GB2382626A

GB2382626A - Pump for removing leachate from a landfill site

Info

Publication number: GB2382626A
Application number: GB0223134A
Authority: GB
Inventors: Geoffrey Kevin Ellison; Francis Allan Hay
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-12-12
Filing date: 2002-10-07
Publication date: 2003-06-04
Anticipated expiration: 2022-10-07
Also published as: GB2382626B; GB0223134D0; GB0129677D0

Abstract

A liquid pump 1 comprises a hollow cylindrical pump body 2 having a float valve 3 mounted on a lower end thereof and a non-return valve 4 and an air inlet pipe 5 mounted on an upper end thereof and terminating in a lower region of the pump body 2. The float valve 3 comprises a buoyant valve member 21 which, when immersed below the level of the leachate in a landfill site, lifts off the valve seat 13 to allow leachate to enter the body 2 of the pump 1. A strainer 17 is connected to the float valve 1. The non-return valve 4 comprises a spring loaded valve member 21 biased downwardly against a valve seat 23. A leachate outlet pipe 24 is secured to the upper end of the non-return valve 4. Each time a pulse of compressed air is supplied to the valve body the float valve 3 closes and the non retrun valve 4 opens, whereupon a mixture of leachate and some compressed air within the valve body 2 passes through the non-return valve 4 and up the leachate outlet pipe 24.

Description

PUMP FOR REMOVING LEACHATE FROM A LANDFILL SITE The present invention relates to a pump for removing liquid leachate from a landfill site.

A common method of disposing of solid domestic and/or industrial waste is to place such waste in a landfill site. Such landfill sites generate leachate due to liquids present in the wastes and rain water percolating through the waste.

Unless properly contained, leachate can contaminate groundwater under and around the landfill leading to serious pollution problems. To avoid such problems, legislation exists requiring landfill sites to have containment liners comprising layers of impervious material. Furthermore, the level of leachate in the landfill cannot be allowed to exceed a certain depth, therefore leachate recovery or removal systems are required whereby leachate is removed from the base of the landfill or otherwise recovered to a holding tank for proper disposal.

Landfill sites, particularly more recently established sites, have a range of leachate recovery systems arranged therein. A common system is the provision of concrete chimneys extending up through the landfill. As well as the removal of leachate, such chimneys are used to vent potentially explosive methane gas from the landfill. However, such systems can fail due to blockage or breakage caused by lateral displacement of landfill material and older landfill sites may not have adequate, or any, leachate recovery facilities.

As such, it is often necessary to bore, drill or drive a vertical shaft into the leachate into which is placed a pipe or hose attached to a liquid pumping device for recovering excess leachate.

Prior art liquid pumps have met limited success when used for recovering leachate due to the extremely difficult environment in which they must operate. The conditions in which the pump has to operate comprise a combination of a highly corrosive and humid environment and, due to the

formation of methane within the landfill site, a potentially explosive environment. The leachate itself comprises a cocktail of corrosive and hazardous liquids and may contain a considerable amount of solid material.

Furthermore, recent legislation has imposed energy balance restrictions on landfill sites such that any leachate recovery pumping system must meet specific energy efficiency requirements.

An object of the invention is to provide a reliable, dependable and energy efficient, low cost liquid pump which can reliably operate in the difficult conditions of a landfill site and can pump leachate with minimal risk of failure due to blockage or corrosion.

Compressed air operated submersible pumps are known for use in raising water from a bore hole. An example of such a known pump is disclosed in WO 87/03938. Such known pumps are highly effective for such purpose.

However, such pumps are not suitable for use in the recovery of leachate due to the corrosive nature and high solids content of leachate. Such pumps are overly complicated for this purpose, containing a large number of potentially unreliable moving parts, and are liable to clogging and rapid degradation when used for the purpose of recovering leachate.

According to the invention there is provided a liquid pump for removing leachate from the base of a landfill site, said pump comprising a chamber adapted to be at least partially submerged below the level of the leachate in a landfill site; a liquid inlet having a first non-return valve, said liquid inlet being provided in or adjacent a lower region of the chamber communicating with the exterior thereof, said first non-return valve being arranged to allow leachate to pass into the lower region of the chamber via the liquid inlet ; a liquid outlet having a second non-return valve, said liquid outlet being provided in or adjacent an upper region of the chamber, said second non-return valve being arranged to allow leachate to pass therethrough out of the chamber but preventing return flow of the leachate into the chamber, said liquid outlet

being adapted for connection to a leachate recovery or outlet pipe; an air inlet being provided in the chamber and being adapted for connection to a supply of compressed air, wherein the pump has only two operatively moving parts comprising respective valve members of the first and second non-return valves.

Preferably the air inlet terminates in or adjacent the lower region of the chamber.

Preferably the first non-return valve comprises a moveable valve member which is buoyant in the liquid to be pumped, the valve member being moveable from a lower closed position wherein the valve member abuts a valve seat and an upper open position wherein the valve member is spaced from the valve seat to allow leachate to pass through the first non-return valve and into the valve chamber. The valve member moves towards its upper open position due to the buoyancy of the valve member when the pump is immersed in the liquid to be pumped. The valve member moves towards its closed position to close the first non-return valve when the fluid pressure within the valve chamber exceeds the fluid pressure at the inlet of the first non-return valve (i. e. the ambient fluid pressure of the leachate surrounding the pump).

Preferably the second non-return valve comprises a valve member movable between a closed position wherein the valve member engages a valve seat and an open position wherein the valve member is spaced from the valve seat, biasing means being provided for biasing the valve member towards its closed position, the valve being arranged such that the valve member is urged towards its open position, against the action of the biasing means, when the fluid pressure within the valve chamber exceeds a predetermined level.

The invention also provides a method of removing leachate from the base of a landfill site comprising the steps of :-

a) at least partially immersing a liquid pump below the level of leachate in the lower region of a landfill site, said pump comprising a chamber, a liquid inlet having a first non-return valve, said liquid inlet being provided in or adjacent a lower region of the chamber communicating with the exterior thereof, said first non-return valve allowing leachate to pass into the lower region of the chamber via the liquid inlet ; a liquid outlet having a second non-return valve, said liquid outlet being provided in or adjacent an upper region of the chamber, said second non-return valve being arranged to allow leachate to pass therethrough out of the chamber when the fluid pressure within the chamber exceeds a predetermined level but preventing return flow of the leachate into the chamber, said liquid outlet being connected to a leachate recovery pipe; an air inlet being provided in the chamber, preferably terminating in or adjacent the lower region thereof, and being connected to a supply of compressed air via an air supply pipe and a control valve ; b) opening the compressed air supply control valve to supply a pulse of compressed air to the chamber such that the fluid pressure within the pump chamber rapidly rises causing the first non-return valve to close and the second non-return valve to open such that leachate within the chamber is passed into the leachate recovery pipe; c) closing the compressed air supply control valve to isolate the pump chamber from the compressed air supply, such that the pressure returns to the ambient pressure within the leachate causing the first non-return valve to open and the second non-return valve to close ; d) repeating steps b) and c) continuously to provide a substantially continuous flow of leachate through the leachate recovery pipe.

Preferably, the control valve vents the air supply pipe to the atmosphere to allow any remaining air contained within the pump chamber to escape.

The present invention will be described further, by way of example, with reference to the accompanying drawings, in which :- Fig. 1 is a sectional view of a pump according to the invention during a first stage of operation; Fig. 2 is a sectional view of the pump of Fig. 1 during a second stage of operation.

As shown in the drawings, the pump 1 comprises a hollow cylindrical pump body 2 having a float valve 3 mounted on a lower end thereof and a nonreturn valve 4 and an air inlet pipe 5 mounted on an upper end thereof and terminating in the lower region of the pump body 2.

The float valve 3 comprises a hollow valve member 21 which is buoyant in the liquid to be pumped (leachate). When the pump 1 is immersed below the level of the leachate in a landfill site, the valve member 10 lifts away from the valve seat 13 to the position shown in Fig. 1, allowing leachate to enter the body 2 of the pump 1. The lower face 11 of the valve member 10 is substantially hemispherical to minimise resistance to leachate flow and reduce the possibility of blockages. A circular seal 12 is provided around a lower region of the valve member 10 which is sealingly engageable on the valve seat 13 of the float valve 3. Movement of the valve member 10 is guided by an elongate pin 14 formed on the upper face of the valve member 10 which passes through a guide ring 15 supported by radial struts 16. A strainer 17 is connected to the lower end of the float valve 1 to prevent solid material from entering the float valve 10.

The non-return valve 4 comprises a cylindrical body 20 containing a spring loaded valve member 21 biased downwardly by means of a compression spring 22 against a valve seat 23 formed in a lower region of the cylindrical body 20. A leachate outlet pipe 24 is secured to the upper end of the nonreturn valve 4.

The air inlet pipe 5 sealingly passes through an aperture 30 in an upper region of the valve body 2 and extends into the lower region of the pump body 2. The air inlet pipe 5 extends upwardly from the pump body 2 and is connected to a supply of compressed air via a control valve (not shown).

Once at least the lower region of the pump body 2 has been immersed below the level of the leachate recovery of leachate is initiated by opening the control valve every three to four seconds to supply pulses of compressed air into the lower region of the pump body via the air inlet pipe 5. Each time the control valve is opened compressed air passes into the lower region of the pump body 2, increasing the pressure therein. The sudden increase in pressure causes the valve member 10 of the float valve 3 to move downwardly until it seals against the valve seat 13 (see Fig. 2).

Once the float valve 3 has closed, the pressure inside the pump body 2 increases further until the biasing force of the spring 22 of the non-return valve 4 is overcome and the valve member 21 thereof moves away from the valve seat 23 to the position shown in Fig. 2, whereupon a mixture of leachate and some compressed air within the pump body 2 passes through the nonreturn valve 4 and up the leachate outlet pipe 24. Once the control valve has closed, the supply of compressed air is shut off and the pressure within the pump body 2 rapidly reduces until the valve member 21 of the non-return valve 4 is abuts its valve seat 23 under the action of the spring 22, preventing the leachate which has been forced up the leachate outlet pipe 24 from returning to the pump body 2. Simultaneously the valve member 10 of the

float valve 3 moves upwardly away from its valve seat 13 by virtue of its buoyancy in the leachate and allows more leachate to pass into the pump body 2. The air inlet pipe is vented to the atmosphere when the control valve is closed to allow any remaining air within the pump body 2 to escape and be replaced with more leachate.

By passing a pulse of compressed air directly into the lower region of the pump body 2, the efficiency of the scavenging effect of the air pulse is improved since the compressed air pulse forces a volume of leachate above the terminal end of the air inlet pipe 5 through the non-return valve 4 and up the leachate outlet pipe 24.

The process is repeated each time the control valve is opened and closed.

The continued cyclic opening and closing of the control valve provides a substantially continuous flow of leachate via the leachate outlet pipe 24.

Whilst the strainer 17 prevents large particles of solid waste from entering the inlet of the float valve 3 and causing blockage of the float valve 3, smaller solid particles can pass through the strainer and into the float valve 3. The design of the float valve 3, in particular the shape of the valve member 10, enables the float valve to operate correctly, without blockage, despite the presence of such small solid particles. As such, the lower region of the pump body 2 may contain a mixture of leachate and solid material. To substantially reduce the likelihood of such solid material entering the non-return valve 4 and causing blockage problems, the non-return valve 4 is mounted directly on the upper end of the pump body 2 such that it receives leachate from the upper region of the pump body, which is substantially free of solid material.

In an alternative embodiment (not shown), the air inlet pipe 5 may terminate at the upper end of the valve body 2, thus reducing the possibility of air passing through the float valve 3 and out of the valve 1. However, such arrangement

does not provide the scavenging effect achieved by providing the outlet end of the air inlet pipe 5 in the lower region of the pump body 2.

The entire pump and fittings thereof can be formed from a chemically stable polymeric material, such as MDPE, or from other corrosion resistant materials.

The pump 1 comprises only two moving parts, the respective valve members 10,21 of the float valve 3 and the non-return valve 4. As such, the pump is simple, durable and maintenance free. Furthermore, the pump is cheap to produce and hence is expendable should it eventually fail in use. This is advantageous because, once placed in the landfill site, due to the environment in which the pump operates, removal of the pump for maintenance is difficult and undesirable. The use of air as a motive force minimises the risks of explosion inherent when electrically operated pumps are used. The operation of the pump also uses very little energy and hence meets the energy balance requirements of the landfill site.

Whilst the pump is primarily intended for use in the recovery of leachate from a landfill site, the pump may also be for pumping water from bore holes, particularly in remote locations where the low cost and the reliability and robustness of the pump will be beneficial.

Claims

CLAIMS 1. A liquid pump for removing leachate from the base of a landfill site, said pump comprising a chamber adapted to be at least partially submerged below the level of the leachate in a landfill site; a liquid inlet having a first non-return valve, said liquid inlet being provided in or adjacent a lower region of the chamber communicating with the exterior thereof, said first non-return valve being arranged to allow leachate to pass into the lower region of the chamber via the liquid inlet ; a liquid outlet having a second non-return valve, said liquid outlet being provided in or adjacent an upper region of the chamber, said second non-return valve being arranged to allow leachate to pass therethrough out of the chamber but preventing return flow of the leachate into the chamber, said liquid outlet being adapted for connection to a leachate recovery or outlet pipe; an air inlet being provided in the chamber and being adapted for connection to a supply of compressed air, wherein the pump has only two operatively moving parts comprising respective valve members of the first and second non-return valves.
2. A liquid pump as claimed in claim 1, wherein the air inlet terminates in or adjacent a lower region of the chamber.
3. A liquid pump as claimed any preceding claim, wherein the first non-return valve comprises a moveable valve member which is buoyant in the liquid to be pumped, the valve member being moveable from a lower closed position wherein the valve member abuts a valve seat and an upper open position wherein the valve member is spaced from the valve seat to allow leachate to pass through the first non-return valve and into the valve chamber, the valve member being moved towards its upper open position due to the buoyancy of the valve member when the pump is immersed in the liquid to be pumped, the valve member being moved towards its

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closed position to close the first non-return valve when the fluid pressure within the valve chamber exceeds the fluid pressure at the inlet of the first non-return valve (i. e. the ambient fluid pressure of the leachate surrounding the pump).
4. A liquid pump as claimed in any preceding claim, wherein the second non- return valve comprises a valve member movable between a closed position wherein the valve member engages a valve seat and an open position wherein the valve member is spaced from the valve seat, biasing means being provided for biasing the valve member towards its closed position, the valve being arranged such that the valve member is urged towards its open position, against the action of the biasing means, when the fluid pressure within the valve chamber exceeds a predetermined level.
5. A liquid pump as claimed in any preceding claim, wherein said chamber comprises an elongate hollow cylindrical body.
6. A liquid pump as claimed in any preceding claim, wherein the pump is adapted to be inserted down a bore hole or vertical circular section shaft in a landfill site.
7. A liquid pump as claimed in any preceding claim wherein strainer means is provided downstream of the liquid inlet.
8. A method of removing leachate from the base of a landfill site comprising the steps of :- a. at least partially immersing a liquid pump below the level of leachate in the lower region of a landfill site, said pump comprising a chamber, a liquid inlet having a first non-return valve, said liquid inlet being provided in or adjacent a lower region of the chamber communicating with the exterior thereof, said first non-return valve allowing leachate to

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pass into the lower region of the chamber via the liquid inlet ; a liquid outlet having a second non-return valve, said liquid outlet being provided in or adjacent an upper region of the chamber, said second non-return valve being arranged to allow leachate to pass therethrough out of the chamber when the fluid pressure within the chamber exceeds a predetermined level but preventing return flow of the leachate into the chamber, said liquid outlet being connected to a leachate recovery pipe; an air inlet being provided in the chamber and being connected to a supply of compressed air via an air supply pipe and a control valve ; b. opening the compressed air supply control valve to supply a pulse of compressed air to the chamber such that the fluid pressure within the pump chamber rapidly rises causing the first non-return valve to close and the second non-return valve to open such that leachate within the chamber is passed into the leachate recovery pipe; c. closing the compressed air supply control valve to isolate the pump chamber from the compressed air supply, such that the pressure returns to the ambient pressure within the leachate causing the first non-return valve to open and the second non-return valve to close ; d. repeating steps (b) and (c) continuously to provide a substantially continuous flow of leachate through the leachate recovery pipe.
9. The method of claim 8, wherein the air inlet is provided in or adjacent a lower region of the chamber.
10. The method of claim 8 or claim 9, wherein the control valve vents the air supply pipe to the atmosphere, to allow any remaining air contained within the pump chamber to escape, when the control valve is closed during step (c).
11. A liquid pump substantially as herein described with reference to the accompanying drawings.

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12. A method of removing leachate from the base of a landfill site as herein described with reference to the accompanying drawings.