WO1996011476A1

WO1996011476A1 - A method of decontamination

Info

Publication number: WO1996011476A1
Application number: PCT/GB1995/002347
Authority: WO
Inventors: Jennifer Benson; Harry Eccles; Leslie Hugh Glyn Morton
Original assignee: British Nuclear Fuels Plc
Priority date: 1994-10-05
Filing date: 1995-10-03
Publication date: 1996-04-18
Also published as: GB9420095D0

Abstract

A method for reducing the volume of decontamination liquid required for the decontamination of surfaces which constitute the surfaces of a volume such as a room or pond is described. The method comprises the steps of providing a device to fill a part of said volume so as to produce a void between said surfaces to be decontaminated and said device such as to reduce the volume of said decontaminating liquid required to cover said surfaces.

Description

A METHOD OF DECONTAMINATION

The present invention relates to a method for the decontamination of cementitious or metallic surfaces and particularly, though not exclusively, where such surfaces form the boundaries of a volume such as a room or pond, for example.

In copending International patent application number PCT/GB95/01772, of common ownership herewith, a method is described for the decontamination of cementitious or metallic surfaces having contaminants of, for example, metal ions which made be toxic heavy metal ions or radionuclide contaminants. The method comprises the steps of supplying to the surface at least one microorganism under conditions conducive to growth of the at least one microorganism; maintaining those conditions conducive to growth and the consequent generation of an acid or other metabolite to degrade or corrode the surface to a desired depth; terminating the conditions conducive to growth on achieving the desired depth of degradation and then removing and disposing of the degradation or corrosion products so formed.

However, a significant practical problem arises when the surfaces to be decontaminated are vertical surfaces on which the growing microorganisms need to be maintained or, the surfaces constitute, for example, the walls, floor and, if appropriate, the ceiling or roof; of a pond, room or building. In the case where a flood- type delivery system is used to deliver and maintain a biological decontamination system within a pond or room, the amount of liquid required to fill the volume of the structure is large and would itself generate a large volume of waste liquor to be subsequently dealt with.

According to the present invention there is provided a method for reducing the volume of decontamination liquid required for the decontamination of surfaces which constitute the surfaces of a volume, the method comprising the steps of providing a device to fill a part of said volume so as to produce a void between said surfaces to be decontaminated and said device such as to reduce the volume of said decontaminating liquid required to cover said surfaces.

The term "decontamination liquid" used herein does not necessarily mean that the whole volume of liquid is active during the actual decontamination reaction but that the liquid is merely present in the region between the volume reducing member and the surface to be decontaminated.

It is emphasized that not only biological decontamination methods may be employed with the method of the present invention but also other decontamination liquids such as acids, complexing agents, alkalis or mixtures for example.

In one embodiment the device may comprise an inflatable plastics material device placed inside the pond or room.

Where such an inflatable device is used, it may be specifically shaped so as to fit within the intended volume when inflated.

The device may be tethered to the floor or walls of the pond or room so as to maintain a desired gap at the base. Furthermore, the device may itself be filled with a liquid or gel or otherwise weighted to maintain it in position. An inflatable plastics material device may be suitably internally strengthened and braced so as to resists undesirable expansion when filled with a liquid or gel, for example.

The device may comprise a framework constructed of suitable material such as metal or wood, for example, within the volume and covering the framework with a suitable sheet material such as a plastics material such that a gap is formed between the resulting covered framework so produced and the surfaces to be decontaminated. The framework may preferably be covered in a single piece of plastics material so as to prevent leakage.

An inflatable device or a structure having sheet material walls may be pulsed by suitable means such as mechanical, hydraulic or pneumatic means, for example, so as to promote the agitation of the liquid trapped between the device and the walls to be decontaminated. Thus, in the case of decontamination by microorganisms, the feedstock and/or nutrients, for example, may be agitated in this manner.

An inflatable device may be provided with internal conduits or conduits on the device surface for the supply of fresh feedstock and/or nutrients to remote positions within the liquid filled gap which may not otherwise be easily reached. Such conduits may be provided with pump means for the circulation of fluid to and from such positions. Such conduits may also be used for the extraction of spent fluids and subsequent replenishment. The method may include the step of filling the gap between the surfaces to be decontaminated and the device with decontamination fluid, and filling the device with fluid such as water, if appropriate, substantially simultaneously such that the fluid levels within and without the device rise substantially together.

In order that the present invention may be more fully understood, an example will now be described by way of illustration only with reference to the accompanying drawing which shows a schematic cross section through a pond having a volume reducing device therein according to the method of the present invention therein.

A pond 10 having walls 12 and a floor 14 to be decontaminated has therein a device 16 to take up a substantial proportion of the volume thereof. The device comprises an inflatable bag 20 having an outer surface made of flexible plastics sheet material having panels 22 joined together by welding of the seams therebetween. The bag 20 is provided with internal cross bracing, indicated by the lines 24. At the base or floor 14, the bag 20 rests upon a metal or plastics material grid 26 which provides a positive separation between the floor and bottom 28 of the bag 20 but also allows free circulation of decontaminating fluid in the gap 30. The bag 20 is attached to the floor 14 and walls 12 by tether straps 32, 34, respectively, these tether straps being also attached to fixings 36, 38 on the floor and walls, respectively.

The bag 20 has two valve ports 40, 42 for the admission of a gas such as air and a fluid such as water, for example, respectively. The bag 20, in this case, is filled with water and the gap 30 is filled with decontaminating fluid of any desired kind.

Conduits 50, 52 shown as dashed lines are attached to the outer surface of the device 16 to enable fresh or additional decontaminating fluid or feed stock to be supplied as needed to otherwise inaccessible regions of the gap 30. Alternatively, air or oxygen may be supplied through such conduits where biological cultures which require aeration are used. As many of the conduits as are required may be employed. The conduits may be in the form of flexible pipes attached to the bag 20 surface or formed from two layers of plastics sheet material for example.

In operation, the empty and deflated bag 20 is placed in the pond 10 and the tether straps 32, 34 are attached to the fixings 36, 38.

The bag 20 is then expanded by blowing air into it through the valve port 40 so that it adopts its planned shape. Decontaminating fluid 44 is then fed into the gap 30 such that it fills the space formed at the base by the grid 26. Further decontaminating fluid 44 is then fed into the gap 30 simultaneously with water 46 being fed into the bag 20 through the valve port 42, the rate of feeding the fluid 44 and water 46 being such that the rate of rise of the level of fluid 44 and the water 46 is substantially the same so as to substantially balance hydrostatic pressures inside and outside the bag 20. As water is fed into the bag 20 through the port 42, air is expelled through the port 40.

Claims

1. A method for reducing the volume of decontamination liquid required for the decontamination of surfaces which constitute the surfaces of a volume, the method comprising the steps of providing a device to fill a part of said volume so as to produce a void between said surfaces to be decontaminated and said device such as to reduce the volume of said decontaminating liquid required to cover said surfaces.

2. A method according to claim 1 where the device is an inflatable device having a desired shape when inflated.

3. A method according to claim 1 wherein the device is a covered framework.

4. A method according to any one preceding claim wherein both the void and the device are filled with liquid.

5. A method according to claim 4 wherein the void and the device are filled with liquid such that the respective levels rise as substantially the same rate.

6. A method according to any one preceding claim wherein said device is provided with conduits for the supply of feedstock to desired regions in the void.

7. A method according to any one preceding claim wherein movement of the decontamination liquid is assisted by pulsation of the device.