WO2007054196A1

WO2007054196A1 - Process for rejuvenation of carbon block filters

Info

Publication number: WO2007054196A1
Application number: PCT/EP2006/010135
Authority: WO
Inventors: Mahendrakumar Maganlal Mistry; Nikhileshwar Mukherjee; Madalasa Srivastava
Original assignee: Unilever N.V.; Unilever Plc; Hindustan Lever Limited
Priority date: 2005-11-08
Filing date: 2006-10-20
Publication date: 2007-05-18

Abstract

The present invention relates to a process for rejuvenation of used carbon blocks of a filter cartridge used for filtration of water. It is an object of the present invention to provide a process for rejuvenation of used carbon blocks of a water filter cartridge, that restores the ability of the carbon block to remove particulate material including micro-organisms, like cysts, while giving the desired high flow rate, consistently over a large volume of inlet water. Accordingly, the present invention provides a process for rejuvenating a used carbon block of a filter cartridge for filtration of water comprising the step of drying said carbon block to a moisture content of 1% to 30%.

Description

PROCESS FOR REJUVENATION OF CARBON BLOCK FILTERS

FIELD OF INVENTION The present invention relates to a process for rejuvenation of used carbon blocks of a filter cartridge used for filtration of water.

BACKGROUND AND PRIOR ART

Water contains contaminants, which typically include particulate matter, chemicals and microorganisms. In case of potable water, it is especially desirable to remove these harmful contaminants before consumption, to maintain good health and avoid diseases.

Several different methods for purification of water are known, 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.

It is desirable to also remove or kill the harmful microorganisms, such as bacteria and viruses that are present in potable water. Several methods are employed e.g. use of UV devices, membrane filtration, reverse osmosis, use of halogenated (chlorinated or iodinated) compounds for this purpose. In the absence of a device, water is generally boiled to kill the microorganisms.

It is also desirable to remove particulate matter that includes pathogenic protozoan cysts. Sometimes, particulate matter, which is generally larger than 3 microns, is filtered using a cloth-filter or a depth filter e.g. a bed made of activated carbon or clay, in loose form or in the form of a moulded block. Carbon and clay additionally have the advantage of being highly porous materials which also facilitate the removal of soluble impurities e.g. dissolved organic compounds, compounds that impart an offensive odour and taste, pesticide and pesticide residues etc, by adsorption. Water available in many remote and water-scarce parts of the world is highly contaminated with soil that contains Iron, Aluminium oxides and hydroxides. The present inventors have experienced that the currently available filter cartridges, having carbon block filters get choked very often, especially in gravity water filters. This leads to very low flow rates of water, over a period of time, which is undesirable to the consumer. Upon such choking, the consumer tries to rejuvenate the cartridge by agitating in water or back flushing. These methods are effective to some extent, but after a few cycles of use, such methods of rejuvenation are no longer effective and the carbon block becomes useless. In such a case, the consumer is required to replace the filter cartridge with a new filter cartridge and due to frequency of occurrences; it turns out to be a costly option. The present inventors have sought to solve this problem by providing a novel method of rejuvenatation of used and choked carbon blocks. They have devised, after extensive experimentation, a process of rejuvenation that restores to a large extent, the original flow rate and filtration efficiency.

Some methods like back flushing, electrical currents, and ultrasound have been used to rejuvenate clogged carbon block filters. The present inventors have found that these methods are not completely effective, as in the case of back flushing, the original flow rate and filtration efficiency is not achievable. Many remote areas, either do not have access to electrical power supplies or have erratic supplies and therefore, methods like use of electrical currents or ultrasound are not suitable to all.

Expensive and complex rejuvenation and/or regeneration methods for activated carbon, mostly granular or powdered activated carbon are know in the art (e.g. US 4,030,876). These processes generally require a very high temperature and take a long time. They are also very complex and cannot be carried out by the consumer.

There thus exists a need for a cost effective, user-friendly and simple method to rejuvenate used carbon blocks which will ensure that their capability to provide high flow rates while ensuring the removal of particulate material including micro-organisms and dissolved matter is restored to a large extent.

It is thus the basic object of the present invention to provide a process for rejuvenation of used carbon blocks of a water filter cartridge, that restores the ability of the carbon block to remove particulate material including micro-organisms, like cysts, while giving the desired high flow rate, consistently over a large volume of inlet water.

Another object of the present invention is to provide for a process to rejuvenate used carbon blocks of a water filter cartridge, which process is user friendly and does not require sophisticated equipments or electrical power. SUMMARY OF THE INVENTION

According to the present invention, there is provided a process for rejuvenating a used carbon block of a water filter cartridge comprising the step of, drying said carbon block to moisture content of 1% to 30%.

It is particularly preferred that the carbon block is a carbon disc.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides for a process to rejuvenate a carbon block of a water filter cartridge. The term "carbon block" means a filter medium, which is prepared using activated carbon and polymeric binder, which are moulded together into a block by the application of heat and preferably pressure.

Carbon block

The process of rejuvenation is especially useful in those carbon blocks comprising activated carbon and a binder material having a Melt Flow Rate (MFR) of less than five grams/10 minutes, preferably less than 1 gram/10 minutes. The melt-flow rate (MFR) is measured using ASTM D 1238 (ISO 1133) test.

The binder material is preferably thermoplastic polymers having the low MFR values above described. Suitable examples include ultra high molecular weight polymers 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 commercially available under 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 particle size distribution that is substantially the same as that of the activated carbon, but the particles passing 200 mesh is preferably less than 40 wt%, more preferably less than 30 wt%. The activated carbon preferably has a particle size such that not more than 5% carbon passes through a sieve of 200 mesh and not more than 5% is retained on a sieve of 12 mesh. More preferably, the particle size of activated carbon is such that not more than 5% carbon is retained on 30 mesh and not more than 5% passes 60 mesh. The activated carbon is preferably selected from bituminous coal, coconut shell, wood, or petroleum tar. The surface area of the PAC (powder activated carbon) is preferably selected such that it exceeds 500 m²/g, more preferably exceeds 1000 m2/g. The size uniformity co-efficient of activated carbon is preferably less than 2, more preferably less than 1.5. The Carbon Tetrachloride number of activated carbon preferably exceeds 50%, more preferably exceeds 60%. The activated carbon preferably has Iodine number greater than 800, more preferably greater than 1000.

The proportion of the binder material to activated carbon particles, by weight, is chosen such that it is preferably in the range of 1:1 to 1 :12, more preferably in the range of 1 : 3 to 1:9.

The carbon blocks that may be rejuvenated by the process of the invention are those having a short path length that include shapes like hemisphere, torisphere and trapezoid. A highly preferred carbon block is disc shaped. The disc may have a circular, oval, square or polygonal cross-section, preferably a circular cross-section. When a carbon disk is used, 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 process of the invention is especially suitable for rejuvenating carbon blocks, especially carbon disks which are detachably attachable in the filter cartridge. An especially preferred configuration of such a detachably attachable carbon block has been disclosed in our co-pending application 801 /MUM/2005. The carbon block therein is seated in a receptacle having an orifice for outlet of water wherein the carbon block is detachably attachable in the receptacle using a fastening means and a gasket means such that all inlet water passes through said carbon block before exiting said filter cartridge. Preferred 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.

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

A replaceable sediment filter can optionally, externally envelop the carbon block, such that water passes through the replaceable sediment filter before passing through the carbon block.

Process

The step of rejuvenation comprises drying the used carbon block to moisture content in the range of 1 to 30%, preferably to 5 to 25%. Drying is preferably carried out at temperatures in the range of 20 to 15O⁰C, more preferably 20 to 8O⁰C, further more preferably 20 to 60⁰C. This temperature can be attained by any known method of heating e.g. heating on a hot plate, drying in an oven, sun drying, heating using microwave energy or drying at ambient conditions. It is preferred that high temperature is achieved by drying the carbon block in an oven. A current of gas, preferably air, enhances the rejuvenation. Although the drying could be achieved at any drying rate, it is preferably achieved in less than 6 hours.

Drying is preferably carried out under vacuum, suitable pressures being from 1 to 0.1 atmospheres absolute.

By way of the above process of rejuvenation of the carbon block, it is possible to revive the efficacy of the carbon block such that it is capable of providing an average flow rate of 600-50 ml/min, preferably 200-50 ml/min filtered water, from a starting height of 200 mm down to 50 mm, under gravity, without compromising on the removal of particulates including microorganisms, and chemical contaminants.

The invention is especially suitable for rejuvenating carbon blocks such that the rejuvenation restores the ability of the carbon blocks to filter water contaminated with particles including dust and microorganisms e.g. protozoan cyst like Cryptosporidium and

Giardia. The invention is capable of restoring the ability of the carbon blocks to provide more than 99% removal (2 log removal) preferably 99.9% removal (3 log removal) of cysts. Log removal is defined as the logi₀ of the number of input particles minus the log ₁₀ of the number of output particles. The process of the invention is especially suitable for rejuvenating carbon block that has filtered more than 100 liters of water, preferably more than 300 liters of water.

The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to the following non-limiting examples by way of the invention.

Examples

Example-1 : Rejuvenation of used carbon block by oven drying.

A tapered carbon disk of 35 g was prepared using activated carbon having particle size distribution such that 5% particles pass through 60 mesh and 5% particles are retained on 30 mesh. High density polyethylene having molecular weight 10⁶ and MFR of - 0 was used as the binder. The binder and activated carbon were mixed in a ratio of 1:3.3. Diameter of the carbon disk at the top waslOO mm and that of the bottom was 90 mm. Thickness of the disk was 10 mm. The carbon disk was fitted in a water filter cartridge, where the carbon disk could be removed for rejuvenation and replaced after rejuvenation.

A model water sample containing about 19 mg/liter dust particles of size about 10 micrometers was prepared and filtered using the water filter cartridge prepared above. The input water had a turbidity of about 13 to 15 NTU and was visually turbid. Initial head height of water was 200 mm. When the flow rate of water fell below 50 ml/minute, the cartridge was back flushed and cleaned with a jet of water and this step of back flushing was termed as "one intervention". The flow rate of water obtained after multiple interventions is summarized in Table -1.

Table-1

Turbidity of the output filtered water was less than 1 NTU and it was visually clear. Thus, about 357 liters of water could be filtered by using the carbon disk with three interventions of back flushing/washing in water. After three interventions, the carbon disk could not be rejuvenated using conventional steps like back flushing or washing in water and the flow rate of filtered water was abysmally low (approximately below 50 ml/minutes). The carbon disk was then rejuvenated using the process of the invention by drying the disk in an oven at 60⁰C for one hour to bring down the moisture content to 5%. The carbon disk was then replaced in the water filter cartridge and was used to filter the same model water. The flow rate of filtered water is summarized in Table 1A.

Table-1A

The output filtered water from the rejuvenated carbon disk also had a turbidity of less than 1 NTU and was visually clear. Thus it can be readily seen that the flow rate and clarity of filtered water remains acceptably high after it undergoes oven drying according to the invention and thereby becomes fit for reuse.

Example-2: Rejuvenation of used carbon block by ambient drying.

A tapered carbon disk of 35 g was prepared and tested as described above.

The flow rate of water obtained after multiple interventions is summarized in Table -2.

Table-2

Turbidity of the output filtered water was less than 1 NTU and it was visually clear. Thus, about 250 liters of water could be filtered by using the carbon disk with four interventions of back flushing/washing in water. After four interventions, the carbon disk could not be rejuvenated using conventional steps like back flushing or washing in water and the flow rate of filtered water was abysmally low (approximately below 50 ml/minutes). The carbon disk was then rejuvenated by drying the disk at room temperature, under ambient conditions for four days to bring down the moisture content to -30%. The carbon disk was then replaced in the water filter cartridge and was used to filter the same model water. The flow rate of filtered water is summarized in Table 2A.

Table-2A

The output filtered water from the rejuvenated carbon disk also had a turbidity of less than 1 NTU and was visually clear. Thus it can be readily seen that the flow rate and clarity of filtered water remains acceptably high after it undergoes drying according to the invention, under ambient conditions, and thereby becomes fit for reuse.

The invention thus provides for rejuvenation of a carbon block using the process of the invention to provide a carbon block capable of filtering water like a new carbon block.

Claims

1. A process for rejuvenating a used carbon block of a filter cartridge for filtration of water comprising the step of drying said carbon block to a moisture content of 1 % to 30%.

2. A process according to claim 1 wherein said carbon block is dried at a temperature in the range of 2O⁰C to 150 ⁰C.

3. A process according to claim 1 or claim 2 wherein said carbon block is dried at a temperature of 2O⁰C to 8O⁰C.

4. A process according to any one of the preceding claims wherein said carbon block is dried under vacuum.

5. A process according to any one of the preceding claims wherein said block is dried in less than 6 hours.

6. A process for rejuvenating a carbon block according to claim 1 , wherein said filter cartridge comprises carbon block 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.

7. A process according to claim 6 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.

8. A process according to any one of the preceding claims wherein more than 100 Liters of water to be purified has been passed through said carbon block before rejuvenation.

9. A process according to any one of the preceding claims wherein more than 300 Liters of water to be purified has been passed through said carbon block before rejuvenation.

10. A process according to n any one of the preceding claims wherein said carbon block is a carbon disk.

11. A process according to claim 9 wherein said carbon disk has a circular cross- section and the ratio of the longest dimension of the disk to the thickness of the carbon disk in the range of 2: 1 to 20:1.

12. A process according to any one of the preceding claims wherein a replaceable sediment filter envelops said carbon block externally such that water passes through said replaceable sediment filter before passing through said carbon block.

13. A process according to any one of the preceding claims wherein the rejuvenation of the carbon block restores the ability of the carbon block to filter water contaminated with particles including microorganisms like protozoan cysts e.g. cryptospodium parvum and Giardia Lamblia.

14. A process according to any one of the preceding claims wherein the rejuvenation of the carbon block restores the ability of the filter cartridge of more than two log removal of cyst.

15. A process according to any one of the preceding claims wherein the rejuvenation of the carbon block restores the ability of the filter cartridge of obtaining filtered water at flow rates in the range of 50 to 600 ml/minute.