How to turn pig poo into green power

STINKING lagoons of pig manure created by thousands of animals in giant hog farms can pollute rivers, poison groundwater and pump out clouds of methane and carbon dioxide. So finding alternative uses for the slurry - to generate electricity, say - makes a lot of sense. The problem was that no one has been certain which way of doing it makes the most electricity for the least greenhouse gas production.

Now a Danish team has analysed the various ways in which firms in that country treat pig manure and use it to generate electricity in systems such as anaerobic digesters or incinerators. In anaerobic digestion, bacteria break down waste material by warming it in an oxygen-free vessel, releasing methane which is used in gas turbines. Incinerators burn material to boil water and drive a steam turbine.