GB2430198A - Contamination barrier - Google Patents

Abstract

A contamination barrier comprises a blanket having at least one biofilm layer 1 (upper layer) attached to a support layer 3 (reinforcing layer). Preferably, the bioflim layer is attached to or into the support layer by stitching 4. The biofilm layer may comprise vermiculite, zeolite, sand, fertiliser, glucose, sucrose, lime, or an organic material such as coir. The biofilm layer is intended to allow a biofilm to grow, which is able to degrade contaminants as they pass with groundwater through soil. A netting layer may be interposed between the bioflim layer and the support layer. A further layer 2 (lower layer) may be included, which may contain carbon, activated carbon, glucose, or sucrose.

Description

Title: DEVICE FOR PRODUCING A CONTAMINANT BARRIER The present invention

relates to a device for producing a barrier in ground to reduce permeability, to retard contaminants through sorptionlsorptiofl and/or cause increased degradation of contaminants as they pass with ground water through soil.

According to the present invention there is provided a contamination barrier comprising a blanket having at least one bio-film layer attached to a support layer.

Preferably the bio-film is stitched to or into the support layer in the fonTn of a natural or synthetic textile forming a reinforcing layer.

A constructional embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, wherein:- Figure 1 shows a blanket according to the invention.

The sorption degradation bio-like blanket retards through sorption and/or causes the increased degradation of contaminants carried by water as they pass through it. Contaminated water passing through the blanket is wholly or partly purified. The blanket provides complete or partial protection of ground water and/or surface water from spillages and/or discharges of contaminated water.

The blanket comprises one or more layers depending upon the level of protection required. The layers could comprise the following:- 1. Contents of Upper Layer 1:- Vermiculite or Zeolite or Sand/FertiliSer/GIUC0Se/Sucr0se'Ime or Organic Material such as Coir The objective of this layer is to allow a bio film to grow on which contaminants will be sorbed and/or degraded. The slow release fertiliser would probably include ground rice, phosphate, nitrogen, nitrogen potassium and chelated metals such as iron, manganese, copper, boron, magnesium, copper and molybdenum. This layer would be designed to achieve the following:- Provide the conditions to create a bio-film to absorb the following - soluble heavy metals, Dense Non-Aqueous Phase Liquids (especially polyaromatic hydrocarbons and chlorinated solvents, hydrocarbons), light non- aqueous liquids, some chloride, pesticides, particulates containing sorbed contaminantS, some bacteria, some nitrate and some phosphate. The vermiculite and the zeolite have cation - exchange properties and in particular should be able to absorb phosphate. The aerobic conditions should lead to the oxidation of ammonia to nitrite and then nitrite. Where vermiculite or zeolite was not needed, sand could be used.

Organic material such as coir would absorb heaving metals, dense and light non-aqueous phase liquids, pesticides, hydrocarbons (dissolved) and chlorides.

2. Contents of Lower Layer 2:- Carbon or Activated carbon/gIuCOSe/5UCr0 This layer is designed to achieve the following: The carbon would absorb DNAOLS, pesticides, dissolved hydrocarbons and provide anaerobic condition for the reduction of nitrate to nitrate and then to nitrogen gas.

The layers are 10mm to 20mm thick. If greater thickness is required then multiple layers are used.

The width of layers is Im to 3m and length 3m to 1Dm.

The mesh size of the fabric material 5 is sufficiently small to contain excessive dust loss, e.g. less than 0.25mm. Where plastic fabric is used a geo- textile used to strengthen soils provides stiffness and a textile used to rap around well screen is used to hold the filling. Where a geo-textile is used to strengthen a slope it could be incorporated into the RD Blanket. In some places the fabric must be bio-degradable, either bio- degradable plastic or cotton fabric with coconut fibres for stiffness. The plastic blanket would be joined using the techniques to weld plastic sheets in lining landfills. Where a natural material is used, grout would be sprayed along the joining edges of blankets to act as seal and reduce io bypass flow.

Stitching 4 runs the length of the blanket to prevent movement of contents.

The complete blanket shown comprises the following layers from top to bottom, viz: - A large mesh textile fonning a reinforcing layer 3 Upper layer 1 Fine netting formed by fabric material 5 A fine netting layer 5 A reinforcing layer 3 A fine netting layer 5 Lower layer 2 A fine netting layer 5 A reinforcing layer 3.

The blanket may be fixed to steeply inclined surfaces using U-shaped nails. Grout may be sprayed over them to prevent by-pass flow.

3. Possible uses of the blankets are as follows:- a) soakaway/drainage trenches b) lining of trenches taking sewers, c) beneath structures which if leaked could cause pollution, i.e. diesel tanks, central heating tanks, landfills, factories using hydrocarbons, farm silage tanks, slurry pits, areas where pesticide tanks are washed out, d) replacing the use of reed beds in some circumstances, e) beneath permeable hardstanding or swales along roads, in some circumstances it may be possible to replace blankets, e.g. to substitute a fresh blanket for a soiled one.

In Patent No 2699855 "Composite flexible sheet for dispensing water, absorbing oil or chemical liquid" there is defined a composite material which claims to hold a liquid or absorb oils or chemical product. As the product works due to its physical and or chemical properties it is limited to the ability of the material to absorb chemicals through physiochemiCal absorption.

The present invention in additional to the ability to absorb chemicals through physio-chemical absorption, promotes the growth of bio-films created by bacteria, viruses and/or life fonns due to the presence of fertilisers, nutrients and minerals. In particular, chemicals such as petroleum hydrocarbons, chlorinated solvents, solvents in general, polyaromatic hydrocarbons, polychioride biphenyls or other organic compounds could become a source of energy for the organisms creating the bio-film. The nature of bio-films is such that aerobic and anaerobic conditions promoting the existence of aerobic and anaerobic bacteria may be found in close proximity. Aerobic and anaerobic bacteria may preferentially breakdown different compounds. In addition bio-films may absorb metals and other pollutants such as sulphate, nitrates, ammonia, nitrites, phosphates, metals and chlorides. In addition the anaerobic bacteria may reduce the more soluble salts of metals to the lower solubility ones such s sulphides which may cause them to be precipitated. Metal compounds may be absorbed by the bacteria such that they are removed from the water and/or the air. Nitrates or nitrites may be reduced to nitrogen gas which could volatilise from the groundwater.

The ability of a hio-film to absorb or remove contaminants from water and/or air can increase as the bio-film grows as the contaminants becomes a food source and therefore is not so self-limiting as the existing sheet which depends upon physio-chernical processes. The bio-film not only absorbs chemicals but can cause the biological breakdown of organic compounds and/or the reduction of nitrates or nitrites to nitrogen. Therefore contaminants are converted to different forms and removed from the water and/or air. The existing flexible sheet system could absorb sufficient amounts of contaminants such that it can no longer absorb further contaminants. However, the present invention, by creating a biofilm, enables organisms to adapt to their surroundings and therefore creating a barrier which can adjust to the environment. Once established, the bacteria can continue to grow as long as nutrients which can include contaminants, are carried to their location as groundwater flow.

Claims (14)

1. An contamination barrier comprising a blanket having at least one biofilm layer attached to a support layer.

2. A contamination barrier as claimed in claim 1, wherein the bio-film is stitched to or into the support layer in the form of a natural or synthetic textile forming a reinforcing layer.

3. A contamination barrier as claimed in claim I or claim 2, wherein the bio- film layer comprises vermiculite or zeolite.

4. A contamination barrier as claimed in any one of claims 1 to 3, wherein io the bio-film layer includes any one or more of the following: sand, fertiliser, glucose, sucrose, lime or organic material.

5. A contamination barrier as claimed in claim 4, wherein the organic material consists of coir.

6. A contamination barrier as claimed in any one of the preceding claims and including a second bio-film layer.

7. A contamination barrier as claimed in claim 6, wherein the second biofilm layer comprises one or more of the following: carbon, activated carbon, glucose or sucrose.

8. A contaminatiO1 barrier as claimed in claim 6 or claim 7, wherein the thickness of each bio-film layer is 10-20mm.

9. A contamination harrier as claimed in any one of the preceding claims, wherein a netting layer is interposed between the bio-film layer(s) and the support layer.

10. A contamination barrier as claimed in claim 9, wherein the netting layer comprises a large mesh textile layer.

II. A contamination barrier as claimed in claim 10, wherein the mesh size of the textile layer is less than 0.25mm.

12. A contamination barrier as claimed in any one of the preceding claims, wherein the blanket comprises the support layer which serves as a first reinforcing layer, a first bio-film layer, a first netting layer, a second bio-film layer, a second netting layer and a second re-inforcing layer.

13. A contamination barrier as claimed in claim 12, wherein the blanket further comprises a further re-inforcing layer and a further netting layer interposed between the first netting layer and the second bio-film layer.

14. A contamination barrier substantially as described herein with reference to the drawing.