WO1999016715A1

WO1999016715A1 - Water treatment method and device

Info

Publication number: WO1999016715A1
Application number: PCT/IL1998/000453
Authority: WO
Inventors: David Itzhak
Original assignee: Argad Water Treatment Industries Ltd.
Priority date: 1997-10-01
Filing date: 1998-09-17
Publication date: 1999-04-08
Also published as: IL121880A0; HUP0004372A3; JO2053B1; CA2304762A1; HUP0004372A2; EP1023243A1; WO1999016715A9; AU9183298A; PL339563A1

Abstract

A method of treatment of aqueous media comprises applying to the aqueous medium in an electrolytic cell (I) an electrical direct current of a magnitude and at a flow-rate of the liquid in said electrolytic cell such that a combined effect of scale removing and disinfecting is achieved.

Description

WATER TREATMENT METHOD AND DEVICE

Field of the Invention

The present invention relates to water treating systems, particularly to scale removing

and biocidal water treating systems.

Background of the Invention

The problem of scale is inherent to all systems in which there is a flow of water that

contains any of Ca7 and Mg^""^" ions together with any of OH^", CO₃ ⁼, HCO₃ ^", SiO₃ ⁼,

or SO₄ ^". Under certain temperature and pH conditions, carbonates, silicates, sulfates

and hydroxide salts precipitate and cause blockage of nozzles, reduction of cross-

section area of pipes, heat insulation and underdeposit corrosion. The well-known

methods of removing scale from aqueous liquids are reverse osmosis and ion

exchange. Another method for removing scale is direct current (DC) electrolysis.

US 4,384,943 discloses a method of fluid treatment which comprises applying DC

current to aqueous liquids.

Electrolytic treatment of aqueous fluids to produce biocides is well known in the art.

For example, US 4,384,943 describes such a treatment which comprises maintaining

in the fluid a compound that is electrochemically decomposable to yield bromine,

chlorine or iodine and/or by decomposing water to produce biocidally active O₂ or O₃

oxidants.

US 5,424,032 describes a method of treating water using innocuous chemicals for the

treatment of microorganisms, or employing ultraviolet light or electrolysis in order to

destroy microorganisms. The term "disinfecting", as used herein, means destroying various types of

microorganisms to the extent that this prevents the formation of biological fouling,

and disinfection of drinking water or of water for use in bathing.

Since scale removing and scale preventing are related processes, each of the terms

"scale removing" and "scale preventing" herein mean both scale removing and scale

preventing.

It is a purpose of the present invention to provide a process for preventing or at least

inhibiting the growth of microorganisms in aqueous solutions, e.g., water, and for

precipitating scale therefrom, which does not require the addition of chemicals to

said solutions, and thus is an environmentally-friendly process. Thus, the invention

solves many severe problems inherent to prior art methods. For instance, there are

cooling systems in which the water is treated by the addition of chemicals. The bleed

stream of such cooling systems cannot be used in many applications, due to the

presence of said chemicals, and in many cases said bleed stream is wasted or requires

expensive purification treatments to remove the chemicals, before it can be released

into the environment.

It is another purpose of the present invention to provide a process for disinfecting

aqueous liquids and for removing scale therefrom which permits to operate at a pH

higher than 7, and even higher than 8.5, It has now been found, and this is still another object of the invention, that in a

system where a DC treatment having a combined effect of in situ production of

biocides and of scale precipitation was applied to an aqueous fluid, e.g., pure water

with no further additives, a dramatically lower percentage of scale was required to be

precipitated than described in the prior art, in order to achieve substantially the same

results of disinfecting and scale removing, as achieved for softened water described

in the prior art.

Summary of the Invention

The present invention provides a method of treatment of aqueous media, comprising

applying to said aqueous medium in an electrolytic cell an electrical direct current of

a magnitude and at a flow-rate of the liquid in said electrolytic cell such that a

combined effect of scale removing and disinfecting is achieved.

The present invention further provides an aqueous fluid treatment device for scale

removing and disinfecting comprising an electrolytic cell operated by a direct current

source, said electrolytic cell being adapted to allow an aqueous medium to circulate

therethrough.

The amount of direct current applied to said aqueous fluids varies according to the

type of aqueous medium. For example, in the case of the treatment of cooling water,

the preferred amount of direct current applied thereto is about lA/5m /hour.

Aqueous media that can be treated include, but are not limited to, drinking water, tap

water, agriculture water, industrial water, sea water and sewage water. An advantage of the present invention is that the pH at which it is possible to operate is not limited,

so that it is possible to operate at a pH much higher than the prior art. As will be

apparent to the skilled person, at pH of about 8-9 no corrosion inhibitors are required,

because of the basic nature of the water, and this is another substantial advantage of

the invention.

The device of the present invention can be used in any watering system, cooling

system, heating system, water supplying system, and fogger. Said watering systems

is can include, but are not limited to, drippers, sprinklers and foggers. Cooling

systems include, e.g., cooling towers. Heating systems include, e.g., kettles, boilers,

washing machines, dishwashers, quick water heaters, evaporators, radiators, steam

generators, steam irons, steam cleaners, module water heaters, heating boosters,

thermal convectors, greenhouse heaters, and central heating systems. Heating

systems may further include, e.g., showers, sinks, bidets, bathtubs, hot tubs such as

Jacuzzi-type tubs and whirlpools, spas and swimming pools.

Optionally, the aqueous medium can further be filtered, and thus the device of the

present invention optionally further comprises, in case said device includes a liquid

outlet, a filter connected to said outlet, through which the electrically treated aqueous

fluid is driven.

Brief Description of the Drawing

- Fig. 1 schematically shows a water treatment device according to a preferred

embodiment of the invention. Detailed Description of Preferred Embodiments

The present invention provides a method of treating aqueous solutions, which

achieves a combined effect of scale removing and disinfecting. Such a method can

meet the need of many systems in which both effects are required, such as

agricultural systems in which water is distributed through narrow nozzles of

sprinklers, drippers and foggers, and even a small quantity of scale and/or biofilm is

liable to cause a blockage of said nozzles.

A treatment according to the present invention can be carried out, e.g., by a unit

which comprises a liquid container having at least one liquid inlet and one liquid

outlet, e.g., a pipe, further comprising at least one cathode and one anode placed

within said liquid container, said cathode and anode being in electrical contact with

the "-" and "+" poles of a direct current source, respectively. Said liquid inlet is

connected to a water source, and said liquid outlet is connected to a target system,

e.g., sprinklers, drippers and foggers, in which the disinfected, scale removed water is

desired.

Furthermore, as stated above, the present invention is suitable for disinfecting liquids

and for removing scale therefrom, in systems in which it is required to maintain a pH

in the range 7 - 10. In the process of the invention, the pH changes only locally, near

the electrodes, whereas in other systems, in which chemicals are added, the pH

changes homogeneously, and may cause severe operational problems, such as

corrosion. As will be further discussed hereinafter, when the invention is applied to the

treatment of cooling water no chemicals are added and therefore the bleed stream can

be used in a wide range of applications, e.g., crops watering. Furthermore, as will be

further illustrated in the examples to follow, the invention permits to employ water

having a conductivity of 3,000 μS or higher, up to about 6,000 μS, without causing

any substantial increase in corrosion. A typical pH for operating under these

conditions is pH « 9. In this specification "μS" indicates the μSiemens unit (which

equals μΩ^~ ). This result is both unexpected and remarkable, particularly since

current standards, in cooling towers employing chemicals, is not greater than 3,000

μS, and often as low as 2,000 μS. The ability of allowing high conductivities, while

preventing biofouling and scale formation, practically means that a smaller bleed -

and consequently a smaller make-up of water - is needed in the operation of the

cooling tower. Thus, when operating according to the invention, a reduction of up to

about 30% in the make-up can be achieved, as well as a reduction of up to about 60%

of the bleed, thus leading to a substantial saving in water usage and waste disposal.

The present invention can be carried out by means of any electrolytic cell. An

example of such a cell is described, e.g., in Whitten et al., "General Chemistry with

Qualitative Analysis", Saunders College Publishing, 4th ed., pp. 12-13.

It should be understood that the two processes that take place simultaneously

(biocidal effect and scale prevention or removal) each require different, sometime

contrasting operating conditions. Thus, in order to obtain a biocidal effect it is

required to operate with high currents (the production rate of biocidal species in the water is a function of the current) and high water flow-rates. On the other hand, in

order to achieve a substantial anti-scale effect low water flow-rates are needed, while

the magnitude of the current is of no consequence. It should further be noted that pH

and precipitation conditions are much more severe at the electrodes than on the

surfaces of the water apparatus.

Accordingly, preferred illustrative - but non-limitative - operating conditions are as

follows:

The current required to obtain a substantial biocidal effect depends on the type of

water treated and on the oxidant demand of the water. This can be estimated as:

1 A = 1 gr O_x/hr

wherein O_x is a gr_(eq) of a monoelectronic oxidant such as Cl*, OH*, YzO* or Br*.

In order to obtain a substantial biocidal effect in a typical water, it is required to

provide a detectable residual amount - e.g., about 0.05 ppm, of active chlorine

equivalent. The active chlorine equivalent present in the water can be determined

using conventional methods, e.g., using the Chlor-Test kit manufactured by Merck

KgaA, Germany, or the Lovibond kit manufactured by The Tintometer Ltd., UK, or

by any other suitable method. In order to obtain a substantial anti-scale effect, the linear flow velocity of water in

the electrolytic cell (calculated as the flow rate divided by the cross section of the

cell) should not exceed 500 m/hr, and should preferably be 100 m/hr or lower.

According to a particular embodiment, the invention is exploited in a Jacuzzi-type

(whirlpool) hot tub or spa. In such environments there is a further important

parameter, which is the turbidity of the water. A normal turbidity for clear water

should not exceed 0.8 NTU (normal turbidity units). According to a preferred

embodiment of the invention a whirlpool bath should operate with a current density

of at least 1 A/m , in order to achieve normal turbidity and at the same time to avoid

scaling effects and biofouling.

A water treatment device according to the present invention can be in a form such as

that illustrated in Fig. 1, in which numeral 1 is a pipe, numeral 2 is a rectangular

anode, and 3 and 4 each are rectangular cathodes (cathode boards). Anode 2 is

positioned along the longitudinal axis of pipe 1. Cathode boards 3 and 4 are

positioned along the longitudinal axis of pipe 1, one on each side of anode board 2

and both cathodes face anode 2. According to an alternative embodiment of the

invention (not shown in the figure), pipe 1 , made of metallic material may, by itself,

function as the cathode, instead of cathodes 3 and 4, or in addition.

In the examples to follow a device essentially as described in Fig. 1 was employed,

having the following dimensions: pipe 1 was a plastic pipe 60 inches long and having

a diameter of 10 inches, the anode was a rectangular board made of titanium, coated

with a catalytic coating and the two cathodes were each rectangular boards made of steel. All three electrodes were each 50 inches long and 5 inches wide. The distance

between each of the cathodes and the anode was 3 inches. Of course, the above

dimensions will vary in different arrangements and shapes of the device, and they are

provided herein for the purpose of exemplification only, and are in no way meant to

limit the invention.

Example 1 (comparative)

A stream of non-treated water was used in a fog-generator used in a greenhouse, in

which tomatoes were cultivated, for the purpose of cooling and keeping the

temperature at a fixed level of about 25-30°C. Due to the precipitation of scale and

the growth of microorganisms and algae around the nozzle, a blockage occurred at

the nozzle and the nozzles had to be replaced. The average lifetime of nozzles in

such system was 3 to 4 days.

Example 2 (comparative)

A stream of water treated by reverse osmosis was used in the same system as in

Example 1. The average lifetime of the nozzles, in this case, was 1 to 2 months.

Example 3

A stream of water treated by DC current according to the present invention was used

in the same system as that of Example 1. After three months there were no blockages

registered in any of the approximately 1000 nozzles, and the upkeep of said nozzles

was spared. Due to the use of the direct current treatment device of the invention, the

water was disinfected and scale was removed therefrom to the extent that the problem of blockages was solved for all practical purposes. Furthermore, the water

was free from chemical additives and was suitable for a wide range of uses.

Tomatoes that were watered with the treated water showed no decay of growth.

These results show a substantial improvement over the systems of Examples 1 and 2.

Example 4 (comparative)

A stream of non-treated water was used in a cooling tower operating at a flow rate of

500 m /hr, with a make-up of 30 m /hr, and a bleed of 10 m /hr. The conductivity of

the tap water was about 1,000 μS, and that of the bleed stream (and, hence, of the

recirculating water) was 3,000 μS. After two weeks, a substantial layer of biofϊlm

and scale was observed on the walls of the tower. The water in the tower was turbid.

Example 5 (comparative)

A stream of water treated by polyphosphonates, sulfuric acid and corrosion inhibitors

at a pH of less than 8 was used in the cooling tower of Example 4. As a result, the

pH was unstable and scale and biofilm appeared on the walls of the tower, and were

removed every three months in order to allow a smooth functioning of the tower.

Metallic elements showed some corrosion. The water in the tower was turbid, and

was not suitable for watering processes.

Example 6

A stream of water of with a recirculation stream of 50 m /hr treated by DC current

according to the present invention was used in the system of Example 4 at the time

that a layer of biofilm, as well as scale, were already present. The conductivity of the bleed stream was 5,000 μS. The pH was 8.8. The make-up was 20 m^J hr and the

bleed 4 m /hr. After two weeks, said layer disappeared, and the water in the tower

was clear. No corrosion was noted. The bleed flow was of a quality suitable for

watering processes. Due to the use of the direct current treatment device of the

invention, the water was disinfected to the extent that not only did further biofilm not

appear on the walls of the tower, but the existing biofilm vanished. The clear water,

scale and biofilm removal, and the "green" use of the bleed flow of the present

example show a substantial improvement over the results of Examples 4 and 5.

Example 7

A 2 m Jacuzzi-type hot-tub was used for this example. The turbidity in the water

was 0.5 NTU. The whirlpool was operated for 4 consecutive hours with 4 persons

bathing each during 1 hour, without the addition of any chemicals. The turbidity at

the end of this 4-hour period was 3 NTU. The whirlpool was then operated empty,

together with an electrolytic cell treating water with a maximal recycle ratio of 6/hr

(number of volumes recirculated per hour), at 10A for 2 hours, at the end of which

period the turbidity was 0.1 NTU. The redox potential was 600 mV. The make-up of

water to the tub was effected on demand by a level indicator that controlled the level

ofwater in the tub.

The experiment was repeated daily during two weeks, without any water

replacement, and the turbidity dropped each time to the same value of 0.1 NTU. Additionally, the redox potential of the water was measured about 3 hours after the

bathing, and was found consistently to be in the range 500 - 700 mV, with a

detectable amount of oxidants. Furthermore, during this experiment 150 gr of scale

were removed from 2 m of water, containing mainly CaCO₃ and Mg(OH)₂.

A comparative test was also run with currents below 2A, and it was found that below

this value it was not possible to reach a redox potential greater than 500 mN. The

turbidity of the water, however, still remained at a suitable level (0.1 NTU).

As will be apparent to the skilled person, the above results are greatly advantageous

for use in bathing systems, such as whirlpool. It should further be noted that the

control of the turbidity is of great importance, since it is undesirable to replace the

water in the whirlpool, because fresh water carries with it added amounts of

carbonates which cause the clogging of orifices.

The above description and examples have been provided for illustrative purposes

only, and are not intended to limit the invention in any way. It will be apparent to the

skilled person that many modifications, variations and adaptations may be made to

the invention by persons skilled in the art, without departing from the spirit of the

invention or exceeding the scope of the claims.

Claims

CLAIMS:

1. A method of treatment of aqueous media comprising applying to said aqueous

medium in an electrolytic cell an electrical direct current of a magnitude and at a

flow-rate of the liquid in said electrolytic cell such that a combined effect of scale

removing and disinfecting is achieved.

2. A method according to claim 1, wherein the current is such as to generate

detectable residual amount of active chlorine equivalent in the water.

3. A method according to claim 2, wherein the residual amount of active chlorine

equivalent in the water is 0.05 ppm or higher.

4. A method according to any one of claims 1 to 3, wherein the linear flow-rate of

aqueous medium through the electrolytic cell is 500 m/hr or less, preferably 100 m hr

or less.

5. A method according to any one of claims 1 to 4, wherein the aqueous medium is

water from a whirlpool, the current density is at least 1 A m .

6. A method according to any one of claims 1 to 4, wherein the aqueous medium is

water from a cooling tower, and the conductivity in the recirculating water is between

3,000 ╬╝S and 6,000 ╬╝S.

7. A method according to any one of claims 1 to 4, wherein the aqueous medium is

selected from a group which consists of tap water, agricultural water, industrial

water, sea water and sewage water.

8. A method according to any one of claims 1 to 7, wherein the pH of the water is

maintained at a value above 7.

9. A method according to claim 8, wherein the pH is in the range 8 - 9.

10. An aqueous fluid treatment device for scale removing and disinfecting

comprising an electrolytic cell operated by a direct current source, said electrolytic

cell being adapted to allow an aqueous medium to circulate therethrough.

11. An aqueous fluid treatment device according to claim 8, for use in agriculture

watering systems.

12. A device according to claim 11 wherein the watering systems are selected from

the group which consists of drippers, sprinklers and foggers.

13. An aqueous medium treatment device according to claim 10, for use in a cooling

system.

14. A device according to claim 13, wherein said cooling system is a cooling tower.

15. An aqueous medium treatment device according to claim 10, for use in a heating

system.

16. A device according to claim 15, wherein said heating system is selected from the

group consisting of kettles, boilers, washing machines, dishwashers, quick water

heaters, evaporators, radiators, steam generators, steam irons, steam cleaners, module

water heaters, heating boosters, thermal convectors, greenhouse heaters, and central

heating systems.

17. An aqueous medium treatment device according to claim 10, for use in a water

supplying system.

18. A device according to claim 15, wherein said heating system is selected from the

group that consists of showers, sinks, bidets, bathtubs, hot tubs, particularly Jacuzzi-

type tubs and whirlpools, spas and swimming pools.

19. An aqueous medium treatment device according to claim 10, for use in a fogger.

20. A cooling tower system comprising:

a cooling tower; and

a device according to claim 10;

said cooling tower being adapted to bleed water and to receive make-up water when

the conductivity of said water is in the range 3,000 ╬╝S - 6,000 ╬╝S.