What happens to your rubbish these days? It’s a very good question, and the answers aren’t quite as straightforward as you might hope for. Over the past decade, we have all been more or less trained to separate out our waste. Most local authorities now have collections for a variety of products like paper, glass, plastics and aluminium cans. And most now try to separate organic waste (food, cardboard, garden clippings, etc) from ordinary, indestructible household waste (packaging mostly in my house at least).
Now the non-organic, non-decomposable waste used to go into landfill mostly, at least it does in Cambridgeshire, my council, although it can be incinerated to produce usable power and heat. In contrast, the green, bio-degradable waste was composted.
Cambridgeshire County Council has just spent £42 million on a gigantic waste sorter cum compost heap known as a Mechanical Biological Treatment Plant (PFI money) and you can read about it here. It’s so state-of-the-art, that it can extract the organic material from the black bin waste, and they estimate that something like 80% of the waste currently being landfilled will end up going through this MBT plant. Good news? Maybe.
Look a little bit more closely. There is an interesting sentence at the end of their guide to MBT which states: Due to the fact that the input is mixed waste, the material produced cannot be used by farmers or the public, but we hope to use the compost-like output of the MBT plant for quarry restoration, growing energy crops or as a fuel. In other words, they haven’t really got a use for all this compost yet.
Organic matter left in landfill slowly undergoes anaerobic digestion which release methane very slowly (can take up to 100 years), whereas the stuff that is fed through the MBT plant undergoes aerobic digestion very quickly. Now aerobic digestion produces CO2 instead of methane, but unfortunately both of these happen to be greenhouse gases. I know methane is something like 300 times more potent but the landfill digestion process seems to last about 300 times as long, so do they not more or less cancel each other out in terms of climate sensitivity?
So now instead of having holes in the ground filling up with untreated waste, we now have all this expensively treated but low-grade compost looking for a home because they are not allowed to give it away to farmers or the public (something to do with the old BSE scare, methinks). And they may end up incinerating it! Which, of course, they could have done in the first place without treating it.
Still, it’s a fine looking building, the size of three football pitches, and stuffed full of trommel screens, tilting vibrating plates, electro magnets, eddy current separators, not to mention targeted air jets and waste grinders. I wonder how much energy it consumes?