Use of an oxidising alkaline gel to remove a biofilm on a surface of a solid substrate

Abstract

The use of a gel consisting of a colloidal solution comprising, preferably consisting of: 5% to 30% by weight, preferably 5% to 25% by weight, more preferably 8% to 20% by weight relative to the weight of the gel, of at least one inorganic viscosifying agent; a mineral base selected from among hydroxides of alkaline metals, hydroxides of alkaline-earth metals and the mixtures thereof, said mineral base being present in a proportion of 0.05 to 10 mol/L of gel, preferably in a proportion of 0.1 to 5 mol/L of gel; an oxidizing agent stable in a basic medium selected from among permanganates, persulfates, ozone, hypochlorites and the mixtures thereof, said oxidizing agent stable in a basic medium being present in a proportion of 0.05 to 5 mol/L of gel, preferably 0.1 to 2 mol/L of gel; 0.1% to 2% by weight relative to the weight of the gel, of at least one surfactant; and a solvent; the gel not containing any super-absorbent polymer, to remove a biofilm present on a surface of a solid substrate.

Claims

1. A method, comprising removing a biofilm present on a surface of a solid substrate with a gel, wherein the gel is a colloidal solution comprising: 5% to 30% by weight, relative to the weight of the gel, of at least one inorganic viscosifying agent; a mineral base selected from the group consisting of hydroxides of alkaline metals, hydroxides of alkaline-earth metals and mixtures thereof, said mineral base being present in a proportion of 0.05 to 10 mol/L of gel; an oxidising agent stable in a basic medium selected from the group consisting of permanganates, persulfates, ozone, hypochlorites and the mixtures thereof, said oxidising agent stable in a basic medium being present in a proportion of 0.05 to 5 mol/L of gel; 0.1% to 2% by weight relative to the weight of the gel, of at least one surfactant; and a solvent; the gel not containing any super-absorbent polymer.

2. The method according to claim 1, wherein the mineral base is selected from among sodium hydroxide, potassium hydroxide and mixtures thereof, and the oxidising agent stable in the basic medium is selected from hypochlorites and mixtures thereof.

3. The method according to claim 2, wherein the gel comprises a combination of sodium hydroxide and sodium hypochlorite.

4. The method according to claim 1, wherein the inorganic viscosifying agent is selected from the group consisting of metal oxides, metalloid oxides with the exception of silica, metal hydroxides, metalloid hydroxides, metal oxyhydroxides, metalloid oxyhydroxides, aluminosilicates, clays, and the mixtures thereof.

5. The method according to claim 4, wherein the inorganic viscosifying agent consists of one or more aluminas.

6. The method according to claim 5, wherein the aluminas represent 5% to 30% by weight, relative to the total weight of the gel.

7. The method according to claim 1, wherein the surfactant is selected from among non-ionic surfactants; and the mixtures thereof.

8. The method according to claim 1, wherein the solvent is selected from the group consisting of water, organic solvents and the mixtures thereof.

9. The method according to claim 1, wherein the gel further comprises one or more mineral pigments.

10. The method according to claim 1, wherein the substrate comprises at least one material selected from the group consisting of metals and alloys; painted steels; organic polymers; glasses; cement materials; plasters; bricks; roof tiles; baked or unbaked earth; natural or artificial stones; coats; glass fibre; fibro-cements; asphalt; tar; slate; cellulose-based materials; and ceramics.

11. The method according to claim 1, wherein at least one cycle is performed comprising the following: a) applying the gel on said surface; b) maintaining the gel on the surface at least for a sufficient time so that the gel destroys the biofilm, and so that the gel dries and forms a dry, solid, non-powdery residue comprising compounds resulting from destruction of the biofilm; and c) removing the dry, solid, non-powdery residue comprising the compounds resulting from destruction of the biofilm.

12. The method according to claim 11, wherein the gel is applied to the surface of the solid substrate in the proportion of 100 g to 2000 g of gel per m.sup.2 of surface area.

13. The method according to claim 11, wherein the gel is applied on the surface of the solid substrate by spraying, or using a brush or float.

14. The method according to claim 1, wherein the b) drying is conducted at a temperature of 1° C. to 50° C., under a relative humidity of 20% to 80%.

15. The method according to claim 11, wherein the gel is maintained on the surface for a time of 2 to 72 hours.

16. The method according to claim 11, wherein the dry, solid residue is in the form of particles having a size from 1 to 10 mm.

17. The method according to claim 11, wherein the dry, solid, non-powdery residue is removed from the surface of the solid substrate by brushing and/or suction.

18. The method according to claim 11, wherein the described cycle is repeated 1 to 10 times using the same gel for all cycles or using different gels for one or more cycles.

19. The method according to claim 11, wherein during the maintaining b), the gel, before complete drying, is re-wetted with a solution of mineral base and oxidising agent.

20. The method according to claim 7, wherein the non-ionic surfactants are selected from block copolymers, ethoxylated fatty acids; and the mixtures thereof.

21. The method according to claim 20, wherein said block copolymers are block copolymers of ethylene oxide and propylene oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 (A, B, C) gives photographs showing the appearance of the surface of a wall treated according to the invention, at the different steps of the test conducted in Example 2, namely: the initial state of the wall surface (A); the appearance of the wall surface after application of the gel to part of the wall surface using a brush (B); the appearance of the wall surface after 48-hour drying and removal of the dry gel flakes by gentle brushing (C).

(2) FIG. 2B is a graph showing the results of a grey values analysis carried out on the image in FIG. 1C converted to grey levels along the line drawn in FIG. 2A (similar to FIG. 1C).

(3) In FIG. 2B, the distance (in pixels) is plotted along the X-axis and the grey levels along the Y-axis.

(4) FIG. 3 (A, B, C, D) gives photographs showing the appearance of the surface of a rail treated according to the invention, at different steps of the test conducted in Example 3, namely: the initial state of the rail surface(A); the appearance of the rail surface after brush application of the gel to part of the surface of the rail (B); the appearance of the surface of the rail after 48-hour drying of the gel applied to part of the surface of the rail (C); the appearance of the surface of the rail after removal of the dry gel flakes by gentle brushing (D).

(5) FIG. 4 shows the two areas of the surface of the rail (first area 41 located in the part of the surface treated with the gel and a second area 42 located in the part of the surface non-treated with the gel) for which an average greyscale was calculated in the image in FIG. 3D converted to grey levels.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(6) The gel used in the invention can easily be prepared at ambient temperature.

(7) For example the gel used in the invention can be prepared by adding, preferably gradually, the inorganic viscosifying agent(s) e.g. the aluminium oxide(s) and/or the silica(s) to a solution containing the combination of an inorganic base and oxidising agent, the surfactant(s) and optional pigment(s). This solution can be prepared for example by first preparing a solution of oxidising agent e.g. a solution of sodium hypochlorite in demineralised water then mixing, together with this solution of oxidising agent, the mineral base, the surfactant(s) and optional pigment(s). This mixing can be performed by mechanical agitation e.g. using a mechanical agitator equipped with a three-blade impeller. The rotation speed is 200 rpm for example and agitation time 3 to 5 minutes for example.

(8) The adding of the inorganic viscosifying agent(s) to the solution containing the mixture of an inorganic base and oxidising agent, the surfactant(s) and optional pigment(s) can be conducted simply by pouring the viscosifying agent(s) into said solution. When adding the inorganic viscosifying agent(s) the solution containing the mixture of an inorganic base and oxidising agent, the surfactant(s) and optional pigment(s) is generally held under mechanical agitation.

(9) For this agitation a mechanical agitator can be used for example equipped with a three-blade impeller.

(10) The agitation speed is generally gradually increased as and when the viscosity of the solution increases, to reach a final agitation speed of between 400 and 600 rpm for example without any spattering.

(11) On completion of the addition of the mineral viscosifying agent(s) agitation is continued for 2 to 5 minutes for example to obtain a fully homogeneous gel.

(12) Other protocols can evidently be followed to prepare the gels used in the invention, with the gel components being added in a different order to the order given above.

(13) In general, the gel used in the invention must have viscosity lower than 200 mPa.Math.s under shear of 1000 s.sup.−1 to allow spraying onto the surface to be decontaminated either at a distance (e.g. at a distance of 1 to 5 m) or in the vicinity thereof (e.g. at a distance shorter than 1 m, preferably 50 to 80 cm). The setting time of the viscosity must generally be shorter than one second and the viscosity under low shear higher than 10 Pa.Math.s so as not to run off the wall surface.

(14) It is to be noted that the surfactant of the gel used in the invention has a distinct, favourable impact on the rheological properties of the gel used in the invention. This surfactant particularly allows spraying of the gel used in the invention avoiding risks of run-off or dripping when treating vertical surfaces and ceilings. This surfactant also allows limiting of the bleeding phenomenon observed during storage of the gel.

(15) The gel thus prepared is then applied to the solid surface to be cleaned of a substrate made of a solid material.

(16) By solid surface to be cleaned is meant a solid surface on which a biofilm has formed that it is desired to remove.

(17) Possibly aside from alloys of lightweight metals of aluminium type, there is no limitation as to the constituent material of the surface to be cleaned; the gel used allows the treatment of all kinds of materials, even fragile materials, without any damage.

(18) The gel used in the invention does not generate any deterioration, erosion, chemical, mechanical or physical attack of the treated material. The gel used in the invention is therefore not in any way harmful to the integrity of the treated materials and even allows reuse thereof. Therefore sensitive materials such as military equipment are preserved and can be reused after cleaning, whilst monuments, buildings, works of art such as sculptures treated with the gel of the invention are absolutely not degraded and have their visual and structural integrity preserved.

(19) This substrate material can therefore be selected from among metals or alloys for example such as stainless steel, polymers such as plastic materials or rubbers of which mention can be made of PVCs, PPs, PEs in particular HDPEs, PMMAs, PVDFs, PCs, glasses, cements, mortars and concretes; plasters, bricks, natural or artificial stone, coats, ceramics.

(20) In all cases (see Examples 2 and 3 and Figures), irrespective of material type e.g. coat or cement, the cleaning of the invention has total efficiency.

(21) The treated surface may or may not be painted.

(22) There is therefore no limitation with regard to shape, geometry and size of the surface to be cleaned; the gel used according to the invention allows the treatment of surfaces of large size, of complex geometries having hollows, corners, recesses for example.

(23) The gel used in the invention ensures the efficient treatment not only of horizontal surfaces such as floors or balcony rails or window sills, but also of vertical surfaces such as walls, facades or inclined or overhanging surfaces such as ceilings.

(24) Compared with existing techniques which use liquids such as solutions, the invention uses a gel which is particularly advantageous for the treatment of materials having a large surface area that cannot be transported and are located outdoors. The method of the invention, through use of a gel, allows in situ cleaning preventing the spill of chemical solutions into the environment and the dispersion of contaminating species.

(25) The gel of the invention can be applied to the surface to be treated using any application method known to the man skilled in the art.

(26) Conventional methods are spraying for example using a spray gun or application using a brush or float.

(27) For application by spraying of the gel onto the surface to be treated, the colloidal solution can be conveyed by a low pressure pump for example a pump using a pressure of 7 bar or lower, i.e. about 7.Math.10.sup.5 Pascals.

(28) The break-up of the gel onto the surface can be obtained using for example a flat jet nozzle or a round jet nozzle.

(29) The distance between the pump and the nozzle may be any distance and for example may be between 1 and 50 m, in particular 1 to 25 m.

(30) The sufficiently short viscosity recovering time of the gels used according to the invention allows the sprayed gel to adhere to any surfaces e.g. to walls.

(31) The amount of gel deposited on the surface to be treated is generally 100 to 2000 g/m.sup.2, preferably 500 to 1500 g/m.sup.2, more preferably 600 to 1000 g/m.sup.2.

(32) The amount of gel deposited per unit surface area and hence the thickness of the deposited gel influences the drying rate.

(33) For example, when a gel film, layer, having a thickness of 0.5 mm to 2 mm is sprayed onto the surface to be treated, the efficient contact time between the gel and the materials is then equivalent to its drying time, a period during which the active ingredient contained in the gel interacts with the biofilm.

(34) In addition it has surprisingly been shown that the amount of deposited gel, when it lies within the above-mentioned ranges and in particular when it is higher than 500 g/m.sup.2 and particularly within the range of 500 to 1500 g/m.sup.2 which corresponds to a minimum thickness of deposited gel greater than 500 μm for example for a quantity of deposited gel higher than 500 g/m.sup.2, allows fracturing of the gel to be obtained after drying in the form of millimeter-size flakes for example having a size of 1 to 10 mm, preferably 2 to 5 mm which can be suctioned.

(35) The amount of deposited gel and hence the thickness of deposited gel, preferably higher than 500 g/m.sup.2 i.e. 500 μm, is the fundamental parameter impacting the size of the dry residues formed after drying of the gel, and which therefore ensures that dry residues of millimeter size are formed and not powdery residues, such residues being easy to remove using a mechanical method and preferably by suction.

(36) However, it is also to be noted that, by means of the surfactant in low concentration, the drying of the gel is improved and leads to a phenomenon of homogenous fracturing with dry residues of monodisperse size and increased capability of the dry residues to detach themselves from the substrate.

(37) The gel is left on the surface to be treated for the time required for drying thereof. Throughout this drying step, which can be considered to be the active phase of the method of the invention, the solvent contained in the gel i.e. generally the water contained in the gel evaporates until a dry, solid residue is obtained.

(38) The drying time is dependent upon the composition of the gel within the concentration ranges of its constituents given above, but also as already indicated upon the amount of gel deposited per unit surface area i.e. the thickness of the deposited gel.

(39) The drying time is also dependent on climate conditions namely temperature, ventilation and relative humidity of the atmosphere in which the solid surface finds itself.

(40) The method of the invention can be implemented under extremely wide-ranging climate conditions namely a temperature T of 1° C. to 50° C. and relative humidity RH of 20% to 80%.

(41) The drying time of the gel of the invention is therefore generally from 1 hour to 24 hours at a temperature T of 1° C. to 50° C. and relative humidity RH of 20% to 80%.

(42) It is to be noted that the formulation of the gel used in the invention, in particular if it contains surfactants such as Pluronics®, generally ensures a drying time substantially equivalent to the contact time between the gel and the biofilm that is necessary, required to destroy, remove the biofilm polluting the material. In other words, the formulation of the gel ensures a drying time that is none other than the time needed to remove, destroy the biofilm and is compatible with biofilm destruction kinetics and in particular the destruction kinetics of the biological contamination contained in the biofilm (the biological organisms are killed).

(43) After drying of the gel, the gel fractures homogeneously giving dry, solid residues of millimeter size e.g. a size of 1 to 10 mm, preferably 2 to 5 mm that are non-powdery and generally in the form of solid flakes. The dry, solid residues contain compounds resulting from destruction of the biofilm.

(44) The dry residues such as flakes obtained after drying adhere weakly to the surface of the cleaned material. On this account the dry residues obtained after drying of the gel can be easily recovered by mere brushing and/or suction. However the dry residues can also be evacuated using a jet of gas e.g. a jet of compressed air.

(45) Therefore no rinsing is necessary and the method of the invention does not generate any secondary effluent.

(46) According to the invention therefore, first major savings in chemical reagents are obtained compared with a washing decontamination method using a solution. Secondly, since waste is obtained in the form of a dry residue that can be directly suctioned, a rinsing operation with water or liquid is avoided. This evidently results in a reduction in the amount of effluent produced but also in notable simplification in terms of treatment and discharge means. In particular according to the invention, the waste obtained on completion of the treatment is not entrained into rainwater evacuation networks in breach of regulations.

(47) On account of the mostly mineral composition of the gel used in the invention and low amount of waste produced, the dry waste can be stored or directed towards an evacuation channel without prior treatment.

(48) For example in the frequent case in which 1000 grams of gel are applied per m.sup.2 of treated surface, the weight of the dry waste produced is less than 300 grams par m.sup.2.

(49) The invention will now be described with reference to the following examples given as non-limiting illustrations.

EXAMPLES

Example 1

(50) In this example the anti-biofilm gel tested in following Examples 2 and 3 is described and prepared.

(51) It is an oxidising, alkaline, basic, mineral gel comprising water, 1 M sodium hydroxide, sodium hypochlorite, alumina and a surfactant.

(52) This gel does not comprise any super-absorbent polymer.

(53) The aluminium oxide is Aeroxide® Alu C marketed by EVONIK INDUSTRIES having a specific surface area of 100 m.sup.2/g (BET), the surfactant is Pluronic® PE6200 marketed by BASF, the sodium hydroxide is 1 M sodium hydroxide marketed by SIGMA-ALDRICH and the sodium hypochlorite contains 10 to 15% active chlorine marketed by SIGMA-ALDRICH.

(54) The gel used in the invention is prepared as follows: the sodium hypochlorite solution is diluted to 50% with demineralised water. This solution, the surfactant and sodium hydroxide are mixed using a mechanical agitator equipped with a three-blade impeller, at a speed of 200 rpm for 3 to 5 minutes. The alumina is then gradually added to the reaction mixture progressively increasing the speed of agitation as and when viscosity increases to reach a final speed of about 400 to 600 rpm without any spattering. The gel is then held under agitation for 5 minutes.

(55) The composition of the tested gel is given in Table 2 below.

(56) TABLE-US-00002 TABLE 2 Composition of the tested gel. Composition Weight percentages (%) 1M NaOH 44.5 Sodium hypochlorite (10-15% act. chl.) 42.5 diluted 50% Alumina 12 Pluronic ® PE6200 1

Example 2

(57) In this example a test was conducted with the anti-biofilm gel prepared in Example 1 to remove a biofilm from a vertical outdoor surface.

(58) The anti-biofilm gel prepared in Example 1 was applied using a brush to part of the surface of an outside wall coated with a traditional sprayed coat.

(59) The test was conducted at a temperature lower than 10° C., under relative humidity in the order of 50%.

(60) After 48-hour drying, the formed flakes were moved by gentle brushing.

(61) FIG. 1 (A, B, C) shows the appearance of the wall surface at the different steps of the test in this example, namely: the initial state of the wall (A); the appearance of the wall surface after application of the gel using a brush on a part of the wall surface, this part of the wall surface is therefore coated with wet gel (B); the appearance of the surface after 48-hour drying and removal of the dry gel flakes by gentle brushing (C).

(62) It can visually be ascertained that the biofilm has effectively been removed from the part of the wall surface, treated, cleaned in accordance with the invention using the gel prepared in Example 1.

(63) This test shows the efficiency of the use according to the invention of the alkaline oxidising gel prepared in Example 1 to remove a biofilm on a vertical surface.

(64) For better quantifying of the action of the gel, image analysis was performed using ImageJ software.

(65) To do so the final image in FIG. 1C showing the wall surface after treatment according to the invention was converted to grey levels (ranging from 0 black to 255 white) and analysis of the grey values was carried out along the line drawn in FIG. 2A (similar to FIG. 1C).

(66) The mean value in the part of the wall surface non-treated with the gel of Example 1 is taken as reference.

(67) The graph in FIG. 2B gives the results of image analysis and confirms the efficient removal of the biofilm by the gel in that part of the wall surface treated according to the invention with the gel prepared in Example 1.

Example 3

(68) In this example, a test was conducted with the anti-biofilm gel prepared in Example 1 to remove a biofilm from a horizontal outdoor surface.

(69) The anti-biofilm gel prepared in Example 1 was applied using a brush to a part of the surface of a balcony railing made of white cement.

(70) The test was conducted at a temperature lower than 10° C., under relative humidity in the order of 50%.

(71) After 48-hour drying the formed flakes were removed by gentle brushing.

(72) FIG. 3 (A, B, C, D) shows the appearance of the surface of the railing at the different steps of the test performed in this example, namely: the initial state of the part of the surface of the railing (A); the appearance of the surface of the railing after application of the gel using a brush onto part of the surface of the railing, this part of the railing surface is therefore coated with wet gel (B); the appearance of the surface after 48-drying of the gel applied to part of the railing surface, this part of the railing surface is therefore coated with dry gel (C); the appearance of the railing surface after removal of the dry gel flakes by gentle brushing (D).

(73) It can visually be ascertained that the biofilm has effectively been removed from the treated part of the railing surface, cleaned according to the invention using the gel prepared in Example 1.

(74) This test shows the efficiency of the use according to the invention of the alkaline oxidising gel prepared in Example 1 to remove a biofilm from a horizontal surface.

(75) To better quantify the action of the gel, image analysis was carried out using ImageJ software as in Example 2.

(76) To do so as in Example 2 the final image in FIG. 3D showing the rail surface after treatment according to the invention was converted to grey levels (ranging from 0 black to 255 white).

(77) On the other hand the difference being less distinct (strong background noise), the result is expressed in grey levels averaged over two areas of the railing surface, a first area 41 being located in that part of the surface treated with the gel and a second area 42 located in part of the surface non-treated with the gel (FIG. 4).

(78) It is noted that the non-treated area has an average level of 156 whereas the treated area has an average grey level of 169.

(79) The results of image analysis confirm the efficacy of biofilm removal by the gel in that part of the railing surface treated according to the invention using the gel prepared in Example 1.

REFERENCES

(80) [1] NOBATEK Report http://www.nobatek.com/downloads/Etudes%20publiques/ENSEL%20Micro%20biologie%20_NOBATEK_.pdf [2] US-A1-2012/0232153. [3] Biofilm quand les microbes s'o rganisent by R. Briandet, L. Fechner, M. Naïali & C. Dreano, Editions Quae 2012. [4] K. Ammerman, Algae, the growing problem, Interface, January 2007, pages 37-42. [5] FAURE S., FOURNEL B., FUENTES P., LALLOT Y. “Procédé de traitement d'une surface par un gel de traitement, et gel de traitement”, FR-A1-2 827 530. [6] FAURE S., FUENTES P., LALLOT Y. “Gel aspirable pour la décontamination de surfaces et utilisation”, FR-A1-2 891 470. [7] CUER F., FAURE S. Gel de décontamination biologique et procédé de décontamination de surfaces utilisant ce gel, FR-A1-2962046 and WO-A1-2012/001046.