GB2532447A - Treatment of contaminated land - Google Patents

Abstract

A method for land decontamination comprises the steps of: removing contaminated soil 2 and other material from the land to be decontaminated; placing the soil and other material on a conveyer 1; passing the soil and other material on the conveyor beneath one or more spray heads 3 covering the width of the conveyor, wherein the spray heads are fed with a bioremediation material; gathering and placing in open or closed storage the treated soil and other material, leaving the treated soil and other material for sufficient time for the bioremediation material fully to have reacted with the soil and other material. The treated soil and other material may be placed in an open container (14, Fig. 3) with an impervious bottom and sides. Suitably, the container has one or more pipes (19, Fig. 3) extending into the material, wherein the pipe(s) has/have multiple holes for the delivery of oxygen to the treated soil. Upon completion of the treatment, the treated soil can be reloaded onto the conveyor, which is reversed allowing the treated material to be drained of excess water and any bioremediation material. Preferably, the conveyor is a conveyor belt comprising a fine mesh.

Description

Treatment of Contaminated Land [0001] This invention relates to the bioremediation treatment of land contaminated by hydrocarbons.

[0002] It has been proposed to use bioremediation materials to treat large areas of polluted land. The area, such as a field or part of a field requires a trench to be dug around it to a depth below the water table. The outside perimeter trench is then lined with an impermeable membrane, such as polythene, to a depth below the water table. The lining is to prevent hydrocarbons flushed from the land escaping into the surrounding land during treatment. The polluted area of land is then sprayed with bioremediation material to spread and activate the bioremediation material which has also been preheated as described. The bacilli will digest hydrocarbons present in the soil. Any hydrocarbons flushed into the trench can be recovered from there if they are on the liquid surface of the trench, or treated with further spraying with the bioremediation material. As the bacilli are naturally occurring and the other remaining products of the remediation process are water and biodegradable ingredients in the bioremediation material, the land thus cleared of contamination is suitable for immediate reuse.

[0003] The process of the previous paragraph is not always practical.

[0004] Thus according to the present invention a bioremediation method for land decontamination comprises, removing contaminated soil and other material form the land to be decontaminated, placing said soil and other material on a conveyer, passing the soil and other material on the conveyor beneath one or more spray heads covering the width of the conveyor, said spray heads being fed with a bioremediation material, gathering and placing in open or closed storage the treated soil and other material, leaving the treated soil and other material for sufficient time for the bioremediation material fully to have reacted with the soil and other material.

[0005] Ideally the height of the soil and other material passing below the spray nozzles is restricted to allow maximum penetration of the bioremediation material.

[0006] Normally the soil and other material would be left for up to 30 days to enable the bioremediation treatment to complete.

[0007] After the reaction is complete, the soil and other material would be retumed to its origin or used elsewhere.

[0008] In a preferred embodiment of the invention, the treated soil and other material is placed in an open container with an impervious bottom and sides, the container having one or more pipes extending into the material, said pipes having multiple holes, to which is supplied oxygen, normally in compressed air. The oxygen allows the micro-organisms in the bioremediation material sprayed to continue to flourish act.

[0009] In a development of the preferred embodiment, one or more of the pipes may be supplied with further bioremediation material to replenish the bioremediation material in the treated soil and other material.

[0010] Normally the conveyor comprises a fine mesh material with a collecting tank below into which excess bioremediation material sprayed can fall. The tank is connected to a pump through a filter to recycle the bioremediation material in the tank.

[0011] In a further development of the invention, after completion of the treatment in a container as described the treated soil and other material is reloaded onto the conveyor, which is reversed allowing the treated material to be drained of excess water and remediation material remaining.

[0012] Preferably the bioremediation material is one which has been produced by the method of UK Patent Application GB1412458.0.

[0013] One embodiment of the invention is illustrated by way of example only with reference to the accompanying drawings, in which: [0014] Figure 1 is a schematic side view of the embodiment; [0015] Figure 2 is a top view of a section of the conveyer belt of figure 1; and [0016] Figure 3 is a side section through a pile of treated soil and other material after being passed over the conveyor but before it is returned.

[0017] Soil from a site contaminated by hydrocarbons is brought in the bucket of a heavy duty digger 9 to one end of a conveyor 1. The soil is placed on the conveyor 1, inevitably forming something of a pile 8. The conveyor 1 moves the soil beneath a screen 4 where the pile is flattened and spread evenly across the conveyor. The soil 2 then passes beneath a row of nozzles 3 directing bioremediation material onto the soil across the width of the conveyor -more than one row of nozzles may be deployed.

[0018] As seen in figure 2, the conveyor belt comprises a fine mesh.

[0019] Excess bioremediation material which is not absorbed by the soil and other material on the conveyor, drops though the mesh of conveyor 1 into a tank 5, from here it is pumped by a pump 7 through a filter 6 and recycled.

[0020] The soil 2 is conveyed to the end of the conveyor, where it gathers 11. Another digger or moving device moves the treated soil and other material to open store in piles 13 formed in one or more dishes 14, the diches having an impervious base 15 and sides 17. Conveniently, the dishes can be formed using metal side walls and the solid round, the walls and ground lined, for example with standard heavy grade polythene pond liner.

[0021] One or more pipes 19 about lm high and having multiple hoses in their side walls are in the dish 14, and the treated soil and other material is placed around thesel3 as seen in figure 3. The pipes 19 have connections 21 to one or more pumps 23 though which compressed air is pumped gently to the interior of the pile 13 to aerate it. From time to time, say one every 5 days, further bioremediation material may also be pumped through the pipe 19 to the interior of the piles 19. Generally the hydrocarbons in the treated soil and other material will have degraded sufficiently in about 30days or less to enable to soil and other material to be reused.

[0022] However, to ensure maximum recycling of the active bioremediation material, the treated soil and other material is placed on the conveyor 1, which is run in the opposite direction. Water and excess bioremediation material falls into the tank 5 from where it is pumped, as before, for recycling. The treated soil and other material reaching the end of the conveyer is removed by the digger 9 and returned to its origin. In this was a treatment process for contaminated land can be completed without the need to transport soil etc. way from the treatment site, greatly diminishing local congestion, dirt and pollution.

[0023] The manufacture of a suitable bioremediation treatment material for use in this invention has been set out in UK Patent Application GB1412458.0 (incorporated by reference) describes a bioremediation material. For completeness UK Patent Application 1412458.0 is summarised below.

[0024] In UK Patent Application GB1412458.0 there is set out and described a method of manufacturing a bioremediation material for deployment comprising preparing an alkali cleaner comprising an inorganic aqueous alkali having an initial ph of between 11 and 14, the steps of mixing with water a source of bacilli, a biodegradable anionic surfactant up to 15% by weight inclusive, a source of hydrocarbons comprising 0.3% by volume or less, mixing the alkali cleaner adding water so that the concentration of bacilli being at least 106/m1 in the final mixture. Other compounds may be present in small quantities such as thickeners, foaming agents, dyes and preservatives.

[0025] Preferably the inorganic aqueous alkali is sodium hydroxide or potassium hydroxide.

[0026] Other aqueous alkali based cleaners include those based on ammonium carbonate; but these have a lower ph than sodium of potassium hydroxide and appear a little less effect in the context of the invention of UK Patent Application GB1412458.0 than those based on sodium or potassium hydroxide.

[0027] Preferably the hydrocarbon is an aliphatic hydrocarbon.

[0028] The surfactant typically is alcohol ethoxylate, others include a range of products sold under the trade mark TERGITOLTM L Series, or Linear Alkyl Benzene Sulfonate. There are many suitable naturally occurring solvents and surfactants that can be used with this invention, examples include Eco-friendly solvents used in recent times include solvents that are derived from alcohols and esters of soy, corn, rice, palm, cottonseed, linseed, safflower sunflower, Jojoba soil, Jatropha, mustard, walnut and almond oils which are all readily biodegradable and non-toxic.

[0029] The inventors have found that a water based potassium hydroxide cleaner is particularly suitable.

[0030] There are many microorganisms in the bacilli family some of which are pathogens; harmless bacilli suitable for use in the invention of UK Patent Application GB1412458.0 are the soil bacilli, bacillus pumulus, bacillus subtili and bacillus lichinformis. An easy way to isolate Bacilli is by placing non-sterile soil in a container with water, shaking, placing in melted mannitol salt agar, and incubating for at least a day. Colonies are usually large, spreading and irregularly-shaped. Under the microscope, the Bacillus cells appear as rods, and a substantial portion usually contain an oval endospore at one end, making it bulge. The resulting culture contains a variety of soil bacilli. The source of hydrocarbons is conveniently an aliphatic hydrocarbon.

[0031] There are also areas of a high hydrophobic nature arising close to the microbes which attract the oil and draw it towards the microorganisms further accelerating the process.

[0032] It is practicable to mix a basic starting material using a metal alkali base having a ph of between 12 and 14and adding a known bio-degradable surfactant to between 5% and 15% by weight other solvents can also be added if required. However, with good commercially available aqueous water based cleaners being available with bio-degradable surfactants, the inventor has found it convenient to start with one of these. One such commercially available alkali based cleaner has a pH of more than 12 comprises potassium hydroxide, between 5 and 15% by weight surfactant and 5% by weight aliphatic hydrocarbons with all other ingredients less than 5% apart from water, which made up the residual weight was mixed with a source of bacilli microorganisms used containing up to 15% by weight bacilli and 15% by weight surfactant with the rest being water to reach the material according to the invention. One preparation comprises mixing 2 parts to alkali based cleaner diluted with 100 parts with 3 parts bacilli source. The pH of the alkali based cleaner was 13.0. Originally it was thought that the high alkali content of the cleaner would kill the bacilli, however it has been found that in high concentrations of bacilli (above 106) this is not the case if the mixing is carried out as described. The mechanism for this unexpected result is unclear, but it is theorised that the bacilli may be using the hydrocarbons in the cleaner as a source of nourishment becoming dormant spores when the hydrocarbon source is exhausted. The final pH of such a mixture is 11.3 to 11.6. The mixture formed as a result is hereinafter described as the "First Mixture".

[0033] The first mixture has a pH of 11.3 to 11.6; but for normal use this first mixture should be further diluted 20 or more times (a 5% concentration of the original preparation) or less. At his level the interfacial tension increases dramatically and the pH falls to 10.5. With further dilution to 2% the pH falls to below 9. At these levels the product is permissible for general use, the interfacial tension remains high. The best compromise between all the properties is found at a dilution of the original mixture to around 2%.

[0034] Other alkali non-toxic alkali cleaners are available for mixing with the source of bacilli, including some using naturally occurring substances. The main criteria to be met is that a starting material is prepared containing an aqueous alkali cleaner is that it is strongly alkali before the bacilli are added that the initial mixture surfactant generally between 5 and 15% by weight and a source of hydrocarbons. Normally the hydrocarbon source would constitute 0.3% by weight of the initial mixture.

[0035] In a further development of the invention of UK Patent Application GB1412458.0, a water based alkali cleaner containing between 5 and 15% by weight surfactant and 5% by weight aliphatic hydrocarbons with all other ingredients less than 5% apart from water was diluted in the ratio 2 parts water based alkali cleaner to 10 parts granite spring water and aerated at 20°C to 40°C, and a source of bacilli comprising at least 106 was placed in a bioreactor and aerated at 20°C to 40°C (which is very low in ion content) for about 20 minutes. Once fully aerated and at a stable temperature the diluted water based alkali clear was added to the bacilli source in the bioreactor in the ratio 4 tot, such that the final mixture contains 200m1 of water based alkali cleaner, 300m1 of bacilli source and 10 parts granite spring water. Air or oxygen is passed through the bioreactor for 20 minutes and the mixture continuously agitated, for example by using an aquarium pump to pump up liquid from the bottom of the bioreactor to the to the top of the liquid surface. It was found the bacilli concentration rapidly increased further to 1010/ml, to form an even more effective Second Mixture. Granite spring water is water coming from springs in areas in which the underlying rock is granite The water used was pure granite pure spring water with a very low ion content found on the higher ground in the Enniskillen area of Co Fermanagh, Northern Ireland, but di-ionised water can be used instead, although for reasons which are not entirely clear at present the reproduction of the bacilli is slightly less extreme. On completion the hydrocarbon source becomes exhausted and the bacilli are believed to form dormant spores, helped possibly by the surfactants. For use this second mixture can be diluted to below 1% concentration of the original second mixture and typically between 0.1% and 0.2% concentration and remain a very powerful cleaner of hydrocarbons, making it very economical to use. It is also feasible to recycle the material for even greater economy.

[0036] In a further development, the material of the invention of UK Patent Application GB1412458.0, especially a 0.1% to 0.2% concentration of the second material containing 1010 bacilli/ml, has been found to be very suitable for decontaminating concrete and areas of land. It has been found, surprisingly, and in contract to other hydrocarbon cleaners, the material will penetrate the concrete to a considerable depth. Spraying activates the bacilli and aids penetration into concrete, preheating the material as described in the previous paragraph aide activity of the bacilli. The warmth of the material encourages digestion of the hydrocarbons by the bacilli. The minimum air temperature for this method to work is low just above the 0°C, although more material is necessary for effective treatment.

[0037] The minimum temperature mentioned in the previous paragraph is the lowest working temperature of the present invention.

Claims (11)

1. Claims 1. A method for land decontamination comprising the steps of: removing contaminated soil and other material form the land to be decontaminated; * placing said soil and other material on a conveyer; * passing said the soil and other material on the conveyor beneath one or more spray heads covering the width of the conveyor, said spray heads being fed with a bioremediation material; * gathering and placing in open or closed storage the treated soil and other material, leaving the treated soil and other material for sufficient time for the bioremediation material fully to have reacted with the soil and other material.
2. 2. A method according to claim 1 in which the height of soil or other material on the conveyor is restricted.
3. 3. A method according to claim 1 or 2 in which the treated soil and other material is placed in an open container with an impervious bottom and sides.
4. 4. A method according to claim 3 in which the container having one or more pipes extending into the material, said pipes having multiple holes.
5. 5. A method according to claim 4 in which the treated soil and other material in the container is supplied with oxygen through one or more of said pipes.
6. 6. A method according to claim 4 in which the soil another material in the container is supplied intermittently with further bioremediation material through one or more of the pipes.
7. 7. A method according to any one of claims 3 to 6 in which, after removal of the soil and other material from the container on completion of the treatment, the treated soil and other material is reloaded onto the conveyor, which is reversed allowing the treated material to be drained of excess water and any bioremediation material remaining therein.
8. 8. A method according to any previous claim in which the conveyor comprises a fine mesh material and a collecting tank is provided below the conveyor below into which excess bioremediation material sprayed can fall.
9. 9. A method according to claim 8 in which the tank is connected to a pump to recycle the bioremediation material in the tank.
10. 10.A method according to any previous claim carried out adjacent to the land being decontaminated.
11. 11.A method substantially as hereinbefore described with reference to the accompanying drawings.