 with two sets of electrodes in series. In this arrangement one (upper) set of electrodes is formed by the positive electrodes 23i and 232 an<^ a negative electrode 2 2 j . The (lower) set of electrodes consists of a positive electrode 233 and two negative electrodes, namely electrodes 222 ancl 223. Both sets of electrodes are connected with a common generator 40. If required it is also possible to have a separate generator 40 provided for each of the sets of electrodes.

The end walls of the electrodes 22], 23] and 232 anc^ nf pipr*trodes 222 , 223 and 233 - which face towards one •1-nsulating electrode support 49. From the electrical are in this case connected by a further 21 9 1 5 § point of view this support divides the electrode device 20 into two completely separate halves. In the electrode device 20 in Fig. 3 the coaxial spaces are henee interconnected both in series and in parallel, while in electrical terms there are both two parallel connected and ^ series connected electrodes. Due to the opposite polarity V of the electrode groups in series, two field intensity directions are created in the electrode device 20 of Fig. 3, which act in succession on the liquid (with bacteria) to be treated.

In the embodiment of the invention shown in Fig. 4 the electrodes 22\ - 223 and 23j - 233 have gaps 25 and are placed transverse to the direction of flow in the enclosure 21. In contrast, in electrical terms the electrodes are connected in parallel and are connected with a genera t or 40 .

In the case of the device shown in Fig. 5, again in longitudinal section, the electrodes 22j - 223 and 23j -233 are also connected in parallel, while in terms of flow they are arranged in series in the form of a labyrinth in the enclosure 21, through which, via insulating elements 24, they are supported or passed. This circuit arrangement leads, in the same way as shown in Fig. 4, to a longer duration of flow through an inter-electrode space.

Fig. 6 shows the electrode device 20 according to Fig. 5, but with grouped electrodes. Disregarding the upper and lower electrodes 22] and 235 respectively, the *\\ ~ „ "ji remaining electrodes are built up as double electrodes »vM/\kt987£j J 23^, 222? 232» 223; 233, 244; 234, 225. They are 21 9 15 5 insulated from each other by non conductive materials not shown in Fig. 6.

However, here again all the electrodes are fed from a common generator 40. The circuit connection of the electrodes is in this case carried out in such a way that electrodes of opposite polarity restrict the flow path of rC> the liquid through the electrode device 20. This means that in each labyrinth section the field intensity acts on the bacteria-enriched liquid from a different direction.

Fig. 7 shows a preferred embodiment of the electrode passage 30. The electrode passage here has a two-fold function: i.e. it is at. the same time a heat exchanger and a degermination device. At opposite ends of the electrode passage 30 there are two intakes 31/33 and, also at opposite ends, two outlets 32/34. The electrode passage 30 has an outer casing 35, an intermediate casing 36 and a central electrode 37. The intermediate casing 36 is situated between an inner space, which is closed off in terms of flow, and the outer space, also closed off in terms of flow. The throughflow occurs in countercurrent via the intermediate casing 36. The inner electrode 37 and the outer casing 35 are electrically connected, and the intermediate casing 36 forms the second electrode for both electrodes. This electrode pair is connected with a sterilizer-pulse generator 38, which conveys pulses of <2 / 3shi&h field intensity onto the plates.

*-A * o\> 'V (fa llz -■> Fig. 8 shows an extension of the electrode passage 30 ^p|Qo7o;j 'u/'r;£hown in Fig 7; here, however, there are two sets of V,.- * - 'oj— r."" electrodes arranged in series. The individual sets of electrodes are delimited by the insulating means 50, shown d i agr amrna t i ca 11 y only in Fig. 8, through which in electrode passage 30 there are in each instance two electrodes, 35,36 or 37 arranged in series. Here the electrodes arranged in series are in each case of different polarity. In the embodiment example of Fig. 8 in the left half of the electrode passage 30 the electrodes 35 and 37 are poled positive, while the electrode 36 is poled negative. In contrast, in the right half of the electrode passage 30 the electrodes 35 and 37 are poled negative, whereas the electrode 36 placed between them is in this case poled positive.

In the above embodiment example each set of electrodes has a separate sterilizer-pulse generator 38. As an alternative it is however also possible to have both sets of electrodes supplied by a comnon sterilizer-pulse generator 38.

The electrical circuit of the pulse generator required for the implementation of the process according to the invention will now be described in more detail. This pulse generator has a pow unit 42 which in customary fashion consists of a mains switch, a transformer, a rectifier and a downstream filter capacitor. The power unit 42 is connected with one pole of a reversing switch 43, which can be switched via a control generator 41. The v <pxVher pole of the reversing switch 43 is connected with an . electrode 23. The middle pole of the reversing switch 43 OMAR 19873 is connected with one pole of a charging capacitor 44, whose other pole is selectively connected via a second reversing switch with the power unit 42 and the second capacitor plate 22.

When the reversing switch 43 is operated, the capacitor 44 is connected in initial position with the power unit 42, during switching-over it is divided from the power unit 42, and on completion of switching-over it is connected with the electrodes 22/23. There is hence a pause between the two phases, so that the electrodes 22/23 are not connected with the power unit 42.

In the embodiment of the invention shown in Fig. 10 the switch 43 consists of a (single pole) reversing switch made up of two thyristors. The first thyristor Tyj is connected between the power unit 42 and the storage capacitor 44, and the second thyristor (poled in the same direction) between the storage capacitor 44 and one electrode, 23. The other electrode 22 is directly connected with the other end of the storage capacitor 44 and the power unit 42. The control circuit of the first thyristor Ty^ is connected via a time-lag element 45 with the control circuit of the second thyristor Ty2- This connection point is on the pole of a (switching) field effect transistor 46, whose other pole is on the output of a pulse generator 48. The gate of the field effect transistor 46 is on the output of a further generator 47. Th'i s arrangement makes up the drive pulse generator 41. If pulse generator 48 feeds a pulse to its output and the r 219 15 5 ■O, output of the other generator 47 is at this time on high level, then the field effect transistor 46 is conductive and the second thyristor Ty£ is turned on. When this happens the charge stored in the capacitor 44 is discharged via the plates 22/23 and the electrolytes located between these plates (contents of the reactor). As soon as the capacitor 44 has discharged the current flow through the thyristor Ty2 stops, and the thyristor hence shuts down automatically. The time constant of the time-lag element 45 is selected such that now- after discharge of capacitor 44 via the electrodes 22/23 - the first thyristor Tyj is turned on. After activation of this first thyristor Ty i the capacitor 44 is now charged via the power unit 42. As soon as the capacitor 44 is charged, the current flow through the first thyristor Tyj ceases, the thyristor shuts down automatically, and the cycle can begin afresh.

The electrical circuit shown in Figs. 9 and 10 for the implementation of the process according to the invention can where appropriate be modified in such a way that the ^ circuit has a periodically operating reversing switch facility, not shown, which the electrodes 22 and 23 can be alternately commutated to obtain a periodic reversal of the direction of the electric field. With such a pulse generator, given the electrode device 20 of Figs. 2 and 5 ° 0 MAR logy pi! and the electrode passage 30 of Fig. 7, alternately t] differently directed electric fields can be produced, "ly^ithout it being necessary to arrange several sets of . <•**» /•' v '• 219155 electrodes in series, as shown in figs. 3, 6 and 8, for example. This also makes it possible to obtain, in very simple fashion, field reversal in smaller, more compact plants.

Claims (30)

1. A process for the cultivation of micro-organisms, the process comprising subjecting the micro-organisms to an electric field which is applied in discrete pulses, the voltage waveform of each pulse being substantially that of a discharging capacitor and the electric field having a maximum intensity within the range 100 V/cm to 3.5 kV/cm.

2. A process according to claim 1 in which the field intensity during each pulse increases to a maximum within 1 ms and then decays exponentially.

3. A process according to claim 1 or claim 2 in which the field intensity has a maximum in the range 0.1-1 kV/ cm.

4. A process according to claim 3 in which the field intensity has a maximum in the range 0.2 to 0.5 kV/cm.

5. A process according to any one of the preceding claims in which the field direction is alternated.

6. A process according to any one of the preceding claims in which the electrical pulses are applied with repetition rates which are lower than the reciprocal pulse duration.

7. A process according to any one of the preceding claims in which the electrical pulses are applied in groups with pauses between the groups, the groups of pulses and the pause intervals each being shorter than 30 min.

8. A process according to claim 7 in which the groups of pulses and the intervals are shorter than 15 minutes.

9. A process according to any one of the preceding claims in which the maximum field intensity is reached in 10 ys. /' r. - 21 - JL kJ -L

10. A process according to any one of the preceding claims in which the field intensity decays to its minimum within 10 to 100 ps.

11. The use of the process according to any one of claims 1 to 10 for the microbial production of gaseous products.

12. The use according to claim 11 in which methane is produced.

13. The use of a process according to any one of claims 1 to 10 in the microbiological production of solid and/or liquid products.

14. The use according to claim 13 in which enzymes are produced.

15. An apparatus for implementing the process according to one of claims 1 to 10, the apparatus comprising at least one reactor having inlet and outlet ducting; at least a pair of electrodes which are arranged so that at least part of the contents of the reactor are at least temporarily between the electrodes; and a pulse generator circuit for supplying the electrodes with pulsed electrical voltage, the voltage of each pulse having a waveform substantially that of a discharging capacitor.

16. An apparatus according to claim 15 in which the electrodes are arranged in an enclosure which is spaced from the reactor, the contents of the reactor being pumped from the reactor and through the enclosure using a circulation pump.

17. An apparatus according to claim 15 or claim 16 comprising a plurality of electrodes. 22 . ^

18. An apparatus according to claim 16 or claim 17 in which the electrodes are arranged in the enclosure in labyrinth fashion.

19. An apparatus according to any one of claims 15 to 18 in which the electrodes are arranged coaxially with respect to each other.

20. An apparatus according to any one of claims 15 to 19 in which each electrode is spaced from each other and the contents of the reactor flows between the electrodes substantially perpendicularly to their surfaces.

21. An apparatus according to any one of claims 15 to 20 in which the inlet and outlet ducts extend through a common electrode passage and/or a degerminating device.

22. An apparatus according to claim 21 in which the electrode passage has at least a pair of electrodes arranged to allow flow through spaces between the electrodes, the electrodes being connected with a further pulse generator circuit, the pulse output voltage of which increases steeply, but diminishes exponentially, and has a peak amplitude of no more than 3.5 kV/cm.

23. An apparatus according to any one of claims 15 to 22 in which the pulse generator circuit comprises a power unit, at least one storage capacitor and at least one reversing switch which is connected in circuit with the power unit, the storage capacitor, and the electrodes in such a way that, in a first switch position, the storage capacitor is charged by the power unit and, in a second switch position, the storage capacitor is discharged via the electrodes 4 ""1- 1 A CCDJOOO n!j - 23 - 21913-

24- An apparatus according to claim 23 in which the storage capacitor is electrically operable.

25. An apparatus according to claim 23 or claim 24 in which the reversing switch is in controlled connection with a control oscilator, the output pulses of which are controllable periodically.

26. An apparatus according to claim 25 in which the output pulses are controlled using the control means of a generator.

27. An apparatus according to any one of claims 23 to 26 in which the reversing switch has at least two on/off switching elements with the first switching element arranged between the storage capacitor and the power unit and the second switching element between the storage capacitor and the electrodes.

28. An apparatus according to claim 15 and substantially as described in this specification with reference to any one of the accompanying drawings.

29. A process according to claim 1 and substantially as described in this specification with reference to any one of the accompanying drawings.

30. Micro-organisms whenever cultivated by a process according to any one of claims 1 to 10.