A culture that loves to chew the fat

Grease-eating bacteria can unclog blocked drains. By Tom Wilkie
Greasy water from fast-food restaurants is going into the sewers smelling sweet and pure thanks to a process developed by a subsidiary of British Nuclear Fuels.

Scientists from Viridian Bioprocessing of Whitstable in Kent scoured the outlet pipes from restaurants around the country to take samples of naturally occurring microbes that live in and eat grease. The researchers cultured the bacteria and developed them into a unit that naturally digests grease from restaurant kitchens and prevents drains being blocked.

Dr Paul Sallis, development manager of Viridian, says that, up until now, restaurants have fitted grease traps to outlet pipes. After water flows in at the top, the grease separates out on the surface, and the cleaner water is drawn off at the bottom of the box. The grease is not broken down, and the traps have to be manually cleaned out or they will clog.

Viridian's digester separates the grease into a broth of microbes that eat the material, breaking it down into carbon dioxide and water or to fatty acids and glycerol, which are not only soluble in water, but have properties similar to detergents. "Turning insoluble grease into a detergent- like soup improves dispersal of grease," he says.

Although the digester costs three to four times as much as a conventional trap, Dr Sallis said it runs without input from people in the restaurant. "They don't have to stop cooking, lift a smelly lid, dig out a grease trap, and then go back to making burgers," he says.

The grease digester does have to be emptied from time to time, but because the bacteria are self-replicating, they replace themselves when the next load of grease comes in, Dr Sallis says.

McDonald's has installed a couple of Viridian's grease digesters. The director of quality at McDonald's, Mike Matthews, says: "A digester was fitted at one of our busier high street restaurants following years of grease build-up in the drains. Grease-related problems have been effectively eliminated and call-out costs for drain clearance have ceased."

BNFL took a 65 per cent stake in Viridian in 1993 as part of its policy of diversification and after the two companies had collaborated on a non- nuclear bio-remediation project to clear (non-radioactive) heavy metals from soil.