THE murky depths of Britain鈥檚 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.
鈥淯ntil now, it has taken three to five days to get samples analysed in the
laboratory,鈥� says Rafi Ahmad of the Centre for Applied Laser Spectroscopy at
Cranfield University鈥檚 site in Shrivenham, Wiltshire. Attempts to operate
continuous monitors based on chemical analysis have been messed up by the
pollution itself. 鈥淭he equipment gets fouled up by the slime,鈥� says Ahmad.
Now a collaborative project involving Ahmad鈥檚 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. 鈥淚t鈥檚 just like shining a torch into the water,鈥� says
Ahmad.
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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鈥檚 biological oxygen demand
(BOD)鈥攖he 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鈥檚 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鈥檚 sewage treatment works are also keen
on the idea. 鈥淚nstant analysis could help us improve process control and meet
pollution laws,鈥� says Richard Kelly of Anglian Water鈥檚 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. 鈥淕iven a
suitable number of laser sensors, a whole river could be mapped from the river
bank,鈥� says Darren Reynolds, who heads the Hertfordshire end of the
collaboration. The ultraviolet light should not affect fish, says Ahmad.
With further development, mobile laser monitors could also be flown on planes
to check for high levels of sewage in seawater off beaches and issue instant
warnings to bathers.