Title of Invention	A FILTER ASSEMBLY AND A METHOD OF FILTERING LIQUIDS
Abstract	The invention relates to a filter assembly for filtration of liquids that provides water, which is substantially free of particulate contaminants including microorganisms like cysts, while providing for relatively high flow rates.There exists a need to have a simple, easy-to-manufacture and cost effective gravity-fed water filter which can be used over a long period of time while providing consistently high flow rates and also ensuring the removal of harmful micro-organisms like cysts. In one aspect, the invention provides for a filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks comprising substantially identical composition. In another aspect, the present invention provides a filter for filtration of liquids by gravity comprising: (a) a washable or replaceable sediment filter for removing particulates generally above 3 microns and (b) filter assembly of the invention. such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly.

Title of Invention

A FILTER ASSEMBLY AND A METHOD OF FILTERING LIQUIDS

Abstract

The invention relates to a filter assembly for filtration of liquids that provides water, which is substantially free of particulate contaminants including microorganisms like cysts, while providing for relatively high flow rates.There exists a need to have a simple, easy-to-manufacture and cost effective gravity-fed water filter which can be used over a long period of time while providing consistently high flow rates and also ensuring the removal of harmful micro-organisms like cysts. In one aspect, the invention provides for a filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks comprising substantially identical composition. In another aspect, the present invention provides a filter for filtration of liquids by gravity comprising: (a) a washable or replaceable sediment filter for removing particulates generally above 3 microns and (b) filter assembly of the invention. such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly.

Full Text	C2136 FORM - 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENT RULES, 2003 COMPLETE SPECIFICATION (See Section 10 and Rule 13) A FILTER ASSEMBLY AND METHOD OF FILTERING LIQUIDS HINDUSTAN LEVER LIMITED, a company incorporated under the Indian Companies Act, 1913 and having its registered office at Hindustan Lever House, 165/166, Backbay Reclamation, Mumbai -400 020, Maharashtra, India The following specification particularly describes the nature of the invention and the manner in which it is to be performed. FIELD OF INVENTION The present invention relates to a filter assembly for filtration of liquids and more particularly to a cost-effective gravity fed filter assembly that provides water, which is substantially free of particulate contaminants including microorganisms like cysts, while providing for relatively high flow rates. BACKGROUND AND PRIOR ART Liquids typically contain contaminants, which include particulate matter, chemicals and microorganisms. In liquids like water, especially drinking water, it is desirable to remove the harmful contaminants from the liquids before consuming them for maintenance of good health. Several different methods are known for purification of water, based on which, many devices and apparatus have been designed and are also commercially available. These methods and devices vary depending on the type of impurities present in water. Particulate matters, which are generally larger than 3 microns are filtered using cloth filters a depth filters e.g. a bed of activated carbon or clay which has been moulded into a block. Carbon and clay additionally have the advantage of being highly porous materials which also facilitates the removal of soluble impurities by adsorption e.g. dissolved organic compounds, compounds that make the water have an offensive odour and taste, pesticide and pesticide residues, etc. In addition to particulate mater, it is also desirable to remove or kill the harmful microorganisms like protozoan cysts and bacteria present in potable water. Several methods are known, which are employed towards this end. In the absence of a device, water is generally boiled to kill the microorganisms, but this method is cost-intensive and makes the water have a poor taste. Biocides like halogens e.g. chlorine and iodine, are sometimes used to kill the microorganisms. These are very effective in killing the microorganisms but additional precautions have to be taken to ensure that the water is freed of remaining biocide before it is consumed. Traces of chlorine in water lends bad odor and is corrosive to the human body, while intake of excess iodine is known to be harmful to some individuals. Ultra-violet radiation has also been 2 used in many water-purification devices to kill micro-organisms. But ultraviolet radiation requires continuous availability of electric supply which may not be available at all times, everywhere. The present inventors have sought to develop a filtration assembly comprising a series of molded filter blocks which is capable of not only filtering particulate matter like dust but also the harmful microorganisms present in water, in a cost-effective manner. US4753728 (Amway, 11988) describes a double shell filter comprising an inner shell of 80 to 400 U.S. mesh screen carbon particles and an outer shell of bonded 20 to 80 mesh screen carbon particles wherein the inner and outer shells are bonded internally to each other with a specific high molecular weight polymeric binder. This publication teaches use of gradation of particle sizes of carbon particles in a composite carbon block wherein the outer shell functions to filter larger particles and the inner shell functions to filter smaller particles thereby improving the overall filtration capability of the filter. The carbon block in US4753728 is moulded as a composite and so does not provide for replacement of a part of the. block and also suffers from the drawback of complexities at the manufacturing end. US5164085 (NRG Enterprises, 1992) describes a filter cartridge for water purification consisting of several layers of filter material with successively smaller pore size, with i the outer layer being a pre-filtration material with a pore size of approximately 10 microns, a central layer being an extruded carbon filter with a pore size of about 5 microns, preferably with a chemical agent for removal of heavy metals and an inner layer being a ceramic filter with a pore size of about 0.9 microns preferably with impregnated silver for biostatic efficacy. This publication, in addition to using gradation of particle sizes to selectively remove particles of different sizes, uses different materials over its various parts thereby having the problem of manufacturing complexity. US5328609 (Magnusson 1994) describes a manifold mounted liquid filtration system including a disposable filter cartridge having first and second radial flow filtration stages containing filtration media of uniform porosity. A first 3 suspended bacteria described in this pub stage includes a pair of annular concentrically mounted, fibrous sediment and cast carbonaceous filter media and the second stage includes an annular cast carbonaceous filter media. While the first stage is used to remove suspended sediments, lead and other heavy metals, the second stage removes and other organic impurities. The filtration system ication requires the entire filter cartridge to be disposed when completely choked and replaced with a new cartridge which would be cost-extensive. US5151180 (Cuno, 1992) relates to a filter device for use in a residential water supply system which includes a container having an enclosed cavity, and includes a filter unit having a two-stage filter having a first radial flow filter subassembly and a second axial flow filter subassembly. This specific configuration is adapted to minimize the loss in pressure head due to excessive number of turns usually present in filter devices thereby providing high flow rates. Although this filter device minimizes frictional losses with the help of a suitable filter configuration, it is not adapted to filter microorganisms like bacteria and virus' while minimizing the overall cost and providing high flow rates. US 2003/0213750 (Koslow, 2003) describes a filter medium for enhanced removal of bacteria and virus comprising a microporous structure having a mean flow path of less than or equal to about 1 micron; and a microbiological interception enhancing agent comprising a cationic metal complex capable of imparting positive charge on at least a portion of the microporous structure. The process to make these filters is cost-extensive and requires complexity and high degree of quality control in manufacture and would be difficult to implement in simple household gravity fed water filter systems. JP11104623 (Tokyo Yogyo, 1999) describes an activated carbon block filter water purifier comprising! an outer cylinder block filter composed of crushed granular carbon which has low capacity for adsorption but has a long durability/life and an inner cylinder block filter based on pitch type fibrous activated carbon which has high capacity for adsorption but low durability/life. 4 The inner block which exhausts faster is replaced more often than the outer block, thereby maintaining enhanced adsorption of the impurities. This publication uses two carbon blocks of different compositions for trapping/ adsorbing different types of impurities. Importantly, it does not teach filtration of water free of microorganisms, like cysts. There thus exists a need to have a simple, easy-to-manufacture and cost effective gravity-fed water filter which can be used over a long period of time while providing consistently high flow rates and also ensuring the removal of harmful micro-organisms like cysts. Some filters e.g. one in US4753728 have solved this problem by providing a gradient in the pore size of the filter such that the water first encounters sections having larger pores wherein the larger particles are trapped while the filter has smaller pore sizes towards the exit of the filter where the smaller particles are trapped. This system suffers from the problem that the entire filter will have to be discarded once the flow rate through the filter reduces, which is a cost extensive proposition. i i '■■'• ••• The present inventors! have developed a novel filter assembly, which is uniquely configured to maximize the filtration efficiency and the throughput of the liquid to be filtered while minimizing the amount of filter media material being consumed to achieve these ends. It is thus the basic object of the present invention to provide for a filtration unit which would provide for the desired particulate removal, including microorganisms, like cysts, while giving the desired flow rate. i i Another object of the present invention is directed to provide a gravity fed filter which would provide for effective filtration of up to 99.9% removal (three log removal) of even chlorine resistant cysts such as Cryptosporidium parvum and Giardia lamblia which are; in the size range of 3 to 6 microns. 5 Yet further object is directed to the gravity fed filtration system which would be simple to manufacture and would be cost effective and which would meet the present day extensive demand for such filters for domestic/rural use, thus i providing safe drinking water for one and all. SUMMARY OF THE INVENTION According to one aspect of the invention there is provided a filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks comprising substantially identical composition. i The filter blocks are preferably carbon block filters. According to another aspect of the present invention, there is provided a filter for filtration of liquids by gravity comprising: (a) a washable or replaceable sediment filter for removing particulates generally above 3 microns and (b) said filter assembly such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly. According to yet another aspect of the present invention there is provided a method of filtering liquids comprising (a) passing the input liquid through said filter assembly and (b) replacing the first filter block with a new filter block whenever there is substantial reduction in the flow rate of the output water thereby consistently obtaining high flow rates of filtered liquid from the filter assembly. i DETAILED DESCRIPTION OF THE INVENTION The first aspect of the invention provides for a filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks comprising substantially identical composition. The invention is especially suitable for gravity filtration of water, which is contaminated with particles including dust and harmful microorganisms e.g. protozoan cyst like Cryptosporidium and Giardia. The filter assembly provides three log removal of cysts from water. 6 Log removal is defined as the log 10 (logarithmic to the base 10) of the number of particles fed to the filter divided by the number of particles exiting the filter. The number of detachably connected filters in series could be any number, but preferably is in the range of 2 to 20 filter blocks, more preferably 2 to 8 filter blocks. The filter blocks can be made of any material, preferably carbon, ceramic, clay, polyester or polypropylene, more preferably carbon. When carbon is the material used to make the filter block, it is preferred to use activated carbon, more preferred material being powder activated carbon. The block filters for use in the filter assembly of the invention preferably comprises powder activated carbon (PAC) and a binder material having a Melt Flow Rate (MFR) less than 5g/10 minutes, preferably less than 1 g/10 minutes. The melt-flow rate (MFR) is measured using ASTM D 1238 (ISO 1133) test. The test measures the flow of a molten polymer through an extrusion plastometer under specific temperature and load conditions. The extrusion plastometer consists of a vertical cylinder with a small die of 2 mm at the bottom and a removable piston at the top. A charge of material is placed in the cylinder and preheated for several minutes. The piston is placed on top of the molten polymer and its weight forces the polymer through the die and on to a collecting plate. The time interval for the test ranges from 15 seconds to 6 minutes in order to accommodate the different viscosities of plastics. Temperatures used are 220, 250 and 300 °C (428, 482 and 572°F). Loads used are 1.2, 5 and 10 kg. The amount of polymer collected after a specific interval is weighed and normalized to the number of grams that would have been extruded in 10 minutes: melt flow rate is expressed in grams per reference time. The binder material is preferably thermoplastic polymer having low MFR values above described. Suitable examples include ultra high molecular weight polymers, preferably polyethylene or polypropylene having low MFR values as described above. The molecular weight is preferably in the range of 106 to 109 g/mole Binders of this class are commercially available under the trade names HOSTALEN from Tycona GMBH, GUR, Sunfine (from Asahi, Japan), Hizex (from Mitsubishi) and from Brasken Corp (Brazil). Other 7 suitable binders include LDPE sold as Lupolen (from Basel Polyolefins) and LLDPE from Qunos' (Australia). The bulk density of the binder material is preferably less than or equal to 0.6 g/cm3, more preferably less than or equal to 0.5 g.cm3, and further more preferably less than or equal to 0.25 g/cm3. The binder material preferably has a particle size distribution substantially the same as that of the PAC but the particles passing 200 mesh is preferably less than 40 wt%, more preferably less than 30 wt%. The carbon block when used preferably comprises powder activated carbon (PAC) having particle size such that 95 wt % of the particles pass through 50 mesh and not more than 13%, preferably not more than 12%, more preferably not more than 10%, passes through 200 mesh. The PAC is preferably selected from bituminous coal, coconut shell, wood, or petroleum tar. The surface area of the PAC is preferably selected such that it exceeds 500 m2/g, more preferably exceeds 1000 m2/g. Preferably, the PAC has a size uniformity co-efficient of less than 2, more preferably less than 1.5, Carbon tetrachloride-number exceeding 50%, more preferably exceeding 60%. The PAC preferably has Iodine number greater than 800, more preferably greater than 1000. The filter media preferably has a particle size distribution profile across its height. It is preferred that the PAC particles are distributed across the height of the carbon block such that 55 to 80 wt %, preferably 55 to 70 wt% of the PAC particles in the particle size range of 100 to 200 mesh are present in the lower 50 volume% of the carbon block filter media. i It is preferred that the! PAC particles are distributed across the height of the carbon block such that 55 to 95 %, more preferably 60 to 95 % of the PAC particles in the particle size range smaller than 200 mesh are present in the lower 50 volume % of the carbon block filter media. The proportion of the! binder material to the PAC particles by weight is chosen such that it is preferably in the range of 1:1 to 1:10, more preferably in the range of 1: 2 to 1:6. ; i By way of the above filtration media of the invention it is possible to attain average flow rate of i 100-300 ml/min of water, under gravity, from a starting height of 200 mm down to 50 mm, preferably 120-200 ml/min., without compromising on the requirements of removal of particulate material including microorganisms, and chemical contaminants. The carbon block filter can be of desired shape and size depending on the end application/ uses. Suitable shapes include flat circular disc of low thickness, square disc of low thickness, low height tapered flat disc, cylinder, solid cone, hollow cone. In a preferred aspect, the side walls of the carbon filter blocks are fluted, pleated or corrugated so as to increase the effective surface area of contact with the water to be treated. This would enhance the efficiency of the filer blocks, vis-a-vis blocks having regular surface morphologies. Any known process for making carbon block filters can be used. A suitable process of preparation of carbon block filters for use in the filter assembly of the invention has been disclosed in our co-pending application 320/MUM/2004. A desirable construction of the filter assembly is such that each carbon block filter is fixedly housed in a collar/bracket, said collar/bracket capable of being detachably connectable to each other with screw threaded joints or snap-fit joints. 9 Another aspect of the invention provides for a filter for filtration of liquids by gravity comprising: ; (a) a washable or replaceable sediment filter for removing particulates generally above 3 microns and (b) a filter assembly of the invention such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly. The sediment filter can be washable or replaceable and is preferably made of i woven or non-woven fabric, more preferably non-woven fabric having microporous structure. This sediment filter ensures filtration of particles generally above 3 microns. The sediment filter can be washed and rinsed under flowing tap water or by using a small amount (0.1-10 g/L) of fabric wash detergent in water. This facilitates wider and more extensive application of the filter assembly of the invention. The present inventors have determined that in the filter assembly of the invention, the reduction in flow rate of the liquid exiting the filter assembly is principally due to choking of the pores in the first filter block. On replacement of the first filter block with a new carbon block, high flow rates of the liquid is again obtained by the filter assembly of the invention. Thus according to yet another aspect of the invention there is provided a method of filtering liquids comprising; (a) passing the input liquid through a filter assembly of the invention and (b) replacing the first filter block with a new filter block whenever there is substantial reduction in the flow rate of the output water thereby consistently obtaining high flow rates of filtered liquid from the filter assembly. The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to the following non-limiting exemplary embodiments of the invention: 10 BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, Fig. 1 is a schematic of a filter assembly with the various carbon block filters assembled Fig. 2 is a schematic of the filter assembly of Fig. 1 with the first carbon block filter detached from the filter assembly. DETAILED DESCRITION OF THE DRAWINGS The views of Fig 1 and Fig 2 depict a preferred embodiment of the filter assembly of the invention. Referring first to the view of Fig.1, the filter assembly (FA) comprises a series of four carbon block filters (F1, F2, F3, and F4) each having substantially identical composition and detachably connected to each other. The carbon block filters are fixedly housed in. brackets (B1, B2, B3, B4) which are provided with threaded joints (T) such that said brackets are detachably connectable to each other. The view of Fig. 2 shows the filter assembly disassembled such that the carbon block filter F1 is detached from the filter assembly. When in use, the filter assembly (FA) of the invention is attached to the bottom of a reservoir of contaminated water (WT). The water flows in the direction indicated by the arrow (IN) and is filtered after passing through a series of carbon block filters of the filter assembly to exit the filter assembly in the direction marked by the arrow (0). After a large amount of water has been filtered and there is substantial reduction in the flow rate of the water, the filter assembly is disassembled, as shown in Fig.2. The filter block (F1) which accounts for the maximum amount of choking is replaced with a new filter block. Very high flow rates are thereafter obtained. The filter assembly of the invention comprising the detachably connectable carbon block filters in series thus necessitates replacement of only a part of the filter assembly for 11 continuously obtaining high flow rates, as opposed to filters of the prior art where the entire filter would have to be replaced, thereby enabling high cost-effectiveness. 12 We claim: 1. A filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks, comprising substantially identical composition. 2. A filter assembly as claimed in claim 1 comprising 2 to 20 filter blocks. 3. A filter assembly as claimed in any preceding claim wherein each said filter block is housed in a collar or bracket, said collars or brackets capable of being detachably connectable to each other through screw threaded joints or snap-fit joints. 4. A filter assembly as claimed in any preceding claim wherein each said filter block is a cylindrical disc, annular cylinder or a hollow dome. 5. A filter assembly as claimed in any preceding claim wherein each said filter block comprises, • powder activated carbon having particle size such that 95 wt% of the particles pass through 50 mesh and not more than 13% particles pass through 200 mesh; • binder material having Melt Flow Rate less than 1 g/10 minutes. 6. A filter assembly as claimed in claim 5 wherein said binder material is high molecular; weight polyethylene or high molecular weight polypropylene having molecular weight between 106 to 109 g/mole. 13 7. A filter for filtration of liquids by gravity comprising: (a) a washable or replaceable sediment filter for removing particulates, generally above 3 microns and (b) a filter assembly as claimed in any one of the preceding claims, such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly. 8. A filter as claimed in claim 7 wherein said sediment filter is made of non-woven fabric having micropores. 9. A method of filtering liquids comprising (a) passing the input liquid through a filter assembly as claimed in any preceding claim 1 to 6; (b) replacing the first filter block with a new filter block whenever there is substantial reduction in the flow rate of the output water thereby consistently obtaining high flow rates of filtered liquid from the filter assembly. 10. A filter assembly substantially as herein described with reference to the accompanying figures. Dated this 30th day of June 2006. Hindustan Lever Limited 14 Abstract The invention relates to a filter assembly for filtration of liquids that provides water, which is substantially free of particulate contaminants including microorganisms like cysts, while providing for relatively high flow rates. There exists a need to have a simple, easy-to-manufacture and cost effective gravity-fed water filter which can be used over a long period of time while providing consistently high flow rates and also ensuring the removal of harmful micro-organisms like cysts. In one aspect, the invention provides for a filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks comprising substantially identical composition. In another aspect, the present invention provides a filter for filtration of liquids by gravity comprising: (a) a washable or replaceable sediment filter for removing particulates generally above 3 microns and (b) filter assembly of the invention. such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly.

Full Text

C2136
FORM - 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
A FILTER ASSEMBLY AND METHOD OF FILTERING LIQUIDS
HINDUSTAN LEVER LIMITED, a company incorporated under the Indian Companies Act, 1913 and having its registered office at Hindustan Lever House, 165/166, Backbay Reclamation, Mumbai -400 020, Maharashtra, India
The following specification particularly describes the nature of the invention and
the manner in which it is to be performed.

FIELD OF INVENTION
The present invention relates to a filter assembly for filtration of liquids and more particularly to a cost-effective gravity fed filter assembly that provides water, which is substantially free of particulate contaminants including microorganisms like cysts, while providing for relatively high flow rates.
BACKGROUND AND PRIOR ART
Liquids typically contain contaminants, which include particulate matter, chemicals and microorganisms. In liquids like water, especially drinking water, it is desirable to remove the harmful contaminants from the liquids before consuming them for maintenance of good health.
Several different methods are known for purification of water, based on which, many devices and apparatus have been designed and are also commercially available. These methods and devices vary depending on the type of impurities present in water. Particulate matters, which are generally larger than 3 microns are filtered using cloth filters a depth filters e.g. a bed of activated carbon or clay which has been moulded into a block. Carbon and clay additionally have the advantage of being highly porous materials which also facilitates the removal of soluble impurities by adsorption e.g. dissolved organic compounds, compounds that make the water have an offensive odour and taste, pesticide and pesticide residues, etc.
In addition to particulate mater, it is also desirable to remove or kill the harmful microorganisms like protozoan cysts and bacteria present in potable water. Several methods are known, which are employed towards this end. In the absence of a device, water is generally boiled to kill the microorganisms, but this method is cost-intensive and makes the water have a poor taste. Biocides like halogens e.g. chlorine and iodine, are sometimes used to kill the microorganisms. These are very effective in killing the microorganisms but additional precautions have to be taken to ensure that the water is freed of remaining biocide before it is consumed. Traces of chlorine in water lends bad odor and is corrosive to the human body, while intake of excess iodine is known to be harmful to some individuals. Ultra-violet radiation has also been
2

used in many water-purification devices to kill micro-organisms. But ultraviolet radiation requires continuous availability of electric supply which may not be available at all times, everywhere. The present inventors have sought to develop a filtration assembly comprising a series of molded filter blocks which is capable of not only filtering particulate matter like dust but also the harmful microorganisms present in water, in a cost-effective manner.
US4753728 (Amway, 11988) describes a double shell filter comprising an inner shell of 80 to 400 U.S. mesh screen carbon particles and an outer shell of bonded 20 to 80 mesh screen carbon particles wherein the inner and outer shells are bonded internally to each other with a specific high molecular weight polymeric binder. This publication teaches use of gradation of particle sizes of carbon particles in a composite carbon block wherein the outer shell
functions to filter larger particles and the inner shell functions to filter smaller

particles thereby improving the overall filtration capability of the filter. The
carbon block in US4753728 is moulded as a composite and so does not
provide for replacement of a part of the. block and also suffers from the
drawback of complexities at the manufacturing end.
US5164085 (NRG Enterprises, 1992) describes a filter cartridge for water
purification consisting of several layers of filter material with successively
smaller pore size, with i the outer layer being a pre-filtration material with a
pore size of approximately 10 microns, a central layer being an extruded
carbon filter with a pore size of about 5 microns, preferably with a chemical
agent for removal of heavy metals and an inner layer being a ceramic filter
with a pore size of about 0.9 microns preferably with impregnated silver for
biostatic efficacy. This publication, in addition to using gradation of particle
sizes to selectively remove particles of different sizes, uses different
materials over its various parts thereby having the problem of manufacturing
complexity.
US5328609 (Magnusson 1994) describes a manifold mounted liquid filtration system including a disposable filter cartridge having first and second radial flow filtration stages containing filtration media of uniform porosity. A first
3

suspended bacteria described in this pub
stage includes a pair of annular concentrically mounted, fibrous sediment and cast carbonaceous filter media and the second stage includes an annular cast carbonaceous filter media. While the first stage is used to remove suspended sediments, lead and other heavy metals, the second stage removes
and other organic impurities. The filtration system ication requires the entire filter cartridge to be disposed
when completely choked and replaced with a new cartridge which would be
cost-extensive.
US5151180 (Cuno, 1992) relates to a filter device for use in a residential water supply system which includes a container having an enclosed cavity, and includes a filter unit having a two-stage filter having a first radial flow filter subassembly and a second axial flow filter subassembly. This specific configuration is adapted to minimize the loss in pressure head due to
excessive number of turns usually present in filter devices thereby providing

high flow rates. Although this filter device minimizes frictional losses with the
help of a suitable filter configuration, it is not adapted to filter microorganisms
like bacteria and virus' while minimizing the overall cost and providing high
flow rates.
US 2003/0213750 (Koslow, 2003) describes a filter medium for enhanced removal of bacteria and virus comprising a microporous structure having a mean flow path of less than or equal to about 1 micron; and a microbiological interception enhancing agent comprising a cationic metal complex capable of imparting positive charge on at least a portion of the microporous structure. The process to make these filters is cost-extensive and requires complexity and high degree of quality control in manufacture and would be difficult to implement in simple household gravity fed water filter systems.
JP11104623 (Tokyo Yogyo, 1999) describes an activated carbon block filter water purifier comprising! an outer cylinder block filter composed of crushed granular carbon which has low capacity for adsorption but has a long durability/life and an inner cylinder block filter based on pitch type fibrous activated carbon which has high capacity for adsorption but low durability/life.
4

The inner block which exhausts faster is replaced more often than the outer block, thereby maintaining enhanced adsorption of the impurities. This publication uses two carbon blocks of different compositions for trapping/ adsorbing different types of impurities. Importantly, it does not teach filtration of water free of microorganisms, like cysts.
There thus exists a need to have a simple, easy-to-manufacture and cost
effective gravity-fed water filter which can be used over a long period of time
while providing consistently high flow rates and also ensuring the removal of
harmful micro-organisms like cysts. Some filters e.g. one in US4753728
have solved this problem by providing a gradient in the pore size of the filter
such that the water first encounters sections having larger pores wherein the
larger particles are trapped while the filter has smaller pore sizes towards the
exit of the filter where the smaller particles are trapped. This system suffers
from the problem that the entire filter will have to be discarded once the flow
rate through the filter reduces, which is a cost extensive proposition.
i
i '■■'• •••
The present inventors! have developed a novel filter assembly, which is uniquely configured to maximize the filtration efficiency and the throughput of the liquid to be filtered while minimizing the amount of filter media material being consumed to achieve these ends.
It is thus the basic object of the present invention to provide for a filtration unit which would provide for the desired particulate removal, including microorganisms, like cysts, while giving the desired flow rate.
i i
Another object of the present invention is directed to provide a gravity fed filter which would provide for effective filtration of up to 99.9% removal (three log removal) of even chlorine resistant cysts such as Cryptosporidium parvum and Giardia lamblia which are; in the size range of 3 to 6 microns.
5

Yet further object is directed to the gravity fed filtration system which would be simple to manufacture and would be cost effective and which would meet the present day extensive demand for such filters for domestic/rural use, thus
i
providing safe drinking water for one and all.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks comprising substantially identical composition.
i
The filter blocks are preferably carbon block filters.
According to another aspect of the present invention, there is provided a filter
for filtration of liquids by gravity comprising:
(a) a washable or replaceable sediment filter for removing particulates generally above 3 microns and
(b) said filter assembly
such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly.
According to yet another aspect of the present invention there is provided a method of filtering liquids comprising
(a) passing the input liquid through said filter assembly and
(b) replacing the first filter block with a new filter block whenever there is substantial reduction in the flow rate of the output water
thereby consistently obtaining high flow rates of filtered liquid from the filter assembly.
i
DETAILED DESCRIPTION OF THE INVENTION
The first aspect of the invention provides for a filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks comprising substantially identical composition. The invention is especially suitable for gravity filtration of water, which is contaminated with particles including dust and harmful microorganisms e.g. protozoan cyst like Cryptosporidium and Giardia. The filter assembly provides three log removal of cysts from water.
6

Log removal is defined as the log 10 (logarithmic to the base 10) of the number of particles fed to the filter divided by the number of particles exiting the filter. The number of detachably connected filters in series could be any number, but preferably is in the range of 2 to 20 filter blocks, more preferably 2 to 8 filter blocks. The filter blocks can be made of any material, preferably carbon, ceramic, clay, polyester or polypropylene, more preferably carbon. When carbon is the material used to make the filter block, it is preferred to use activated carbon, more preferred material being powder activated carbon.
The block filters for use in the filter assembly of the invention preferably comprises powder activated carbon (PAC) and a binder material having a Melt Flow Rate (MFR) less than 5g/10 minutes, preferably less than 1 g/10 minutes. The melt-flow rate (MFR) is measured using ASTM D 1238 (ISO 1133) test. The test measures the flow of a molten polymer through an extrusion plastometer under specific temperature and load conditions. The extrusion plastometer consists of a vertical cylinder with a small die of 2 mm at the bottom and a removable piston at the top. A charge of material is placed in the cylinder and preheated for several minutes. The piston is placed on top of the molten polymer and its weight forces the polymer through the die and on to a collecting plate. The time interval for the test ranges from 15 seconds to 6 minutes in order to accommodate the different viscosities of plastics. Temperatures used are 220, 250 and 300 °C (428, 482 and 572°F). Loads used are 1.2, 5 and 10 kg. The amount of polymer collected after a specific interval is weighed and normalized to the number of grams that would have been extruded in 10 minutes: melt flow rate is expressed in grams per reference time.
The binder material is preferably thermoplastic polymer having low MFR values above described. Suitable examples include ultra high molecular weight polymers, preferably polyethylene or polypropylene having low MFR values as described above. The molecular weight is preferably in the range of 106 to 109 g/mole Binders of this class are commercially available under the trade names HOSTALEN from Tycona GMBH, GUR, Sunfine (from Asahi, Japan), Hizex (from Mitsubishi) and from Brasken Corp (Brazil). Other
7

suitable binders include LDPE sold as Lupolen (from Basel Polyolefins) and LLDPE from Qunos' (Australia). The bulk density of the binder material is preferably less than or equal to 0.6 g/cm3, more preferably less than or equal to 0.5 g.cm3, and further more preferably less than or equal to 0.25 g/cm3. The binder material preferably has a particle size distribution substantially the same as that of the PAC but the particles passing 200 mesh is preferably less than 40 wt%, more preferably less than 30 wt%.
The carbon block when used preferably comprises powder activated carbon (PAC) having particle size such that 95 wt % of the particles pass through 50 mesh and not more than 13%, preferably not more than 12%, more preferably not more than 10%, passes through 200 mesh. The PAC is preferably selected from bituminous coal, coconut shell, wood, or petroleum tar. The surface area of the PAC is preferably selected such that it exceeds 500 m2/g, more preferably exceeds 1000 m2/g.
Preferably, the PAC has a size uniformity co-efficient of less than 2, more preferably less than 1.5, Carbon tetrachloride-number exceeding 50%, more preferably exceeding 60%. The PAC preferably has Iodine number greater than 800, more preferably greater than 1000.
The filter media preferably has a particle size distribution profile across its height. It is preferred that the PAC particles are distributed across the height of the carbon block such that 55 to 80 wt %, preferably 55 to 70 wt% of the PAC particles in the particle size range of 100 to 200 mesh are present in the lower 50 volume% of the carbon block filter media.
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It is preferred that the! PAC particles are distributed across the height of the carbon block such that 55 to 95 %, more preferably 60 to 95 % of the PAC particles in the particle size range smaller than 200 mesh are present in the lower 50 volume % of the carbon block filter media.

The proportion of the! binder material to the PAC particles by weight is chosen such that it is preferably in the range of 1:1 to 1:10, more preferably in the
range of 1: 2 to 1:6. ;
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By way of the above filtration media of the invention it is possible to attain average flow rate of i 100-300 ml/min of water, under gravity, from a starting height of 200 mm down to 50 mm, preferably 120-200 ml/min., without compromising on the requirements of removal of particulate material including microorganisms, and chemical contaminants.
The carbon block filter can be of desired shape and size depending on the end application/ uses. Suitable shapes include flat circular disc of low thickness, square disc of low thickness, low height tapered flat disc, cylinder, solid cone, hollow cone. In a preferred aspect, the side walls of the carbon filter blocks are fluted, pleated or corrugated so as to increase the effective surface area of contact with the water to be treated. This would enhance the efficiency of the filer blocks, vis-a-vis blocks having regular surface morphologies.
Any known process for making carbon block filters can be used. A suitable process of preparation of carbon block filters for use in the filter assembly of the invention has been disclosed in our co-pending application 320/MUM/2004.
A desirable construction of the filter assembly is such that each carbon block filter is fixedly housed in a collar/bracket, said collar/bracket capable of being detachably connectable to each other with screw threaded joints or snap-fit joints.
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Another aspect of the invention provides for a filter for filtration of liquids by gravity comprising: ;
(a) a washable or replaceable sediment filter for removing particulates generally above 3 microns and
(b) a filter assembly of the invention
such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly.
The sediment filter can be washable or replaceable and is preferably made of
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woven or non-woven fabric, more preferably non-woven fabric having microporous structure. This sediment filter ensures filtration of particles generally above 3 microns. The sediment filter can be washed and rinsed under flowing tap water or by using a small amount (0.1-10 g/L) of fabric wash detergent in water. This facilitates wider and more extensive application of the filter assembly of the invention.
The present inventors have determined that in the filter assembly of the invention, the reduction in flow rate of the liquid exiting the filter assembly is principally due to choking of the pores in the first filter block. On replacement of the first filter block with a new carbon block, high flow rates of the liquid is again obtained by the filter assembly of the invention.
Thus according to yet another aspect of the invention there is provided a method of filtering liquids comprising;
(a) passing the input liquid through a filter assembly of the invention and
(b) replacing the first filter block with a new filter block whenever there is substantial reduction in the flow rate of the output water thereby consistently obtaining high flow rates of filtered liquid from the filter assembly.
The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to the following non-limiting exemplary embodiments of the invention:
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BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
Fig. 1 is a schematic of a filter assembly with the various carbon block filters assembled
Fig. 2 is a schematic of the filter assembly of Fig. 1 with the first carbon block filter detached from the filter assembly.
DETAILED DESCRITION OF THE DRAWINGS
The views of Fig 1 and Fig 2 depict a preferred embodiment of the filter assembly of the invention.
Referring first to the view of Fig.1, the filter assembly (FA) comprises a series of four carbon block filters (F1, F2, F3, and F4) each having substantially identical composition and detachably connected to each other. The carbon block filters are fixedly housed in. brackets (B1, B2, B3, B4) which are provided with threaded joints (T) such that said brackets are detachably connectable to each other.
The view of Fig. 2 shows the filter assembly disassembled such that the carbon block filter F1 is detached from the filter assembly.
When in use, the filter assembly (FA) of the invention is attached to the bottom of a reservoir of contaminated water (WT). The water flows in the direction indicated by the arrow (IN) and is filtered after passing through a series of carbon block filters of the filter assembly to exit the filter assembly in the direction marked by the arrow (0). After a large amount of water has been filtered and there is substantial reduction in the flow rate of the water, the filter assembly is disassembled, as shown in Fig.2. The filter block (F1) which accounts for the maximum amount of choking is replaced with a new filter block. Very high flow rates are thereafter obtained. The filter assembly of the invention comprising the detachably connectable carbon block filters in series thus necessitates replacement of only a part of the filter assembly for
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continuously obtaining high flow rates, as opposed to filters of the prior art where the entire filter would have to be replaced, thereby enabling high cost-effectiveness.
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We claim:
1. A filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks, comprising substantially identical composition.
2. A filter assembly as claimed in claim 1 comprising 2 to 20 filter blocks.
3. A filter assembly as claimed in any preceding claim wherein each said filter block is housed in a collar or bracket, said collars or brackets capable of being detachably connectable to each other through screw threaded joints or snap-fit joints.
4. A filter assembly as claimed in any preceding claim wherein each said filter block is a cylindrical disc, annular cylinder or a hollow dome.
5. A filter assembly as claimed in any preceding claim wherein each said filter block comprises,

• powder activated carbon having particle size such that 95 wt% of the particles pass through 50 mesh and not more than 13% particles pass through 200 mesh;
• binder material having Melt Flow Rate less than 1 g/10 minutes.
6. A filter assembly as claimed in claim 5 wherein said binder material is
high molecular; weight polyethylene or high molecular weight
polypropylene having molecular weight between 106 to 109 g/mole.
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7. A filter for filtration of liquids by gravity comprising:
(a) a washable or replaceable sediment filter for removing particulates, generally above 3 microns and
(b) a filter assembly as claimed in any one of the preceding claims, such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly.

8. A filter as claimed in claim 7 wherein said sediment filter is made of non-woven fabric having micropores.
9. A method of filtering liquids comprising

(a) passing the input liquid through a filter assembly as claimed in any preceding claim 1 to 6;
(b) replacing the first filter block with a new filter block whenever there is substantial reduction in the flow rate of the output water
thereby consistently obtaining high flow rates of filtered liquid from the filter assembly.
10. A filter assembly substantially as herein described with reference to the
accompanying figures.
Dated this 30th day of June 2006. Hindustan Lever Limited

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Abstract
The invention relates to a filter assembly for filtration of liquids that provides water, which is substantially free of particulate contaminants including microorganisms like cysts, while providing for relatively high flow rates. There exists a need to have a simple, easy-to-manufacture and cost effective gravity-fed water filter which can be used over a long period of time while providing consistently high flow rates and also ensuring the removal of harmful micro-organisms like cysts.
In one aspect, the invention provides for a filter assembly for filtration of liquids comprising a series of detachably connectable filter blocks comprising substantially identical composition.
In another aspect, the present invention provides a filter for filtration of liquids by gravity comprising:
(a) a washable or replaceable sediment filter for removing particulates generally above 3 microns and
(b) filter assembly of the invention.
such that the liquid to be filtered passes through said washable or replaceable sediment filter before passing through said filter assembly.

A FILTER ASSEMBLY AND A METHOD OF FILTERING LIQUIDS

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