[Salmo]

My local Council says that if I compost garden waste at home, or take it to their recycling centre to be composted, it will be better for the environment than sending it to landfill because less harmfull methane will then be produced.

Am I missing a trick somewhere. Is not the same amount of methane produced wherever it decomposes?

[Kristen]

Dunno the chemistry, but does Anarobic decomposition (which I presume would be the case underground) produce Methane, and Aerobic (as per home composting) not?

[Lindeggs]

That's pretty much it.  When food or garden waste is composted it creates some gases but most of it is turned into yummy goodies that can be used by the garden.

When it's sent to landfill it doesn't compost at all.  It basically gets buried, liquifies and turns really, really nasty.  Some turns into nasty gases like methane and some turns into a toxic liquid that leeches into the ground.   

So yes, a totally different mechanism if it's composted or sent to landfill.

[Zippy]

While I do not agree about the organic waste turning toxic in landfill, I do agree that aerobic decomposition does not produce methane, though it does produce carbon dioxidewhich is a harmless gasnaturally in out atmosphere anyway.

http://www.telegraph.co.uk/earth/3310409/Top-tips-for-composting.html

[Salmo]

That is a good article from the telegraph. To save others reading it all

Sally Smith, Garden Organic's Head of Inforamtion and Training responds; "Composting does not create methane as long as it is done properly i.e. aerobically. Practically, this means that air must be introduced into the heap so that the microbes have plenty of oxygen in order to respire and digest all the organic matter.

"This is why turning the heap is so important. If the heap becomes stagnant and anaerobic, then methane may be produced. However new research shows that even if there are pockets of methane within a heap, the rest of the aerobic heap acts as a bio-filter to break down the methane as it moves through the heap, leaving only carbon dioxide."

Probably most darlek composters are still methane producers but the ivcentive is there to turn the heap and do the job properly.

[Lindeggs]

While I do not agree about the organic waste turning toxic in landfill...

This might help:

This article http://leachate.co.uk/main/ goes some way to explaining how toxic leachate is generated from "putrescible" waste in landfills.  ('Putrescible' means it is made from organic compounds that putrify under anaerobic conditions instead of composting.)

Basically the organic compounds turn incredibly acidic, which in turn enables them to collect and transform other chemicals on their way through the landfill, creating new, highly toxic substances.

One example of this is when acidic leachate meets gypsum waste (here we call it "Gib board" - the plasterboard used in a lot of construction).  Anyway the result is hydrogen sulphide - a very toxic, flammable gas.

[Zippy]

Thank you Lindeggs - understood. Being acidic I imagine the anaerobic biproduct could be responsible for a lot of mixed reactions in landfill even though the materials are organic.