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Microbes: Forgotten Recycling Helpers

By: Dr Gareth Evans - Updated: 16 Jan 2013 | comments*Discuss
 
Microbes Micro-organisms Bacteria

As you fill your recycling box, or place those cleaned, washed and colour-sorted bottles in the bottle-bank, spare a thought for some of the unsung recyclers, without whom at least a third of household waste recycling – and a whole lot more besides – simply wouldn’t work!

They are, of course, the world’s microbes, and this is a small part of their story.

Composting Co-Workers

We’re all aware, at least to some extent, that the composting process depends on the action of bacteria and a few of their fellow micro-organisms, but few of us have any real idea of just what a complex community of microbes a compost heap really is.

There’s 100 million bacteria that breathe air in every gram of decomposing material – and a further tenth of that number that don’t – along with perhaps a million nitrogen-fixing ones and around 10,000 microscopic fungi. That’s just for starters! There’s a whole other zoo of microbes in there too, including wonderful characters with names like actinomycetes and pseudomonads, all doing their little bit to turn your waste into useful garden compost.

The 2.6 million tonnes of kitchen and garden waste – three-quarters of it from households – that’s composted each year in centralised schemes, and all the material busily breaking down in heaps and bins in back gardens across the country, depend on these microbes. The good news is, they take the job very seriously.

Anaerobic Assistance (or What Do You Do with the Doo-Doo?)

In Britain, anaerobic digestion – or AD – hasn’t become as popular as a means of dealing with domestic waste, although there are a few plants across the UK where it is used instead of composting. Where AD really assumes centre stage, however, is when it comes to recycling sewage sludge (oh yes, we really do mean doo-doo!).

Breaking down the poo means no smell, less bulk and you get a useable biogas fuel into the bargain – and as you’ve doubtless guessed, making it all happen, there’s another bunch of helpful microbes. Amongst them are examples of some of the oldest life forms on the planet – the archaeons.

There are fermenting bacteria, such as Clostridium and Eubacterium, acid forming characters rejoicing in names, like Desulfovibrio and Syntrophomonas and then finally come the old guys from the dawn of time – the methane producing Methanobacterium and its kin.

Between them they take a slurry of organic matter and, in the warm environment of a purpose-built biological treatment tank, completely free of oxygen, turn it into a compost-like material and a methane-rich gas that can be burnt to produce renewable power. Not a bad trick for something which first appeared around 3,800 million years ago; and you thought the dinosaurs were old! They’re no more than babes in arms by comparison.

Incredible Diversity

A lot of the older biology textbooks talk of microbes as “primitive” and it is undoubtedly true that their physical organisation is simpler than our own, but that sort of thinking misses one important point. A decade or so back, we got ourselves all excited over the millennium – the passage of a thousand years – or 40 generations of our species. Under the right conditions, some kinds of bacteria can reproduce in 20 minutes; that’s three generations an hour, or a bacterial millennium in little over half a day – and they have been doing it, uninterrupted, since life began.

The bottom line is, “primitive” they may be, but they are so very much more highly evolved than us – they’ve just been through so many billions more generations – and so incredibly diverse. It has allowed them to develop some amazingly clever tricks, some of which we’re only just beginning to understand and find a way to exploit for our own benefit. We’ve begun to use bacteria to recycle waste waters into hydrogen to drive fuel cells, to harness their abilities to help us clean up pollution and even to reclaim precious trace levels of metals from the spoil heaps of long-exhausted mines.

It’s the sort of thing the alchemists of old could only dream about, but with the help of this incredible gang of largely forgotten helpers, the future of 21st Century recycling could be pretty exciting indeed.

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