WO2001014259A1

WO2001014259A1 - A method and apparatus for reducing pollution from run-off water from highways

Info

Publication number: WO2001014259A1
Application number: PCT/GB2000/003120
Authority: WO
Inventors: Richard Paul John Swannell; David James Mitchell
Original assignee: Aea Technology Plc
Priority date: 1999-08-19
Filing date: 2000-08-16
Publication date: 2001-03-01
Also published as: GB9919520D0

Abstract

Rain water on highways is collected in drainage structures, before discharge elsewhere, and is initially collected in a sump structure such as a gully pot (12) to trap sediment. The water in such a gully pot (12) may be contaminated with organic materials such as oil, petrol, or rubber from vehicle tyres. A device (26, 28) is therefore provided within the gully pot (12) to enhance natural biodegradation processes, that is to say, to achieve bioremediation. Lack of oxygen is often a limiting factor, and in this case the device would provide oxygen to the water, for example comprising a canister (26) containing solid magnesium peroxide (34) which gradually releases oxygen into the water.

Description

A METHOD AND APPARATUS FOR REDUCING POLLUΗON FROM RUN-OFF WATER FROM HIGHWAYS

The invention relates to a method of reducing pollution arising from run-off water from highways, and 5 to an apparatus for use in this method.

In this specification, the term highway should be understood as encompassing roads, tunnels, bridges and viaducts. Rain water on highways is collected in drainage

10 structures, usually at the side of the highway, before discharge elsewhere. The discharge may take place to a variety of different end-points, such as soakaways, ditches or small water courses, or rivers. The water is commonly collected, initially, in a sump structure which

15 may be referred to as a gully pot or catch pit. This is principally a sediment trap, and is emptied on a regular basis to remove the solid material. The water collecting in such a sump structure may be contaminated with organic materials such as oil, petrol, or rubber from vehicle

20 tyres, and it would be desirable to reduce the level of contamination before the water is discharged from the sump structure during the next rainfall. The sediment is also likely to be contaminated, and during storm conditions some of the sediment may be discharged into

25 the environment, so it would also be desirable to reduce the level of contamination in the sediment.

According to the present invention there is provided a method of reducing pollution arising from run-off water 30 from highways, where the highway incorporates a drainage structure including a sump structure, the method comprising installing within the sump structure a means to enhance natural biodegradation processes. It has been found that naturally occurring microorganisms are capable of destroying such pollution, but that in practice this scarcely happens because of a lack of certain nutrients in the water. Hence the enhancing means comprises a device to supply a nutrient to the water, the device containing a source of the nutrient in solid form, so the nutrient gradually dissolves in water in the sump structure, so as to enhance the natural biodegradation processes, that is to say to achieve bioremediation. In this specification the term nutrient is used to mean a substance required by the microorganisms if they are to live. The device desirably contains sufficient material to supply the nutrient for several months, so that replacing or re-filling the device can be done when the sump structure is emptied.

In particular it has been found that lack of oxygen is often a limiting factor, and hence that the device should provide oxygen, as the requisite nutrient, to the water. For example the device may contain a chemical such as magnesium peroxide, which when in contact with water gradually releases oxygen. The use of magnesium peroxide to assist bioremediation of soils, and a way of making magnesium peroxide in the presence of phosphate ions so that it releases oxygen over a prolonged period, are described in US 5 264 018 (Koenigsberg et al) . In particular the device may comprise a canister containing solid magnesium peroxide (for example magnesium peroxide formed in the presence of phosphate ions) , the canister having a liquid permeable wall to allow water to enter, and to allow oxygen to diffuse out. There may be circumstances in which lack of nitrate or phosphate ions limits the growth of micro-organisms, in which case the device would supply the required ions to the water. In some circumstances a further limiting factor may be an insufficiency of surface area for micro-organisms to form a film on. In this case a canister containing a high permeability, high surface area packing, for example many short lengths of plastic pipe may also be provided. Where contamination by heavy metals is of concern, a canister containing a metal absorbing material, such as a zeolite, may be provided.

The invention also provides a means for performing the method.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawing which shows a sectional view through a gully. Referring to the drawing, a gully 10 incorporates a gully pot 12 which defines an upright cylindrical chamber of internal diameter 0.45 m. The gully pot 12 has an outlet pipe 14 about 0.35 m above its base, and the gully pot 12 is constructed with the pipe 14 at least 0.75 m below the surface of a road 16. Above the gully pot 12 is a rectangular concrete cover slab 18 defining a circular aperture of diameter 0.45 m, above which is a brick work structure 19 to support a gully frame 20 in which is a cast iron grating 22. The frame 20 is next to the kerb 24 of the road 16. Whenever it rains, the rain water flows to the edge of the road 16, along the gutter next to the kerb 24, and so through the grating 22 into the gully pot 12, carrying with it dirt, soil, and any pollutants from the road surface. Solid matter sinks to the bottom of the gully pot 12, with water above it. When the water in the gully pot 12 reaches the outlet pipe 14, the extra water is discharged.

Two canisters 26 and 28 are installed in this gully pot 12. Each comprises a cylindrical canister 30 with stainless steel mesh sides, and with stainless steel plates at top and bottom, of diameter 0.10 and of height 0.25 m. Each canister 30 is provided with legs 32 so the bottoms of the canisters are 0.10 m above the bottom of the gully pot 12, and the tops of the canisters 26 and 28 are clipped to a plastic spider 33 to ensure the canisters 26 and 28 are stable. One canister 26 is filled with a slow release magnesium peroxide powder 34. The other canister 28 is filled with a packing consisting of 10 mm lengths of plastic pipe 36 of diameter 10 mm.

Naturally occurring micro-organisms grow in the water within the gully pot 12, degrading and breaking down pollutants such as oil, petrol and rubber. The packing 36 in the canister 28 provides a large surface area for a biofilm to form on, so a large population of micro-organisms can grow. The magnesium peroxide 34 in the canister 26 gradually reacts with the water, generating oxygen in solution, which diffuses throughout the water in the gully pot 12, increasing the rate of growth of the micro-organisms. Consequently a significant proportion of these organic pollutants are biodegraded, such that the next time it rains the water discharged through the pipe 14 does not contain a large concentration of the pollutants, and the discharged water is also not anaerobic. Thus the process provides bioremediation of the potential pollution from highway drainage. Because of the oxygen in the water, biodegradation of solid pollutants in the sediment also takes place. At regular intervals, for example every six months, the grating 22 is removed. The canisters 26 and 28 along with the spider 33 are taken out, and the sediment is pumped out of the gully pot 12. The old canister 26 is undipped from the spider 33, and a new canister 26 containing fresh magnesium peroxide is clipped on in its place. The spider 33 and the canisters 26 and 28 are then replaced in the gully pot 12, and the grating 22 replaced. The old canisters 26 may subsequently be emptied, and then re-filled with fresh magnesium peroxide, so they can be reused.

It will be appreciated that the method is applicable to other designs of gully pot, for example those with an oil trapping outlet, and to other types of sump such as catch pits. It will also be appreciated that the canisters may be of a different size or shape to those described above, and that in some cases only one such canister may be required. For example, if the only limiting factor is the lack of oxygen, then only the magnesium peroxide canister 26 would be required. It will be understood that other oxygen-releasing materials might be used in place of magnesium peroxide, although magnesium peroxide is beneficial in that it does not generate any polluting materials. Furthermore, in some circumstances, it may be necessary to provide nitrate or phosphate ions if those are found to be limiting the bioremediation process.

Where pollution arises from heavy metal ions in the water, a canister containing a suitable zeolite may be provided. Zeolites are crystalline alumino-silicate- based materials that can bind and retain metal ions. The zeolite may be incorporated in the canister 26 along with the magnesium peroxide, or be in a separate canister. At intervals, when its capacity to absorb metal ions has been exhausted, the used zeolite is removed and replaced with fresh zeolite.

It will also be appreciated that a single canister might contain both an oxygen-releasing material and also a large surface area packing. For example a canister (not shown) , suitable for use in a gully pot of diameter 0.6 m in which the outlet duct is 0.6 above the base, might consist of a cylindrical canister of stainless steel mesh of diameter 0.15 m and of height 0.5 m, with for example a central conically- tapered tube along its longitudinal axis also of stainless -steel mesh; the canister also has a mesh base and a mesh lid. The generally annular space between the tube and the outside of the canister is packed with high surface area packing (e.g. 25 mm lengths of 25 mm diameter plastic pipe with corrugated walls). A conical cloth bag packed with slow release magnesium peroxide locates within the central tube. This annular arrangement ensures that the microorganisms that grow on the surfaces of the packing are provided with oxygen diffusing radially outwards from the central tube, and are contacted by pollutant materials that diffuse radially inwards through the packing. The cloth bag may also include sources of other nutrients (e.g. nitrate or phosphate ions) if necessary, mixed with the magnesium peroxide. When the gully pot is serviced only the cloth bag would need to be replaced.

Claims

1. A method of reducing pollution arising from run-off water from highways (16) , where the highway (16) incorporates a drainage structure (10) including a sump structure (12), the method being characterised by installing within the sump structure (12) a device (26) to supply a nutrient to the water, the device (26) containing a source of the nutrient in solid form (34), so the nutrient gradually dissolves in the water in the sump structure (12) , so as to enhance the natural biodegradation processes.

2. A method as claimed in claim 1 wherein the device (26) contains sufficient material (34) to supply the nutrient for several months.

3. A method as claimed in claim 1 or claim 2 in which the device (26) contains magnesium peroxide (34), to provide oxygen.

4. A method as claimed in any one of the preceding claims also comprising installing within the sump structure (12) a canister (28) containing a high permeability, high surface area packing (36) , for a biofilm to grow on.

5. A method as claimed in any one of the preceding claims also comprising installing within the sump structure (12) means to absorb metal ions.

6. A device for reducing pollution arising from run-off water from highways, the device comprising a canister

(26) with a water-permeable wall (30) , the canister containing a source of a nutrient in solid form (34) , such that with the device installed in a sump structure (12) the nutrient gradually dissolves in the run-off water in the sump structure (12), and so enhances the natural biodegradation processes.

7. A device as claimed in Claim 6 wherein the canister (26) contains magnesium peroxide (34) to provide oxygen.

8. A device as claimed in Claim 7 wherein the magnesium peroxide is such as to provide prolonged release of oxygen.

9. A device as claimed in any one of claims 6 to 8 wherein the canister also contains a high permeability, high surface area packing for a biofilm to grow on.

10. A device as claimed in claim 9 wherein the source of the nutrient in solid form is surrounded by the high surface area packing.