GB2381761A

GB2381761A - Apparatus and method for removing dissolved methane from a liquid.

Info

Publication number: GB2381761A
Application number: GB0222047A
Authority: GB
Inventors: Geoffrey Kevin Ellison
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-09-24
Filing date: 2002-09-24
Publication date: 2003-05-14
Anticipated expiration: 2022-09-24
Also published as: GB2381761B; GB0222047D0

Abstract

An apparatus for removing dissolved methane from a liquid comprising a first conduit 1 to supply liquid from a source, a venturi aerator 3 comprising a narrowed throat portion 4 of the first conduit adjacent to an air inlet 5, the venturi aerator having an inlet in communication with the first conduit and an outlet in communication with a degassing chamber 6 which has a liquid outlet 8 in communication with a second conduit for the discharge of liquid, either to a sewer for discharge or to a further treatment stage. A pump 2 may be provided to pump the liquid from the first conduit through the venturi aerator. A second pump 9 may be provided downstream of the degassing chamber. The further treatment stage may comprise a second venturi aerator 11 and a second degassing chamber 13. In use, the device may be used to separate and remove methane gas from liquid trade waste such as leachate from landfill sites so that the processed liquid effluent may be safely disposed of into a sewerage system.

Description

Method and apparatus for the removal of dissolved methane from trade effluent The present invention relates to a method and apparatus for the removal of dissolved methane from a liquid and in particular for reducing the concentration of dissolved methane in trade effluent such as leachate removed from a landfill site.

Liquid leachate from a landfill site frequently contains a high proportion of dissolved methane formed during to anaerobic decomposition of the waste within the landfill site. Leachate, comprising a mixture of rainwater draining through the waste and the liquid components of the waste itself, must be constantly removed from the landfill site to avoid contamination of the surrounding ground water. In most countries legislation places limits on the amount of dissolved methane trade effluent (the generic term for liquid waste) can contain before the effluent can be disposed of into the sewers since methane is an extremely flammable gas and any build up of methane in the sewerage system could lead to an explosion within the sewer. In the UK liquid waste can only be disposed of into the sewerage system if it contains no more than 0.14 parts per million dissolved methane. By contrast, raw leachate can contain more than 14 parts per million dissolved methane.

In order to reduce the amount of dissolved methane to acceptable levels to permit trade effluent to be disposed of into the sewerage system, prior art systems have utilised large treatment tanks in which trade effluent is treated, usually by aeration and subsequent degassing, over a period of time to reduce the amount of dissolved methane contained within the trade effluent sufficiently to permit disposal thereof into the sewerage system. Such prior art systems are costly, bulky and limit the flow rate at which the treated liquid that can be disposed of into the sewerage system.

The present invention overcomes the disadvantages of the prior art systems by providing an apparatus for removing dissolved methane from a liquid comprising a conduit for conducting liquid from a source, a venturi aerator having a liquid inlet communicating with said conduit, a constricted throat portion, a liquid outlet and an air inlet at or adjacent said throat portion, the liquid outlet communicating with a liquid inlet of a degassing chamber having a liquid outlet at or adjacent a lower region thereof, said liquid outlet of the degassing chamber communicating with a second conduit for conducting the treated liquid to a sewer for disposal or to a further treatment stage, a gas outlet being provided at or adjacent an upper region of the degassing chamber. Preferably a pump is provided for pumping the liquid from the first conduit through the venturi aerator.

A preferred embodiment of the invention provides a two stage methane removal process, the apparatus comprising a first pump supplying liquid to be treated from a source to a first venturi aerator having a liquid inlet, a constricted throat portion, an air inlet at or adjacent the throat portion and a liquid outlet, the liquid outlet of the first venturi aerator communicating with a liquid inlet of a first degassing chamber having a gas outlet and a liquid outlet, the liquid outlet of the first degassing chamber communicating with to a second pump connected in turn to a liquid inlet of a second venturi aerator having a constricted throat portion, an air inlet at or adjacent the throat portion and a liquid outlet communicating with a liquid inlet of a second degassing chamber, said second degassing chamber having a liquid outlet communicating with a liquid disposal point, such as a sewer, or a further treatment stage.

The present invention also provides a method of reducing the concentration of dissolved methane in trade effluent comprising the steps of passing the liquid effluent through a first venturi aerator having a liquid inlet, a constricted throat portion, an air inlet at or adjacent the throat portion and a liquid outlet, the liquid from the outlet of the first venturi aerator passing into a first degassing

tank wherein gaseous methane and air is separated from the liquid, the liquid passing out of the first degassing tank via a liquid outlet thereof and passing into a delivery conduit connected to a subsequent treatment process or to a disposal means, such as a sewer. Preferably a pump is provided for pumping the trade effluent from a source to through the first venturi aerator.

Preferably the method comprises the further steps of passing the liquid from the delivery conduit of the first degassing tank through a second venturi aerator having a liquid inlet, a constricted throat portion, an air inlet at or adjacent the throat portion and a liquid outlet, the liquid from the outlet of the second venturi aerator passing into a second degassing tank wherein further gaseous methane and air is separated from the liquid, the liquid passing out of the second degassing tank via a liquid outlet thereof and passing into a further delivery conduit connected to a disposal means, such as a sewer.

The use of the method and apparatus of the present invention, proving an inline methane removal system, allows trade effluent, such as leachate, to be pumped straight through the apparatus and into the sewerage system, avoiding the need for large volume storage tanks, while reducing the concentration of dissolved methane contained in the trade effluent sufficiently to meet the environmental requirements for trade effluent disposal into the sewerage system. The use of a two pass system as described in the preferred embodiment has been found to reliably reduce the concentration of dissolved methane in trade effluent from approximately 14 ppm to less than 0.14 ppm.

The present invention will be described further, by way of example, with reference to the accompanying drawing, in which Fig. 1 is a schematic diagram of a dissolved methane removal apparatus according to the invention.

A pipe 1 for supplying trade effluent, such as leachate from a landfill site, is connected to the inlet of a first pump 2, the outlet of which is connected to a further pipe connected to the inlet of a first venturi aerator 3 having a constricted throat portion 4 and an air inlet 5 at said throat portion 4. The liquid outlet of the first venturi aerator 3 is connected to a first degassing chamber 6 having a gas outlet 7 in an upper region thereof and a liquid outlet 8 in a lower region thereof. The liquid outlet 8 of the first degassing communicates with the inlet of a second pump 9 connected in turn to a liquid inlet of a second venturi aerator 10, having a constricted throat portion 11 and an air inlet 12 opening into the throat portion 11. The liquid outlet of the second venturi aerator 10 is connected to the liquid inlet of a second degassing chamber 13 having a gas outlet 14 in an upper region thereof and a liquid outlet 15 adjacent a lower region thereof, said liquid outlet 15 being connected to a pipe leading to a sewer for disposal of the leachate.

In operation, leachate is supplied to conduit 1 from a leachate recovery system, such as that shown in the applicants copending UK patent application No. 0129677.1 and is pumped through the first venturi aerator 3 by the pump 2. The flow of leachate through the constricted throat portion 4 of the venturi creates a pressure drop resulting in air being drawn the air inlet 5, said air being entrained into the flow of leachate. The aerated leachate then passes into the first degassing chamber 6, wherein air and methane forced out of solution by the air mixed with the leachate in the venturi 3 is separated from the liquid leachate is removed from the degassing chamber via the gas outlet 7. The mixture of air and methane may then be treated further or burned off.

The action of the first venturi aerator 3 and its associated degassing chamber 6 will significantly reduce the concentration dissolved methane in the leachate. However, tests have shown that a single venturi aerator 3 does not reduce the level of dissolved methane in leachate sufficiently to allow the leachate to comply with the requirement of less than 0.14 ppm to permit disposal into the mains sewerage system.

Accordingly, a second stage methane removal system is provided comprising a second pump 9 having an inlet connected to the outlet of the fist degassing chamber 6, said pump 9 pumping the leachate through a second venturi aerator 10 wherein further air is entrained into the flow of leachate, the leachate then passing into a second degassing chamber 13 wherein the gasesous methane and air mixture is separated from the liquid leachate. The concentration of dissolved methane contained in the leachate at the liquid outlet of the second degassing chamber 13, following passage of the leachate through the second venturi aerator 10 and its associated degassing chamber 13, has been found to be below the permitted level for disposal of the leachate into the mains sewerage system. Accordingly, the treated leachate can be pumped though the first and second venturi aerators 3,10 and their associated degassing chambers 6,13 and thereafter passed directly into a sewer.

A further pump (not shown) may be provided downstream of the second degassing chamber 13 for drawing the leachate out of the second degassing chamber 13.

While the preferred embodiment describes a two stage methane removal system having two venturi aerators connected in series, it is envisaged that the required reduction in the concentration of dissolved methane may be achieved using just a single venturi aerator or, conversely, three or more venturi aerators connected in series may be required to achieve the necessary reduction in the concentration of methane in the leachate.

In an alternative embodiment only a single venturi aerator and associated degassing chamber may be provided and at least a portion of the leachate, after having passed through the venturi aerator and degassing chamber, may be recirculated through the venturi aerator one or more times to further reduce the concentration of dissolved methane in the leachate to the required level.

Whilst the preferred embodiment is described in terms of a method and apparatus for reducing the concentration of dissolved methane in leachate from a landfill site, the method and apparatus of the invention may also be suitable for reducing the concentration of dissolved methane in waste liquids, for example trade effluent from chemical plants or other industrial operations.

Claims

CLAIMS 1. An apparatus for removing dissolved methane from a liquid comprising a conduit for conducting liquid from a source, a venturi aerator having a liquid inlet communicating with said conduit, a constricted throat portion, a liquid outlet and an air inlet at or adjacent said throat portion, the liquid outlet communicating with a liquid inlet of a degassing chamber having a liquid outlet at or adjacent a lower region thereof, said liquid outlet of the degassing chamber communicating with a second conduit for conducting the treated liquid to a sewer for disposal or to a further treatment stage, a gas outlet being provided at or adjacent an upper region of the degassing chamber.
2. An apparatus as claimed in claim 1, wherein a pump is provided for pumping the liquid from the first conduit through the venturi aerator.
3. An apparatus as claimed in any preceding claim, wherein a further pump is provided downstream of the degassing chamber.
4. An apparatus for removing dissolved methane from a liquid comprising a first pump supplying liquid to be treated from a source to a first venturi aerator having a liquid inlet, a constricted throat portion, an air inlet at or adjacent the throat portion and a liquid outlet, the liquid outlet of the first venturi aerator communicating with a liquid inlet of a first degassing chamber having a gas outlet and a liquid outlet, the liquid outlet of the first degassing chamber communicating with to a second pump connected in turn to a liquid inlet of a second venturi aerator having a constricted throat portion, an air inlet at or adjacent the throat portion and a liquid outlet communicating with a liquid inlet of a second degassing chamber, said second degassing chamber having a liquid outlet communicating with a liquid disposal point, such as a sewer, or a further treatment stage.

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5. An apparatus as claimed in claim 4, wherein a further pump is provided downstream of the second degassing chamber.
6. A method of reducing the concentration of dissolved methane in trade effluent comprising the steps of passing the liquid effluent through a first venturi aerator having a liquid inlet, a constricted throat portion, an air inlet at or adjacent the throat portion and a liquid outlet, the liquid from the outlet of the first venturi aerator passing into a first degassing tank wherein gaseous methane and air is separated from the liquid, the liquid passing out of the first degassing tank via a liquid outlet thereof and passing into a delivery conduit connected to a subsequent treatment process or to a disposal means, such as a sewer.
7. A method as claimed in claim 6, comprising the further steps of passing the liquid from the delivery conduit of the first degassing tank through a second venturi aerator having a liquid inlet, a constricted throat portion, an air inlet at or adjacent the throat portion and a liquid outlet, the liquid from the outlet of the second venturi aerator passing into a second degassing tank wherein further gaseous methane and air is separated from the liquid, the liquid passing out of the second degassing tank via a liquid outlet thereof and passing into a further delivery conduit connected to a disposal means, such as a sewer.
8. An apparatus for removing dissolved methane from a liquid substantially as herein described with reference to the accompanying drawings.
9. A method of reducing the concentration of dissolved methane in trade effluent substantially as herein described with reference to the accompanying drawings.