BEER that’s past its sell-by date could help clean up pollution from old mine
workings, a meeting of the American Chemical Society in San Diego, California
was told last week.
When a mine is abandoned, groundwater seeps into the tunnels, where it reacts
with minerals containing sulphides to form an acidic solution of heavy-metal
ions. This floods out again, forming a toxic marsh on surrounding soils.
But the marshy wetlands this creates can help clean up the water, as
sulphate-reducing bacteria neutralise the acid and precipitate the metals as
sulphides. But to clean up an entire mine would require a huge wetland that
would be left contaminated with heavy metals. Tom Harris, a chemist at the
University of Tulsa in Oklahoma, reckoned he could use less land by making the
bacteria work harder. He did this by encouraging a different set of
bugs—the fermenting bacteria that break down organic matter into fragments
that the sulphate-reducing bacteria can digest. Harris prescribed a diet of
beer—for its high sugar content—and because he knows a beer
distributor who throws out 3500 litres of old ale every month.
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With student Brooke Stephenson, Harris poured two cans of beer over a
1-metre-long test bed of wetland soil, and then pumped 5 litres of acid mine
water through it each day. A month later, the bacteria were still chewing up 60
per cent of the sulphate. But in a beer-free test bed, the bacteria were
exhausted and had stopped reducing the sulphate.