GB1602768A

GB1602768A - Method and apparatus for producing biologically safe drinking water from natural water

Info

Publication number: GB1602768A
Application number: GB22269/78A
Authority: GB
Original assignee: Cons Foods Corp; Consolidated Foods Corp
Current assignee: Hillshire Brands Co; Cons Foods Corp
Priority date: 1977-06-15
Filing date: 1978-05-25
Publication date: 1981-11-18
Also published as: AU524522B2; AU3666978A; JPS5418149A; AR224863A1; FR2394495A2; NL7806042A; ZA783257B; DE2826107A1; SE7805918L; BR7803778A

Description

(54) METHOD AND APPARATUS FOR PRODUCING BIOLOGICALLY SAFE DRINKING WATER FROM NATURAL WATER (71) We, CONSOLIDATED FOODS CORPORATION, a corporation of the State of Maryland, United States of America, located at 51 Forest Avenue, Old Greenwich, State of Connecticut, United States of America, do hereby declare the invention for which owe pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method of and apparatus for producing biologically safe drinking water from natural water.

The treatment of water by oxidizing bactericides such as chlorine is well known.

However, it has recently been shown that the action of chlorine on organic materials in water will produce halogenated organics with suspected carcinogenic properties.

These organics include the trihalomethanes such as chloroform and bromoform. Efforts to reduce the formation of halogenated organics in water have included changing the point of chlorination in the water treatment process or replacing chlorine by another disinfectant such as ozone. As a stronger oxidizing agent than chlorine, ozone can oxidize halide ions to the halogen form resulting in the formation of halogenated organics. Other oxidizing agents used in the practice of this invention also produce halogenated organics such as trihalomethanes. The present invention is based on the realisation that the production of halogenated organics from oxidizing bactericides can be avoided if the halide ions are removed from the water in an initial treatment station. If the halides are replaced by another anion, i.e., bicarbonate, the ionic character of the water is maintained, a natural buffer is added to the water and the bicarbonate will not be effected by any known oxidizing bactericide.

Accordingly, the invention resides in one aspect in a method of producing biologically safe drinking water from natural water comprising the steps of removing halide ions from said natural water and exchanging for said halide ions an ion which will substantially maintain the original ionic character of said natural water and not form halogenated organics with oxidizing bactericides nor inhibit the biocidal effects of said oxidizing bactericides, and introducing an oxidizing bactericide to said water in a biologically acceptable amount to kill bacteria in said water.

In a further aspect, the invention resides in apparatus for producing biologically safe drinking water from natural water, comprising container means, an inlet for introducing natural water into said container means, ion exchanging means for exchanging halide ions in said natural water for an anion which does not inhibit the bactericidal effect of oxidising bactericides or form halogenated organics with oxidising bactericides and substantially maintains the total ionic balance of said treated water, means in said container means downstream of said ion exchanging means for the solution fed chemical addition of an oxidising bactericide or combination of oxidising bactericides, means in said container means for removing organics from the treated water, means in said container means for removing oxidising bactericides from the treated water and an outlet for discharging said treated water from said container.

The natural water may additionally be treated with silver ions, as a further bactericide, in the manner described and claimed in our British Patent No. 1,543,590.

In the accompanying drawings: Figure la to Id is a schematic representation of a method according to one example of the invention, Figure 2 is a diagrammatic elevation of one embodiment of a water treatment unit for carrying out the process according to Figures la to Id, Figure 3 is a cross-sectional view of the unit 10 shown in Figure 2, Figure 4 is a top view of a schematic illustration of a second embodiment of apparatus for carrying out the process according to said one example, Figure 5 is a schematic side elevation of the apparatus according to Figure 4, and Figure 6 is a cross-sectional view of the number one unit shown in Figures 4 and 5.

Referring to the drawings, and more particularly Figure la to Figure Id, the method of said one example is for producing biologically safe drinking water from a source of natural water at ambient temperature, i.e., water which is intended for drinking purposes such as tap water whether the tap is connected to a domestic or commercial well or private or municipal household water source, as well as surface waters contained in lakes or streams. It will be understood that natural water excludes distilled and deionized water, raw sewage and/or industrial waste water or process waste water and salt waters.

In Figure la, the natural water is initially fed to a treatment station Al which eliminates or significantly reduces the halide ions (X-) in the input water to prevent the complexing of silver ions which are introduced in Unit A2 and to prevent the production of halogenated organics from the oxidising bactericides introduced in Unit A3. In Unit A2 silver ions (Ag+) are introduced to the input water at high levels compared to the fifty micrograms per liter level allowed by the Environmental Protection Agency Standard for Drinking Water. The content of Ag+ found to be effective as a bactericide is of the order of 600 to l000,ug'l more or less. The high Ag+ water from Unit A2 is held for a period of time of the order of six minutes for water having a bacterial level of E. coli up to ten thousand Colony Forming Units (CFU) per 100 milliliters (ml). Laboratory tests have shown the need for high silver levels for rapid kill of E. coli.

In Unit A3 oxidising agent bactericides are introduced following the elimination of halide ions in Unit Al. This absence of halide ions prevents any oxidation to the halogen form and subsequent oxidation to carcinogenic halogenated organics. The oxidizing agents that can be safely used in this embodiment include ozone (03), permanganate (MnO4-), peroxide (H2O2), ferrate (FeO4=), and persulfate (S2O8=). The practice of this invention also permits the use of the above mentioned oxidizing disinfectants without an initial introduction of silver ions (Ag+) as discussed in connection with the description of Unit A2 in Figure la. While not illustrated in Figure la, it is to be understood that under these circumstances Unit A2 would be eliminated or modified to perform substantially the same function as that of Unit A3.

Figure lb illustrates a further step in the process of Figure 1 whereby water containing a high silver ion level is treated in Unit B to lower the silver ion (Ag+) level to 50 gfl or less to meet the legal standard for silver in drinking water. As an alternative to silver ions (Ag+), mercury ions may be introduced as the bactericide in Unit A2 in an amount of 400 600 g/l, in which case the water is treated in Unit B to reduce the mercury ion level to 2 g/l or less to meet the legal standard.

In Figure 1 c the process according to said one example is modified to process input water with a high mineral content in a mixed bed resin Unit C partly to deionize the input water prior to treatment in Units Al and A2, Figure la. A part of the input water bypasses the mixed bed resin Unit D to preserve the natural minerals present in the input water which are desirable for taste and health reasons. The water effluent from Unit C is totally deionized.

Alternatively, as - shown in Figure id where the input water has a high mineral content, the process is modified so as completely to deionize a portion of the input water in Unit C, and the remaining input water is treated to remove halides, sulfates and nitrates, i.e., selective removal of anions. The combined effluent from Unit Al and Unit D is then passed through Unit A2 containing a media of activated carbon impregnated with silver salts and metallic silver before proceeding to Unit A3 (not shown in Figure Id). Unit Al, Figure Id is identical to Unit Al, Figure la.

Referring now particularly to Figure 2, reference numeral 10 designates an open topped container in which the first stage of the process is carried out. Located in zone No. 1 of the container is an ion exchange resin bed for removing halide ions from the water to be treated. A suitable material for this purpose is an ion exchange resin bed in which halide ions are removed from the input water without significantly changing the pH and anion content of the water. A method of achieving this halide ion removal is by the use of an anion exchange resin in the bicarbonate form. An anion exchange resin in the bicarbonate form will exchange with all anions (S04=, NO3-, Br-, C1-) until equilibrium is established between the concentrations of all anions (SO4=, NO3-, Br-, C1-, HCO3-) associated with the resins' functional groups and their concentrations in the input water.

The efficacy and capacity of a given resin for halogen X-) removal to the desired X concentration will be determined by the exchange equilibrium constants, kinetics of exchange, flow rate through the resin bed, input ion concentrations, temperature, etc.

A resin suitable for this purpose is Rohm & Haas IRA 410.

As an additional feature of this invention the anion exchange resin for the removal of halide ions also accomplishes the partial removal of organics which in the presence of halogen would ultimately oxidize to form trihalomethanes. Thus, it is shown that the formation of halogenated organics can be avoided by the simultaneous removal of halides and precursor organics in the treated water. Another feature of the anion exchange resin is the removal of minor and/or trace anions in water, such as phosphate and carbonate which can interfere with disinfectants such as silver.

In zone 2 of stage 1 (Figure 2) is a bed consisting of a composition of silver seal(s) absorbed and/or impregnated on activated charcoal. Any silver salt or combination of silver salts whose solubility product is such that the resulting silver ion concentration in the water is in excess of 50 micrograms of silver per liter may be used. The silver salts are present in the amount approximately equal to 1% by weight of the activated charcoal. Other suitable media for the release of silver ions in zone 2 include alumina, silica gel and diatomaceous earth.

If the oxidizing bactericides are to be added in sequence with the discharge of silver ions, stage I would include a third treatment station, zone 2A, which would accommodate the addition of said oxidizing bactericide. However, if said oxidizing bactericides are to be introduced in place of silver ions zone 2 of stage I (Figure 2) would be modified to provide means for the solution fed chemical addition of said bactericides. Oxidizing bactericides may be added before, after or with silver ions whatever is found most advantageous.

Reference character 12 designates a container which is placed beneath container 10 for the purpose of collecting the storing water which has passed through stage I.

A container 14 is provided, which structurally may be the same as container 10. In container 14, above zone 3, is an open space for receiving water from container 12.

The water from container 12 passes through zone 3 for the removal of objectionable organics and the partial removal of oxidizing bactericides introduced in zone 2 or zone 2A. The residual oxidizing bactericides are removed in zone 4. Zone 3 may be a bed of plain activated charcoal such as Calgon "Filtersorb 200" or "Filtersorb 400", but preferably consists of a self-sanitizing activated charcoal media. A self-sanitized activated charcoal bed or media may be a composition of activated charcoal having silver salts adsorbed or impregnated on the charcoal. The following treatment zone, zone 4, contains an ion exchange resin bed for selective removal of the silver ions to a concentration below 50 micrograms per liter from a silver ion concentration provided by zone 2 of stage I, i.e., in excess of 800 micrograms per liter.

As noted above, zone 4 also accomplishes the removal of residual oxidizing bactericide in order to maintain the natural character of the water.

One method of achieving the silver ion removal is by the use of an anion exchange resin in the chloride form. It is believed that the silver combines with this resin in such a way as the silver concentration in the effluent appears to be governed by the solubility product of silver chloride. Other anionic forms whose solubility product with silver is sufficiently small as to lower the concentration of silver in the treated water to less than 50,ug/1 may also be used to remove silver. Although not widely known, the anion exchange resin may also remove silver by chelation. (I. M. Abrams, N.A.C.E.

Meeting-Houston, Texas, Oct. 8, 1974 Selective Removal of Heavy Metals from Wash Waters by Ion Exchange and Adsorbent Resins.) Cation exchange resins may also be used selectively to remove silver. With both types of resins, its form must be such as to not adversely alter the treated water. Although it may adversely alter the water, deionization by ion exchange is also a possible method for silver removal.

A suitable ion exchange resin for removing a silver ions from water is Rohm & Haas "Amberlite IRA 410" consisting of styrene DVB in chloride form. A selfsanitized media subsequent to the silver removal resin would require a silver salts which releases residual silver ions to water passing there through at less than 50,ug/l.

Stage II may be also arranged inversely to that described above. That is, zone 3 may contain the ion exchange resin for silver ion removal and zone 4 may contain the selfsanitizing activated charcoal.

In operation, a quantity of raw water, such as a glassful, is poured into the open top of container 10, which has sufficient space above zone 1 to accommodate this quantity. As the water percolates by gravity through zone 1, an ion exchange takes place which removes halide ions and adds bicarbonate ions to the water and thus retains the natural character of the water.

The water thus treated then passes through the activated charcoal impregnated with oligodynamic silver in zone 2. Here, the activated charcoal adsorbs organic materials which may be present in the water as a bactericide and virucide. The concentration of silver ions produced in the water in zone 2 is 600 to 1000 micrograms per liter (ag/l) which is substantially greater than the allowable EPA Standard for Drinking Water (50 micrograms per liter).

At this concentration the silver ions act very rapidly to kill bacteria and also appear to inactivate some viruses in the water, but the virus inactivation rate is slower than the bacteria kill rate.

If an oxidizing bactericide such as permanganate (MnO4-) is to be introduced in place of silver ions a solution fed chemical addition takes place in zone 2. If a sequential addition is utilized the water with a silver ion concentration of 600 to 1000 micrograms per liter .(yg/1) first passes to zone 2A where an oxidizing bactericide is introduced in solution.

After passing through zone 2, the water is collected in container 12 where it is held for a period of time, six minutes or more, and is then poured into container 14. In passing by gravity flow through the bed of zone 3, an ion exchange takes place which removes silver ions from the water so as to bring the concentration thereof below the allowable value of 50jug/1 and partially removes oxidizing agent bactericides introduced in zone 2 of zone 2A.

The water then passes through a final bed of self-sanitized activated charcoal in zone 4 for further adsorption of residual oxidizing bactericides and organic material which may not have been adsorbed in zone 2.

Alternatively, the bed of zone 3 may contain the self-sanitized activated charcoal for adsorption of organic matter. The water subsequently passes through an ion exchange resin in zone 4 for removing silver ions to a level below 50 micrograms per liter (us/1). Each embodiment of this invention accomplishes the removal of solution fed oxidizing bactericides thereby maintaining the natural character of the treated water.

In Figure 3 there is shown an actual container 20 which corresponds to container 10 in Figure 2. As shown, it is an upper compartment 22 having an open top.

At the bottom of compartment 22 is a grating 24 over a screen 26 forming the top of zone 1. Below this screen and above a grating 28 is the bed of ion exchange resin for removing halides, as described above in connection with Figure 2. Between grating 28 and a lower grating 30 is zone 2 which contains the bed of silver impregnated carbon. A section 32 underlies grating 30 and is over an outlet opening 34 which may be provided with a normally closed manually operable valve 36.

Although it is not shown in Figure 3, it should be understood that where a sequential addition of oxidizing bactericides is utilized a third grating would be inserted below grating 30 thereby creating a third treatment station for the introduction of said oxidizing bactericides. In this case, screen 32 would be placed below the third grating in between such grating and said outlet opening 34.

An actual container corresponding to container 14 of Figure 2 would be constructed identically with container 20 of Figure 3 but, of course, would have the beds in zones 3 and 4 as described in connection with Figure 2.

The apparatus diagrammatically shown in Figures 4 and 5 is intended for the continuous flow of water to be treated.

Container 40 corresponds to zone 1 in container 10 (Figure 2), into which water is admitted under pressure at the top. After flowing through the ion exchange bed in tank 40, the water passes out the bottom and into the lower end of container 42 which corresponds to zone 2. From here the water passes through a series of containers 44A-44F, which correspond to the collecting container 12 of Figure 2 but of relatively greater capacity in order to provide sufficient time for the silver ions and/or oxidizing bactericides to act on the flowing water within the containers.

From container 44F the water passes into the top of a container 46 which corresponds to zone 3 in Figure 2. After passing through the ion exchange bed in container 46, where excess silver ions are removed, the water flows into the bottom of a container 48, corresponding to zone 4 of Figure 2, which contains the self-sanitized activated charcoal bed. From this last container the water passes out, either to be used directly or to be stored.

As described above, the containers 46 and 48 may be transposed whereby the water passes through an ion exchange resin to remove the silver ions and subsequently passes through a self-sanitized activated charcoal bed as described in more detail above in connection with Figure 2.

In Figure 6 there is shown in cross section an actual container 50 which corresponds to any of the containers 40, 42, 46 and 48 of Figure 5. It consists of a cylinder 52 threaded at opposite ends to which threaded caps 54 and 56 may be removably secured. At the upper inlet end, a cupshaped felt packing 58 and a similarly shaped screen 60 are pressed against the interior of cylinder 52 by a tube 62 formed with notches 64 to permit the flow of water from an inlet fitting 66 in the cap 54. The construction at the the bottom is similar, except the felt packing 68 is not formed with a central opening and also serves as a filter.

As shown in Figure 6, the bottom of container 50 is connected to the bottom of a similar container 70, which corresponds to container 42 in Figures 4 and 5. As stated above, the construction of the containers corresponding to 46 and 48 in Figures 4 and 5 are the same as that of container 50 in Figure 6. The actual containers corresponding to 44A through 44F in Figure 5 and 6 are simply hollow tanks. In order to obtain a holding time of at least six minutes, the combined volume of tanks 44A through 44F should be 3 gallons if the flow rate is 1/2 gallon per minute.

Laboratory tests appear to establish virus inactivation by silver at the concentrations described above of type 1, Polio Virus and Echo Virus, type 7. The same laboratory tests have established the efficacy of silver as a bactericide for E. colt, Salmonella typhimurium, Shigella sonnei, Candida albicans and Pseudomonas aeruginosa.

Airborne bacteria which have contaminated water, such as Streptococcus Beta Haemolyticus and Staphylococcus aureus, appear to be killed by silver at the concentrations described above. However, for the airborne bacteria noted above, a twelve to twenty-minute holding time is required as opposed to six minutes holding time for the first noted bacteria.

The holding time required for the operation of silver ions and/or oxidizing disinfectants as bactericides will differ from that required for virus inactivation.

Thus, the holding time for virus inactivation may be determined by suitable tests which are known to the art.

WHAT WE CLAIM IS: 1. A method of producing biologically safe drinking water from natural water comprising steps of removing halide ions from said natural water and exchanging for said halide ions an ion which will substantially maintain the original ionic character of said natural water and not from halogenated organics with oxidizing bactericides nor inhibit the biocidal effects of said oxidizing bactericides, and introducing an oxidizing bactericide to said water in a biological acceptable amount to kill bacteria in said water.

2. A method as claimed in Claim 1, in which the step of introducing said bactericide includes the use of an amount rapidly to kill the bacteria, followed by reducing said bactericide to a biologically acceptable level after it has acted as a bactericide.

3. A method as claimed in claim 1 or 2, wherein said ion exchanged for said halide ions is an anionic bicarbonate ion.

4. A method as claimed in any preceding Claim, wherein a portion of said natural water is de-ionized while another portion thereof is not so treated and both the deionized and untreated portions are combined before halide ion removal.

5. A method as claimed in any one of Claims 1 to 3, wherein a portion of said natural water is de-ionized while another portion of said water has the halide ions removed therefrom and both said portions are brought together prior to introducing the bactericide thereto.

6. A method as claimed in any preceding Claim, wherein said oxidising bactericide is selected from ozone, permanganate, peroxide, ferrate and persulfate.

7. A method as claimed in any preceding Claim, comprising the steps of introducing as a further bactericide mercury ions substantially in excess of 2 micrograms per liter to said water after removal of the halide ions, holding the treated water containing said mercury ions for a period of time sufficient for said mercury ions to act as a bactericide, and thereafter reducing the mercury ions in said water to not more than 2 micrograms per liter.

8. A method as claimed in any one of Claims 1 to 6, comprising the steps of introducing as a further bactericide silver ions substantially in excess of 50 micrograms per liter to the water after removal of the halide ions, holding the water containing said silver ions for a period of time sufficient for said silver ions to act as a bactericide, and thereafter reducing the silver ions in said water to not more than 50 micrograms per liter.

9. A method as claimed in Claim 8, wherein the step of reducing the silver ions is accomplished by contacting the water with an anion exchange resin regenerated with an anion that forms a silver salt of low solubility and which is associated with anion exchange resin.

10. A method as claimed in Claim 9, wherein the anion resin is in the chloride form.

11. A method as claimed in Claim 10, wherein said resin for removing halide ions and said resin for removing silver ions are cleaned by a silver wash while being regenerated in the bicarbonate and chloride form respectively.

12. A method as claimed in any one of Claims 8 to 11, wherein said silver ions are introduced into said water by passing the water through a medium containing a silver salt whose solution product provides a silver ion concentration in excess of 50 micrograms per liter.

13. A method as claimed in Claim 12, wherein said medium is selected from activated charcoal, alumina, silica gel and diatomaceous earth.

14. A method as claimed in any preceding Claim, wherein said halide ions are removed

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. container 50 is connected to the bottom of a similar container 70, which corresponds to container 42 in Figures 4 and 5. As stated above, the construction of the containers corresponding to 46 and 48 in Figures 4 and 5 are the same as that of container 50 in Figure 6. The actual containers corresponding to 44A through 44F in Figure 5 and 6 are simply hollow tanks. In order to obtain a holding time of at least six minutes, the combined volume of tanks 44A through 44F should be 3 gallons if the flow rate is 1/2 gallon per minute. Laboratory tests appear to establish virus inactivation by silver at the concentrations described above of type 1, Polio Virus and Echo Virus, type 7. The same laboratory tests have established the efficacy of silver as a bactericide for E. colt, Salmonella typhimurium, Shigella sonnei, Candida albicans and Pseudomonas aeruginosa. Airborne bacteria which have contaminated water, such as Streptococcus Beta Haemolyticus and Staphylococcus aureus, appear to be killed by silver at the concentrations described above. However, for the airborne bacteria noted above, a twelve to twenty-minute holding time is required as opposed to six minutes holding time for the first noted bacteria. The holding time required for the operation of silver ions and/or oxidizing disinfectants as bactericides will differ from that required for virus inactivation. Thus, the holding time for virus inactivation may be determined by suitable tests which are known to the art. WHAT WE CLAIM IS:

1. A method of producing biologically safe drinking water from natural water comprising steps of removing halide ions from said natural water and exchanging for said halide ions an ion which will substantially maintain the original ionic character of said natural water and not from halogenated organics with oxidizing bactericides nor inhibit the biocidal effects of said oxidizing bactericides, and introducing an oxidizing bactericide to said water in a biological acceptable amount to kill bacteria in said water.

by passing said water through a bed of halide ion removing anionic resin.

15. A method as claimed in Claim 14, wherein said anionic resin is regenerated in the bicarbonate form and imparts bicarbonate ion to said treated water to retain the natural character of the treated water.

16. Apparatus for producing biologically safe drinking water from natural water, comprising container means, an inlet for introducing natural water into said container means, ion exchanging means for exchanging halide ions in said natural water for an anion which does not inhibit the bactericidal effect of oxidising bactericides or form halogenated organic with oxidising bactericides and substantially maintains the total ionic balance of said treated water, means in said container means downstream of said ion exchanging means for the solution fed chemical addition of an oxidising bactericide or combination of oxidising bactericides, means in said container means for removing organics from the water, means in said container means for removing oxidising bactericides from the treated water and an outlet for discharging said treated water from said container.

17. Apparatus as claimed in Claim 16 and further including metal ion adding means in said container means downstream of said ion exchanging means for adding to said water a further bactericide in the form of metallic ions substantially in excess of permissible limits, and means in said container means for removing metallic ions from said treated water to reduce the metallic ion level below said permissible limits, said metallic ions cleaning said organic removal means and providing residual metallic ions for killing bacteria in said treated water located between said organic removal means and said metallic ion reducing means.

18. Apparatus as claimed in Claim 17, wherein said metallic ion adding means and said means for removing organics includes a composition having silver salts adsorbed and impregnated on a medium selected from activated charcoal, alumina, silica gel and diatomaceous earth.

19. Apparatus as claimed in any one of Claims 16 to 18, wherein said ion exchanging means removes anions having a higher exchange potential than bicarbonate anions at their relative concentrations in said treated water.

20. Apparatus as claimed in Claim 16 wherein said container means includes a treatment zone downstream of said ion exchanging means, said treatment zone having means for adding silver ions to the water substantially in excess of 50 micrograms per liter and simultaneously removing organics from the water, and said container means also being provided with means for partially removing silver ions to reduce the level of silver ions in the treated water to less than 50 micrograms per liter.

21. Apparatus as claimed in Claim 20, wherein said ion exchanging means and said means for removing silver ions are cleaned by a silver salt wash while being regenerated in the bicarbonate and chloride form respectively.

22. Apparatus as claimed in any one of Claims 16 to 21 with the addition of a mechanical filter means for removing suspended solids from said natural water prior to introducing said natural water into said container means.

23. A method as claimed in Claim 1 for producing biologically safe drinking water from natural water substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

24. Apparatus as claimed in Claim 16, for producing biologically safe drinking water from natural water comprising the combination and arrangement of parts substantially as hereinbefore described with reference to, and as shown in Figures 2 and 3 or Figures 4 to 6 of the accompanying drawings.