WO2009106084A1

WO2009106084A1 - Centrifugal liquid filter

Info

Publication number: WO2009106084A1
Application number: PCT/DK2009/050046
Authority: WO
Inventors: Mikkel Vestergaard Frandsen
Original assignee: Vestergaard Sa
Priority date: 2008-02-28
Filing date: 2009-02-27
Publication date: 2009-09-03
Also published as: MX2010009044A; BRPI0907894A2; TW200946205A; ZA201005389B; TR201006311T1

Abstract

Liquid filtration device with a filter capable of filtering microbes from the liquid passing through the filter media by preventing the microbes from traversing the filter. The filter is arranged rotatably inside a housing for causing liquid to be pressed through the filter by centrifugal force during rotation of the filter, wherein the devicecomprises a manual drive mechanism for rotation of the filter.

Description

Centrifugal liquid filter

Field of the Invention

The present invention relates to centrifugal fluid filters, especially drinking water filters.

Background of the Invention

Typically, household water purification equipment for elimination of microbes in drinking water can follow 2 paths: Chemical deactivation or mechanical filtration.

In case of chemical deactivation, usually, halogenated media, such as Chlorine or Iodine, is being used. For example, in water purification tools, where iodine sources are used, iodine and iodide is released from a resin to the water in order to deactivate microbes, usually, in relative short contact time and dwell time in the water flowing through the device. The deactivation efficacy is a product of the contact and dwell time and the concentration of halogenated media. The shorter the contact-time and dwell- time, the higher the concentration of halogenated media must be to achieve significant microbe deactivation. This high concentration of halogens in the up-taken water by the consumer is leading to taste and odour distortion and may lead to health risks, when permanently used. In order to avoid this negative impact, the residual iodine and iodide is, normally, being removed by an iodine scavenger in a final treatment step before release of the water for consumption. Activated carbon, for example in the granular form (GAC), is a commonly used scavenger, where the activated carbon, in addition, may be treated with silver or copper to enhance an antimicrobial efficiency. However, using iodine resin is disadvantageous in rural areas, where it may be difficult to provide new iodine resin when the resin is used up due to the water cleaning. In addition, as iodine is a rather expensive substance, it is desirable to reduce the iodine consumption.

This can be achieved with halogen-free mechanical filters used for microbial purification by particle size separation. For example, ceramic filters are known in the art, where the filters can be used for water filtration without iodine or chlorine addition. For example, the companies JP Ceramics Ltd and Fairey Industrial Ceramics Limited (FICL) provide ceramic filters commercially. Another example with a mechanical filter is disclosed in US patent application No. 2006/144781 by Carlson et al. describing a gravity filter with a microporous membrane.

A combination of a microporous filter and a ion exchange resin is disclosed in US patent No. 6,453,941 by Cutler et al. describing a gravity filter with an upper chamber containing ion exchange resin and a lower chamber comprising a microfiltration element with a filtering capability of 99.95% reduction of 3-4 micrometer sized particles when tested in accordance with NSF 53 standards. The flow through speed was meas- ured to 5 minutes per litre. This is generally experienced by the consumer as a disadvantageous low filtration speed.

In general, though the use of microfiltration or ultrafiltration membranes is advantageous from the perspective of avoiding resin, the flow speed through the filter may become very low if the inlet water pressure is not substantially high. For a gravity filter, where the pressure of the water at the water inlet is in the order of 0.1 bar or less corresponding to a height difference of one meter or less, the speed is experienced to very low by the consumer.

Another example of a halogen- free water filter is disclosed in U. S Patent No. 6,838,005 and is commercially available as the product with registered trade name Nanoceram® by the company Argonide®. In this case, alumina nanofibres are provided in a porous glass fibre matrix filtering microbes by attachment to the nanofibres. The microbes and anorganic sediments are attracted by the highly electropositive charged alumina and stay permanently, un-releasable in the filter matrix. The flow speed of the filter is dependent on the path length of the water through the filter, In order to have high filtration efficiency, this path has to be rather long. However, a long filtration path reduces the flow speed of the water, which - as mentioned above - is experienced as a disadvantage by the consumer.

Description of the Invention It is therefore the purpose of the invention to provide a liquid filtering device, primarily a water filtering device, with high microbial filtering capabilities but with high throughput through the device. It is a further object of the invention to provide such a filtering device which is suited in rural areas, where the supply of halogenated resin may be scarce.

This purpose is achieved by a liquid filtration device comprising a housing with a liquid inlet and a liquid outlet between which a filter is arranged. The filter is capable of filtering microbes from the liquid passing through the filter by preventing the microbes from traversing the filter, which is arranged rotatably inside the housing for causing liquid to be pressed through the filter by centrifugal force during rotation of the filter. The device comprises a manual drive mechanism for rotation of the filter.

The manually driven centrifugal water filter according to the invention is an apparatus with a high filtration speed and suited for use in rural areas, refugee camps and for fast clean water production in connection with military purposes and during mountaineering and hiking. Though the use of the filter for water filtration is preferred, the filter may also be used in connection with other liquids.

Though not strictly necessary, but preferably, the housing is a closed compartment, and the drive mechanism is accessible from outside of the housing. For example, the housing comprises a base part closed by a cover. Suitably then, the drive mechanism comprises a handle in or above the cover with a drive connection extending through the cover. In certain embodiments, the drive mechanism is a rotational mechanism with a handle arranged to be rotated around an axle extending through the cover. In order to achieve an efficient filtering, the drive mechanism may comprise a gearing for multiplying the rotation frequency of the rotation of the filter relative to the rotation of the handle.

The acceleration in the rotating filter is given by a=(2π)² • r • f ² ≡ 40 • r • f ², where r is the radius of the rotating filter and f the rotation frequency in rounds per second. Given r=0.15 m and f=5, corresponding to a single turn in a second and a gearing of 5, the acceleration yields about 15 times the force of gravity. The filtration device according to the invention has certain similarities to salad spinners, for example as known from the companies Guzzini® or Tupper® or as disclosed in US patent 5,904,090, which is reproduced in FIG. 1. However, the mechanism to drive the filter in the device according to the invention may be constructed in different ways, for example by including the driving principles of other salad spinners. Examples of different drive mechanisms are disclosed in European patent application EPO 176450, French patent application FR2618998, US patent No. 5,562,025, and US patent No. 7,111,546.

Preferably, the filter is substantially tube formed. The term "tube formed" has to be understood in a wide sense, such that the filer need not be cylindrical but can have tapering forms or other forms, instead. An option is to have a liquid filtration path through the filter that is substantially along the direction of the centrifugal force.

In a practical embodiment, the filter comprises a microporous filter media with a pore size adapted for filtering microbes from a fluid by mechanical particle size separation. In this case, microbes, for example bacteria and virus, are held back from entering or generally traversing the microporous filter medium, as the pores have a size smaller than the microbes for preventing microbes to flow into and through the pores. This is in contrast to the disclosure of US patent 6,838,005 by Tepper and Kaledin and the commercially available Nanoceram®, where particles are attracted to nano-alumina particles inside the filter medium due to an electric charge.

The term "microporous" refers to pores in the micrometer and/or sub-micrometer range, for example in the range 0.01-1 micrometer. Thus, the term is not limiting the pore size to the micrometer range for micro-filtration but refers equally well to pores that are used for ultra-filtration to filtrate viruses. Micro -Filtration membranes (MF), typically, have a porosity of about 0.1 - 0.3 micron and are able to filter bacteria, para- sites and anorganic particles bigger than the pores. Ultra-Filtration membranes (UF), typically, have a porosity of about 0.01 - 0.04 micron and are able to filter bacteria, parasites, and anorganic particles bigger than the pores and virus. MF membranes have normally higher flow rates than UF membranes. The porosity according to the above figures is related to the well known test method for this kind of filters termed bubble point measurement, which also relates to the figures as mentioned in connection with the invention.

The microporous membranes may be produced with various porosities for particle size seperation. The filter according to the invention may comprise a microfiltration membrane with microfiltration properties to filtrate bacteria or an ultrafiltration membrane with ultrafiltration properties having pores with a pore size adapted to filter virus, or both. In order for the micropores to filtrate bacteria, micropores of the size between 0.1 micrometer and 0.3 micrometer are applicable, whereas to filter viruses, smaller pore sizes are required, for example pores in the range between 0.01 and 0.04 micrometer.

In one example, the microfiltration membrane has a porosity with a pore size of be- tween 0.05 - 0.4 micrometer, preferably, between 0.05 and 0.15 micrometer. In addition or alternatively, the filter may comprise an ultrafiltration membrane. In another example, the ultra-filtration membrane has a porosity with pore sizes of less than 0.04 micrometer.

Typically, in the US, according to the EPA protocol, filters are tested in order to yield a filtration of log 4 for the bacteriophage MS2 virus having a size of 20nm - 30nm. However, among the viruses dangerous for humans and typically present in tropical countries' water supplies, only the polio virus has this similar size. Other viruses that are dangerous for humans are typically larger, such as the Rotavirus with a size of around 70 nm. In as much as the polio virus is very scarce on Earth, it would suffice in many situations to have a log 4 reduction on viruses with a size larger than 50nm.

Though the size of the pores has been defined above to be configured for filtering bacteria and virus, it is within the scope of the invention that other biological or non- biological material may be filtered with a device according to the invention. For example, the device according to the invention may be used to filter fungi, parasites, colloidal pesticides or chemicals, humic acid, aerosols and other microparticles from the liquid. Different materials may be used for such filters. One option is a solid microporous ceramic wall with a flow path through the wall separating the fluid inlet from the fluid outlet. Another option is a microporous filter comprises a microporous hydrophilic polymer wall with a flow path through the wall separating the fluid inlet from the fluid outlet, for example as disclosed in European patent EP 1 140 333 by Adriansen et al. The polymers normally being used are Polyether sulphone (PES), Polyvinylidene fluoride (PVDF) or Polyacrylonitrile (PAN). For example, such filters are disclosed in European patent EP 241 995 and references therein. Other examples in the form of hollow capillaries are disclosed in International patent application WO98/53901 and in WO98/15243 by Scharstuhl. Such hollow fibres may be arranged in different suitable orientations, for example tangentially, spirally or radially, in a rotatable filter according to the invention.

Alternatively, the filter may contain electropositive adsorptive nano-particles, for example nano-fibres, that are metal based, for example based on zirconia or alumina. In a further embodiment, the fibrous matrix contains inorganic fibres to which the nano- particles are attached. Such a fibrous matrix is disclosed in US patent No. 6,838,005 by Tepper and Kaledin or as in the product with registered trade name Nanoceram® by the company Argonide®, and meanwhile licensed to Ahlstrom® and sold under the name Disruptor™. In this case, the fibrous matrix is provided by glass fibres. However, other fibres are possible as alternatives or in addition to glass fibres. For example organic polymer fibres, may be used. The nano-particles may be attached to the organic polymer fibres or the inorganic fibres or both.

Candidates for the material of such polymer fibres are polyolefins among other polymers, including PTFE (polytetrafluorethylene, Teflon) and PVC (polyvinyl chloride). The organic fibres can contain releasable antimicrobial substance, such that the antimicrobial substance is part of the fibrous matrix. In one embodiment, the antimicrobial substance is embedded in the polymer matrix of the fibres, but capable to migrate to the surface of the fibres. Alternatively or in addition, antimicrobial substance is provided as a surface coating of the fibres. In order to coarse filter particles before entering a fine filter, the filter may comprise a prefilter with a filter mesh having a pore size of between 25 and 100 micrometer. One practical option is a washable polymer textile mesh. This prefilter may be partly over- moulded by a stability enhancing plastic structure. The prefilter may be a separate filter unit in itself and mounted as part of the liquid filter, or it may be moulded or otherwise connected to the other filter media in the liquid filter. In a further embodiment, also the filter for the microfiltration or ultrafiltration may be overmoulded.

In addition, the liquid filtration device according to the invention may comprise a fine mesh filter downstream of the prefilter, the fine mesh having a mesh size of between 1 and 25 micrometer, for example between 1 and 3 micrometer, or between 5 and 10 micrometer. Also, this filter is, optionally, a washable polymer textile mesh. The fine mesh filter may be a separate filter unit in itself partly overmoulded by a stability enhancing plastic structure. The fine mesh filter may be mounted as part of the liquid fil- ter together with the prefilter or, alternatively, separate from the prefilter but connected to other filter media in the liquid filter.

A further embodiment, in order to prevent biofilm formation in the liquid filter or in order to generally support the filtering properties of the liquid filter, the device com- prises an antimicrobial source for release of antimicrobial substance to the liquid between the inlet and the filter. Alternatively, the antimicrobial source is arranged between the inlet and the exit of the filter, in as much as the antimicrobial source can be contained in the filter.

Another advantage of omitting creation of biofilm is understood from the following argument. Biofilm growth in filters may evolve into microbial clusters with the capabilities of releasing vast amounts of microbes to the end user in the case where the porous membranes rupture. Thus, the omission of biofilm growth due to halogenic killing or otherwise antimicrobial killing of the microbes or the mere prevention of microbial growth in the filter reduces the risk for infection in case that the filter is damaged.

The antimicrobial source, for example halogen source, is, preferably, upstream of the microporous filter, for example as in the filtration membrane, in analogy to US patent No. 6,454,941, which is in contrast to many other prior art systems, where halogen is used downstream of a membrane in order to deactivate micro-organisms slipping through the membrane due to a porosity of the membrane not being small enough to separate particles of the corresponding size.

As halogenated resin is rather expensive means, the source may be free from halo- genated resin. The above mentioned halogen source may, instead, be a halogenated liquid, for example a liquid solution of Na-hypochlorite, or gas that is provided from a reservoir and dispenser at a suitable rate to the fluid through the device.

Alternatively, the halogen source could be a solid media, for example in the form of a tablet or granules, which is/are dissolved at a suitable rate in the flow path. Among suitable candidates in connection with the invention are tablets with high trichloro iso- cyanic acid content (TCCA). Preferably, these TCCA tablets have a slow dissolving characteristic, which is leading to a low elution of the halogen. Alternatively, a TCCA tablet with high elution characteristic can be installed into a rigid, porous tablet chamber, where influent water is bypassing most of the TCCA tablet chamber, while only a fraction of the influent water penetrates through the tablet chamber. This will lead to dilution of halogenated influent water, which had contact with the TCCA tablet, by the remaining influent water, which was bypassing the TCCA tablet. It should be remarked at this point that such tablets are free from halogenated resin.

Alternatively, the halogen source is provided as a halogenated resin located in the path between the inlet and the microporous filter.

The concentration of the halogen, for example iodine, may be of a low elution type. Biofilm growth occurs steadily with time, and a filter, which is subject to storage between intermitted use, has growth of biofilm during the storage time due to the remaining fluid in the filter. To prevent biofilm growth, the release of antimicrobial substance is sufficient even at low rate, because the content of antimicrobial substance in the fluid during storage increases steadily. It should be acknowledged at this point that, usually, a filtration of microbes is not filtering all microbes, but only filters the microbes to a certain degree, generally mentioned as "log reduction" referring to the log 10 of the ratio between the level of contaminants in the inlet fluid and the level of contaminants in the outlet fluid of the filter. For example, a log 4 reduction in contaminants corresponds to 99.99% reduction in contaminants, whereas a log 5 reduction in contaminants corresponds to a 99.999% reduction.

In connection with the filtering device according to the invention, the term "adapted for filtering bacteria or bacteria and virus by mechanical particle size separation" implies a reduction of the microbes in accordance with predetermined reduction levels, for example the above mentioned log 4, log 5 or even log 6 or log 7 reduction. In this respect, the reduction levels for bacteria may be different from the reduction level for viruses, because a fairly efficient virus filter may be highly efficient against bacteria due to their larger size.

However, in the low-elution embodiment, the log reduction is smaller. Thus, if the fluid filtration device is provided with a design flow through the device during rotation of the filter, wherein the design flow assures a proper filtration of the fluid flowing through the device with a cleaned fluid at the flow outlet, the antimicrobial source, preferably halogen source, may be configured to release the antimicrobial substance, for example halogens, at a rate, which is substantially less than necessary to reduce the microbes in the fluid by a log 4, or even log 3 or log 2, during the time it takes the fluid to flow through the device at the design flow. A design flow may be based on the filter- ing capacity during normal speed rotation of the filter in the device according to the invention.

Another definition of the low elution antimicrobial is given by the following. Also in this case, it is assumed that the fluid filtration device is provided with a design flow through the device, the design flow assuring a proper filtration of the fluid flowing through the device with a cleaned fluid at the flow outlet. However, in this case, the antimicrobial source, for example a halogen source, is configured to release the antimicrobial substance at a rate, which implies a content of antimicrobials in the fluid after microfiltration of less that a predetermined limit according to a predetermined health protocol. In other words, the amount and rate of release of antimicrobials is selected to such a low level, that a predetermined official health protocol, for example WHO protocol, is not violated. Experiments have shown that the level of antimicrobials, for ex- ample iodine or chlorine, can be kept so low that they do not violate typical health protocols though still being efficient for preventing biofilm formation and fouling. This is due the relatively long time of action of the antimicrobials on the microbes, for example during storage between intermitted sequences of use.

In the case of low elution antimicrobial content in the fluid, the release rate of antimicrobials is low. For example, it may be adjusted to yield a relative amount of between 0.01 ppm and 1 ppm, rather between 0.01 and 0.25 ppm, if the halogen is iodine, while the fluid is flowing through the device. For example, the iodine concentration may be around 0.1 ppm or even less, such as between 0.1 ppm and 0.01 ppm in the fluid flow- ing through the device. A target value in this connection is between 0.01 and 0.05 ppm, preferably in the order of 0.02 ppm, if the device according to the invention is to be operated without additional iodine scavenger. The elution of halogenated media may be chosen so low, that just the build-up of biofilm is being prevented, but no halogen absorbent is needed to reduce the concentration before human uptake. For example CDC (Center for Disease Control, Atlanta, USA) recommends for babies with an age of 0-3 months a maximum daily iodine uptake at permanent consumption of 0.01 mg/day. Based on an assumed water need at this age of 0.51itre/day, the maximum iodine concentration in the uptaken water should not be higher than 0.02 mg/1. Thus, ideally, the source does not elute more than 0.02 mg iodine per litre water.

This is in contrast to the concentration of more than 4 ppm iodine in devices, where a killing of the microbes is necessary during short contact and dwell time with halogen and without microporous filters. In connection with chlorine, the concentration ranges and target values are about a factor of 5 to 10 higher than for iodine, for example be- tween 0.1 and 0.5 ppm, preferably in the order of 0.25 ppm.

In the case, where the above mentioned fibrous matrix with electroposite nano-particles is used, the halogen values of above may be used in the low elution case. However, in order to achieve a high flow rate through the filter, the release rate may be moderately higher. For example, the rate may be adjusted to yield a relative amount of more than 0.25 ppm of iodine in the fluid and, preferably less than 2 ppm, preferably between 0.8 and 1.2 ppm, most preferably around 1 ppm. For Chlorine, the release rate is such that less than 20 ppm are in the fluid, and, preferably more than 1 ppm.

It is well known that iodine resins yield a higher concentration of iodine when the resin is new than resin which has been subject to a long term flow of fluid through the resin. Concerning the above mentioned ranges and target values according to the invention, these are directed towards long term values rather than initial values of the resin.

In those cases, where the resin or other halogen source has a sharp high peak value of the released halogen during the very first flow through the device, this sharp peak halogen concentration may be removed by a halogen scavenger after the filter. Option- ally, this scavenger may be designed to be used up by the peak value, such that no scavenger is remaining as soon as the peak concentration has been overcome, and the resin or other type of halogen source has entered a quasi steady state halogen release.

The halogen release from the resin or other media, for example a tablet, may be de- pendent on the temperature, the pH, the flow rate, the viscosity of the fluid and the degree of contamination. However, as the rate of halogen release is not critical for the filtering properties but only has the task to prevent biofilm growth, the influence of these parameters is not crucial. For the low halogen concentration, as mentioned above, the halogen source may be a low elution iodine resin

In the case, where the filter comprises a fibrous matrix containing electropositive ad- sorptive nano-particles, one option is an antimicrobial source separate from the fibrous matrix. Alternatively, the antimicrobial source is embedded in the fibrous matrix, or even incorporated in the material of the fibrous matrix.

The term antimicrobial source does not limit the invention to a single antimicrobial source. The device may, optionally, contain more than one antimicrobial source. This may be of interest, if combinations of antimicrobial sources are advantageous in order to achieve a high efficiency, despite a low elution of the antimicrobial substances. Likewise, the term fibrous matrix containing electropositive adsorptive nano-particles covers not only one type of fibrous matrix but also several fibrous matrices successively contained in the device, mixed or in other combinations.

In many cases, the moderate or high elution embodiments are further improved by comprising a scavenger for taking up the antimicrobial substance downstream of the fibrous matrix. Therefore, the device comprises an adsorbent or absorbent between the filter and the liquid outlet. For example, in the case of the antimicrobial substance con- taining halogen, the halogen scavenger may be activated carbon, optionally silver enriched. Alternatively or in addition, the scavenger may be a strong anionic exchange resin, for example Dow Maraton A® or Rohm & Haas Amberlite®.

Though the device according to the invention is primarily directed towards purification of water, the principles of the device may be applied for other liquids as well.

Concerning the structural features of the device, the following options may serve as practical examples not limiting the scope of the invention. In a preferred embodiment, the device has a design orientation for proper functioning, wherein the design orienta- tion comprises a vertical rotation axis of the tube formed filter. Another useful option is a substantially tube formed filter with an inner wall comprising blades or fins for shovelling the liquid along the filter during centrifugation of the filter. The latter assures that the liquid, preferably water, follows the centrifuging filter quickly for efficient filtering.

For example, for a household filter fresh water filter, the filtering capacity should be between 1 and 100 litre per hour, for example between 10 and 100 or between 10 and 50 litre per hour.

In order to prevent biofilm formation inside the housing, the housing may have an inner wall with an antimicrobial source for release of antimicrobials from the surface of the wall. This may be achieved with an antimicrobial coating on the surface of the wall or by incorporated the antimicrobials in the material of the wall. As a further alternative, the antimicrobial source is contained in a reservoir behind the wall, wherein the wall is configured for migration of the antimicrobial substance through the wall to the surface of the wall.

A large number of different coatings are available. Examples of antimicrobial organosi- lane coatings are disclosed in US patent No 6.762,172, No. 6,632,805, No 6,469,120, No. 6,120,587, No. 5,959,014, No. 5,954,869, No. 6,113,815, No. 6,712,121, No. 6,528,472, and No. 4,282,366.

Another possibility is an antimicrobial coating that contains silver, for example in the form of colloidal silver. Colloidal silver comprising silver nanoparticles (lnm to lOOnm) can be suspended in a matrix. For example, the silver colloids can be released from minerals such as zeolites, which have an open porous structure. Silver can also be embedded in a matrix such as a polymer surface film. Alternatively, it may be embedded in the matrix of the entire polymer during plastic forming processes, typically known as injection moulding, extrusion or blow moulding.

A silver containing ceramic, applicable for the invention, is disclosed in US patent No. 6,924,325 by Qian. Silver for water treatment is disclosed in US patents No. 6,827,874 by Souter et al, No. 6, 551,609 by King, and it is known in general to use silver en- hanced granular carbon for water purification. Silver coating for water tanks is disclosed in European patent application EP1647527.

Other antimicrobial metals that may be employed in connection with the invention are copper and zinc, which, alternatively or in addition, may be incorporated in an antim- icrobial coating. An antimicrobial coating containing silver and other metals is disclosed in US patent No 4,906,466 by Edwards and references therein.

A coating may, in addition or alternatively, comprise titanium dioxide. Titanium dioxide can be applied as a thin film that is synthesized by sol-gel methods. As anatase TiC>2 is a photo catalyst, thin films with titanium dioxide are useful on external surfaces that are exposed to UV and ambient light. Also, nanocrystals of titanium dioxide may be embedded within polymers. In addition, silver nanoparticles can be complexed with titanium dioxide for enhanced effectiveness. For example, a thin film coating may have a thickness as little as a few micrometers. A coating may in addition, or alternatively, comprise a reactive silane quaternary ammonium compound, like it is known from the company AEGIS® under the trademark Microbe Shield™ used for air conditioning. When applied as a liquid to a material, the active ingredient in the AEGIS® Antimicrobial forms a colourless, odourless, positively charged polymer coating, which chemically bonds & is virtually irremovable from the treated surface.

From the inner wall, release of antimicrobials may be provided to an extent that only prevents microbes to live on the surface of the wall and prevent biofilm formation, but it may also be provided to an extent, which involves a release of antimicrobials at a rate which suffices to provide the fluid with enough antimicrobials, such that biofilm formation is also prevented in and on the microporous filter.

In this connection, the following observation is important. When filters of the kind of the inventions are used in rural areas as a clean water filter for a family, the filter is repeatedly used only during short time intervals. Water is typically fetched at a water hole or at the nearby river and is subsequently filtered. This occurs several times a day but only during short time. This implies that the filter is without flow most of the time. In case that the surface of the inner wall is provided with an antimicrobial, the release of the antimicrobial does not need to provide all the water through the filter with a certain dose of antimicrobial substance. It suffices that the release is at a rate that the content of antimicrobials in the time lapses between the filtering gets high enough to pre- vent biofilm formation. Thus, by taking this filtering habit into consideration, even a low elution of antimicrobials released from the inner walls of the housing is sufficient to prevent fouling and biofilm production. The need of only low elution facilitates the provision of long lasting antimicrobial inner wall of the housing.

The release of antimicrobials from the inner wall of the housing may be caused by a surface coating of the inner surface, for example a surface coating releasing silver, as described above. An alternative is an inner wall with a surface through which antimicrobials are possible to migrate from inside the wall, for example, due to antimicrobials that are incorporated in the material of the wall or due to antimicrobials that are provided in a reservoir behind the wall and which are capable of migrating through the wall and into the fluid in the housing. The inner wall of the housing may be configured as part of a laminate also containing the reservoir.

Short Description of the Drawing

In the following the invention will be explained in more detail with reference to the drawings, where

FIG. 1 is a reproduction of a salad spinner according to prior art US patent 5,904,090, FIG. 2 illustrates a first embodiment according to the invention, FIG. 3 a through d illustrate different kinds of filters,

FIG. 4 illustrates a top view of an embodiment of the filter.

Detailed Description of the Invention

FIG. 1 is a reproduction of a salad spinner according to prior art US patent 5,904,090. The salad spinner 10 has a base 12 and a basket 14 which is closed by a cover 16. In the cover 16, a rotational drive plate 30 is mounted which connects to the basket 14 and causes the rotation of the basket when driven by a rotational handle 32. Between the handle and the drive plate 30, a gear is provided. This principle has been used as inspiration for a liquid filter according to the invention, which will be explained in more detail in the following.

FIG. 2 illustrated the principle of a liquid filtration device 20 according to the invention, preferably a water purification device. The device 20 has a housing with a base 22, the base having a base bottom 24 and a cylindrical wall 26 defining an upward open concave, which is covered by a cover 28. Inside the base 22 is arranged a rotatable filter 30 in the form of a cylindrical tube arranged between a filter bottom 32 and a filter top 34 defining a first storage compartment 36 for prior-filtration liquid, preferably water. The filter bottom 32 is closed, whereas the filter top 34 has a central opening 38 serving as a liquid inlet into which liquid can be provided into the first storage compartment 36 inside the filter 30. The cylindrical filter is rotational supported on a sup- port post 40, for example an axle. This support post 40 rests on a partition wall 42 having an opening to a second, lower storage compartment 45 for purified liquid, preferably purified water. Liquid from the first storage compartment 36 flows through the filter 30 and through an opening 44 in the partition wall 42 and into the second storage compartment 45. This filtering of the liquid occurs due to gravity pressure of the fluid through the filter 30. However, the fluid pressure through the filter 30 is enhanced by centrifugal force when the filter 30 is spun. Spinning of the filter 30 is achieved by rotating a handle 46 on a rotatable handle support 48 around axle 50. The axle 50 drives a gearing 52 with a connection 54 engaging to the filter top 34 and causing is spinning when the handle 46 is rotated about axle 50. The spinning speed is dependent on the gearing 52, which can be of various kinds, for example a spur gear, planetary gear, worm gear or according to other types of gear. Preferably, the rotation speed of the filter 30 is multiplies relative to the rotation speed of the handle 46. For example, one full rotation of the handle 46 may result in two or three or more rotations of the filter 30. Once purified and stored in the second storage compartment 45, the liquid can be drained through liquid outlet 54 when valve 56 is open.

As a pre-treatment for water filtering, an antimicrobial source 58 can optionally be arranged inside the first liquid compartment 36. The antimicrobial source 58 releases antimicrobial substance to the pre-filter- water in the first liquid compartment 26. The release may be to such an extent that a final scavenger is used for the final removal of the antimicrobial substance. Alternatively, the antimicrobial substance, for example a halogenated substance, is added to the water at a slow rate for low elution, such that no removal steps are necessary for consumption of the filtrated water.

In order to release only small amounts of antimicrobial substance to the water, the source may, alternatively, be arranged just downstream of the water inlet 38 such that water is passing over the source in order to pick up slight amounts of antimicrobials, for example a halogenated substance, only during filling of the compartment 36.

In FIG. 2, the filter is shown as being cylindrical, however, other forms are possible, for example tapering forms, tapering in an upward or downward direction, shapes with a curve tube, or even filters that are semispherical or spherical with an upper opening. Furthermore, though a vertical rotation axis is preferred, this is not strictly necessary for the invention; the rotation axis may, alternatively, be horizontal or inclined.

The filter 30 with its media will be explained in more detail in the following, where an enlarged view of part 60 of the filter 30 is illustrated in FIG. 3. FIG 3a is a first embodiment of a filter 30 according to the invention. The filter 30 comprises a relatively coarse prefilter 61 for preventing particles and microbes with a size in the order of 25- 100 micrometer to enter the filter. Preferably, the prefilter is a washable polymer textile filter with a mesh size of between 25 and 100 micrometer. After the prefilter 61, a sec- ond prefilter 62 with slightly smaller mesh size is arranged in the filter 30. Preferably, the second prefilter 62 is a washable polymer textile mesh or a non-woven polymer filter medium with a mesh or pore size of between 1 and 25 micrometer. These two prefilters 61, 62 may be separate filters in the sense that they can be dismounted individually or as a twin unit from the remaining filer 30. In order to keep the shape of the meshes or the non- woven, these filters may be overmoulded with a stabilising polymer grid.

The next filtration step 63 in the filter 30 is a microporous filter layer with microfiltra- tion or ultrafiltration capabilities, for example with filtration capabilities to remove par- tides and microbes with a size of between 0.02 and 0.2 micrometer. Examples of such filters are ceramic filters or porous polymer membranes with pores that withhold particles and microbes with a size larger than the pore size. Alternatively, the microporous filter comprises a fibrous matrix with electropositive adsorptive nano-particles, for example nano-alumina, such as Nanoceram®. This fibrous matrix may be a multi layer arrangement held between an overmoulded plastic structure, such as a net.

Optionally, there may be included a further filtration step 64 with granular activated carbon for removal of residual substances or with a halogen scavenger of another type, in the case that added antimicrobial agent in the form of halogenated substance has to be removed before consumption. This step is only optional, because in many cases, the addition of antimicrobial in the form of halogen is chosen to be at a low elution rate which does not require any further steps for removal of the added substance. In FIG. 3b, an alternative filter arrangement is illustrated with an antimicrobial source 65 between the two prefilters 61, 62 and the microporous filter 63. This antimicrobial source may substitute the antimicrobial source 58 as shown in FIG. 2 or add further antimicrobial substance to the fluid. The type of antimicrobial source 65 in the filter 30 may be different from the type of antimicrobial source 58 upstream of the prefilter.

The upstream source 58 may be a separate source 58 as illustrated in FIG. 2 or it may be integrated as part of the filter as illustrated in FIG. 3c. As a further option, as illustrated in FIG. 3d, the antimicrobial substance may be incorporated in the microporous filer 63.

FIG. 4 illustrates a top view of the filter 30, where the filter is provided with a number of fins 66 in order to accelerate the water easily during rotation. The shown number of fins in FIG. 4 is not limiting for the invention. More fins or fewer fins may be arranged in dependence of the circumstances.

Though the salad spinner according to FIG. 1 has been used for inspiration of the liquid filtration device according to the invention, the invention is not limited to the lay-out and driving mechanism of this prior art example. The device according to the invention can have a variety of modified embodiments and drive mechanisms within the scope of the claims.

Claims

1. Liquid filtration device comprising a liquid housing with a liquid inlet and a liquid outlet between which a filter is arranged, the filter being capable of filtering microbes from the liquid passing through the filter media by preventing the microbes from traversing the filter, wherein the filter is arranged rotatably inside the housing for causing liquid to be pressed through the filter by centrifugal force during rotation of the filter, wherein the device comprises a manual drive mechanism for rotation of the filter.

2. Liquid filtration device according to claim 1, wherein the housing is a closed compartment, and the drive mechanism is accessible from outside of the housing.

3. Liquid filtration device according to any preceding claim, wherein the filter is substantially tube formed.

4. Liquid filtration device according to any preceding claim, wherein the liquid filtration path through the filter is substantially along the direction of the centrifugal force.

5. Liquid filtration device according to any preceding claim, wherein the housing comprises a base part closed by a cover.

6. Liquid filtration device according to claim 5, wherein the drive mechanism comprises a handle in or above the cover with a drive connection extending through the cover.

7. Liquid filtration device according to claim 6, wherein the drive mechanism is a rotational mechanism with a handle arranged to be rotated around an axle ex- tending through the cover.

8. Liquid filtration device according to claim 7, wherein the drive mechanism comprises a gearing for multiplying the rotation frequency of the rotation of the filter relative to the rotation of the handle.

9. Liquid filtration device according to any preceding claim, wherein the filter comprises a microporous filter media with a pore size adapted for filtering microbes from a fluid by mechanical particle size separation.

10. Liquid filtration device according to claim 9, wherein the filter comprises a mi- croporous membrane with microfiltration properties.

11. A device according to claim 10, wherein the microfiltration membrane has a porosity with a pore size of between 0.05 - 0.4 micrometer.

12. A device according to claim 10, wherein the microfiltration membrane has a porosity with a pore size of between 0.05 and 0.15 micrometer.

13. Liquid filtration device according to claim 10, wherein the filter comprises a microporous membrane with ultrafiltration properties having pores with a pore size adapted to filter virus.

14. A device according to claim 13, wherein the ultra-filtration membrane has a porosity with pore sizes of less than 0.04 micrometer.

15. A device according to any preceding claim, wherein the microporous filter comprises a solid microporous ceramic wall with a flow path through the wall separating the fluid inlet from the fluid outlet.

16. A device according to any preceding claim, wherein the microporous filter comprises a microporous hydrophilic polymer wall with a flow path through the wall separating the fluid inlet from the fluid outlet.

17. Liquid filtration device according to any preceding claim, wherein the filter comprises a fibrous matrix containing electropositive adsorptive nano-particles.

18. Liquid filtration device according to claim 17, wherein the electropositive adsorptive nano-particles are nano-alumina particles.

19. Liquid filtration device according to claim 18, wherein the electropositive adsorptive nano-particles are aluminum hydroxide fibers..

20. Liquid filtration device according to claim 19, wherein the filter comprises Nanoceram®.

21. Liquid filtration device according to any preceding claim, wherein the filter comprises a prefilter with a filter mesh having a pore size of between 25 and 100 micrometer.

22. Liquid filtration device according to claim 21, wherein prefilter is a washable polymer textile mesh.

23. Liquid filtration device according to claim 21 or 22, wherein the prefilter is partly overmoulded by a stability enhancing plastic structure.

24. Liquid filtration device according to claim 21, 22, or 23, wherein the the filter comprises a fine mesh filter downstream of the prefilter, the fine mesh having a mesh size of between 1 and 25 micrometer.

25. Liquid filtration device according to claim 24, wherein the fine mesh filter is a washable polymer textile mesh.

26. Liquid filtration device according to claim 24 or 25, wherein the fine mesh filter is partly overmoulded by a stability enhancing plastic structure.

27. Liquid filtration device according to any preceding claim, wherein the device comprises an antimicrobial source for release of antimicrobial substance to the liquid between the inlet and an exit of the filter.

28. Liquid filtration device according to any preceding claim, wherein the device comprises an antimicrobial source for release of antimicrobial substance to the liquid in the housing between the inlet and the filter.

29. Liquid filtration device according to claim 27 or 28, wherein the antimicrobial source is a halogenated source.

30. Liquid filtration device according to any one of the preceding claims 27-29, wherein the antimicrobial source is free from halogenated resin.

31. Liquid filtration device according to any one of the preceding claims 27-30, wherein the antimicrobial source comprises solid, compressed resin-free halo- genated media.

32. A fluid filtration device according to claim 31, wherein the solid compressed media is a tablet.

33. A fluid filtration device according to claim 32, wherein the solid compressed media is a granular media.

34. A fluid filtration device according to claim 31 or 32, wherein the solid compressed resin-free media comprises a chlorinated media.

35. A fluid filtration device according to claim 34, wherein the compressed resin- free chlorinated media comprises Tri-Chloro-Isocyanuric-Acid (TCCA).

36. Liquid filtration device according to claim 29, wherein the antimicrobial source is a halogenated resin.

37. A fluid filtration device according to claim 29, wherein the antimicrobial source comprises a liquid dispenser and the antimicrobial substance is a halogenated liquid added to the fluid.

38. A fluid filtration device according to any one of the preceding claims 21-31 , wherein the antimicrobial substance contains iodine and the release rate for the antimicrobial substance is adjusted to yield a relative amount of less than 2 ppm of iodine in the fluid or wherein .

39. A fluid filtration device according to claim 38, wherein rate is adjusted to yield a relative amount of more than 0.25 ppm of iodine in the fluid.

40. A fluid filtration device according to claim 38, wherein the antimicrobial substance contains iodine and the rate is adjusted to yield a relative amount of less than 0.1 ppm of iodine in the fluid.

41. A fluid filtration device according to any one of the claims 27-40, wherein rate is adjusted to yield a relative amount of more than 0.01 ppm of iodine in the fluid.

42. A fluid filtration device according to any one of the claims 27-41, wherein the antimicrobial substance contains chlorine and the release rate for the antimicro- bial substance is adjusted to yield a relative amount of chlorine of between 0.1 and 20 ppm of chlorine in the fluid.

43. A fluid filtration device according to any one of the claims 27-42, wherein the antimicrobial substance contains chlorine and the release rate for the antimicrobial substance is adjusted to yield a relative amount of chlorine of less than 0.5 ppm of chlorine in the fluid.

44. A fluid filtration device according to claim 42 or 43, wherein the antimicrobial substance is a liquid solution of Na-hypochlorite.

45. Liquid filtration device according to any one of the claims 27-44, wherein the filter comprises a fibrous matrix containing electropositive adsorptive nano- particles and wherein the fibrous matrix is separate from the antimicrobial source.

46. A fluid filtration device according to any one of the preceding claims 27 and 29-44 when dependent on claim 27, wherein the antimicrobial source is embedded in the fibrous matrix.

47. A fluid filtration device according to any one of the preceding claims 27 and

29-44 when dependent on claim 27, wherein the antimicrobial source is incorporated in the material of the fibrous matrix.

48. Liquid filtration device according to any one of the claims 27-47, wherein the fluid filtration device is provided with a design flow through the device during rotation of the filter, the design flow assuring a proper filtration of the fluid flowing through the device with a cleaned fluid at the flow outlet, wherein the antimicrobial source is configured to release the antimicrobial substance at a rate, which is substantially smaller than necessary to reduce the microbes by a log 3 reduction in the fluid during the time it takes the fluid to flow through the device at the design flow.

49. Liquid filtration device according to any one of the claims 27-47 ^', wherein the fluid filtration device is provided with a design flow through the device, the design flow assuring a proper filtration of the fluid flowing through the device with a cleaned fluid at the flow outlet, wherein the antimicrobial source, for example a halogen source, is configured at the design flow to release the antimicrobial substance at a rate, which implies a content of antimicrobials in the fluid after micro filtration of less that a predetermined limit according to an official health protocol.

50. A device according to any one of the claims 27-49, wherein the device comprises an adsorbent or absorbent between the filter and the liquid outlet.

51. A device according to claim 50, wherein the adsorbent is a strong ion exchange resin, for example Iodosorb® or Dow Marathon A®.

52. A device according to claim 50, wherein the adsorbent or absorbent comprises activated carbon.

53. A device according to claim 53, wherein the activated carbon is silver enriched

54. A device according to any preceding claim, wherein the fluid is water.

55. A device according to any preceding claim, wherein the device has a design orientation for proper functioning, wherein the design orientation comprises a vertical rotation axis of the tube formed filter.

56. A device according to claim 55, wherein the filter is substantially tube formed with an inner wall comprising blades for shovelling the liquid along the filter during centrifugation of the filter.

57. A device according to any preceding claim, wherein the housing has an inner wall with an antimicrobial source for release of antimicrobials from the surface of the wall.

58. A device according to claim 57, wherein the antimicrobial source is a coating on the surface of the wall.

59. A device according to claim 57, wherein the antimicrobial source is incorporated in the material of the wall.

60. A device according to claim 57, wherein the antimicrobial source is contained in a reservoir behind the wall, wherein the wall is configured for migration of the antimicrobial substance through the wall to the surface of the wall.

61. A device according to any on the preceding claims 57-60, wherein the antimicrobial substance contains silver.