EP2556030A2

EP2556030A2 - Purification device and method for purifying a fluid

Info

Publication number: EP2556030A2
Application number: EP11715071A
Authority: EP
Inventors: Mateo Jozef Jacques Mayer; Jaap Caro; Hendrik Jannis Cappon; Cees Jan Nico Buisman; Karel Keesman
Original assignee: Stichting Wetsus Centre of Excellence for Sustainable Water Technology
Current assignee: Stichting Wetsus Centre of Excellence for Sustainable Water Technology
Priority date: 2010-04-09
Filing date: 2011-04-08
Publication date: 2013-02-13
Also published as: WO2011126371A2; WO2011126371A3

Abstract

The invention relates to a purification device and method for purifying a fluid. The purification device comprises: –wave-generating means for generating acoustic and/or electromagnetic waves capable to produce wave interference and/or local enhancement of wave intensity;and –control means for controlling the wave generating means capable to achieve a structure with the generated waves such that the structure behaves as a filter.

Description

Purification device and method for purifying a fluid

The present invention relates to a purifying device for purifying a fluid, like drinking water.

Known purification devices often use chemicals and/or require significant amounts of energy to enable the purification of the fluid.

The object of the present invention is to provide an effective and efficient purification device for purifying a fluid, like drinking water.

This object is achieved with the purification device according to the invention, the device comprising:

wave-generating means for generating acoustic and/or electromagnetic waves capable to produce wave interference and/or local enhancement of wave intensity; and

control means for controlling the wave

generating means capable to achieve a structure with the generated waves such that the structure behaves as a filter.

The device according to the invention is capable of purifying a fluid, including air and liquids, with purification involving separating and/or filtering of contaminations in the fluid, including separation of

particles. For example, contaminations include grass seed, graphite, micro-organisms, algae. Other substances and particles can also be considered as contaminations.

The purification according to the invention is based upon interference of acoustic waves or electromagnetic waves in regular structures and/or on local concentration of these waves in a periodic structure. Through the induced interference, in case of electromagnetic waves wave energy is concentrated, while in case of acoustic waves pressure nodes result. These pressures nodes and/or energy

concentrations enable the formation of a structure. To achieve such structure control means control the wave generating means that generate the acoustic and/or

electromagnetic waves that are capable to achieve wave interference and/or local enhancement of the acoustic and/or electromagnetic field in a periodic structure. The control means generate a structure such that this structure behaves as a reactor or filter. Such reactor or filter purifies the fluid that is forced through this structure.

In fact, the waves accumulate contaminations in the fluid. The accumulated contaminations are removed from the device more or less continuously through a separate exit and/or periodically by interrupting the flow of fluid for a short time period to enable the accumulated contaminations to leave the device separately from the purified fluid.

The control means control the frequency and/or the amplitude of the wave and/or waves that are generated. The frequency and/or amplitude are selected as function of particle characteristics, for example. Preferably, the selection is made such that the use of energy is minimised. The device according to the invention can be applied in a continuous and/or semi-continuous and/or batch process, periodically or continuously.

In one of the presently preferred embodiments according to the invention the fluid comprises drinking water that is purified with the purification device

according to the present invention. It is also possible to purify other liquids and gasses. Other applications include the application of the device according to the invention in clean rooms. In such application particles are concentrated in pressure modes and/or energy concentrations. Next, the concentrated particles are removed from the clean room. This improves climate and quality of the clean room. Also, in processes particles can be separated as function of weight and/or diameter by selecting the frequencies and/or

amplitude of the waves on the particle characteristics. This can be applied as alternative to, or in combination with, membranes or filters in the processes. Also it is possible to provide "traps", created by the pressure modes and/or energy concentrations operating as a sort of membrane-less membrane. A number of these traps can be provided in series, each trap directed towards a specific particle or

contamination. Micro-organisms can be provided in a trap to feed on the substrate.

The forming of the structure with the purification device according to the invention shows some similarities with optical tweezing, which is a known method of trapping small particles of the micro- to nano-scale, including micro-organisms, using highly focussed laser beams, or the locally enhanced electromagnetic field at a photonic crystal cavity. In optical tweezing light waves are concentrated generating an electromagnetic field attracting the small particles. Energy is required for the particle to enable movement from this position and a barrier against such movement results. The use of electromagnetic waves and/or acoustic waves according to the invention enables filtering of particles that can even be larger as compared to the micro- to nano-scale.

As an additional advantage of the device according to the invention it is possible to control the formation of a three dimensional structure by the control means using the wave interference and/or local wave concentration. Such structure provides channels for the fluid to be purified in stead of holes in a two dimensional structure. Such three dimensional effect improves the effect of the filter on the fluid .

The purification device according to the invention is able to purify a fluid effectively and efficiently without requiring additional chemicals and/or the use of a significant amount of energy for the purification. A further advantage is that the purification device can be used on a small scale with a production rate of a few liters per hour as well as on a large scale with a production rate of thousands of m³ fluid per hour. Another advantage of the purification device according to the present invention are the relatively low investment costs associated with such device. In case of the fluid being drinking water this enables the provision of low cost drinking water in a sustainable manner, for example.

The purification device is able to purify a fluid containing particles preferably in a range of up to 0.5 mm, and possibly even up to 1 mm, and preferably in a range of 0.01-0.5 mm. This range includes grass seed, graphite, and larger algae. Furthermore, micro-organisms can be

inactivated, such as the algae. The purification can be performed both by using acoustic and/or electromagnetic waves. Acoustic waves have the beneficial effect that forces acting on the particles are relatively small as compared to conventional membranes for example, although this effect requires modulated radio waves, for example. In this respect it is noted that although forces can be relatively small, the forces should be larger than the drag force acting on the particles by the flowing fluid. A beneficial effect of electromagnetic waves is that these waves require less energy when propagating through the fluid, like water or another fluid, when operating in a transparency window. In a preferred embodiment according to the present invention, the waves comprise ultrasound acoustic waves with one or more frequencies in the range of 1 MHz-10 MHz.

Using ultrasounds as relatively high frequency acoustic waves provides a structure that can be used as a filter for purifying a fluid. In fact, providing such structure can be considered as a type of acoustical tweezing method for capturing particles in a fluid. In case this acoustical tweezing is used as a water filter, this filter structure is capable of trapping particles thereby purifying the fluid, like drinking water, that contains these

particles. The frequency range of 1-10 MHz is effectively used to perform such acoustical tweezing. Especially this frequency range is capable of being performed effectively both in a small scale and in a large scale application of the purification device according to the present invention. For this range of applications the mentioned frequency range can be applied efficiently without requiring a significant amount of energy.

Moreover, surprisingly, the use of frequencies of

1-10 MHz, preferably 2-10 MHz, further brings about a disinfection of a fluid. Micro-organisms, such as artemia, are killed when applying acoustic waves having a frequency of 1-10 MHz, preferably 2-10 MHz. Especially artemia is considered a tough species which are hard to kill using, for example UV-C, chlorine or ozone. The invention provides a device capable of killing artemia. Possibly, this can be attributed to the sound pressure. Furthermore, when algae, such as Chaetoceros and Tetraselmis, are present in the fluid, applying the acoustic waves at a frequency of 1-10 MHz, preferably 2-10 MHz, the algae contents, such as proteins, fat and oils, are released. The algae are damaged by the application of the ultrasound waves and the contents are released. At least a part of the content will float to the surface of the fluid, where it can be skimmed. The method and apparatus according to the invention are

therefore applicable in harvesting algae products.

It is noted that the invention further relates to a method for harvesting algae products. The method comprises the steps of:

- providing a fluid containing algae; and

- generating acoustic waves having one or more

frequencies in the range of 1-10 MHz, preferably 2-10

MHz .

In a preferred embodiment according to the present invention the ultrasound acoustic waves comprise one or more frequencies in the range of 20-50 kHz.

The relatively low frequency range of 20-50 kHz can be used for disinfecting purposes in the purification device according to the present invention, although

providing this relatively low frequency requires the use of additional energy. At these frequencies the ultrasound is able to disinfect a fluid like water by cavitation. The acoustic wave provides air bubbles in the fluid that

collapse after a short period of resonance at the ultrasound frequency. These collapses create high energy implosions that are associated with shock waves and locally high temperatures. These effects disrupt cell structures and also decompose organic compounds that are present in the fluid.

Optionally, the frequency range for the acoustical tweezing mentioned above is combined with the low frequency for disinfecting purposes. Such combination of frequencies for trapping and treatment like disinfection provides an efficient purification device for purifying a fluid. As an additional effect of such combination the energy efficiency of the acoustic wave generating means can be improved through the design of resonant structures.

In a preferred embodiment according to the present invention the electromagnetic waves comprise one or more frequencies in the range of 1 GHz-30 GHz.

The range of 1-30 GHz appears to be relevant to purifying a fluid. Experiments and/or calculations have shown that this range is most attractive.

In a preferred embodiment according to the

invention the device comprises one or more resonant

structures or resonators in a periodic structure.

By providing one or more resonant structures, the energy efficiencies of especially the ultrasonic waves are improved. This minimises energy consumption while improving the purification operation.

According to the invention the resonant structures may comprise photonic and/or sonic crystals. Photonic crystals are made from dielectric material with a periodic modulation of the dielectric constant, or equivalent

therewith a periodic modulation of the refractive index. Sonic crystals are the sonic equivalent of the above

photonic crystals with a periodic variation of the mass density and the bulk modulus.

Both the photonic and sonic crystals have a band gap restricting transmission through the crystal. By

introducing a defect in the structure locally a transmission peak is achieved in the band gap. In fact, the defect acts as a resonator or cavity and has a local amplifying effect of the electromagnetic or acoustic/ultrasonic field

achieving significant field gradients. For example, with a cavity or defect in the sonic crystal particles and/or contaminations in the fluid are "pushed" away from the field maximum thereby achieving a purifying effect of the fluid. Providing a periodic geometrical structure in connection with a flow tube or flow reactor to make this tube or reactor a cavity for electromagnetic or sonic waves a purifying effect can be achieved. To improve the

throughput of the device according to the present invention more than one defects or resonators can be provided. In such an embodiment the flow tube or flow reactor works as a defect and thus induces locally the resonant behaviour.

In an advantageous embodiment according to the present invention the use of acoustic and electromagnetic waves is combined to provide an efficient and effective purification device. Such device may comprise any

combination of features mentioned above and below in

relation to the present invention. The combination of these two types of waves has as an additional effect that the energy consumption, especially for the low frequency

acoustic waves, is minimised, thereby further improving the purification device.

In a preferred embodiment according to the

invention the structure comprises more than one stage, wherein each stage behaves as a filter.

By providing different stages behaving as a filter each stage is optimised for a specific contamination in the fluid and/or substance that that requires filtration or separation. Preferably, the stages are provided in series. The series configuration enables a continuous purification of the fluid.

In a further preferred embodiment according to the invention the structure comprises micro-organisms feeding on substrate trapped or filtered by the structure.

By configuring the structure as a filter with one or more stages and providing micro-organisms in some or all of these stages the fluid is purified effectively. Preferably, the micro-organisms are monitored to ensure a correct operation with these micro-organisms. In addition, the behaviour of the micro-organisms, like growth, is related to the type and quantity of contamination in the fluid .

In a further preferred embodiment according to the invention the structure comprises one or more node lines in a direction substantial perpendicular to the flow direction of the fluid.

By providing the node lines in a direction substantially perpendicular to the flow direction an

effective filtering can be realised.

In a preferred embodiment according to the invention, the control means comprise switching means for switching the wave-generating means between an on-state, in which waves are generated, and an off-state in which no waves are generated or waves with less intensity are

generated. By switching the waves off periodically,

particles in the fluid are allowed to settle more quickly. In this way an improved sedimentation is obtained.

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

providing a purification device as described above, and generating acoustic and/or electromagnetic wave interference with wave generating means;

realising a structure with the generated wave interference by control means controlling the wave generating means such that the structure behaves as a filter; and

purifying the fluid by forcing the fluid through the structure .

Such method provides the same effects and advantages as those stated with reference to the purification device. In addition, the method preferably comprises filtering the fluid from particles with a size of up to 0.5 mm, and preferably larger than 20 ym. These particle sizes include filtering the fluid from grass seed, graphite and larger algae. In the presently preferred embodiment according to the present invention purifying the fluid further comprises generating ultrasound acoustic waves for inactivating micro-organisms that are present in the fluid. This inactivation of micro-organisms in the fluid can be performed at the relatively low frequencies that are mentioned above. The disinfecting of the fluid is preferably combined using generating of cavitations with acoustic waves in the fluid.

Further advantages, features and details of the invention are elucidated on basis of preferred embodiments thereof, wherein reference is made to the accompanying drawing wherein:

figure 1 illustrates a purification device according to the invention;

- figure 2 illustrates an experimental set up of a

purification device according to the invention; figures 3A-D illustrate particle movements in the device of figure 2;

figures 4A and B illustrate wave patterns generated in the device of figure 2;

figure 5 illustrates simulation results with node lines substantially perpendicular to the flow direction; and

figure 6 illustrates a two-dimensional resonant structure of a sonic or photonic crystal.

A purification device 2 (figure 1) is provided with a pipe 4 that enables a fluid 6 to flow from inlet 8 to outlet 10. In the illustrated embodiment from outlet 10 a purified flow 9 and a flow 11 with the separated particles or contaminations from fluid 6. Alternatively, a separate outlet (not shown) , for example shaped as a gap, is provided for flow 11 with the separation between flows 9, 11 being achieved using bends, for example, thereby achieving a type of cyclone. Alternatively, ratchets are provided in device 2 to deflect the particles or contaminations. Also, separation can be achieved by periodically flushing device 2 to achieve a periodic flow 11 with the separated particles or

contaminations that are maintained in device 2 in between two flushing operations. The above approaches can also be combined together to further improve the performance of device 2. Purification device 2 enables a continuous operation of the purification process. Pipe 4 is provided with wave-generating means 12. Controller 14 activates generating means 12. Controller 4 is provided with

information from sensor 16 that is provided in pipe 4 by measurement signal 18. Depending on signal 18 and the desired characteristics of the purification operation controller 14 sends a control signal 20 to the wave

generating means 12.

To purify a fluid 6 this fluid 6 is pumped through pipe 4. Preferably, relevant properties, like the amount of particles in the fluid, are measured by sensor 16. This measurement enables adjustment of the settings of the wave generating means 12 by controller 14 to optimise the

purification operation in purification device 2.

A separating device 22 (figure 2) comprises a signal generator 24 (Velleman PCGU 1000), 12V DC power unit 25, an audio amplifier 26 (Raveland XCA 1200), a computer 27, and four low budget 50W piezo tweeters, 28, 30, 32, 34 (Conrad, brandless TE-300) of which the horns were removed. The tweeters 28, 30, 32, 34 are placed on a table or plate 36 and are set up to create a resonance field in between them.

Polystyrene particles 38 (figure 3A) of various sizes, in the illustrated embodiment in the range of 0.5-3 mm, were randomly placed in the resonance area and the determined optimal resonance frequency was about 12.6 kHz for the illustrated embodiment. When applying the optimal resonance frequency the particles 38 were moved (figure 3B) towards the stable position and consistently separated in three band 40 (figure 3C en D) .

Rows 40 resemble the nodal bands of the resonance area. Particles 38 could even be made to spin or be placed upright when applying the frequency.

Further experimental results show the resonance area 42 between the four tweeters 28, 30, 32 and 34 of the illustrated device 22 with one and a half cosine using two tweeters 28, 34 (figure 4A) and with one and a half cosine, also using the two other tweeters 30, 32 operating. The results show the nodes 44, 46 representing stable positions for particles 38.

Simulation results (figure 5) show a line of nodes 48 extending in a direction substantial perpendicular to the flow direction of the fluid. This enables a continuous treatment of particles captured by the device and/or method according to the present invention. Lines of nodes 48 are placed in series with each line aiming to filter a specific contamination, based on the corresponding dimensions of this contamination, for example.

A sonic or photonic crystal 50 (figure 6) comprises long massive bars 52 of an appropriate material. Crystal 50 is provided with defect or cavity 54. Locally in and around cavity 54 the applied field is amplified. In the illustrated embodiment the applied electromagnetic or acoustic field is indicated with arrows and oriented

substantially perpendicular to the length direction of the bars or tubes 52. The typical periodicity of the raster is about 1-2 cm. for electromagnetic and ultrasound waves.

The present invention is by no means limited to the above described embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged. For example, instead of the pillar slab 52 (figure 6) it is also possible to use a so-called hole slab where holes are provided in a plate achieving similar effects.

Claims

1. Purification device for purifying a fluid, the device comprising:

control means for controlling the wave generating means capable to achieve a structure with the generated waves such that the structure behaves as a filter.

2. Purification device according to claim 1, wherein the wave interference comprises pressure nodes and/or local enhancement of the waves.

3. Purification device according to claim 1 or 2, wherein the wave interference comprises energy

concentrations .

4. Purification device according to claim 1, 2 or 3, wherein the fluid comprises a liquid, preferably drinking water.

5. Purification device according to any of claims 1-4, wherein the waves comprise ultrasound acoustic waves with one or more frequencies in the range of 1 MHz-10 MHz, preferably in the range of 2 MHz-10 MHz.

6. Purification device according to any of claims 1-5, wherein the waves comprise ultrasound acoustic waves with one or more frequencies in the range of 20-50 kHz.

7. Purification device according to any of claims 1-6, wherein the waves comprise electromagnetic waves with one or more frequencies in the range of 1 GHz-30 GHz.

8. Purification device according to any of claims 1-7, wherein the device further comprises one or more resonant structures and/or resonators in a periodic structure .

9. Purification device according to any of claims 1-8, the structure comprising more than one stage, wherein each stage behaves as a filter.

10. Purification device according to claims 9, wherein the stages are provided in series.

11. Purification device according to any of claims 1-10, wherein the structure comprising micro-organisms feeding on substrate trapped or filtered by the structure.

12. Purification device according to any of claims

1-11, wherein the structure comprising one or more node lines in a direction substantially perpendicular to the flow direction of the fluid.

13. Purification device according to any of claims 1-12, wherein the control means comprise switching means for switching the wave-generating means between an an on- state, in which waves are generated, and an off-state, in which no waves or waves with less intensity are generated.

14. Method for purifying a fluid, comprising the steps of:

providing a purification device according to any of claims 1-13, and generating acoustic and/or

electromagnetic wave interference with wave

generating means;

realising a structure with the generated wave

interference by control means controlling the wave generating means such that the structure behaves as a filter; and

purifying the fluid by forcing the fluid through the structure .

15. Method according to claim 14, wherein

purifying the fluid comprises filtering the fluid from particles with a size of up to 0.5 mm.

16. Method according to claim 14 or 15, wherein purifying the fluid comprises generating ultrasound acoustic waves for inactivating micro-organisms in the fluid .

17. Method to claim 16, further comprising the step of generating cavitations with the acoustic wave.