Les, Over asked:
I saw a programme in which they sank a bore hole into a rubbish dump over in America and within what they extracted there were pieces of newspaper that were 25 years old that remained readable. If newspaper can sit in the ground for 25 years, what is the prospect for a plastic cup breaking down?
We put this to John Williams, Polymers and Materials Manager at the National Non-Food Crops Centre:
John - Well, for a start, letís just say we donít obviously want these things go to landfill, for a start. I mean there are Ė if you look at the two systems of landfill at the moment, there are sort of dry sanitized landfills, well, actually not a lot breaks down at all, deliberately so. There are wetter landfills where you actually try to derive methane off which is now tapped off as an energy source. Now the old landfill, he's quite right. You can actually derive off all sorts of materials. Newspaperís actually the classic but newspaper you got to bear in mind, actually, has quite - a very, very high lignin content. Itís not processed greatly in a paper making process. You've got a high lignin content there and lignin doesnít break down at all. Hence, for instance, trees and branches and so forth that donít break down very well. It's exactly the same principle;but weíve moved away from that now.
Chris - Can I just ask you? In the context of what weíve already dumped in the ground with landfill, what are people doing about, for instance, tapping off the methane that is being produced by the breakdown of that material thatís in the ground? Is that common practice and is that being used effectively?
John - I think that seems increasingly common practice because, obviously, thereís a route now to actually deriving an energy source and not wishing to dodge the question but I know Peter Jones actually knows an awful lot about this in terms of landfill; methane tap-off than I do.
Chris - Which we ask him.
John - Yeah.
Chris - Peter, what do you think?
Peter - Yes, the theoretical recovery rate on a landfill of around 1-2 million cubic meters should be in the order of 60% to 70 %. Thatís effectively a figure we arrived at by calculating what a given mass of carbon would convert to. But what you have to do is line those systems with a basal liner. You have to make sure, as youíve heard from John, that youíve effectively got plenty of liquid in that landfill and those bio they Ė it is a bio reactor that is capped. But you will always get methane. This is the bÍte noir of landfill. Youíll always get methane formation within almost hours, certainly days, of waste being deposited on a face.