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  Fluoro sensors to monitor recycled water
Technology that uses fluorescence to pick up trace sewage contamination may help increase public confidence in recycled water, say researchers.

Dr Rita Henderson of the University of New South Wales Water Research Centre and colleagues recently published a paper on the possible uses of fluorescence spectroscopy in the journal, Water Research.

"[A] rapid, highly sensitive and selective detector is urgently required to detect contamination events in recycled water systems," says Henderson.

She says fluorescence spectroscopy may provide the solution because of its high sensitivity.

Fluorescence monitoring is also an attractive approach because it is a rapid technique that requires no sample preparation before analysis, adds Hederson.

Fluorescence spectroscopy is now used to monitor the quality of marine water and river ecosystems.

Plant decay products and protein material produced by microbes are known to fluouresce in water.

The fluorescence sensors are able to detect the presence of this organic material, as an indicator of microbial contamination.
Recycling concerns

Henderson's paper comes as concerns have been raised over a Queensland government scheme to pump recycled water from sewage into storage dams.

Some microbiologists are concerned about the safety of processes designed to screen out harmful micro-organisms.

For example, University of Sydney infectious diseases expert Professor Ray Kearney recently said it would be difficult to stop hospital waste being recycled in drinking water.

Henderson dismisses these concerns, saying the quality of properly-treated recycled water is much better than current drinking water.

"We can see from the research we've done that there is almost nothing that can get through [the screening processes used]," she says.

But, says Henderson, failures in treatement and water delivery systems do occur.

She says current methods of online water monitoring generally rely on chemical analysis, including assessment of conductivity (salt content), total organic carbon and, in membrane processes, trans-membrane pressure.

However Henderson says fluorescence can detect changes in water quality that these techniques miss.

She says there is a need for a sensitive technology that provides 24-hour, real-time monitoring of water quality to increase public safety and confidence.
Sensors on tap

Henderson and colleagues have been looking at the ability of portable fluorescence sensors to detect microbial contamination in dual reticulation systems.

In such systems both recycled and drinking-quality water are delivered to homes with the recycled water used for flushing toilets and irrigation.

But, Henderson says, evidence shows that recycled water can sometimes be accidentally mixed with drinking water in dual reticulation systems.

Henderson and team are developing a fluorescence sensor that can be held under running water to detect whether drinking water in a dual reticulation system has been compromised.

She says they have been able to detect recycled water at levels as low as 5% of the mix.

Henderson says in the future, fluorescence sensors could be installed in home pipes to monitor the purity of water piped from a recycling plant to dual reticulation systems in homes.

She says sensors could feed back information to the water treatment plant and set off an alarm should any contamination be detected.

Henderson says further research is required to improve the stability of the fluorescent light source used to detect contaminants.

She says the impact of the treatment processes of water on the fluorescence characteristics of dissolved organic matter also needs to be better understood.
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