WO2001053219A1

WO2001053219A1 - Method and apparatus for controlling microbiological activity in water storage tanks

Info

Publication number: WO2001053219A1
Application number: PCT/GB2001/000213
Authority: WO
Inventors: Geoffrey Forbes Adam
Original assignee: R.P. Adam Limited
Priority date: 2000-01-21
Filing date: 2001-01-19
Publication date: 2001-07-26
Also published as: GB0001439D0; AU2001226940A1; GB2360278A; GB0101487D0

Abstract

The invention relates to a method and apparatus for sterilising water storage tanks (for example on aircraft) and supplying service water to the tanks having a specified content of sterilising agent. The preferred embodiments of apparatus comprises an inlet hose (7) which, in use, is connected to a mains water supply. A valve (10) allows water from the hose to be directed to either of two dosing pumps (14, 15). The dosing pumps derive a sterilising agent, for example chlorine dioxide, from a single source, e.g. drums (24, 25). The respective pumps (14, 15) are pre-set so that one pump (14) delivers water suitable for service use (typically containing 0.5ppm chlorine dioxide) and the other pump (15) delivers water suitable for sterilising use (typically containing 40ppm chlorine dioxide). The outlets of the pumps (14, 15) supply respective hoses connectable to the tanks to be sterilised and/or filled. The pumps (14, 15) preferably derive their operating power from the water flowing through them.

Description

METHOD AND APPARATUS FOR CONTROLLING MICROBIOLOGICAL ACTIVITY IN WATER STORAGE TANKS

The present invention relates to a method of controlling microbiological activity in water storage tanks and to apparatus for use in such a method. The invention is of particular utility in controlling microbiological activity within water storage tanks of passenger aircraft. However, it will be appreciated that the invention is not limited to such usage and, indeed, may be applied to the problem of controlling microbiological activity within a wide range of water storage installations.

Passenger aircraft are fitted with water storage tanks to provide water to the galleys and washrooms of the aircraft. It is well recognised that microbiological activity within the tanks must be controlled in order to provide water which is potable and free of taint. Existing airline operating procedures require the periodical sterilisation of water storage tanks and the dosing of water carried in the tanks with a sterilising agent. The methods and apparatus available to carry out both the sterilisation function and the dosing function are less than satisfactory.

So far as sterilisation is concerned the existing procedure is to use a sterilisation cart which includes a large water tank. The tank is filled with water and sodium hypochlorite is added to the water in the tank to produce a sterilising solution. Alternatively, a kit containing an inactive form of chlorine dioxide is manually mixed and activated and added to the tank in order to produce a sterilising solution. The sterilising solution from the sterilising cart is then pumped into the previously drained water tanks of the aircraft and is allowed to stand for a specified contact period. The tanks are then drained and refilled with service water for use during a subsequent flight. The service water is obtained by mixing tap water with sodium hypochlorite to obtain a chlorine level of 0.5ppm. The mixing of the sodium hypochlorite and tap water is carried out either in the storage tank of the sterilisation cart referred to above or in a separate water bowser. Typically, water tank sterilisation is earned out when an aircraft is brought into hangar for other work to be carried out on it. Between sterilisations service water refills are obtained from a bowser which contains a mixture of mains water and sodium hypochlorite to deliver service water at the required 0.5ppm chlorine content level.

The procedures outlined above are recognised to suffer from a number of disadvantages.

Firstly, the fact that both the sterilisation cart and the water bowsers contain a large tank used for holding water and mixing it with the required chemicals means that the sterilisation cart and water bowsers themselves are liable to be contaminated by a microbiological growth. The problem is particularly acute in water bowsers which must, as a result, themselves be periodically sterilised in order to avoid microbiological build-up.

The second problem is that the mixing of both the sterilisation solution and the service water is carried out by manual addition of chemicals to bulk tanks of mains water. Such manual mixing of chemicals has a number of well recognised disadvantages. For example, the chemical agents may be added to the water in incorrect quantities and/or may be inadequately mixed with the bulk of water within the tank. Also, the manual measuring and addition of aggressive chemicals requires special training of staff and the use of protective clothing. Even if existing procedures are implemented correctly, the problem of microbiological build up within the tanks and hoses of the bowser system means that higher dosing than the desirable 0.5ppm level is frequently necessary in order to ensure sterility of water within the aircraft tanks. Additional dosing with chlorine at above a level of 0.5ppm results in tainting of the water.

We have now devised new methods and apparatus which may be reliably and effectively used for both sterilisation and normal service filling of the water tanks of aircraft. The method and apparatus of the present invention eliminates the use of water storage tanks on sterilisation carts and accordingly eliminates such tanks as a potential source of contamination. Further, the dosing of water with sterilisation chemicals is effected in an automatic manner which avoids the previous problems of operator error.

The preferred embodiment of the present invention enables pre-activated chlorine dioxide solution to be used for both sterilisation of tanks and the dosing of service water. This eliminates the previous need for sodium hypochlorite and thereby removes difficulties associated with use of this chemical.

According to a first aspect of the present invention a method of sterilising a water storage tank comprises: passing water by hosepipe from a mains water source to the tank to be sterilised via a conduit; and metering chlorine dioxide into the water flow through the conduit to produce a sterilising solution. According to a second aspect of the present invention there is provided a method of filling a water storage tank with service water, the method comprising: passing water by hosepipe from a mains water source to the tank to be filled via a conduit; and metering chlorine dioxide into the water flow through the conduit to produce service water having a specified chlorine dioxide content.

Preferably, dosing of the water with chlorine dioxide is carried out using a metering pump which varies the amount of chemical injected into the water flow in proportion to the rate of water flow whereby the percentage of sterilising chemical in the water remains constant over a wide range of water flow rates. Preferably, the metering pump is driven by the water as it flows from the mains connection through the metering pump.

The preferred apparatus of the present invention comprises a wheel mounted assembly comprising an inlet hose for connection to a source of mains water, an outlet hose for connection to the water storage tank to be serviced and a metering pump having a main inlet connected to the inlet hose, an outlet connected to the outlet hose and a chemical inlet connected to a source of sterilising chemical. The source of sterilising chemical is preferably a pre-activated liquid containing available chlorine dioxide. Preferably, the metering pump is driven by the water which flows through it.

In a particularly preferred embodiment of the invention the apparatus can provide both a sterilising fluid and service water. To this end, the preferred apparatus includes two metering pumps, one adapted to add a required chemical to water at a rate to produce a sterilising solution and the other adapted to add a required chemical to water at a rate to produce service water having a specified sterilising chemical content. In the preferred embodiment, the chemical used for both the production of the sterilising fluid and for dosing the service water is a common source of pre-activated liquid containing available chlorine dioxide. However, the use of a common source of chlorine dioxide is not essential to the broadest aspect of the present invention. For example, a source of available chlorine dioxide may be used to produce sterilising fluid whilst another chemical is used to produce service water, or vice versa. Alternatively, other chemicals may be used to produce both sterilising fluid and service water.

Preferably, the water intakes of both pumps are supplied by a single flexible inlet hose.

In a particularly preferred embodiment of the invention each metering pump has associated with it a separate outlet hose. Accordingly, one outlet hose will provide sterilising solution whilst the other outlet hose will provide service water. Preferably, the apparatus contains operating controls which prevent each metering pump being actuated unless the hose associated with it is connected to a water tank. Thus, the controls will prevent operation of the sterilisation fluid metering pump unless the hose which is connected to it (the sterilisation hose) is connected to a water tank. Similarly, the controls will prevent operation of the service water pump unless the hose connected to it (the service water hose) is connected to a water tank.

An operator, required merely to refill the service tank of an aircraft, will simply connect the intake hose to a source of mains water and the service water hose to the tank to be filled. The service water metering pump is then activated (deriving power from the water passing through it) and operates to provide the required service water having a specified chlorine dioxide content. Variations in flow rate through the inlet hose will result in corresponding variations in the dosage rate of the chlorine dioxide and will not affect the chlorine dioxide concentration in the service water. When the service tanks are filled as required the service water injection pump is stopped and the various hoses disconnected. No substantial quantity of water will remain within the servicing apparatus.

If, on the contrary, sterilisation of the water tanks is required the tanks are firstly drained and then the intake hose of the service apparatus will be connected to a source of mains water and the sterilisation hose will be connected to the tank to be sterilised. The sterilisation metering pump will then be activated and the tank filled with sterilisation solution to a specified level. After a specified contact period the water tanks will be drained, rinsed if necessary with service water solution, and refilled with service water. It will be appreciated that the preferred service apparatus can provide both sterilisation solution and service water.

Preferably, the service water outlet hose and the sterilisation solution outlet hose are colour coded further to reduce the risk of operator error.

Preferably, the various hoses are mounted on colour coded hose reels contained within normally covered compartments. By reducing unnecessary exposure of the hoses to light the risk of microbiological growth within the hoses is correspondingly reduced.

Preferably, the metering pumps are contained within an enclosure which is not accessible to operators of the service apparatus, but only to engineering staff. Accordingly, once dosage levels from the metering pumps have been pre-set there is no possibility that field operators will interfere with the dosage levels.

Preferably, the service apparatus contains storage compartments for plastic drums of active chemical, for example, 20 litre plastic drums.

It has been found that service apparatus which contains storage facilities for two 20 litre drums of pre-activated liquid containing 2000ppm of available chlorine dioxide can provide sufficient sterilising solution to sterilise the water tanks of the largest aircraft (Boeing 747) at present in passenger service.

Preferably, the service apparatus contains audible and visible warnings if the chemical agents required run low.

The above and further features and advantages of the invention will become clear from the following description of a preferred embodiment of service apparatus in accordance with the present invention, and from the following description of operation of that service apparatus in accordance with the method of the present invention. In the following description the single Figure is a schematic plan view of service apparatus according to the present invention.

The service apparatus of the present invention is preferably constructed as a trailer or is mounted on a vehicle chassis to form a self-propelled unit. The exact mounting method is not critical to the present invention and will to an extent be determined by the operating conditions required for the unit. The Figure is a schematic top plan view. It will be noted that the service apparatus body 2 is divided into three compartments - an outlet end compartment 3 which houses outlet hoses, an inlet end compartment 4 which houses an inlet hose and chemical storage bins, and a pump compartment 5 which houses the metering pumps of the system. In general, the pump compartment 5 will be closed and accessible only to service engineers. The inlet and outlet compartments 4,3 will be fitted with hinged covers to facilitate ready access to operating personnel whilst keeping the inlet and outlet hoses out of direct light.

The inlet compartment 4 contains an inlet hose reel 6 on which is wound an inlet hose 7. The inlet hose reel may be manually rotated to recover the inlet hose. In use, the inlet hose 7 is connected to a suitable source of "mains" water - i.e. a fixed water supply point connected to a portable water distribution system. Water from the inlet hose flows through a union 9 to a three-way valve 10. The valve 10 may be set to direct water flow to either of two pipes 1 1,12. The pipes 11,12 in turn pass through a bulkhead 13 which separates the inlet chamber 4 from the pump chamber 5 and within the pump chamber are connected to respective dosing pumps 14,15 via flow restrictors. The pumps 14,15 have respective outlet pipes 16,17 which pass through the bulkhead 13 which separates the pump chamber 5 from the outlet chamber 4. The pipe 16 is connected via a suitable union to a service water outlet hose 18 mounted on a reel 19 whilst the pipe 17 is connected via a suitable union to a sterilisation solution hose 20 mounted on a reel 21. The reels 19,21 may be fitted with manual rewind fittings.

The dosing pumps 14,15 are driven by power derived from the water flowing through them. Each pump has a chemical inlet 22. The inlets 22 are connected to a supply hose 23 which passes through the bulkhead 13. Sufficient supply hose 23 is present within the inlet compartment 4 to allow the hose to be placed in a plastic drum of chemical located within the inlet compartment 4. Preferably, at least two storage compartments 24,25 are provided within the inlet compartment 4, each compartment 24,25 being capable of holding a 20 litre plastic drum of chemical. Suitable means are provided for retaining the inlet hose 23 within a drum. Preferably, low level monitors are provided to indicate low chemical levels within the drum which is supplying the chemical to the metering pumps.

The metering pump 14 is pre-set in light of the strength of the sterilising chemical supplied to provide water to the service water hose 18 having a predetermined chlorine dioxide content, typically 0.5ppm. Because the amount of chemical added by the metering pump is proportional to flow through the pump, the chlorine dioxide content of the service water is constant regardless of variations in flow rate resulting, for example, in variations in water mains pressure. The pump 15 is, in contrast, set to provide a chlorine dioxide content in the water supplied to the sterilising solution hose 20 appropriate for carrying out tank sterilisation. Typically, a chlorine dioxide content of 40ppm will be required for this purpose. Again, the chlorine dioxide concentration in the sterilising solution will be independent of the flow rate of water through the pump. Preferably, the sterilising chemical provided for the system will be a pre- activated liquid form of chlorine dioxide containing at least 2000ppm chlorine dioxide and the pumps will be preset in light of this concentration. It will be appreciated, however, that if safety regulations within the particular territory require the use of a less concentrated source of chlorine dioxide, the less concentrated source may be used provided that the dosing levels of the pumps 14, 15 are re-set or replaced to provide the desired chlorine content in the sterilising solution and the service water.

In use, the servicing unit will be placed near an aircraft to be serviced and the inlet hose 7 will be connected to a suitable source of mains water. The supply hose 23 will be placed in the drum of pre-activated liquid containing chlorine dioxide. If the aircraft tanks are merely to be refilled with service water the hose 18 will be unreeled and connected to the tank inlet and the valve 10 will be operated to direct inlet water via the pipe 11 through the pump 14, pipe 16 and hose 18 into the tanks to be filled. When the tanks are filled the valve 10 is moved to an "off position and the inlet hose and service water hose are re-reeled. It will be noted that a minimum quantity of water remains in the service unit between uses.

If, on the contrary, tank sterilisation is to be carried out the service unit is again placed near the aircraft and the inlet hose 7 is connected to a suitable source of water. In this case, however, the sterilisation solution hose 20 is connected to the tank to be sterilised and the valve 10 is operated to direct incoming water through the pipe 12 to the metering pump 15 whereby a sterilisation solution is produced and fed via the pipe 17 and hose 20 to the tanks to be sterilised. After a suitable contact period, the tanks are drained and may be refilled with service water simply by re-reeling the hose 20, unreeling the hose 18 and connecting it to the tank inlet, and moving the valve 10 to direct water through the pipe 11 etc. as described above. Thus, the service unit described can effect both sterilisation and supply of service water. Preferably, interlock means are provided to ensure that the valve 10 can only be operated to direct water to the outlet hose which is actually connected to a water tank to be filled. Accordingly, if the service water hose 18 is connected to a water tank the interlock means will ensure that the valve 10 can only be operated to direct water to the pipe 11. Similarly, if the sterilisation hose is connected the valve 10 will only be operable to direct water along the pipe 12.

To further reduce the risk of error the outlet hose reels 19 and 21 are preferably colour coded with the service water reel coloured blue and the sterilising solution reel coloured red.

Claims

CLAIMS:

1. A method of sterilising a water storage tank comprising: passing water by hosepipe from a mains water source to the tank to be sterilised via a conduit; and metering chlorine dioxide into the water flow through the conduit to produce a sterilising solution.

2. A method of filling a water storage tank with service water, the method comprising: passing water by hosepipe from a mains water source to the tank to be filled via a conduit; and metering chlorine dioxide into the water flow through the conduit to produce service water having a specified chlorine dioxide content.

3. A method according to claim 1 or claim 2 wherein the dosing of the water with chlorine dioxide is carried out using a metering pump which varies the amount of chemical injected into the water flow in proportion to the rate of water flow whereby the percentage of sterilising chemical in the water remains constant over a wide range of water flow rates.

4. A method according to claim 3 wherein the metering pump is driven by the water as it flows from the mains connection through the metering pump.

5. Apparatus for carrying out the method of any preceding claim comprising: a wheel mounted assembly comprising an inlet hose for connection to a source of mains water, an outlet hose for connection to the water storage tank to be serviced and a metering pump having a main inlet connected to the inlet hose, an outlet connected to the outlet hose and a chemical inlet connected to a source of sterilising chemical.

6. Apparatus for providing a sterilising fluid and service water, the apparatus comprising an inlet hose for connection to a source of mains water; means for directing mains water from the inlet hose to selectively either of two metering pumps, each metering pump being adapted to add a sterilising material to the water, one of the metering pumps being adapted to add a sterilising chemical to water at a rate to produce a sterilising solution and the other of the metering pumps being adapted to add a sterilising chemical to water at a rate to produce service water having a specified sterilising chemical content; and at least one outlet hose for connecting the outlets of the metering pumps to a tank which is to be sterilised and/or filled with service water.

7. Apparatus according to claim 6 wherein each metering pump has associated therewith a separate outlet hose whereby one outlet hose will provide a sterilising solution whilst the other outlet hose will provide service water.

8. Apparatus according to claim 6 or claim 8 wherein the apparatus contains operating controls which prevent each metering pump being actuated unless the hose associated with it is connected to a water tank.

9. Apparatus according to any of claims 6 to 9 wherein the water metering pumps derive the power necessary to operate them from the water passing through them.

10. Apparatus according to any of claims 6 to 9 wherein the service water outlet hose and the sterilisation solution outlet hose are colour coded, preferably by being mounted on colour coded hose reels contained within normally a covered compartment.

11. Apparatus according to any of claims 6 to 10 wherein the metering pumps are contained within an enclosure which is not accessible to operators of the service apparatus, but only to engineering staff.

12. Apparatus according to any of claims 6 to 1 1 including audible and/or visible warnings if the chemical agents required run low.