Methane Stripping from Landfill Leachate
A Methane Stripping Plant is used to provide a safe method of removal of methane from solution, in landfill leachates.
It must do this in compliance with the discharge consent or agreement issued by the water company, or local authority responsible for the sewer into which it discharges.
This is methane which would otherwise pose a risk of explosion or fire, from leachate methane in the sewers to which leachate is discharged.
”Controlling dissolved methane in leachates discharged into public sewers is vital to minimise the risk of generating explosive atmospheres.”
The process of removing dissolved methane, by blowing air through leachate in suitable tanks, is commonly referred to as “methane stripping”.
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The method of methane stripping we have adopted is that of aeration into a series of tanks of leachate placed in series.
An alternative technique is to utilise a tower/ column design and create a contra-airflow within a cascade inside it tower.
Health & Safety
A contra-airflow methane stripping column based upon a cascade would present concerns that in the event of a failure of the air blower the air within the cascade column may become an explosion hazard in it’s own right.
In other words if the pumping system was to continue to run after failure of the ventilation system the air space would become saturated with methane at a concentration above the Lower Explosive Limit (LEL). See our DSEAR page.
Methane Stripping isn’t the only way to remove dissolved methane from water/ leachate!
There are many other ways to solve a dissolved methane problem. Methane can be removed by other methods such as:
- elevating dissolved oxygen levels with longer retention times
- using the reed rhizomes in the aerobic growth media of a reed bed
- chemical dosing.
IPPTS has been applying such alternative methods during 2011. Please email or call if you would like to discuss employing our consultancy services in respect of alternative methane stripping methods.
This is a much larger airspace than the top (freeboard) of a tank, and therefore the stripping column design is likely to be less inherently safe than the tank based design described here.
Common Mistakes in Methane
Stripping Plant Design
We have seen, and replaced, UK methane stripping plants which have failed, on a number of occasions.
Some reasons for failure have been:
- Inadequate air flow rate
- Insufficiently controlled distribution of air to individual tanks
- Inadequate mixing in single tank designs
- Short circuiting of flow
- Excessive calcification.
The all but the last one can be avoided by applying basic science to the methane stripping plant airflow and tank configuration.
The third is achieved in our systems, by unique process design features incorporated into our designs.
The image on the right shows how serious calcification can be for a methane stripping plant.
The arrows point to a 2-3 mm deposit of scale which is visible on the tank wall of this methane stripping plant aeration tank, between the red arrows
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