Diverse types of purification, and particularly water purification, are known in practice. Many of these methods make use of a membrane to filter a liguid. This is a relatively expensive product. A membrane is also relatively susceptible to contamination, whereby the processing time for which functional use can be made of the purification is reduced because of necessary cleaning actions.

An object of the invention is to obviate the above stated problems and to provide an effective and efficient purification of a fluid.

This object is achieved with the device for purifying a fluid according to the invention, the device comprising:

- a container for the fluid;

- electrodes placed in the container and operatively connected to an alternating current source; and

- an ultrasonic wave generator placed in the container. By providing electrodes which are operatively connected to an alternating current source an alternating current field (AC field) can be applied in the fluid, such as a liguid, introduced into the container. A first purifying effect is hereby achieved. At least one ultrasonic wave generator is placed in the container such that it is possible to apply an ultrasonic field in the container therewith. This brings about a second purifying effect.

Surprisingly, it has been found that a combination of the first electrical field and the second ultrasonic field results in a high degree of purification of the fluid. The fluid is preferably water in which undesirable components are present which must be removed therefrom through

purification .

The effects of the AC field and ultrasonic field intensify each other. This is probably caused by the damage to the cell walls resulting from the applied ultrasonic field, whereby the effect of the AC field on the core is intensified. The fields are therefore preferably provided in at least partially overlapping manner. The container preferably comprises an inlet and an outlet for continuous throughflow of the fluid in the container during use. A continuous process is in this way obtained and the

purification can be implemented in effective manner. This is achieved by the effective purification realized by combining an AC field and an ultrasonic field. A type of flow reactor can hereby be realized according to the invention.

In an advantageous preferred embodiment according to the present invention the power source comprises a frequency in the range of 1 kHz - 1 GHz, preferably 10 kHz - 1 MHz, and most preferably 100 kHz - 500 kHz.

It has been found that the alternating current in said ranges, and preferably in the most specific range, results in an effective first purification effect. The specific frequency depends on, among other factors, the fluid and possible contaminants present therein. It has been found here that for purification of an aqueous liquid flow a frequency of about 120 kHz results in an effective

purification .

In a preferred embodiment according to the invention the frequency of the ultrasonic sound produced by the sound source lies in a range of 15 kHz - 100 MHz and preferably of 15 kHz - 25 kHz, 25 kHz - 100 kHz, 100 kHz - 1 MHz and/or 1 MHz - 100 MHz.

It has been found that the cell walls of microorganisms become permeable in the frequency range of 15 kHz - 40 kHz and that an efficient and effective elimination is achieved at higher frequencies. It is moreover possible at these frequencies to generate cavitation bubbles in the fluid .

In the context of the invention ultrasonic sound is understood to mean sound with a frequency higher than 1 kHz, in particular higher than 10 kHz and more particularly higher than 18 kHz. The transition zone of "audible

ultrasonic sound", which differs per person, is included in the term ultrasonic. An upper limit of the frequency of ultrasonic sound is generally defined at 800 MHz. Sound with a frequency above 800 MHz is referred to as hypersonic sound. In this text ultrasonic is understood to mean both ultrasonic sound up to 800 MHz and hypersonic sound above 800 MHz.

In an advantageous preferred embodiment according to the present invention the device comprises a direct current source for applying a direct current over the electrodes.

By applying a direct current field in the fluid chlorine will be formed in the aqueous liquid flow, such as a waste water flow, which has an effective effect on the elimination of for instance micro-organisms. This effect is enhanced by the use of an ultrasonic field with which the cell wall is damaged, so that the chlorine becomes

considerably more effective.

In an advantageous embodiment according to the present invention the device comprises a UV source, which is preferably placed in the container.

UV radiation can be introduced into the fluid by providing a UV source. Such UV radiation has a direct effect on possible contaminants in the fluid to be purified. This radiation can thus cause direct damage to DNA structures.

The device according to the invention is preferably provided with an X-radiation source. X-radiation has a fatal effect on the micro-organisms in particular. As in the case of UV radiation, the effect of the X-radiation is

intensified by application in the ultrasonic field according to the invention. Combining an AC field and an ultrasonic field achieves an intensifying effect. Optionally combining these fields with one or more of DC, UV and X-ray results in a type of hurdle approach, whereby contaminants such as micro- organisms and algae come up against different barriers, the sum of which is too much for many contaminants. This further enhances the purifying effect.

In a further advantageous preferred embodiment

according to the present invention the device comprises recirculation means for recirculating at least a part of the fluid .

The fluid can be wholly or partially recirculated by providing recirculation means. A continuous process is hereby maintained and the degree of purification can in addition be influenced by controlling the degree of

recirculation. An effective purification process is hereby obtained. The degree of recirculation can be made dependent on a degree of purification of the fluid, for instance by measuring the degree of purification.

In an advantageous preferred embodiment according to the present invention the device comprises active carbon particles arranged in the container.

By providing active carbon particles the effect of the AC field in particular is intensified and the purification caused thereby is improved.

The device preferably comprises both active carbon particles and recirculation means, and moreover a system for recovering the active carbon so that it can be recirculated.

The active carbon is for instance provided as free carbon particles in the container, wherein the carbon particles are bounded by filters. A fluidized bed is for instance formed. The carbon particles are for instance provided as granules or pellets. Alternatively, the active carbon is provided as a fixed bed.

In a further advantageous preferred embodiment

according to the present invention the ultrasonic wave generator is provided as an internal tube placed in the container .

By providing the ultrasonic wave generator as a type of internal tube this is placed in the fluid in order to thereby realize an ultrasonic wave field in the fluid in an efficient and effective manner. The internal tube can itself function as transducer. It is also possible to provide transducers over the surface of the internal tube.

This internal tube forming the ultrasonic wave

generator is preferably also utilized as one of the two electrodes. The AC field can hereby be applied over the internal tube and the external tube forming the container or reactor. The ultrasonic field can in this way be combined in effective manner with the AC field.

The invention further relates to a method for purifying a fluid, comprising the steps of:

- providing an above described device;

- applying an alternating current field in the container; and

- generating an ultrasonic wave signal in the container.

Such a method provides the same effects and advantages as those mentioned in respect of the device.

Further advantages, features and details of the invention are elucidated on the basis of preferred

embodiments thereof, wherein reference is made to the accompanying drawings, in which:

- Figure 1 shows a view of a container with an AC field; and

- Figures 2A and 2B show a view of a reactor according to the invention.

A system 2 (figure 1) comprises a container or reactor 4 into which a liquid 6 is introduced. Arranged in liquid 6 are a first electrode 8 and a second electrode 10 which are connected to an AC power source 14 using a circuit 12. A quantity of active carbon particles 16 is also provided in reactor 4. A purifying effect for liquid 6 is hereby achieved in system 2. This effect is intensified by the use of transducers 7 provided on the wall of reactor 4.

Alternatively, the transducers are arranged loosely in reactor 4.

In an alternative system 18 (figures 2A and 2B) use is made of a flow reactor 20 with a reactor wall 22. Liquid flows via inlet 24 into reactor 20 in a direction indicated with arrow A. An internal tube 26 with a tube wall 28 is further arranged in reactor 20. In the shown embodiment a number of transducers 30 are provided on a tube wall 28 for the purpose of realizing an ultrasonic field. The electrodes are formed by tube wall 28 and reactor wall 22, which are connected to an AC power source 34 using circuit 32. This creates an AC field in the space B between reactor wall 22 and tube wall 28. This field is optionally combined with a direct current field.

A liquid flow is preferably exposed in continuous manner to an AC field and an ultrasonic field. This

combination of fields intensifies the effects in the purification of the incoming liquid. These fields are optionally combined with direct current and/or UV radiation and/or X-radiation in order to further intensify this purifying effect. If desired, the continuous system can be combined with recirculation of a part of the liquid flow in order to further improve the purification.

Active carbon is preferably guided through system 18 and recovered, after which it is fed back to inlet 24.

An experiment demonstrating the effect of the invention is described below. Four series of measurements were performed. In each measurements series use was made of a beaker having therein a liquid for treatment comprising a pure bacteria culture of non-pathogenic E. Coli as test organism .

The beaker was place in each case in an ice bath for cooling for the purpose of thus keeping the temperature stable (25±7°C) in order to compensate for the effect of possible heating by the electrodes. The temperature and the pH were measured continuously. Each measurement series was performed in a 6-hour period.

In the control experiment (measurement series 1) only active carbon was applied to the liquid with bacteria, and no ultrasonic sound or AC field. The setup was moreover placed in a Faraday cage in order to prevent the influence of external fields.

In the second measurements series (measurement series 2) an AC field was applied with a frequency of 140 kHz and a field strength of 6 V/cm.

In the third measurement series (measurement series 3) ultrasound was applied, but no AC field. The ultrasound was generated using a transducer of the Branson Disruptor

Sonifier W250/W450 type. The ultrasound had a fixed

frequency and fixed power of 20W.

The treatment with ultrasound was alternately activated and deactivated: at the start of the experiment 10 minutes of ultrasound was applied, after which the sound was

deactivated. After 50 minutes the ultrasound was reactivated for 10 minutes, and so on until the end of the overall treatment period of 6 hours. Samples for determining the number of organisms were taken each time immediately before activation and immediately after deactivation.

In the measurement series without ultrasonic sound a sample was taken each hour. In the final measurement series (measurement series 4) both ultrasound and an AC field were applied in the same manner as described for measurement series 2 and 3.

The measurement results are shown in the table below:

Measurement Specification Energy consumption Log series for 400 ml beaker decrease in E.Coli

1 control 0W*6hour = 0 kWh 0.5 2 AC field only 113W*6hour = 0.678 2.5 kWh

3 ultrasound 20W*10min*6 = 0.02 3.5 only kWh

4 AC field and 20W*10min*6r = 0.698 5

ultrasound kWh

+ 113 W*6hour

Applying both an AC field and ultrasound brings about log 5 decrease in the concentration of E. Coli. A decrease of log 4 was already achieved in the first 3 hours, with a further log 1 decrease in the remaining 3 hours.

The decrease when an AC field only or ultrasound only was applied is insufficient for any practical relevance. The combination of an alternating current and ultrasonic sound does however bring about a log 5 decrease, which makes it attractive for application in practice. There is a

synergistic effect when an AC field and ultrasound are applied.

It is noted that applying active carbon is not

essential, since carbon contributes to only a limited extent to the elimination of organisms when compared to the combination of ultrasound and AC field.

Finally, it is striking that using the method according to the invention a log 5 decrease can be achieved with a relatively low energy consumption.

The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged. It is thus possible for instance to treat a fluid other than water according to the present invention, such as a sugar

solution, beer, blood or urine. It is also possible

according to the invention to make combinations of described measures .