WO2017067773A1

WO2017067773A1 - Filter medium having copper and zinc

Info

Publication number: WO2017067773A1
Application number: PCT/EP2016/073573
Authority: WO
Inventors: Babita Baruwati; Udayan Majumdar; Rajeeshkumar Ramachandran; Satyajit Samadder; Sanket Champaklal SHAH
Original assignee: Unilever N.V.; Unilever Plc; Conopco, Inc., D/B/A Unilever
Priority date: 2015-10-21
Filing date: 2016-10-03
Publication date: 2017-04-27

Abstract

The present invention relates to filter for reducing the number of viable microorganisms from water. It particularly relates to a filter having oligodynamic metal. It is an object of the present invention to provide a filter which provides at least 6 log removal of bacteria, 4 log removal of viruses and 3 log removal of cysts while maintaining the levels of copper in the treated water within acceptable limits throughout the life of the filter. We have determined that at least some of the problems of prior art can be solved by using specified amount of zinc in a filter having copper.

Description

Filter medium having copper and zinc

Field of the invention

The present invention relates to a filter for reducing the number of viable

microorganisms in a fluid. It particularly relates to a filter medium having an

oligodynamic metal.

Background of the invention

Purified water is necessary for drinking, cooking, cleaning, industrial process, military and medical applications. Purification includes removing or reducing the content of undesired biological or chemical entities in water. It can also include either neutralizing or counteracting the activity or harmful effects of such entities.

Methods of water purification include chemical treatment, filtration, oxidation-reduction, adsorption, electrochemical separation, neutralisation and reverse osmosis.

Precipitants and coagulants are also known for use in water purification and can be used in combination with other agents.

Purification of water generally removes microorganisms, such as bacteria or algae, and harmful metal ions, such as mercury and lead by chemical treatment with chemicals such as chlorine, bromine, copper and silver in metallic or ionic form are commonly used to reduce the microbial count and purify water.

Chemical treatments mostly include the use of compounds having chlorine. Chlorine is useful in reducing the bacterial count and is often used in the form of hypochlorous acid or calcium hypochlorite. However, the discharge of chlorinated water causes environmental damage and it can also damage other purification devices such as reverse osmosis filters.

Metals have also been used for water treatment. Metals are less hazardous to human health and less damaging to the environment when compared to chemical treatment using chlorine or bromine. Typical metals used in particulate form for water purification include zinc, copper, and alloys thereof. Metals are either packed to form packed bed of metal particles or mixed with filter media to generate in-situ particulate metal or metallic compound providing antimicrobial activity on a filter medium. Bound carbon blocks having nano-particulate metal or other metal compounds are known.

US2010206799 A (Fluid Treatment Systems Inc) discloses a filter made of reticulate foam media which is substantially coated with metal particles, the coating including copper, zinc particles, metal oxides, activated carbon particles and a mixture thereof. The filter provides for removal of dissolved impurities from the liquids.

W010043472 A1 (Unilever) discloses carbon block filter having uniform metal impregnation obtained by contacting carbon particles with an aqueous solution of salts of metal in presence of ammonium hydroxide followed by application of heat and pressure. The filter provides for removal of organic contaminants.

WO2014067771 A1 (Unilever) discloses a filter made of filter medium and a metal or alloy thereof in the form of fibres which fibre has oligodynamic effect. The metal is selected from the group of silver, zinc, copper, gold and aluminium. The metal or alloy thereof in the form of fibres provides at least 5 log-io removal each of bacteria and virus from water.

US5443735 A (Kirnbauer et al., 1995) discloses a composite sorbent purification element for inhibiting the growth of microorganisms on the sorbent. The sorbent is susceptible to undesirable microorganism growth when exposed to water. It discloses method of treating water includes passing water to be treated over brass particles prior to or concurrently with contacting the sorbent, the contact with the brass particles is sufficient to inhibit the growth of microorganisms on the sorbent while not releasing more than 1 ppmw copper ions and 5 ppmw zinc ions into the effluent water.

The present inventors have found a typical limitation of using filter comprising copper to treat input water with high levels of chlorides, bicarbonates or high levels of total dissolved solids. When used to treat such input water the copper leaches from the filter at an increased rate and consequently copper levels in the treated water exceeds the acceptable limits. Increased leaching rate of copper is particularly observed after certain life points during use of the filter medium. Such treated water may not be safe to drink due to the high levels of copper. Therefore a need remains for a filter for treating fluids, particularly for a filter having copper that effectively reduces the number of viable bacteria, viruses and cysts in an environmentally friendly manner and in which the copper leaching from the filter into the treated water is within permissible limits throughout the life of the filter irrespective of the nature of the input water used. It is further preferred that the filter can achieve the desired reduction in the number of viable microorganisms from the input water using very low levels of, or no chlorine based chemicals.

It is an object of the present invention to provide a filter in which the copper leach is within the acceptable limits throughout the life of the filter.

It is another object of the present invention to provide a filter which provides at least 6 log reduction of bacteria, 4 log removal of viruses and 3 log removal of cysts while maintaining the levels of copper in the treated water within acceptable limits. It is a further object of the present invention to provide a filter which requires low levels of or no chlorine or other chemicals for reducing the number of viable microorganisms in water.

It is a further object of the present invention to provide a filter which reduces the number of viable microorganisms from water in an environmentally friendly manner.

Summary of the invention We have determined that at least some of the problems of the prior art can be solved by using specified amount of zinc in a filter having copper. It was surprisingly found by the present inventors that the problem of copper leach into the water at certain life point of the filter when the input water has high levels of chlorides, bicarbonates or high levels of total dissolved solids is overcome by the inclusion of zinc in elemental form or in the form of an alloy with specified amount of zinc in a filter comprising copper.

Thus, in accordance with a first aspect, disclosed is a filter for reducing the number of viable microorganisms in a fluid having:

(i) a filter medium;

(ii) copper, in elemental form, or in the form of an alloy, or a salt of copper, which salt is sparingly soluble or insoluble in water, or a mixture thereof; and,

(iii) zinc in elemental form or in the form of an alloy which alloy comprises at least 70wt% of zinc.

characterized in that the ratio by weight of the amount of zinc to the amount of copper is in the range of 1 :3 to 1 :25.

In accordance with a second aspect, disclosed is a process for preparing a filter of the first aspect.

In accordance with a third aspect, disclosed is a water purification device having a filter of the first aspect. In accordance with a fourth aspect, disclosed is a method of reducing the number of viable microorganisms present in water by passing the water through a filter of the first aspect.

In accordance with a fifth aspect, disclosed is a use of zinc and copper in a ratio by weight in the range of 1 :3 to 1 :25 in a filter of the first aspect for reducing the number of viable bacteria, virus, cyst present in water by at least 6log, 4log and 3 log respectively.

In accordance with a further aspect, disclosed is a use of zinc and copper in a ratio by weight in the range of 1 :3 to 1 :25 in a filter of the first aspect for providing water having not more than 1 ppm of copper by weight.

The invention will now be explained in details. Throughout the description, the term "amount of zinc" is meant to include the total weight of zinc in the elemental form, which is present in the filter in any of the forms disclosed in the present invention that includes zinc in the elemental form or in the form of an alloy having at least 70wt% of zinc.

The term "amount of copper" referred herein includes the total weight of copper in the elemental form, which is present in any of the forms of copper disclosed in the present invention which are copper in the elemental form or in the form of an alloy, or in the salt form.

The term "log reduction" as used herein means a 10-fold or 90% reduction in the number of viable microorganisms. By "6 log" reduction it is meant that the number of viable bacteria is reduced by 99.9999%, by "4 log" reduction it is meant that the number of viable viruses is reduced by 99.99% and by "3 log" reduction it is meant that the number of viable cysts is reduced by 99.9%.

Detailed description of the invention According to a first aspect of the present invention, disclosed is a filter for reducing the number of viable microorganisms in a fluid, said filter includes a filter medium, copper and zinc.

Preferably the filter of the present invention is for reducing the number of viable microorganisms from fluids, more preferably from liquids and still more preferably for reducing the number of viable microorganisms from water. While the filter of the invention is highly suitable for operation under gravity head, the filter could also be used to operate when the water available is under pressure. The present invention is particularly useful for reducing the number of viable microorganisms from input water having high levels of chlorides, bicarbonates or high levels of total dissolved solids and pH ranges of naturally available water. Disclosed filter provides the claimed benefits when the input water has bicarbonates in the range of 100 to 500 ppm or carbonates in the range of 100 ppm to 500 ppm. Total dissolved solids in the water is yet another factor which may affect the copper leach. The TDS levels of the water depends on the source of water. Ground water generally has a TDS of 500 to 3000 ppm, particularly in the range of 700 to 1200 ppm, TDS of surface water is generally around 350 ppm. The acceptable levels of TDS in drinking water is determined to be not more than 500ppm. Filters having copper generally leach copper when the TDS is above 500ppm, more particularly when the TDS is from 800 to 1000 ppm. It is found that the disclosed filter provides acceptable copper leach throughout the life of the filter with input water having TDS of across TDS ranges present in natural water.

Filter medium

Disclosed filter includes a filter medium which provides for removal of particulate and organic contaminants. Accordingly any granular or particulate material can be used.

The filter medium is preferably selected from alumina, carbon, zeolite, diatomaceous earth, silicate, aluminosilicate, titanate, calcium hydroxyapatite, perlite, talc, activated carbon, sand, clay or ceramic, still preferably the filter medium is selected from activated carbon, diatomaceous earth, sand, clay, activated alumina or ceramic, more preferably the filter medium is sand or activated carbon and most preferred filter medium is activated carbon.

Preferred activated carbon are obtained from bituminous coal, coconut shell, wood or petroleum tar. It is preferred that surface area of the activated carbon particles is greater than 500 m²/g, more preferably greater than 1000 m²/g. The activated carbon can be of two grades; a coarser granular activated carbon (GAC) and a finer powdered activated carbon (PAC). An intermediate grade is also available. This is known as intermediate activated carbon (IAC).

Powdered activated carbon (PAC) of selected particle size distribution is preferred over other forms. Preferably 95% of the particles of PAC pass through standard 50 mesh, more preferably through standard 60 mesh. It is also preferred that not more than 13%, preferably not more than 12% particles pass through 325 mesh. It is preferred that size uniformity coefficient of the particles of activated carbon is less than 2, more preferably less than 1.5. Particles of powdered activated carbon preferably have a carbon tetrachloride number exceeding 50%, more preferably exceeding 60 %. An Intermediate activated carbon (IAC) of selected particle size distribution is also preferred. Preferably 95% of the particles of IAC pass through standard 30 mesh, and not more than 12% particles pass through 60 mesh. It is preferred that size uniformity coefficient of the particles of activated carbon is less than 2, more preferably less than 1.5. Particles of intermediate activated carbon having carbon tetrachloride number exceeding 50%, more preferably exceeding 60 % are preferred.

It is preferred that iodine number of activated carbon particles is greater than 800 units, more preferably greater than 1000 units. Copper

Copper is said to exert its toxicity on microorganisms through several parallel mechanisms (cell membrane damage, protein damage, nucleic acid interaction), which eventually may lead to the microorganism's death. Disclosed filter includes copper in elemental form, or in the form of an alloy, or a salt of copper, which salt is sparingly soluble or insoluble in water, or a mixture thereof.

The copper salt is sparingly soluble in water and preferably selected from but not limited to copper glass, copper zeolite, copper oxide, cuprous oxide, copper carbonate, copper hydroxyl carbonate, copper basic carbonate, copper halide, copper hydroxide or a mixture thereof. Preferably the sparingly soluble salt of copper is selected from copper halides preferably the copper salt is an iodide, bromide or a chloride, still preferably the copper salt is a cuprous iodide or a cupric iodide. By "sparingly soluble" it is meant that the salt of copper has aqueous solubility of less than 1000 micrograms per liter at a temperature of 25°C, preferably less than 500 micrograms per liter and most preferably less than 100 micrograms per liter. When the salt of copper is an insoluble salt it is preferably selected from but not limited to copper carbonates, phosphates, hydroxide, oxides, or mixtures thereof.

By "insoluble" it is meant that the salt of copper has almost no aqueous solubility and is generally less than 1 micrograms per liter at a temperature of 25°C, preferably less than 0.5 micrograms per liter most preferably less than 0.1 micrograms per liter.

Preferably the alloy of copper is with zinc, tin or silver. A preferred alloy is brass or bronze. Both the alloys per-se are well known.

The term "brass" is used herein to indicate a copper and zinc alloy in general and that such alloy can contain other constituents and/or be commonly denominated by different nomenclature. It is further preferred that copper content in brass is at least 80wt% and more preferably at least 90wt% of the alloy.

When the alloy is bronze, preferably the copper content is at least 50wt% of the alloy, more preferably 80wt%, still more preferably 85wt% and most preferably 90wt% of the alloy. It is preferred that when the alloy is brass, it has zinc in an amount not more than 20wt%, more preferably not more than 10wt% of the alloy.

Preferably when the copper is in elemental form or in the form of an alloy, the copper is either granular or fibrous, more preferably the copper is fibrous.

Preferably the granular copper has a particle size distribution such that at least 90 number % of the particles have a particle size of 50 micrometers to 500 micrometers.

The copper may also be fibrous. Every fiber has an aspect ratio which is defined as ratio between its average length to its average diameter. A preferred aspect ratio of copper or its alloy when present in the form of fibers is 3:1 to 200:1. It is particularly preferred that aspect ratio of fiber is in the range of 3:1 to 65:1 and most preferably 3:1 to 25:1 . It is further preferred that the surface of the fibers is serrated. A serrated surface which provides a roughened appearance is believed to be better at retention or trapping of microbes as compared to fibres having comparatively smoother surface. Scanning Electron Microscopy can be used for studying the surface morphology.

Fibers can also be characterized by their mesh size which can be determined by following a standard ASTM method. It is preferred that the ASTM mesh size of the fibers is in the range of -10 to +270. This is roughly equivalent to 2057 μηη and 53 μηη. A preferred range is -18 to +200. The most preferred range is -18 to +120.

It is preferred that average length of fibers is 0.1 mm to 10 mm, more preferably 0.1 mm to 5 mm and most preferably 0.5 mm to 3 mm.

It is also preferred that the fibres of brass or bronze are pre-washed with a dilute mineral acid for example dilute hydrochloric acid for removing contaminants such as iron filing or other foreign matter from the surface of the fibres which might otherwise interfere with the in-use activity of the fibres.

High purity material is always preferred in the context of reducing microorganisms from water for drinking purpose. Copper may contain traces of lead as impurity and the WHO prescribed limit for lead in drinking water is 10 ppb. Therefore, high purity copper is preferred.

In the case of copper, it is preferred that apparent density of fibres is 1.1 g/cm³ to 2.5 g/cm³. It is believed that an increase in the content of metal/alloy in particulate form reduces porosity of the filter. On the other hand, an equivalent increase in fiber content does not adversely affect porosity. As porosity is directly linked to filtration, high porosity is desired. Fibres are more preferred than particulate form.

Irrespective of copper being present in any of the disclosed forms, which is either copper in elemental form or in the form of an alloy or as a salt of copper, preferably the total amount of copper from 4 to 10wt% of the filter. Similarly when the copper (i.e. copper in elemental form or in the form of alloy) is granular the filter preferably has 4 to more preferably 6 to 8wt% of copper in elemental form. When the copper is in the form of fiber the filter preferably includes 8 to 10wt% of copper in elemental form.

Zinc

Disclosed filter includes zinc, in elemental form, or in the form of an alloy which alloy comprises at least 70wt% of zinc. The zinc in the disclosed filter, is in addition to the zinc that may be present in the filter if copper is in the form of an alloy which is brass.

When zinc is in the form of an alloy, the amount of zinc in the alloy is at least 70wt%, preferably at least 80wt%, still preferably at least 85wt% and most preferably at least 90wt% of the alloy. The preferred alloys of zinc are selected from zamaks or zinc- aluminium alloys. Preferably the zinc-aluminium alloys are selected from zinc- aluminum solder, slush alloy or zinc brite alloy.

In the disclosed filter, the ratio by weight of the amount of zinc to the amount of copper is in the range from 1 :3 to 1 :25, preferably the ratio is 1 :4 to 1 :10 and most preferably the ratio is from 1 :4 to 1 :5.

Preferably the zinc is granular or fibrous. When zinc is in the form of fibers, a preferred aspect ratio of the fibre is 3:1 to 200:1. It is particularly preferred that aspect ratio of fibre is in the range of 3:1 to 65:1 and most preferably 3:1 to 25:1 .

It is further preferred that the surface of the fibres is serrated. It is preferred that the ASTM mesh size of the fibres is in the range of -10 to +270. This is roughly equivalent to 2057 μηη and 53 μηη. A preferred range is -18 to +200. The most preferred range is - 18 to +120.

When present in the granular form, preferably the particle size distribution of the zinc is such that at least 90 number % of the particles have a particle size of 50 micrometers to 500 micrometers. The total amount of zinc in the disclosed filter is preferably 0.1 to 3wt%. When the zinc is in granular the total amount of zinc is preferably from 0.1 to 3wt%, more preferably 1 to 3 wt% and still more preferably 1 to 2 wt% of the filter. When the zinc is in the form of fiber the the total amount of zinc is preferably 1 to 3 wt% of the filter.

It is preferred that apparent density of zinc fibres is in the range of 1.1 g/cm³ to 2.5 g/cm³ and for zinc granules the preferred apparent density should be 3.2 to 3.6 g/cm³. In the disclosed filter the zinc is preferably either impregnated on the filter medium or dispersed in the filter medium.

It is preferred that the copper and the zinc are both granular; alternately it is preferred that the copper and the zinc are both fibrous.

Binder

It is preferred that the filter is a bound or a sintered filter. In such a case, addition of a binder becomes necessary. Selection of the binder depends upon several variables but the most important factor is the nature and the type of filter medium.

Accordingly a range of binders can be used.

Binders are substances that bind the particles of the filter medium to hold them together. Suitable binders include polymers like polyethylene resin and inorganic substances like white cement. Polymeric binders are more preferred. A preferred binder is one which has surface coverage of 0.5% to 10%. A hydrophilic binder is preferred. Preferably the binder is a thermoplastic polymer. Suitable examples include ultra high molecular weight polymers, particularly polyethylene and polypropylene. Binders of this class are commercially available under the trade names HOSTALEN™ (from Ticona GmbH), GUR™, Sunfine™ (from Asahi), Hizex™ (from Mitsubishi) 5 and from Brasken Corp (Brazil). Other suitable binders include low density polyethylene (LDPE) sold as Lupolen™ (from Basel Polyolefins) and linear low density polyethylene (LLDPE) from Qunos (Australia). Bulk density of the binder is preferably not more than 2.5 g/cm³, more preferably less than 0.6 g/cm³ and particularly less than or equal to 0.5 g/cm³ and further particularly less than 0.25 g/cm³. It is preferred that particle size distribution of the binder is similar to that of the selected filter medium.

It is preferred that the amount of particles passing 200 mesh is preferably less than 40 wt%, more preferably less than 30 wt%. It is preferred that Melt Flow Rate (MFR) of the binder, e.g. polyethylene is less than 5 g/10 minutes, preferably less than 2 g/10 minutes, more preferably less than 1 g/IO minutes.

In the case of bound filters, it is preferred that ratio of the binder to the filter medium is from 1 :1 to 1 :20, more preferably from 1 :3 to 1 :9.

When the filters in accordance with the invention are bound, it is preferred that the filter comprise 1 wt% to 50 wt% binder.

Size and dimensions of bound filters

Size and dimensions of bound filters can vary depending on the intended use such as on the dimensions of any filter device. The bound filter can be of any desired shape and size.

Suitable shapes include a flat circular disc of low thickness, square disc of low thickness, low height tapered flat disc, cylinder, dome, annular cylinder solid cone, hollow cone, frusto-conical shape, and solid or hollow hemispherical shape. The annular cylindrical shape is more preferred. It is preferred that the shortest path length across the bound block i.e. the shortest distance from the point of entry of water to the point of exit for water where the water exits the bound block is from 5 to 50 mm, more preferably 10 to 30 mm.

Process for preparing the filter

The filters can either be bound or unbound. Such types of bound filters and unbound filters and their method of making is generally known in the art.

The filter according to the present invention may be made in the form of an unbound filter by any method known in the art to prepare such filters. Un-bound filters according to the present invention, is preferably made by mixing a filter medium, copper in any one or more forms as disclosed in the present invention, zinc in any one of the forms disclosed in the present invention to form a mixture and then packing the mixture in a flow-through container which is provided with inlet and outlet for water, generally in the form of mesh. The mixture in an unbound filter medium is devoid of any binder.

In accordance with a second aspect of the present invention disclosed is a process for preparing a filter according to the first aspect having the steps of:

(i) mixing a filter medium, copper, in elemental form, or in the form of an alloy, or a salt of copper, which salt is sparingly soluble or insoluble in water, or a mixture thereof and zinc in elemental form or in the form of an alloy which alloy comprises at least 70wt% of zinc to obtain a mix;

(ii) compacting the mix;

(iii) moulding the mix to form a filter.

Compaction of the mix is preferably carried out in a vibratory compactor to obtain the desired particle size distribution profile across the height of the filter block. The vibratory compaction is preferably carried out in a vibrator at frequency in the range of 30 to 100 Hz. This process step is preferably carried out for a period of at least one minute, more preferably for three to thirty minutes. To obtain an unbound filter it is preferred that the compaction is carried out in a flow-through container having an inlet and an outlet.

In accordance with the second aspect of the present invention disclosed is a further process for preparing a filter which is in the form of a bound filter according to the first aspect having the steps of (i) adding a binder in the mixing step as described above; (ii) applying a pressure in the range of 3.9x10⁵ to 2.9x10⁶ N/m² to the mix in the mould in the compacting step as disclosed above; (iii) heating the mould in an atmosphere maintained at a temperature of 150°C to 400°C in the moulding step as disclosed in the above process; it is preferred that the moulding step is followed by a step of cooling the mould; and, a step of releasing the bound filter from the mould.

In a preferred process, filter medium and binder is mixed in any low shear mixer that does not significantly alter the particle size distribution is suitable, such as a mixer with dulled impeller blades, ribbon blender, rotary mixer. The mixing is carried out to prepare a uniform mix of the filter medium and the binder and is preferably carried out for at least 15 minutes, more preferably 20 to 60 minutes. When water is used in preparing a moist mixture preferably the amount of water used is not more than 4 times the amount of particles, more preferably not more than 3 times the amount of particles. Optimally the amount of water used is from 0.5 to 1.5 times the weight of the carbon particles. The binder is then added to the above mixture and is further mixed. The most preferred mixer is sigma mixer.

Another type in which the filter according to the present invention may be made is in the form of a bound filter. Bound filters are made by using a binder as described earlier. Preferably a pressure in the range of 3.9x10⁵ to 2.9x10⁶ N/m² is applied using either a hydraulic press or a pneumatic press, more preferably a hydraulic press. The mould is made from aluminum, cast iron, steel or any suitable material capable of withstanding temperatures exceeding 400°C. A mould release agent is preferably coated on the inside surface of the mould. The mould release agent is preferably selected from either silicone oil, aluminum foil or any other commercially available mould release agent that has little or no adsorption onto activated carbon or the binder material.

The next step, includes heating the mould in an atmosphere maintained at a

temperature of 150°C to 400°C, preferably in the range of 180 to 320°C, depending on the binder material that is used. The heat is preferably applied for a period of 60 minutes, preferably between 90 and 300 minutes depending on the size and the shape of the mould, and sufficient to ensure uniform heating of the contents of the mould. The mould is preferably heated in an oven such as a non-convection, forced air or forced inert-gas convection oven.

The mould is then cooled and the bound filter is released from the mould.

It is preferred that the filter according to the present invention is obtainable by a process comprising the steps of:

i. mixing a filter medium, copper, in elemental form, or in the form of an alloy, or a salt of copper, which salt is sparingly soluble or insoluble in water, or a mixture thereof; and, zinc, in elemental form or in the form of an alloy which alloy comprises at least 70wt% of zinc to obtain a mix;

ii. compacting the mix in a mould; and,

iii. moulding the mix to form the filter.

It is preferred that a bound filter according to the present invention is obtainable by a process comprising the steps of:

i. mixing a filter medium, copper, in elemental form, or in the form of an alloy, or a salt of copper, which salt is sparingly soluble or insoluble in water, or a mixture thereof; zinc, in elemental form or in the form of an alloy which alloy comprises at least 70wt% of zinc and, a binder to obtain a mix;

ii. compacting the mix in a mould by applying a pressure in the range of 3.9x10⁵ to 2.9x10⁶ N/m²;

iii. moulding the mix by heating the mould in an atmosphere maintained at a

temperature of 150°C to 400°C;

iv. cooling the mould to release the bound filter.

Device

In accordance with a third aspect, disclosed is a water purification device including a filter of the first aspect or the filter obtainable by a process of the second aspect. Basic construction of preferred devices may be found in prior published patents issued to Unilever. In order to make the disclosed filter better suited for use in a device for reducing the number of viable microorganisms from water, it is preferred that the bound filter is attached to a base plate with an orifice for the water exit and additionally has a detachable cover. The base plate is preferably made of plastic such as polypropylene, polyethylene, ABS, SAN. The detachable cover is preferably also made of

polypropylene, polyethylene, ABS, SAN.

Additional sediment filters

In addition to the disclosed filter, in a typical water purification device for reducing the number of viable microorganisms from water, it is customary to use additional sediment filters. Such an additional sediment filter prolongs the life of bound filters such as carbon block filters.

Such additional filters are usually washable or replaceable and are preferably made of woven or non-woven fabric, more preferably non-woven fabric having micropores. The sediment filter is used as a pre-filter having pore size which is meant to retain particles generally above 3 μηη. The sediment filter can be washed and rinsed under flowing water or by using a small amount (0.1 to 10 g/litre) of detergent in water. This use of the sediment filter facilitates wide and extensive application of the disclosed filter by preventing the filter medium from choking.

The sediment filter is preferably moulded separately by using a woven or non-woven fabric of thickness in the range 1 to 10 mm and preferably 2 to 6 mm. The most preferred shape of the filter is hemispherical and the fabric used to cover the moulded filter is cut into a circle with diameter such that the area of the fabric is equivalent to 10 to 50%, more preferably 10 to 20% over the surface area of the filter which is required to be covered by the fabric. The ratio of the fabric to the size of the filter for other shapes is suitably altered so that the coverage is perfect and the fabric and the moulded filter have nearly identical shape and size.

Multiple sediment filters can also be used. Preferably a bound filter is enveloped with spirally wound layer of non-pleated fabric enveloped with spirally wound layer of pleated fabric. Use of the filter

In accordance with another aspect disclosed is a method of reducing the number of viable microorganisms present in water, by passing the water through a filter in accordance with the present invention. In yet another aspect of the present invention disclosed is use of zinc and copper in a ratio in the range of 1 :3 to 1 :25 in a filter as claimed in any one of the preceding claims 1 to 10 for reducing the number of viable bacteria, virus and cyst present in water by at least 6 log, 4 log and 3 log respectively. In yet another aspect of the present invention disclosed is use of zinc and copper in a ratio in the range of 1 :3 to 1 :25 in a filter as claimed in any one of the preceding claims 1 to 10 for providing water having not more than 1 ppm copper by weight. The invention will now be explained in more details with the help of non-limiting examples.

Examples Example-1 : Preparation of filter made of activated carbon, copper fibres and zinc fibres A block filter (Ex 1 ) according to the present invention was prepared by mixing about 90 grams powdered activated carbon, having average particle size in the range of 75 to 250 μηη and 90 grams of Intermediate activated carbon (IAC) with 108 grams water in a container to prepare a moist mixture.

To the obtained moist mixture of the filter medium 36 grams of polyethylene binder (GUR 2122 ex. Ticona GmbH) was added and the contents were mixed thoroughly to get a homogeneous blend. Twenty five (25) grams of copper fibres in the elemental form having diameter ranging from 120 to 850 μηη (equivalent to mesh size of -18 to +120), length ranging from 0.1 mm to 3 mm and aspect ratio from 3:1 to 25:1 was used for this experiment. The surface of the copper fibres was serrated. Purity of copper was 99.9% with the apparent density of fibres being in the range of 1 .2 to 2.5 gm/cm³. 5 grams of fibrous zinc in the elemental form with 99.9% purity having an aspect ratio from 3:1 to 25:1 was used for this experiment. The copper fibres and zinc fibres were slowly mixed with the homogeneous blend of filter medium and binder to get a uniform dispersion. Then the dispersion was transferred to a stainless steel cylindrical mould having 8.5 to 9 cm outer diameter and inner diameter of 1 to 1 .2 cm and a height of 8 to 9 cm. After putting the top lid in place, the mould was compressed at 2.4x10⁶ N/m² pressure with the help of hydraulic press and then it was kept inside an oven maintained at 250°C for 150 minutes. When the mould is cooled to room temperature the moulded filter was released. Thereafter, the moulded filter was attached to a plastic base plate having an orifice for exit of water for use in a water purification device intended to be used for reducing the number of viable microorganisms from water.

A comparative block filter (Ex A) was made as described above. In the comparative block filter fibrous zinc was not added.

The composition of the comparative block filter (Ex A) and the block filter in accordance with the present invention (Ex 1 ) is provided in Table 1 .

Table 1

Example 2: Effect of presence of elemental zinc on copper leach from a filter

A cylindrical block filter (Ex 1 ) prepared by a process as described in Example 1 and was fitted into a standard gravity fed water purifier. A cylindrical comparative block filter (Ex A) was also fitted into a similar standard gravity fed water purifier.

1000 liters of test water was passed through both the filters Ex 1 and Ex A. The composition of the test water is provided in Table 2. The top head flow rate in both the gravity fed water purifiers was in the range of 70 to l OOmL/minute. The copper concentration in the water collected after passing through the filter was measured and is provided in Table 3.

Table 2: Composition of test water

Turbidity (NTU) >10

Bicarbonate (ppm) Approx. 400 to 420

The concentration of copper in the output water was measured at regular intervals and is provided in Table 3. The concentration of zinc was also measured. The copper concentration was measured using an Inductively coupled plasma (ICP-OES) optical 5 emission spectroscopy. It was also verified using Spectraquant Pharo 300 which is a colorimetric technique.

Table 3

10

It is clearly seen from the data in Table 3 that when filters with fibrous copper are used for reducing the number of viable microorganisms in test water with high TDS and high concentrations of bicarbonates, the level of copper leach is not within acceptable limits at certain life points of the filter medium which in Table 3 is shown to be when between 15 70 to 250 liters of water has passed through the filter. In contrast a filter according to the present invention which includes fibrous zinc in the elemental form, consistently delivers treated water with copper amounts within acceptable limits (not more than 1 ppm by weight) throughout the life of the filter. It is further found that the level of zinc in the output water is also within the acceptable limits (not more than 5ppm by weight). Example 3: Effect of zinc on copper leach into treated water in presence of bicarbonate in the input water

A packed filter bed (Ex 2) according to the present invention was prepared with 90 grams of powdered activated carbon, 90 grams of IAC, 25 grams of fibrous copper in the elemental form and 5 grams of fibrous zinc in elemental form.

The powdered activated carbon had an average particle size in the range of 75 to 250 μηι.

Copper fibres with a diameter ranging from 120 to 850 μηη (equivalent to mesh size of - 18 to +120), length ranging from 0.1 mm to 3 mm and aspect ratio from 3:1 to 25:1 was used for this experiment. The surface of the copper fibres was serrated. Purity of copper was 99.9% with the apparent density of fibres being in the range of 1.2 to 2.5 gm/cm³. Zinc fibres with 99.9% purity having an aspect ratio from 3:1 to 25:1 was used for this experiment.

A comparative packed filter bed (Ex B) was made in a similar manner except that the comparative filter bed did not have fibrous zinc. The composition of the comparative packed filter bed (Ex B) and the filter bed according to the present invention (Ex 2) is provided in the Table 4 below.

Table 4

Input water with different concentrations of bicarbonate was passed through the two filter beds namely Ex 2 and Ex B in a batch process and the concentration of copper in the treated water was measured and is provided in Table 5. Table 5

The data in Table 5 clearly shows that when the fibrous zinc are present in a filter bed (Ex 2) according to the present invention having copper fibers, the copper leach into the treated water is within acceptable limits (not more than 1 ppm by weight) even at bicarbonate concentrations of 500 ppm in the input water while when treating water with bicarbonates levels of 300 to 500 ppm, copper leach is significantly higher and outside the acceptable limits in the comparative filter bed (Ex B) having copper fibers but no zinc fibres.

Example 4: Evaluation of filter having copper fibers along with zinc fibers or brass fibers. A block filter (Ex 3) according to the present invention was prepared by mixing about 200 grams powdered activated carbon with water in a container to prepare a moist mixture.

To the obtained moist mixture of the filter medium polyethylene binder (GUR 2122 ex. Ticona GmbH) was added and the contents were mixed thoroughly to get a homogeneous blend.

Twenty five (25) grams of copper fibres in the elemental form having diameter ranging from 120 to 850 μηη (equivalent to mesh size of -18 to +120), length ranging from 0.1 mm to 3 mm and aspect ratio from 3:1 to 25:1 was used for this experiment. The surface of the copper fibres was serrated. Purity of copper was 99.9% with the apparent density of fibres being in the range of 1 .2 to 2.5 gm/cm³. 5 grams of fibrous zinc in the elemental form with 99.9% purity having an aspect ratio from 3:1 to 25:1 was used for this experiment. The copper fibres and zinc fibres were slowly mixed with the homogeneous blend of filter medium and binder to get a uniform dispersion. Then the dispersion was transferred to a stainless steel cylindrical mould having 8.5 to 9 cm outer diameter and inner diameter of 1 to 1 .2 cm and a height of 8 to 9 cm. After putting the top lid in place, the mould was compressed at 2.4x10⁶ N/m² pressure with the help of hydraulic press and then it was kept inside an oven maintained at 250°C for 150 minutes. When the mould is cooled to room temperature the moulded filter was released.

Thereafter, the moulded filter was attached to a plastic base plate having an orifice for exit of water for use in a water purification device intended to be used for reducing the number of viable microorganisms from water.

A comparative block filter (Ex C) was made as described above. The only difference between the block filter (Ex 3) according to the present invention and the comparative block filter (Ex C) is that instead of zinc fibres, brass fibres having 30wt% zinc and an aspect ratio from 3:1 to 25:1 was used.

The composition of the comparative block filter (Ex C) and the block filter in accordance with the present invention (Ex 3) is provided in Table 6.

Table 6

Example 5: Effect of amount of zinc on copper leach from a filter A cylindrical block filter (Ex 3) prepared by a process as described in Example 4 was fitted into a standard gravity fed water purifier. A cylindrical comparative block filter (Ex C) was also fitted into a similar standard gravity fed water purifier.

5 100 liters of test water was passed through both the filters Ex 3 and Ex C. The

composition of the test water is as provided earlier in Table 2. The top head flow rate in both the gravity fed water purifiers was in the range of 70 to l OOmL/minute. The copper concentration in the water collected after passing through the filter was measured and is provided in Table 7.

0

The concentration of copper in the output water was measured at regular intervals and is provided in Table 7. The copper concentration was measured using an Inductively coupled plasma (ICP-OES) optical emission spectroscopy. It was also verified using Spectraquant Pharo 300 which is a colorimetric technique.

Table 7

The data on Table 7, clearly indicates that in the comparative filter (Ex C) having copper fibers and brass fibers with 30 wt% zinc, the level of copper leach increases0 with the amount of water treated through the filter while in the filter according to the present invention (Ex 3) having copper fibers and elemental zinc fibers the amount of copper leach is controlled and lower than the comparative filter.

The illustrated examples provide that at least some of the problems of prior art can be5 solved by using zinc in the elemental form or in the form of an alloy which alloy

comprises at least 70wt% of zinc along with copper in the elemental form, or in form of an alloy, or a salt of copper, which salt is sparingly soluble or insoluble in water, or a mixture thereof in a filter.

Claims

1. A filter for reducing the number of viable microorganisms in a fluid, comprising: i. a filter medium;

ii. copper, in elemental form, or in the form of an alloy, or a salt of copper, which salt is sparingly soluble or insoluble in water, or a mixture thereof; and,

iii. zinc, in elemental form, or in the form of an alloy which alloy comprises at least 70wt% of zinc.

2. A filter as claimed in Claim 1 wherein when copper is in elemental form or is in the form of an alloy, said copper is either granular or fibrous.

3. A filter as claimed in Claim 1 or 2 wherein the zinc is granular or fibrous.

4. A filter as claimed in Claim 3 wherein the copper and the zinc are both granular or wherein the copper and zinc are both fibrous.

5. A filter as claimed in claims 2, 3 or 4 wherein the copper and zinc are fibrous, copper has an aspect ratio in a range of 3:1 to 200:1 and zinc has an aspect ratio in range of 3:1 to 200:1.

6. A filter as claimed in claims 2, 3 or 4 wherein the copper and zinc are granular; copper and zinc each having a particle size distribution such that at least 90 number% of the particles have a particle size of 50 micrometers to 500 micrometers.

7. A filter as claimed in any one of the preceding claims wherein the total amount of copper is 4 to 10wt% of the filter.

8. A filter as claimed in any one of the preceding claims wherein the amount of zinc is from 0.1 to 3wt% of the filter.

9. A filter as claimed in any one of the preceding claims 1 to 8 wherein the filter medium is selected from alumina, zeolite, diatomaceous earth, silicate, aluminosilicate, titanate, calcium hydroxyapatite, perlite, talc, activated carbon, sand, clay or ceramic.

10. A filter as claimed in any one of the preceding claims 1 to 8 wherein the filter comprises a binder.

1 1. A process for preparing a filter as claimed in any one of the preceding claims comprising the steps of:

i. mixing a filter medium, copper, in elemental form, or in the form of an alloy, or a salt of copper, which salt is sparingly soluble or insoluble in water, or a mixture thereof; and, zinc, in elemental form or in the form of an alloy which alloy comprises at least 70wt% of zinc to obtain a mix; ii. compacting the mix in a mould; and,

iii. moulding the mix to form the filter.

12. A process as claimed in claim 1 1 wherein:

i. the mixing step includes a further step of adding a binder;

ii. the compacting step includes applying a pressure in the range of

3.9x10⁵ to 2.9x10⁶ N/m² to the mix in the mould; and,

iii. the moulding step includes heating the mould in an atmosphere

maintained at a temperature of 150°C to 400°C.

13. A method of reducing the number of viable microorganisms present in water, by passing the water through a filter as claimed in any one of the claims 1 to 10.

14. Use of zinc and copper in a ratio by weight in the range of 1 :3 to 1 :25 in a filter as claimed in any one of the preceding claims 1 to 10 for reducing the number of viable bacteria, virus and cyst present in water by at least 6 log, 4 log and 3 log respectively.

15. Use of zinc and copper in a ratio by weight in the range of 1 :3 to 1 :25 in a filter as claimed in any one of the preceding claims 1 to 10 for providing water containing not more than 1 ppm of copper by weight.