THE WORLD'S first full-scale experiment to clean up municipal sewage with a reactor full of algae has recently started near Nottingham in the UK (New Scientist, Vol 140, No 1893).

The reactor or "biocoil" system developed by Stephen Skill at the London-based Biotechna, contains chlorella algae packed into a 5-m-high coil of polyvinyl chloride tubes. The algae absorb nitrogen and phosphate, which are its nutrients, from the effluent and turn them into protein. Nitrogen and phosphate pollution usually harm aquatic life by spurring the growth of algal blooms.

Working at full capacity, the biocoil will detoxify 20 cum of sewage -- the amount produced by a town of 2,500 people -- in an hour. The clumps of algae can later be used as animal feed.