WO2001053212A1

WO2001053212A1 - Method and device for sustaining a clean water supply

Info

Publication number: WO2001053212A1
Application number: PCT/IL2001/000050
Authority: WO
Inventors: Yefim Riskin
Original assignee: Puriel Ltd.
Priority date: 2000-01-18
Filing date: 2001-01-18
Publication date: 2001-07-26
Also published as: AU2001225457A1; IL134104A0

Abstract

A system for maintaining a clean water supply includes one or more filters having a sorbent filter mass arranged for flow through filtration of water containing contaminants including bacteria and organic substances, while substantially preventing passage through the filter mass of the contaminants, thereby to cause an accumulation of contaminants in association with the filter mass; selectably operable apparatus for substantially drying the sorbent filter mass; and selectably operable apparatus for exposing the sorbent filter mass and the accumulated contaminants to a predetermined supply of ozone for a preselected period of time, thereby to destroy the contaminants and thus clean the filter mass.

Description

METHOD AND DEVICE FOR SUSTAINING A CLEAN WATER SUPPLY

FIELD OF THE INVENTION

The invention relates to methods and devices for water treatment by removal of bacteria and organic substances through the use adsorbent filters, and for filter activity regeneration through the use of ozone.

BACKGROUND OF THE INVENTION

In the purification of water, the use of adsorbent filters, particularly made of granulated activated carbon (GAC), is well known. These filters are generally of simple constructions, and are efficient in the removal of bacteria and organic substances from a water supply so as to render it potable. Such filters suffer, however, from a limited adsorbtion capability, normally becoming clogged or saturated at an adsorbtion of about 20% of their weight. An example of an apparatus for treating contaminated fluids by use of GAC is disclosed in U.S. Patent No. 4,687,573 to J. D. Miller et al., entitled "Sorbing Apparatus."

Use of ozone to remove various contaminants from a water supply is also known, such contaminants including pathogenic microorganisms, such as bacteria, fungi and viruses; microalgae; dissolved or suspended organic compounds; and sulfides, including hydrogen sulfide.

U.S. Patent No. 4,214,887 to van Gelder, describes the use of ozone to treat separately almost solid-free sewage effluent, and removed solids.

U.S. Patent No. 4,176,061 to Stopka, teaches the purification of water with entrained micro-bubbles of ozone, subsequently filtering the water in an activated carbon filter.

U.S. Patent No. 5,431,861 to Nagahiro et al., discloses the dissolution in raw material water of fine bubbles of ozone for liquid phase ozone treatment thereof; many industrial applications of this procedure are listed.

U.S. Patent No. 4,412,924 to Feather, describes the use of ozone particularly for the removal of hydrogen sulfide from well water, the concentration of hydrogen sulfide having been reduced initially by aeration. U.S. Patent No. 5,868 945 to Morrow et al., discloses the use of ozone for the reduction of oil and grease content of contaminated water so that it can be used as a drinking or irrigation supply source, or discharged into navigable waters.

U.S. Patent No. 4,352,740 to Grader et al., describes the treatment of wastewater or drinking water with a feed gas containing at least 70% oxygen, ozonized to contain 4-8% ozone.

It is known that microorganisms, especially bacteria, freely proliferate on an adsorbent used to remove organic contaminants from an aqueous feedstock, due to the fact that the bacteria feed on such contaminants. The proliferating bacteria, adsorbed on the external surfaces of the adsorbent, rapidly seal off access to the internal pores of the adsorbent, and thus make the adsorbent inoperative, or at least inefficient, for removal of organic contaminants. The usual solution to this problem is merely to replace exhausted adsorbent with a fresh adsorbent, rather than attempt regeneration. However, as pointed out, for example, in U.S. Patent No. 5,141,636, there are circumstances where it may not be desirable or convenient to replace an adsorbent. Moreover, the use of ultraviolet radiation to solve the problem of bacterial proliferation in adsorbents may not be convenient in all situations.

In U.S. Patent No. 5,141,636 to Flanagan et al., there is described the treatment of water by passing it over the surfaces of GAC configured to receive maximum flux from a U/V radiation source, in order to prevent microbial proliferation on the carbon surfaces and to oxidize organic contaminants, this procedure is especially applicable where the GAC cannot be easily changed, or longer life duration of the GAC is desired.

U.S. Patent No. 5,707,528 to Berry describes a system in which a Block Co-Polymer adsorber, contaminated by organic substances, is regenerated by passing therethrough water previously treated by ozone. This technique of filter regeneration is inefficient, and cannot be used for the destruction of bacteria adsorbed by the filter; this is due to the low solubility of ozone in water, as well as the relatively long time lag between treatment of the water with ozone, and flow of the water through the filter.

All of the above-mentioned methods and devices suffer from various disadvantages, including the following:

1. For efficient ozone dissolution in water, small bubbles, no greater than about 0.8 mm in diameter, must be formed in water, at a high pressure head, typically in the range 3-5 m water; alternatively, complex mixing devices must be used. 2 The need for a high capacity ozone generator, due to the treatment process taking place in real time

3 Undesirable products of ozone reaction with organic substances are left over in the treated water

SUMMARY OF THE INVENTION

The present invention seeks to provide improved method and apparatus for maintaining a clean, filtered water supply

A further aim of the present invention is to provide a novel method of employing ozone for filter regeneration, and a filter regenerated by this method

It is thus a principle object of the present invention to destroy contaminant organisms from adsorbents employed as filter media for the treatment of contaminated water, thus regenerating the filter media

Other objects of the invention will be apparent from the description which follows

There is thus provided, in accordance with a preferred embodiment of the present invention, a method of maintaining a clean water supply in which a predetermined volume of contaminated water is cleansed, by passing it through a filter having at least one mass of a sorbent filter medium, typically a porous material such as activated carbon At the end of a single filtration cycle, any organic substances dissolved in the water are absorbed by pores in the sorbent mass, bacteria having a magnitude greater than the pore dimensions adhering to the surface of the sorbent mass at junction locations between the sorbent particles

Subsequently, the supply of water through the filter is stopped, and an air-ozone mixture is passed through the sorbent mass in the same direction as the water flow during filtration, for a predetermined period of time The time period is determined so as to be sufficient to dry the sorbent mass, so that bacteria and the organic substance become accessible to the direct ozone action

The most effective destruction of the bacteria occurs when the surface of the sorbent mass is dry, but while the pores are still filled with water This is due to the fact that the ozone thus does not enter the pores and so is not used up in oxidation reactions with the organic materials adsorbed in the pores and with the sorbent material, such as carbon Rather, in this situation, the ozone is used to substantially destroy the bacteria adhering to the surface of the filter material Subsequently, after the sorbent material has substantially dried, the organic contaminants trapped in the pores become accessible to ozone for elimination thereby

It will be noted that during filtration, the accumulation of impurities in the porous mass is not uniform, being highest at the upstream filter end, decreasing in a downstream direction

Preferably, therefore, the air-ozone mixture is passed through the filter mass in the same direction, such that the filter drying process advances gradually in the same direction, and such that the destruction by the ozone of the bacteria and organic substances adsorbed by the filter mass is also not uniform with the filter depth, but corresponds to concentration distribution of the accumulated impurities

In accordance with an alternative embodiment of the invention, however, it may be desired, as a further step, to reverse the direction of the air-ozone flow so as to pass it through the filter mass in the opposite direction to that described, to ensure thorough cleaning of the filter

The duration of air-ozone mixture action on the sorbent mass is so determined that the amount of ozone in the air-ozone mixture flow is sufficient for destruction of bacteria and organic substances absorbed by the mass

Due to the fact that the filter material, for example, activated carbon, is chemically inert, the oxidation reaction of the ozone is initially with the bacteria and other organic materials, the ozone ultimately decomposing on the activated carbon

The regeneration time, namely, the time taken for close to 100% of all contaminants to be destroyed, so that the filter can be substantially returned to its original capacity, is based on the productivity of the ozone generator, and a predetermined air-ozone mix flow rate More particularly, the volumetric supply of ozone required to destroy bacteria and organic substances, in accordance with the method of the invention, is similar to that used for water treatment by ozone dissolution in it, namely, in the range 2-4 mg of ozone per liter of treated water Thus, when it is performed over a relatively long time period, for example, of several hours, a relatively small, low output ozone generator may be employed

In accordance with a preferred embodiment of the invention, a single ozone generator can be employed with two water supply conduits - each containing a filter - arranged in parallel, wherein at any one time, one of the conduits is open to water for filtering, while the other conduit is closed, its filter undergoing regeneration

In this manner, ozone regeneration of each filter is performed at different times, while maintaining a continuous water supply

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood and appreciated, from the following detailed description, taken in conjunction with the drawings, in which

Fig 1 is a diagrammatic illustration of a clean water supply system, constructed and operative in accordance with a preferred embodiment of the present invention,

Figs 2A-2C are schematic illustrations showing various stages in operation of the system of Fig 1,

Fig 3 is a diagrammatic illustration of a clean water supply system, constructed and operative in accordance with an alternative embodiment of the present invention, and

Figs 4A-4C are schematic illustrations showing various stages in operation of the system of Fig 3

DETAILED DESCRIPTION OF THE PRESENT INVENTION Referring now to Fig 1, there is seen a system, referenced generally 100, for maintaining a clean water supply, constructed and operative in accordance with the present invention System 100 is installed between a water supply conduit 1 and a water outlet conduit 30, between which is installed a filter 102, having a filter housing 4 An unfiltered water inlet conduit 3, preferably shaped as a siphon, connects between an inlet valve 2 and a filter inlet 5 formed in housing 4, and a filtered water outlet conduit 28 connects between a filter outlet 24 formed in housing 4 and an outlet valve 29 Filter housing 4 contains a mass 16 of a sorbent filter medium 16, arranged between a fixed, water permeable support grid 17, and a movable, water permeable support grid 15. Normally, movable grid 15 is retained in compression with sorbent mass 16 and fixed grid 17, by means of a suitable compression member 6, illustrated herein as a spring.

It should be noted that, in accordance with a preferred embodiment of the invention, water inlet and outlet valves 2 and 29, respectively, are connected to an electrical switching device 26 operated via controller 27, and are normally open.

In accordance with a preferred embodiment of the invention, there is provided an air-ozone supply system 103 which includes an ozone generator 9, controlled via a controller 27 and electrical switching device 26, preferably connected to a mains supply 25. System 103 also includes a compressor 13, also operated via controller 27 and switching device 26, having an inlet 14 open to the atmosphere. The compressor 13 has an outlet 12 connected to ozone generator 9 via a compressed air supply valve 11. Ozone generator 9 is connected to an ozone inlet 7 formed in body 4, upstream of sorbent filter mass 16, via an ozone inlet conduit 8.

An ozone outlet 23 is formed in housing 4, downstream of sorbent filter mass 16, and is connected to the atmosphere via a filter 21, and an exhaust valve 19 having an outlet 18. Exhaust valve 19 is also controlled by controller 27 and switching device 26. Filter 21 is provided for ensuring that any ozone exiting housing 4 via ozone outlet 23, is destroyed before it can reach the atmosphere, in accordance with the method described below. Preferably, filter 21 is a GAC filter.

It should be noted that, in accordance with a preferred embodiment of the invention, air supply valve 11 and exhaust valve 19, both operated by controller 27 via switching device 26, are both normally closed.

In accordance with a preferred embodiment of the present invention, system 100 is operable in two modes, namely, a water treatment mode, and a filter regeneration mode.

In the water treatment mode, unfiltered water is supplied to filter 102 via inlet conduit 1 and inlet valve 2, and exits system 100 after filtration, via outlet conduit 30. In this mode, valves 2 and 29 are open, and air inlet valve 11 and exhaust valve 19 are both closed.

In the regeneration mode, water supply through the filter 102 is stopped, and ozone is generated and supplied, in the form of an air-ozone mixture to the filter mass 16, thereby to destroy contaminants therein, as described herein. In more detail, and referring now to Figs 2A-2C, operation of system 100 of the present invention, is now described It will be appreciated that the presence of an arrow in the drawing indicates flow in the indicated direction, while an X indicates a closed valve position

Referring now particularly to Fig 2A, in the water treatment mode, switching device 26 is operated so as not to supply electrical power to the remainder of system 100, such that water is allowed to flow from inlet valve 2 to outlet valve 29, between which it is filtered in filter 102 In this mode, water cannot exit body 4 via openings 7 and 23, as the normally closed valves 11 and 19 are not powered, and are thus closed

Referring now to Figs 2B and 2C, in the regeneration mode, switching device 26 is set to enable power supply to ozone generator 9, compressor 13 and control unit 27 Control unit 27 generates activation signals arriving at the control inputs of normally open valves 2 and 29, and of normally closed valve 19, as well as the control input of ozone generator 9, in the following sequence

1 Inlet valve 2 is activated so as to be closed (Fig 2B), thus preventing water from entering filter 102

2 Then air inlet valve 1 1 is activated to as to be opened (Fig 2B), and compressor 13 is operated, so as to supply compressed air via conduit 12, air inlet valve 11, conduit 10, ozone generator 9, conduit 8 and air inlet 7, so as to substitute water present in sorbent mass 16 At this stage, ozone generator 9 is not activated, and is merely used to allow passage of air therethrough The substituted water from sorbent mass 16 is discharged from the housing 4 via outlet 24, and via filtered water outlet valve 29, which is still open at this point

3 After sufficient time has elapsed for the water in filter 102 to have substantially completely drained therefrom, controller 27 generates signals to open normally closed exhaust valve 19 (Fig 2C), to close normally open outlet valve 29 (Fig 2C), and so as to operate ozone generator 9

4 Subsequently, the ozone generated mixes with the air already in the system, and the resulting air-ozone mixture enters filter housing 4 via inlet opening 7, passes through sorbent filter mass 16, and exits filter housing 4 via outlet 23 The exiting gas mixture passes through filter 21, such that any remaining ozone is destroyed as it comes into contact with the GAC typically provided therein It will be noted that, in view of the siphon-shape of water supply conduit 3, water is retained therein, so as to shield it from the air-ozone mixture supplied to the filter 102, such that inlet valve 2 does not need to be formed from ozone resistant materials.

It will be appreciated that, during passage of the air-ozone mixture through sorbent filter mass 16, ozone enters into a chemical reaction with bacteria and organic materials absorbed thereby, substantially as described above, and which are generally known, per se, and which are thus not described again herein.

In view of the fact that, over a period of extended use, the sorbent filter mass 16, preferably, but not exclusively, formed of activated carbon, is itself also depleted by chemical reaction with the air-ozone mixture. In view of the provision of movable grid 15, however, and compressive member 6, a desired, tight compaction of the carbon granules is maintained, thereby substantially maintaining the efficiency of the filtration provided thereby.

In a test performed by the Inventor in accordance with the above-described embodiment, sorbent mass 16 consisted of a single cylindrical mass of activated carbon, of diameter 55 mm, and thickness 50 mm. Water was fed through the filter 102 at a rate of 1.0 1/min. Compressed air was supplied by compressor 13 at a rate of 5.0 1/min, and the ozone generator 9 was operated so as to supply ozone at a rate of 200 mg/hour. The required regeneration time after filtering treatment of 10 liters of water, was 2 hours.

The filter cleansing efficiency was checked as follows: a. The concentration of bacteria in the unfiltered water supply was 750 per cc. b. The bacteria amount in the filter material before and after regeneration was measured using a procedure where the filter material (AC) samples were placed in sterile, bacteria-free water, actively mixed to separate the trapped bacteria from the filter material, and than the bacteria content in the resulting mixture was measured by standard bacteria count techniques. c. The resulting bacteria filter cleansing efficiency was observed to be 99.5%.

Referring now to Fig. 3 there is provided a further system referenced generally 200, which is generally similar to system 100, shown and described hereinabove in conjunction with Fig. 1, but in which a pair of alternately operable first and second filters, respectively referenced 102' and 102", are provided. As seen, each of the filters is connected to incoming unfiltered water supply inlet 201, and to outgoing, filtered water supply outlet 206, via switchable inlet and outlet valves, and to a common air-ozone supply system, referenced 303.

In the present embodiment, each of the filters 102' and 102" is provided with an inlet valve, referenced 2' and 2", and an outlet valve, referenced 29' and 29". A main inlet valve 202 is provided upstream of inlet valves 2' and 2", and a main outlet valve 205 is provided downstream of outlet valves 29' and 29".

Air-ozone supply system 303 is similar to system 103 shown and described above in conjunction with Figs. 1-2C, and thus is not specifically described again herein, except with regard to the modifications necessary for alternate use and regeneration of the filter mass in each of filters 102' and 102".

The main modification required is the provision of additional air-ozone inlet valves 203' and 203", and air-ozone outlet valves 204' and 204". These additional pairs of valves are operated by controller 27, so as to ensure correct piping and exhausting of air or air-ozone mixtures required for the regeneration of the filter mass of one of the filters 102' and 102"; and for the continued throughflow of water through the other of the filters, thereby maintaining a constantly available water clean water supply.

Referring now briefly to Figs. 4A-4C, operation of system 200 is illustrated, in its various stages.

In Fig. 4A, it is seen that an uninterrupted, clean water supply is available through inlet valve 2', first filter 102' and outlet valve 29', while second filter 102" is in the final stage of cleansing/regeneration. Accordingly, inlet valve 2" and outlet valve 29" are closed, and a regenerative air-ozone flow is seen to be circulated through second filter 102". This stage is as shown and described above in conjunction with Fig. 2C, and is thus not described again herein in detail.

In Fig. 4B, after termination of the cleansing of second filter 102", it is seen to be fully operational, so as to permit water supply therethrough, while first filter 102' is seen o be in the first stage of cleansing, similar to that shown and described above in conjunction with Fig. 2B.

Finally, as seen in Fig. 4C, while second filter 102" continues to provide a filtered water supply therethrough, first filter 102' enters the second stage of cleansing. A clear advantage of th-3 embodiment described hereinabove in conjunction with Figs. 3-4C is the ability of the system to provide an uninterrupted supply of filtered water. It will be appreciated, however, that, depending on the capacity of the ozone generator employed, and the consequent time taken to clean a single filter mass as described above, the embodiment of Figs. 1-2C may be employed so as to cleanse during a time period when a water supply would not normally need to be available, for example, on working premises during the night, or at weekends.

It will be appreciated by persons skilled in the art that the scope of the present invention is not limited solely by what has been shown and described hereinabove, merely by way of illustrative example. Rather, the scope of the present invention is limited solely by the claims, which follow:

Claims

1. A system for maintaining a clean water supply, which includes: at least one filter having a sorbent filter mass arranged for flow through filtration of water containing contaminants including bacteria and organic substances, while substantially preventing passage through said filter mass of the contaminants, thereby to cause an accumulation of contaminants in association with the filter mass; selectably operable apparatus for substantially drying said sorbent filter mass; and selectably operable apparatus for exposing said sorbent filter mass and the accumulated contaminants to a predetermined supply of ozone for a preselected period of time, thereby to destroy the contaminants and thus clean said filter mass.

2. A system according to claim 1, wherein each said at least one filter includes: a housing having a water inlet and a water outlet; support apparatus for supporting said sorbent filter mass between said water inlet and said water outlet; an ozone supply selectably connectable to said housing via an ozone inlet formed in said housing; ozone exhausting apparatus for permitting exhaustion of ozone from said housing; and switching apparatus for selectably preventing throughflow of water through said housing and for operating said ozone supply so as to expose said filter mass to ozone for a preselected period of time, thereby to destroy the contaminants and thus clean said filter mass.

3. A system according to claim 2, and also including apparatus for exposing said filter mass to an air supply prior to operation of said ozone supply, thereby to dry said filter mass prior to exposure thereof to ozone.

4. A system according to claim 2, wherein said sorbent filter mass is formed of a granular material, and said support apparatus for supporting said sorbent filter mass includes a pair of water permeable grids, operative to contain said filter mass therebetween.

5 A system according to claim 4, wherein a predetermined one of said permeable grids is movable, and said support apparatus also includes resilient apparatus for applying a compression force to said movable grid and thus also to said filter mass, thereby to ensure a desired compaction of said filter mass

6 A system according to claim 2, wherein said water inlet has associated therewith a water inlet conduit having a siphon shape, operative to retain water in a predetermined portion thereof at all times, thereby preventing exit of ozone therethrough toward an inlet valve associated therewith

7 A system according to claim 2, wherein said at least one filter includes first and second filters, said switching apparatus is operative to selectably prevent throughflow of water through said first filter and to enable cleaning of said filter mass therein, while simultaneously permitting throughflow of water through said second filter, thereby to maintain a clean water supply therethrough during cleaning of said filter mass of said first filter, and said switching apparatus is further operative, subsequent to cleaning of said filter mass of said first filter, to selectably prevent throughflow of water through said second filter and to enable cleaning of said filter mass therein, while simultaneously permitting throughflow of water through said first filter, thereby to maintain a clean water supply therethrough during cleaning of said filter mass of said second filter

8 A method of maintaining a clean water supply, which includes. passing through at least one filter having a sorbent filter mass a flow of water containing contaminants including bacteria and organic substances, thereby to cause an accumulation of contaminants in association with the filter mass; substantially drying said sorbent filter mass; and selectably exposing the accumulated contaminants to a predetermined supply of ozone for a preselected period of time, thereby to destroy the contaminants and thus clean the filter mass

9. A method according to claim 8, wherein said step of substantially drying includes the step of exposing the filter mass to an air supply prior to said step of selectably exposing, thereby to substantially dry said filter mass prior to exposure thereof to ozone.

10. A method according to claim 9, wherein the sorbent filter mass is formed of a granular material, and said method includes the additional step of applying a compression force to the filter mass, thereby to ensure a desired compaction thereof.

11. A method according to claim 8, wherein said step of passing through at least one filter includes the step of passing a flow of water through at least two filters arranged in parallel, and said step of selectably exposing includes the steps of: a) preventing a flow of water through and exposing the contaminants accumulated on a first of the filters, to a predetermined supply of ozone for a preselected period of time, thereby to clean the filter mass of the filter, while maintaining a throughflow of water through a second of the filters; b) subsequently, permitting a flow of water through the first of the filter, and preventing a flow of water through and cleaning the filter mass of the second filter; c) repeating said steps a) and b), thereby to repeatedly regenerate each of the filters while permitting a flow of water through the other filter.