WO2007003259A1

WO2007003259A1 - Filter cartridge

Info

Publication number: WO2007003259A1
Application number: PCT/EP2006/005690
Authority: WO
Inventors: Parthiv Ripudaman Dave; Mahendrakumar Maganlal Mistry; Nikhileshwar Mukherjee; Madalasa Srivastava
Original assignee: Unilever N.V.; Unilever Plc; Hindustan Unilever Limited
Priority date: 2005-07-06
Filing date: 2006-06-13
Publication date: 2007-01-11

Abstract

The invention concerns a filter cartridge for filtration of water comprising a carbon block that is seated in a receptacle having an orifice for outlet of water wherein said carbon block is detachably attachable in said receptacle using a fastening means and a gasket means such that all inlet water passes through said carbon block before exiting said filter cartridge.

Description

FILTER CARTRIDGE

Field of invention

The present invention relates to a filter cartridge for filtration of water and more particularly to a cost-effective filter cartridge for gravity filtration of water substantially free of particulate contaminants including microorganisms like cysts while providing high flow rates.

Background and prior art

Raw water typically contains^" contaminants, which irϊclϋde^" paTticTflatelriatteri chemicals and microorganisms. In potable water, it is especially desirable to remove the harmful contaminants before consumption in order to stay healthy. Various methods are known for the purification of water, based on which many devices and apparatus are known. These methods and devices vary depending on the type of impurities present in water.

It is desirable to also remove or kill the harmful microorganisms like protozoan cysts and bacteria present in potable water. Several methods are employed towards this end. Water may be boiled to kill the microorganisms, but this method is cost-intensive and makes the water have a poor taste. Biocides like chlorine and iodine are sometimes used to kill the microorganisms. These are very effective, but additional precautions have to be provided to ensure that the remaining biocide is removed from the water before it is consumed. Remaining chlorine in water provides a bad odour, while intake of excess chlorine or iodine can be harmful. Ultra-violet radiation is used in many water-purification devices, but ultraviolet radiation requires continuous availability of electric power that is sometimes not available in remote areas. Particulate matter generally larger than 3 microns is filtered out using either a cloth filter or a depth filter 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 of e.g. dissolved organic compounds, malodorous and bad tasting compounds, pesticides, pesticide residues etc. Water available in many remote water-scarce parts of the world is highly contaminated with soil which includes iron and aluminium oxides and hydroxides. Known carbon filter blocks get choked easily in use. Especially in gravity fed water filters this causes very low flow rates of water after some use, which is undesirable for the consumer. Consumers often try to rejuvenate a filter cartridge by agitating in water or backflushing, but presently available filter cartridges are difficult to rejuvenate. Thus, the consumer is required to replace the filter cartridge with a new one which is costly.

US 4,753,728 (Amway, 1988) 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 particles are bonded internally to each other and the two shells are bonded together with the help of a specific high molecular polymer binder. The bottom end cap and the top end cap of polypropylene are cast moulded on to the carbon block. This filter is difficult to clean and does not enable easy removal and replacement of the carbon block from the polymeric end caps.

US 5,328,609 (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 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 medium. While the first stage is used to remove fti io nonHarl *-%nr4 hoovn/ rrnatolo ctαnα

suspended bacteria and other organic impurities. The filtration system described in this publication requires the entire filter cartridge to be disposed of when completely choked and replaced with a new cartridge, which is costly.

There thus exists a need for a cost-effective gravity-fed water filter cartridge 5 which provides consistently high flow rates and also ensures the removal of particulate material, including micro-organisms, and dissolved matter.

Summary of the invention 0

Thus, it is an object of the invention to provide a filter cartridge which gives consistently high flow rates of water of desired quality, while providing for easy cleaning and replacement of the carbon blocks contained therein, while ensuring that the overall cost of the ^"cartridge is minimized. 5

It is a further object of the present invention to provide for a filter cartridge which ensures a high flow rate consistently over a large volume of inlet water while providing removal of particulate contaminants, including micro-organisms like cysts, even chlorine resistant cysts such as Cryptosporidium parvum and o Giardia Lamblia which are in the size range of 3 to 6 microns

Yet another object of the present invention is to provide a filter cartridge which provides a high efficiency in terms of the amount of water filtered for a given amount of carbon. 5

Detailed description of the invention

According to one aspect of the invention there is provided a filter cartridge for o filtration of water comprising a disc shaped carbon block with a circular cross- section that is seated in a receptacle having an orifice for outlet of water wherein said carbon block is detachably attachable in said receptacle using a fastening means and a gasket means such that all inlet water passes through said carbon block before exiting said filter cartridge, wherein the ratio of the longest dimension to the thickness of the carbon disk in the range of 2:1 to 20:1.

According to another aspect of the invention there is provided a method of obtaining filtered water at flow rates in the range of 50 to 600 ml/minute comprising the steps of:

(i) filtering water through a filter cartridge of the invention; and (ii) replacing the carbon block in the filter cartridge whenever the flow rate of water is below desired value with a block which provides the desired flow rate.

The first aspect of the invention provides for a filter cartridge for filtration of water comprising a carbon block that is reversibly fastenable in a receptacle using a fastening means with a gasket means suitably position to ensure that all inlet water passes through the carbon block before exiting the filter cartridge.

It has been determined that the reduction in flow rate of the water through carbon block filters is principally due to choking of the pores over a relatively short path length from the inlet surface of the carbon block. On the other hand, a sufficiently long path length is required to ensure sufficient reduction in the number of particles in the water exiting the filter. To meet these opposing requirements the carbon block needs to have a required shape and a short path length. The carbon block of the present invention is disc shaped. The disc may have a circular, oval, square or polygonal cross-section, preferably a circular cross-section. It is preferred that the dimensions are such that the ratio of the longest dimension to the thickness is in the range of 2:1 to 20:1 , more preferably 3:1 to 15:1.

The fastening means may be a closure which may be snap fit on to the receptacle or a clamp which holds the carbon block on to the receptacle. The gasket means may be a gasket, an o-ring or any other means which serves the purpose of a gasket which provides leak tightness to water when a fastening means is used to fasten two articles together. According to a preferred aspect of the invention, the fastening means is a screw threaded closure which comprises an orifice for inlet of water and is screwable on to the receptacle housing the carbon block. The receptacle is provided with corresponding screw threads for urging the carbon block against the gasket means provided in the base of the receptacle thereby attaching the carbon block in the filter cartridge. The closure may be provided on its bottom surface with downwardly projecting members which are urged against the top surface of the carbon block, as the closure is screwed on to the receptacle thereby urging the bottom surface of the carbon block against the gasket means placed in the base of the receptacle thereby ensuring the necessary leak tightness. When the carbon block is desired to be detached from the filter cartridge, the closure is unscrewed from the receptacle thereby releasing the carbon block. One or more orifices are provided on the closure for inlet of water on to the carbon block. It is preferred that the orifice comprises at least 30% of the surface area of the top surface of the closure.

The blocks according to the invention are capable of filtering water which is contaminated with particles including dust and microorgansims e.g. protozoan cyst like Cryptosporidium and Giardia. The invention is capable of 99% removal (two log removal), preferably 99.9% removal (three log removal) of cyst. Log removal is defined as the logi₀of the number of input particles minus the log 1₀ of the number of output particles. The carbon blocks are made from activated carbon, more preferably powder activated carbon.

It is preferred to include a replaceable sediment filter that externally envelops the carbon block such that water passes through the sediment filter before passing through the carbon block. The sediment filter preferably corresponds to the shape of the carbon block. The sediment filter may be washable or replaceable and is preferably a woven or non-woven fabric, more preferably a non-woven fabric having micropores. This sediment filter ensures filtration of particles generally above 3 microns. The sediment filter can be washed and reused or be replaced entirely.

The receptacle and the fastening means are preferably made of polymeric materials. Preferred polymeric materials include polypropylene, polyethylene, acrylonitrile butadiene styrene, or styrene acrylonitrile. The gasket means is preferably made from natural or synthetic rubber, synthetic elastomers, teflon, nitrile rubber or silicone,

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) of less than five, preferably less than one. 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 ⁰C (428, 482 and 572⁰F). 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 polymers having the low MFR values above described. Suitable examples include ultra high molecular weight polymer preferably polyethylene or polypropylene which have these low MFR values. The molecular weight is preferably in the range of 10⁶ to 10⁹. Binders of this class are ccrnrnerciaϋy available undsr the trade names HOSTALEN™ from Tycona GMBH, GUR™, Sunfine™ (from Asahi, Japan), Hizex™ (from Mitsubishi) and from Brasken Corp (Brazil). Other 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 a 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 made from starting material 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, or more preferably less than 1.5, a carbon tetrachloride number exceeding 50%, more preferably exceeding 60%. The PAC preferably has an Iodine number greater than 800, more preferably greater than 1000.

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.

By way of the above filter cartridge of the invention it is possible to attain average flow rate of water, from a starting height of 200 mm down to 50 mm, under gravity of 600-50 ml/min., preferably 200-50 ml/min., without compromising on the requirements of removal of particulate including microorganisms, and chemical contaminants. A suitable process of preparation of carbon blocks for use in the filter cartridge of the invention has been disclosed in our co-pending application 320/MUM/2004.

The present invention facilitates easy removal of the carbon block from the cartridge to rejuvenate it, after which the carbon block is easily re-attachable in the cartridge. Rejuvenation may be done by agitating the carbon block in water or by back flushing with a jet of cold or hot water. After cleaning, the carbon block is preferably replaced in the cartridge the same side-up each time. To facilitate this, the carbon block preferably has indicators thereon to distinguish the top and bottom surfaces.

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:

Description of the drawings

Fig. 1 is a schematic of a filter cartridge of the invention with a carbon disc filter assembled. In Fig.1 , the filter cartridge comprises a carbon block (CB) seated on a gasket (G) provided in the base of a receptacle (R) which has an orifice (OT) for outlet of water. A closure (CL) has an orifice on the top surface (not shown) for water inlet. The closure has screw threads (ST1 ) with which it is screwed on to the receptacle provided with corresponding screw threads (ST2). Downwardly projecting members (M) are provided on the closure for urging the carbon block against the gasket as the closure is screwed on to the receptacle. The gasket ensures leak-proof outlet such that all the water fed to the filter cartridge passes though the carbon block before exiting it.

When in use, the water enters the closure through the orifice provided thereon and flows through the carbon filtration block and exits the cartridge through the outlet (OT). When a large amount of water has been filtered and the flow rate is below a desired value, the closure is unscrewed and the carbon block is removed from the cartridge. The carbon block is rejuvenated by cleaning to the desired degree of cleanliness and replaced in the cartridge with the same side up as in the earlier run. The closure is again screwed on to the receptacle and the cartridge is ready for use with the desired high flow rate again. This procedure is repeated till the carbon block can no longer be rejuvenated. At this stage the carbon block is replaced with a new one.

Examples

Example 1 :

A filter cartridge of the invention (as shown in Fig. 1 ) with a 35 gram carbon disc (95 mm diameter and 12 mm height) is used to filter water which is contaminated with particulates in a gravity filter with a head of 170 mm of water column. The data on the flow rate of the filtered water obtained are shown in Fig. 2. The filtered cartridge removed greater than 99.9% of the cyst present in the inlet water.

Comparative Example 2: A filter cartridge of the prior art made with 127 gram carbon made in a 100 mm hemispherical shape with the carbon block glued to a base plate was used to filter water under the same conditions as example 1. The comparative data are shown in Fig 3. This filter also removed greater than 99.9% of the cyst present in the inlet water.

The data indicates that by using as little as about 28 weight% of the carbon block as compared to the comparative example-2, the filter cartridge of example-1 could filter about 60% of the water (about 300 litres of water as compared to 500 litres of water using the filter of the comparative example-2). Further, the graphs show that the average flow rate of the water obtained in example-1 was significant higher.

Claims

Claims:

1. A filter cartridge for filtration of water comprising a disc shaped carbon block with a circular cross-section that is seated in a receptacle having an orifice for outlet of water wherein said carbon block is detachably attachable in said receptacle using a fastening means and a gasket means such that all inlet water passes through said carbon block before exiting said filter cartridge, wherein the ratio of the longest dimension to the thickness of the carbon disk in the range of 2:1 to 20:1.

2. A filter cartridge as claimed in claim 1 wherein said fastening means is a screw threaded closure which comprises an orifice for inlet of water and is screwable on to said receptacle provided With corresponding screw ^~ threads for urging said carbon block against said gasket provided in the base of the receptacle.

3. A filter cartridge as claimed in claim 2 wherein the area of the orifice on the closure is greater than 30% of the surface area of the top surface of the closure.

4. A filter cartridge according to any one of claims 1 to 3 wherein said ratio is in the range of 3: 1 to 15: 1.

5. A filter cartridge as claimed in any one of the preceding claims wherein a replacable sediment filter externally envelops said carbon block such that water passes through said replaceable sediment filter before passing through said carbon block.

5

6. A filter cartridge as claimed in claim 5 wherein said sediment filter is a non-woven fabric.

7. A filter cartridge as claimed in any one of the preceding claims capable o of filtering water contaminated with particulates including microorganisms like protozoan cysts e.g. cryptospodium parvum and Giardia Lamblia.

8. A filter cartridge as claimed in any one of the preceding claims wherein 5 said receptacle and said fastening means are made of materials selected from polymers which includes polypropylene, polyethylene, acrylonitrile butadiene styrene, or styrene acrylonitrile.

9. A filter cartridge as claimed in any one of the preceding claims wherein 0 said gasket means is made from natural or synthetic rubber, synthetic elastomers, teflon, nitrile rubber or silicone,

10. A filter cartridge as claimed in any one of the preceding claims wherein said carbon block comprises powder activated carbon (PAC) having a 5 particle size such that 95 wt% of the particles pass through 50 mesh and not more than 13% passes through 200 mesh and a binder material having a Melt Flow Rate (MFR) of less than 1 gram/10 minutes

1 1. A filter cartridge as claimed in claim 10 wherein the binder material is o high molecular weight polyethylene or polypropylene having a molecular weight of 10⁶ to 10⁹ D.

12. A filter cartridge as claimed in any one of the preceding claims wherein the carbon block has indicators thereon to distinguish the top and the bottom surface.

13. A method for a two-log cyst removal from water comprising the step of (i) filtering water through a filter cartridge as claimed in any one of the preceding claims.

14. A method of obtaining filtered water at flow rates in the range of 50 to 600 ml/minute comprising the steps of

(i) filtering water through a filter cartridge as claimed in any one of claims 1 to 12; and (ii) replacing the carbon block in the filter cartridge whenever the flow rate of water is below desired value with a block which provides the desired flow rate.