Light fantastic

 作者:荣酌狸     |      日期:2019-03-08 02:17:15
By Fred Pearce THE murky depths of Britain’s polluted rivers are being illuminated by lasers. Engineers say they have come up with ways of using ultraviolet laser light to monitor the polluting potential of discharges from factories and sewage works in real time. “Until now, it has taken three to five days to get samples analysed in the laboratory,” says Rafi Ahmad of the Centre for Applied Laser Spectroscopy at Cranfield University’s site in Shrivenham, Wiltshire. Attempts to operate continuous monitors based on chemical analysis have been messed up by the pollution itself. “The equipment gets fouled up by the slime,” says Ahmad. Now a collaborative project involving Ahmad’s Cranfield team and the water engineering research group at the University of Hertfordshire has perfected a technique that uses ultraviolet lasers to provide an instant reading of key pollution figures. “It’s just like shining a torch into the water,” says Ahmad. By detecting how the polluted water scatters the light, sensors above the surface can measure levels of key pollutants, including nitrates, chlorides, phosphates and organic waste from sewage and food processing. The concentration of organic waste can be used to calculate the water’s biological oxygen demand (BOD)—the amount of oxygen that will be consumed by bacteria feeding on it. A high BOD will asphyxiate fish. The two universities have now applied to Britain’s Engineering and Physical Sciences Research Council for funding to turn their experimental system into a prototype pollution monitor. Companies with licences to discharge pollution into rivers could be the first to benefit. They risk prosecution if their waste treatment processes break down and toxic effluent leaves dead fish floating downstream. Once the laser system has been perfected, says Ahmad, these companies will be able to respond instantly to unexpected changes in effluent quality. The water companies that run Britain’s sewage treatment works are also keen on the idea. “Instant analysis could help us improve process control and meet pollution laws,” says Richard Kelly of Anglian Water’s innovation department. The companies could also use it to test drinking water supplies taken from rivers. Currently, the front-line test for drinking water is to run it through an aquarium to see if fish suffer any ill effects. Ed Gallagher, chief executive of the Environment Agency, which is responsible for rivers in England and Wales, would like to see the quality of their water monitored continuously, something the new system could also do. “Given a suitable number of laser sensors, a whole river could be mapped from the river bank,” says Darren Reynolds, who heads the Hertfordshire end of the collaboration. The ultraviolet light should not affect fish, says Ahmad. With further development,