Leachate Pumping Systems
The following leachate pumping technologies are currently in use in landfills in the UK:
- Electric Pumps; A wide variety of pump types are used, all must be suitably corrosion protected to a high standard, and non leachate compatible materials avoided. The types of electrical pumps used include progressive cavity borehole pumps, multistage submersible pumps, high head dual impeller multistage pumps, explosion proof pumps (inherently safe in explosive landfill gas mixtures). The web site of specialists Viridian Systems gives a list of the types of electric pumps used in leachate pumping here.
- Eductive Pumping; Utilises the “venturi effect” in water as the pumping mechanism. A small volume of water at high pressure provides the motive force at the eductor located at the base of the leachate borehole or well, where the venturi is located. The eductor is based on the principle of using a small volume of water at a high pressure which inducts a larger flow at the venturi nozzle, and both the initial flow and the inducted flow is then delivered back to the starting point using the remaining water pressure (head). At the orginal pump location, a simple header tank is provided which allows the excess flow generated to discharge over a weir, and the remaining portion is recirculated through the pumps where it is pressurised and recirculated to the venturi to again educt and draw in more leachate.
- Pneumatic (air driven) Reciprocating Pumps: Introduced from the US in the mid-1990s,
 these pumps use air as the motive force at the pump head, and are currently very popular in the UK. Pneumatic pumps can be selected for their self-regulating capability, and normally do not require require any external form of level sensor to initiate pumping. The clever design uses a lightweight (often plastic) pump float which rises with the incoming water as the pump cylinder fills. Once the pump bore fills to a sufficient depth the rising float itself activates a small lever which triggers an air valve which starts a one stroke air-cycle which forces the float back down, and with it the water which has filled the cylinder. As the float drops the inlet valve opens and the cylinder begins to fill again for the next cycle. If insufficient depth of water remains in the borehole, the float will not rise and the pump will cease to operate. All the pnuematic equipment (e.g. compressors, actuators, and controls) above the pump itself are available off-the-shelf, as these components are routinely used in so many factory applications (e.g. production line and machine tool equipment). Examples of air pumps used in leachate pumping are available here.
- Centrifugal Pumps (hydraulically driven) : “Hydrainer” pumps are the well known example of a pump which couples a hydraulically driven motor to a pump impeller. These are most commonly used in temporary applications on construction sites, but may also be permanently installed.
The selection of leachate pumping systems is a complex matter and the best system will vary from site to site with site conditions. While most operators do carry out their own trials and make their own pump systems selection at site level, Enviros Consulting is always willing to provide assistance with these tasks, including pump system tendering and installation supervision.
To assist in the choice of pump systems we have compiled a table of the relative merits of the leachate pumping systems available as we perceive them here.
|
Newsletter