GB2398006A

GB2398006A - Method and apparatus for antimicrobial treatment of an airflow

Info

Publication number: GB2398006A
Application number: GB0300409A
Authority: GB
Inventors: Stephen Atkinson
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-01-08
Filing date: 2003-01-08
Publication date: 2004-08-11
Anticipated expiration: 2023-01-08
Also published as: GB2398006B; GB0300409D0

Abstract

An aqueous solution of potassium or sodium formate is used as an antimicrobial agent in the cleaning of an airflow, e.g. in a hospital or operating theatre. The solution, which acts as a dessicant and a biocide, may be supplied to an inner region of a rotor of the "brush fan" type so that it spreads over its surface as the rotor rotates. Apparatus for such treatment comprises a reservoir for the solution, an injection line 9 therefor, brush fans 2 and 8 having inlet ducts 1 and 5, and means for collecting and re-concentrating used solution from a region surrounding the rotor. Distilled water may be supplied through a line 21 to restore the relative humidity of the airflow to that of the inlet.

Description

Method and Apparatus for Antimicrobial Treatment of an Airflow This

invention relates to the antimicrobial treatment of an airflow, and has particular application, for example, in an environment such as a hospital or operating theatre.

The development of systems for the effective removal of harmful airborne micro organisms has increased in importance in recent years, with the increasing development of pathogenic microorganisms which are resistant to many antibiotics.

The use of potassium and sodium formates as drilling brines for petroleum is well know (see, for example, K Howard, Society of Petroleum Engineers, SPE 30498, 1995), and it is also known that in the context of petroleum drilling that if the formate concentrations employed are in a sufficiently high concentration, they inhibit bacterial growth.

T he use of potassium formate solutions in air conditioning systems is also known from, ea. EP-B-611388.

It has not however previously been realised that potassium formate solution can be employed as a powerful antimicrobial agent in the cleaning of an airflow.

The present invention provides the use of an aqueous solution of potassium formate as an antimicrobial agent in the cleaning of an airflow.

According to the invention, an airflow containing microbial matter is contacted with the potassium formate solution. The potassium formate solution acts as a powerful de-humidifying agent, and removes moisture from the airflow at the same time as killing microbes (in particular, bacteria) suspended in it. Although the invention is not intended to be limited by a theory of operation, it is believed that the antimicrobial action of potassium formate takes place by dehydration of the microbial matter.

ln a preferred embodiment, contact between the airflow and the potassium formate solution is caused by providing a rotor and supplying the potassium formate to an inner region of the rotor, for example in the region of the axis of the rotor, whilst rotating the rotor to cause a potassium formate solution to spread over the rotor surface. The airflow is passed over the surface of the rotor which has been wetted by the potassium formate solution. By this method, a large surface area is provided between the solution and the airflow, maximising the effectiveness of the process.

The rotor may be formed as a so called "brush" i.e. it may comprise a plurality of elongate members, in the form of bristles or fibres, which are generally radial disposed, and which provide a contacting surface between the potassium formate solution and the airflow. This has the advantage that the "brush" can also be used as a fan, to cause the movement of the air, as disclosed, for example, in WO97/17585.

Apparatus for treating an airflow may comprise a rotor as described above, together with a reservoir for containing a supply of potassium formate solution, and optionally a recirculating system, including means for heating the potassium formate solution to evaporate water, and thereby increase its concentration. A further similar rotor may be provided downstream, in order to assist in removing entrained potassium formate solution.

In addition to the removal of moisture the rotor assists in the removal of dust from the airflow. Microorganisms carried on the surface of the dust will also be killed by the action of potassium or sodium formate.

The antimicrobial action of the potassium or sodium formate solution on the airflow may occur by direct contact of the airflow with the potassium formate solution. The antimicrobial effect may also be effected by the dessication of microorganisms carried on dust particles or sputum droplets present in the airflow. Such particles or droplets may be removed from the airflow by contact with a rotor such as the brush fan described above, the disinfection operation being completed in a tank or reservoir containing the potassium or sodium formate solution at a later stage. Any microorganisms present which may be resistant to treatment by potassium or sodium formate at the lower temperatures encountered during the removal step may then be killed during the regeneration of the solution, when higher temperatures (typically around 75 C) are used.

A preferred embodiment of the invention will now be described with reference to the accompanying drawing, in which: Figure I shows a general schematic diagram of apparatus according to the invention for the antimicrobial treatment of an airflow.

The apparatus shown in Figure I comprises an inlet duct (1) and a primary brush fan (2), discharging through a fan cowling (4) to an air chamber (28). A second brush fan (8), draw air from air chamber (28) through an inlet duct (5), and discharges it through fan cowling (6) into an air chamber (29), from where it is discharged though outlet duct (7).

Brush fans (2) and (8) are of the general type disclosed in WO-A-97/17585 and have radial bristles (26 and 27) made from a thermoplastic material such as nylon, polyethylene. The bristles 26 and 27 may alternatively be made of metal or any other suitable material. The bristles are fixed in suitable bosses, which are fixed to a vertical bearing mounted shaft rotated by a variable speed electric motor (assembly 3). A solution of concentrated solution of potassium formate, typically having a concentration of up to 75% w/w is injected through line (9) and sprayed axially into the fan (2) The potassium formate acts as a desiccant and a biocide. Brush fan (26) rotates, to cause the potassium formate solution to spread over the surface of the bristles (26) and wet them. Dust particles and airborne microorganisms in the airflow tend to become attached to the wetted bristles and are thus removed. Humidity and microscopic water droplets, for example microscopic drops of sputum containing microorganisms are removed in the same way The bristles are self cleaning as their rotation causes liquid and entrained dust to spin off, and be discharged from the fan (2) through cowling (4) into air chamber (28). Once in the liquid phase, microorganisms are rapidly killed by the dessicant action o the solution.

The liquid desiccant/biocide is re-concentrated in order to remove the additional water introduced during the dehumidification, by heat treatment. The liquid passes through a control valve (15) to the shell side of heat exchanger (16) and thence to a boiler (17).

Steam is discharged from boiler (17) through a tube (25) of the heat exchanger (16) where it condenses and passes as distilled mater through tube (18), equipped with an adjustable back pressure valve, to be stored in water tank (19).

The re-concentrated liquid desiccant biocide passes through tube (24) to storage chamber (I 1). A heating element (12) is provided to enable the liquid to be heated to the desired temperature.

Distilled water in tank (19) is drawn by pump (20) through line (21) to be sprayed axially into the bristles (27) of secondary brush fan (8) to restore the relative humidity of the airflow to that of the inlet ( I) relative humidity. Discharge air passes through air chamber (29) to outlet duct (7). The injection of distilled water through line (21) is controlled so as not to produce free water from fan discharge (6). Any unintentional water discharge can to drain from air chamber (29) through drain (30) through air chamber (28) and drain ( 13) back into the dilute liquid handling system.

Discharge air humidity from (7) can be varied by increasing or decreasing the injection of distilled water from tank (19). Distilled water can be added or removed as needed from tank (19) using a ball and cock valve an overflow discharge, and an separate distilled water supply (not shown)

Claims

Claims I. The use of an aqueous solution of potassium formate or sodium

formate as an antimicrobial agent in the cleaning of an airflow.
2. The use as claimed in Claim 1, wherein the airflow is caused to contact solution by supplying a flow of potassium formate or sodium formate to an inner region of a rotor, rotating the rotor to cause the potassium formate to spread over its surface, and passing the airflow over the surface of the rotor.
3. The use as claimed in Claim 2, wherein the rotor comprises a plurality of elongate and generally radially-disposed members to provide a contacting surface between the potassium formate or sodium formate and the airflow.
4. The use as claimed in Claim 3, wherein the elongate members are bristles or fibres.
S. Apparatus for the antimicrobial treatment of an airflow, comprising a reservoir for containing a supply of a liquid biocidal desiccant solution, a rotor, means for supplying the liquid biocidal desiccant solution from the reservoir to an inner region of the rotor, I S means for rotating the rotor to cause the liquid biocidal desiccant solution to spread over the surface of the rotor, and means for collecting used liquid biocidal desiccant solution from a region surrounding the rotor.
6. Apparatus as claimed in Claim 5, wherein the rotor comprises a plurality of elongate and generally radially-disposed members to provide a contacting surface between the liquid biocidal desiccant solution and the airflow.
7. Apparatus as claimed in Claim 6, wherein the elongate members are bristles or fibres.
8. Apparatus as claimed in any one of Claims 5 to 7, including a recirculating system for the liquid biocidal desiccant solution. the recirculating system including means for heating the said liquid biocidal desiccant solution to evaporate water therefrom and thereby increase the concentration of liquid biocidal desiccant in the solution.
9. Apparatus as claimed in any one of Claims 5 to 8, including means positioned downstream in the airflow of the rotor, for removing entrained liquid biocidal desiccant solution.
10. Apparatus as claimed in Claim 9, wherein the means for removing entrained liquid S biocidal desiccant solution includes a further rotor.
11. Apparatus as claimed in any one of Claims 5 to 10, wherein the liquid biocidal desiccant solution is potassium formate or sodium formate solution.
12. Apparatus for the antimicrobial treatment of an airflow substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.