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Space research finds anthrax killer


Deadly: anthrax spores, pictured here in a thin section micrograph, are inactive forms of the bacterium Bacillus anthracis. Such bacteria can survive for decades inside a spore's tough protective coating; they become active when inhaled by humans. (Pic: NASA)

US research that began as a way to build better greenhouses in space has ended up as a product that can be fitted to public areas to keep the air free of pathogens.

The work was originally undertaken by NASA to try and prevent a buildup of plant gases in greenhouses in space. Research at the University of Wisconsin on Earth-based applications then discovered that the system also killed airborne pathogens.

"This shows how space research, along with its direct benefits, also helps people on Earth in indirect and unexpected ways," said Mr Mark Nall, the director of NASA's Space Product Development program.

The original problem was ethylene (C2H4), a gas released by growing plants that makes fruit and vegetables ripen. If astronauts were to grow their own food in a greenhouse, ethylene would build up in the enclosed area, causing plants to ripen prematurely.

Research by Professor Marc Anderson at the University of Wisconsin discovered that thin layers of titanium dioxide (TiO2) exposed to ultraviolet light act as a catalyst to convert ethylene into carbon dioxide and water.

The team then built titanium dioxide-based ethylene removers, and two systems have been sent to space in growth chambers.

The University of Wisconsin researchers recognised there were Earth-based applications for their finding, such as the fruit and vegetable aisle of the supermarket and florist shops.

Together with KES Science and Technology Inc, they developed a commercial product called Bio-KES that won Discover magazine's Product of the Year award in 1998.

Tests showed that as well as removing ethylene, the system also killed airborne dust mites. The reaction between UV photons and the titanium dioxide produced positive and negative charges on the surface. These reacted in turn with water molecules in the air, forming OH- which disrupts organic molecules.

Testing at the University of Wisconsin found that with extra UV, the machine kills 93.3 per cent of airborne bacteria, viruses, fungi, moulds and spores, including anthrax, streptococcus, E. coli, Legionnaire's disease, meningitis, golden staph, and pneumonia bacteria.

The new machine, called AiroCide TiO2, uses high-energy (254nm) ultraviolet light.

"Spores that pass through the box aren't filtered, they're fried," said Mr John Hayman from KES Science & Technology.

"It was a serendipitous discovery."