WO1998023544A1

WO1998023544A1 - Method and apparatus for water treatment by addition of hydrogen peroxide

Info

Publication number: WO1998023544A1
Application number: PCT/GB1997/003200
Authority: WO
Inventors: Maurice John Hancock; Derek George Carter; Andrew Frank Sweetapple
Original assignee: O2Spray Limited
Priority date: 1996-11-27
Filing date: 1997-11-21
Publication date: 1998-06-04
Also published as: AU5061798A

Abstract

The dissolved oxygen content of a body of water (11) is increased by the addition of hydrogen peroxide to water withdrawn from the body of water (11) by means of a pump (10) and discharged back into the body of water (11) in the form of a jet. The water is pumped through an outlet pipe (15) having a discharge section (16) containing a venturi which operates to draw the hydrogen peroxide from a storage container (18).

Description

METHOD AND APPARATUS FOR WATER TREATMENT BY ADDITION OF HYDROGEN PEROXIDE

Field of the Invention

This invention relates to the treatment of relatively large bodies of comparatively still water such as slow-flowing rivers, canals, ponds, lakes or reservoirs. The invention is of particular application to the treatment of water at fish farms.

Pollution incidents and natural events can cause a significant drop in dissolved oxygen levels or can result in other chemical or biochemical changes which require urgent treatment to restore the water to a life-sustaining condition.

Low dissolved oxygen levels in the water at fish farms adversely affect the health and rate of growth of the fish. It is accordingly important that the dissolved oxygen levels should be maintained and that it should be possible to effect rapid increases in dissolved oxygen levels if and when this is necessary.

Traditional techniques for increasing the dissolved oxygen levels have involved the use of pumps or other large equipment either to remove the polluted water or to increase the dissolved oxygen levels by introduction of gaseous oxygen.

It is an object of the present invention to provide an improved method and apparatus for increasing the dissolved oxygen content

Summary of the Invention

According to a first aspect of the invention there is provided a method of increasing the dissolved oxygen content of a body of water, said method comprising withdrawing water from said body of water, adding hydrogen peroxide to the water which is withdrawn and delivering the hydrogen peroxide-containing water back into the body of water from which it was withdrawn.

According to a second aspect of the present invention there is provided apparatus for use in increasing the dissolved oxygen content of a body of water, said apparatus including pump means for withdrawing water from said body of water and for returning it to said body of water, and dosing means for adding hydrogen peroxide to the withdrawn water prior to return thereof to the body of water.

The hydrogen peroxide is preferably contained within a storage container from which the hydrogen peroxide is withdrawn as a result of a venturi effect obtained as a result of the flow of the withdrawn water through the apparatus. The water containing hydrogen peroxide is preferably returned to the body of water from which it was withdrawn in the form of a jet.

The apparatus may be mounted on a boat and the jet of water may then serve for the propulsion of the boat, with steering of the boat effected by changing the direction of the jet.

The boat can be a small lightweight structure which can be easily and quickly transported to the site and operation of the apparatus on the boat may be controlled either remotely or by the occupants of the boat. If operation of the apparatus is remotely controlled, the remote control may control one or more of the following:- a) the speed of the water jet, b) steering of the boat by adjustment of the jet angle, c) the dosing rate, and d) operation of the water jet, i.e. an on-off control allowing the boat to be stopped.

If the apparatus is intended to be land-based, it may be mounted either on a fixed supporting structure, for example, on a fish farm, or on a trailer so that it can readily be transported from one site to another. The pump means which is used may alternatively be a submersible electric pump which is submersed in the body of water to be treated. The apparatus may include a pump having an inlet or inlet pipe through which water is withdrawn from the body of water to be treated and an outlet pipe through which the water is returned in the form of a jet. The outlet pipe may be, for example, of 50 mm. or 75 mm. in diameter. The hydrogen peroxide from the storage container is preferably fed into the outlet pipe, being connected to the outlet pipe by means of a supply line which contains an adjustable flow control valve.

The use of a venturi to withdraw the hydrogen peroxide from the storage container means that no separate motor or other actuator is required to effect dispensing of the hydrogen peroxide which can be arranged to flow from the storage container under the suction effect generated by the high-pressure flow of the water through the outlet pipe. It also avoids leakage of hydrogen peroxide into the body of water when the pump is not operating.

The apparatus may be arranged for automatic operation under the control of a sensor which senses the level of dissolved oxygen in the body of water and causes the apparatus to be actuated when the dissolved oxygen content falls below a predetermined level.

Brief Description of the Drawings Figure 1 shows a first form of apparatus for use in the treatment of water at a fish farm,

Figure 2 is a detail view showing the method of operation of the venturi,

Figure 3 is a plan view of a boat on which a second form of the water treatment apparatus is mounted,

Figure 4 is a side view of the boat, and

Figure 5 is a schematic diagram showing the interconnections between the main components of the apparatus.

Description of the Preferred Embodiments

The apparatus shown in Figure 1 comprises a submersible electric pump 10 which is submersed in the body of water 11 whose dissolved oxygen content is to be maintained at above a predetermined minimum level. The dissolved oxygen content of the body of water 11 is monitored by a sensor 12 which controls the operation of a switch 13 in the supply line 14 of the pump 10 so that, whenever the dissolved oxygen content falls below the predetermined level, the switch 13 is closed and the pump 10 is operated. The pump 10 has an inlet (not shown) through which the water from the body of water 11 is withdrawn on operation of the pump 10 for discharge through an outlet pipe 15 which terminates in a discharge section 16 mounted on a stand 17 so that the water issues from the discharge section in the form of a horizontal high- pressure jet. Hydrogen peroxide, to be introduced into the jet of water issuing from the discharge section 16, is contained within a storage container 18 connected to the discharge section 16 by a pipe 19 which includes a flow control valve 20. As can be seen from Figure 1 , the pipe 19 extends from the top of the container 18. There will thus be no tendency for the hydrogen peroxide to flow gravitationally from the container 18 along the pipe 19. The hydrogen peroxide in the container is typically a 30% or 35% by weight aqueous solution of hydrogen peroxide.

The discharge section 16 of the outlet pipe 15 is shown in detail in Figure 2 and includes an inner tube 21 which is located adjacent the entry end of the discharge section and has a cross- sectional area which is substantially less than the cross-sectional area of the remainder of the outlet pipe 16. The inner tube 21 is maintained in position on the axis of the discharge section 16 by means of a support sleeve 22 which has a tapering mouth 23 so that the velocity of the water flowing through the outlet pipe 15 will be increased substantially when it enters the inner tube 21 and a venturi effect will be obtained, causing the hydrogen peroxide solution to be withdrawn from the storage container 18 along the pipe 19 so as to enter the discharge section 16 of the outlet pipe 15 through at a position adjacent the support sleeve 22.

The hydrogen peroxide sucked into the discharge section 16 will be mixed with the jet of water flowing out of inner tube 21. The rate at which the hydrogen peroxide is withdrawn from the storage container 18 is adjustable by adjusting the setting of the flow control valve 20 and/or by adjusting the rate at which the pump 10 is running (if the pump 10 is an adjustable pump). When the control valve 20 is fully open, the rate at which the hydrogen peroxide solution is withdrawn from the container 18 is typically 3 litres per minute. Thus, for a standard 30 litre container, the contents of the container can be discharged in a period of ten minutes with the valve 20 fully open. Assuming, therefore, that the solubility of oxygen in water is 10 mg./litre, the dissolved oxygen content of 2.275 million litres of water can be increased from a figure of 60% of the maximum dissolved oxygen content to a figure of 80% in a period of ten minutes.

The discharge of the water and hydrogen peroxide in the form of a jet will create a degree of turbulence enhancing reasonably even distribution of the hydrogen peroxide in the body of water 11. It has, however, been found that, when the dissolved oxygen content in the water at a fish farm has fallen below the desired level and the apparatus is operated causing the discharge of a jet of dilute hydrogen peroxide solution into the water, the fish will tend to swim towards the location at which the jet of water is impinging on the surface of the water, thereby obtaining maximum benefit from the additional oxygen (in the form of dilute hydrogen peroxide solution) with which they are being supplied.

As shown in Figure 1 , the discharge section 16 is supported on a stand 17 which is supported on the land adjacent the edge of the body of water 11. It is to be appreciated that, if required, the stand 17 could be carried by a float which is connected by a rope or other line to the storage container 18.

This unique approach to dealing with low dissolved oxygen problems within fish farms or other fisheries, whether they are caused by pollution, natural events or high stocking densities has a number of significant advantages, as follows:- a) a very rapid increase in dissolved oxygen is possible, even with very large bodies of water, b) the unit is compact and easily deployed, c) the rate of injection of hydrogen peroxide can be varied to suit the circumstances, d) there are low capital and running costs, e) it is an intrinsically safe operation as the undiluted hydrogen peroxide is never under pressure, f) the use of a dissolved oxygen monitor enables automatic operation to be obtained, g) it is possible to use the apparatus for the application of other chemicals if so desired, and h) the apparatus is quiet and can thus be used close to residential properties.

Turning next to the embodiment of Figures 3 to 5, this includes apparatus having a number of features in common within the apparatus of Figures 1 and 2 but mounted on a boat. The boat has a lightweight hull 101 , which may be formed, for example, from polyester resin reinforced with glass fibres. A petrol-driven centrifugal pump 102 draws in water from beside the hull 101 via an inlet pipe 103 and expels the water through an outlet pipe which includes a venturi section 104, a short length of flexible conduit 105 and an outlet nozzle 106 which projects from the rear of the hull 101 to self-propel the boat by emitting a high-speed water jet.

The venturi section 104 is preferably constructed from a non- corrosive material, such as an aluminium alloy and has a side inlet which is provided with a control valve 109 which is connected, via a narrow-bore suction pipe 110 to one of two storage containers 111 and 112 filled with hydrogen peroxide solution so that, as water is caused to flow through the venturi section 104, the hydrogen peroxide solution will be drawn from container 111 for admixture with the jet of water being discharged from the nozzle 106.

The operation of the apparatus is controlled by a control unit 114 the operation of which will now be described with reference to Figure 5. The control unit 114 includes a radio receiver 121 which receives command signals from a four-channel radio transmitter 122 operated from a remote location such as a river bank. Automatic positioning control could be incorporated if desired. The outputs of the four channels from the transmitter 122 are used as follows:-

1) the pump 102 can be stopped via a control line 124,

2) the speed of the pump 102, and hence the speed of the boat, is controlled via a throttle control line 125,

3) the setting of the flow control valve 109 is adjusted via a dosing rate control line 126, and

4) a steering control line 127 is used to control a servo motor 128.

The servo motor 128 can be operated from an on-board battery which also powers the control unit 114. The servo motor 128 is connected to the jet outlet nozzle 106 via a steering linkage 115 so that the boat can be steered by adjusting the direction of the water jet issuing from the nozzle 106.

The rate at which hydrogen peroxide is drawn into the water jet by the action of the venturi can be controlled accurately by adjusting the setting of the flow control valve 109. This accurately controls the rate at which hydrogen peroxide is fed into the body of water to be treated. The vigorous jetting action ensures that the hydrogen peroxide is thoroughly distributed within the water undergoing treatment and, by steering the boat by means of the servo motor 128, a large area of water can be treated fairly evenly in a very short period of time. The boat will typically be steered in a zig-zag path over the required area.

As with the embodiment of Figures 1 and 2, the hydrogen peroxide discharged into the body of water to be treated begins to break down into water and oxygen on contact with the body of water and exposure to daylight. This breakdown generally starts immediately and continues for some time dependant on, for example, the quantity of suspended solids present in the body of water. There is thus a virtually instantaneous increase in the level of dissolved oxygen in the body of water.

The control unit 114 may be connected to a sensor (not shown) for detecting the level of dissolved oxygen in the vicinity of the boat so that, for example, the setting of the valve 109 could be controlled automatically to achieve the correct dosage rate instead of being controlled by the remote transmitter 122. Such automatic operation could be useful in long-term water quality maintenance, for example, on fish farms, at effluent treatment plants, especially those using activated sludge, and below storm sewage overflows.

The advantages of the embodiment shown in Figures 3 to 5 can be summarised as follows: Effectiveness a) very rapid increases in dissolved oxygen levels can be obtained, b) the dosage rate is accurately controllable and infinitely variable, and c) there is minimal disturbance of material at the bed of the water.

Ease of Use a) the boat is compact, lightweight and easily transported, e.g. using a rapid response trailer, b) the apparatus can be made ready for use in minutes, c) operation is possible in a wide variety of situations, including very shallow water, d) operation of the apparatus can be controlled remotely from bridge crossings, avoiding the need to negotiate access or travel over difficult terrain, and e) the method of operation is inherently safe - the use of a venturi ensures that the hydrogen peroxide cannot be drawn from the storage container without being diluted before leaving the outlet.

Cost a) there is a relatively low capital plant cost, and b) the running costs are relatively low.

Other Factors a) the apparatus is simple to operate, therefore a minimum of operator training is required, b) hydrogen peroxide is readily available and can often be delivered on site, c) the apparatus is very versatile and can be used for effluent treatment as well as on fish farms. The specific form of apparatus shown in Figures 3 and 5 is remotely controlled. The boat on which the apparatus is mounted may, however, be steered and controlled by the occupants of the boat. If the outlet through which the jet of water containing hydrogen peroxide is of relatively low diameter, for example, 50 mm. diameter, steering of the boat may be effected by adjusting the direction of discharge of the jet. If, however, a larger diameter outlet is used (and a correspondingly higher output pump is used), for example, a 75 mm. diameter outlet, a separate steering system is preferably provided.

Claims

Claims:-

1. A method of increasing the dissolved oxygen content of a body of water, said method comprising withdrawing water from said body of water, adding hydrogen peroxide to the water which is withdrawn and delivering the hydrogen peroxide-containing water back into the body of water from which it was withdrawn.

2. Apparatus for use in increasing the dissolved oxygen content of a body of water, said apparatus including pump means for withdrawing water from said body of water and for returning it to said body of water, and dosing means for adding hydrogen peroxide to the withdrawn water prior to return thereof to the body of water.

3. A method as claimed in Claim 1 or apparatus as claimed in Claim 2, in which the hydrogen peroxide is contained within a storage container from which it is withdrawn as a result of a venturi effect obtained as a result of the flow of the withdrawn water through the apparatus.

4. The invention of Claim 3, in which the water containing hydrogen peroxide is returned to the body of water from which it was withdrawn in the form of a jet.

5. The invention of Claim 4, in which the apparatus is mounted on a boat and the jet of water serves for the propulsion of the boat, with steering of the boat effected by changing the direction of the jet.

6. Apparatus as claimed in Claim 2, in which the pump means is a submersible electric pump which is submersed in the body of the water to be treated.

7. Apparatus as claimed in Claim 2 , in which operation of the pump is under the control of a sensor which senses the level of dissolved oxygen in the water and causes the pump to be actuated when the dissolved oxygen content falls below a predetermined level.

8. Apparatus as claimed in Claim 2, in which the pump means has an inlet through which water is withdrawn from the body of water to be treated and an outlet pipe through which the water is returned in the form of a jet.

9. Apparatus as claimed in Claim 8, in which hydrogen peroxide is fed from a storage container into the outlet pipe, the storage container being connected to the outlet pipe by means of a supply line which contains an adjustable flow control valve and the hydrogen peroxide being withdrawn from the storage container as a result of the action of a venturi in the outlet pipe.