Saving Sydney's sewers

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Usually associated with the carrying of telecommunications data, an Edinburgh Napier researcher is using fibre optic technology to solve problems of a different kind, from the sewers of Australia’s largest city to the kelp farms of Scotland

Dr Lourdes Alwis describes the sewage tunnels of Sydney as “not as stinky as I make them out to be” and she’s more familiar with them than most. Working alongside Sydney Water and City University, she’s been leading on designing optical fibre sensors that can survive in the harshest conditions.

“Sydney Water has kilometres and kilometres of sewage tunnels that carry waste water, so it’s an acidic environment. These tunnels get corroded very quickly which means they have to spend a lot of money on rehabilitation,” says Dr Alwis.

With this in mind, the water company was keen to implement a monitoring system that would predict corrosion levels and allow maintenance to be planned in good time. However, experiments with electrical sensors to monitor humidity and pressure ended quickly when the sensors themselves only survived for two weeks. That’s when Dr Alwis was called in.

As a result of this successful research Sydney Water will implement these sensors in sewer locations and the findings will contribute to the future design of sewers.

NSW Water Awards

Australian Water Association

She says: “Due to the 20th-century telecommunications boom, a lot of optical fibre-related equipment and resources are available and we are now using this technology in a different way.

“Fibre optics carry light (photons) as opposed to electric wires that carry electrons. When a fibre optic cable is bent of deformed, the amount of light carried by it will be affected and these changes can be precisely monitored. This is very useful when designing sensing devices that measure the likes of temperature, strain, humidity, pressure and so on. Importantly, fibre optics are made of silica (glass) which means they can withstand harsh environments such as temperatures of more than 300C, at which traditional electrical systems will melt.”

In the case of Sydney Water, this was borne out when the first set of optical sensors set up in the sewers lasted two weeks and then passed the six-month stage. Dr Alwis will now return to Australia to oversee the implementation of more sensors across the sewage network.

The success of Dr Alwis’ work was recently recognised by the 2017 Australian Water Association New South Wales Water Awards where the project won the Research Innovation Award. The citation noted: “Sydney Water annually spends around $60m to $80m on the management and rehabilitation of deteriorated concrete gravity sewers and corrosion at treatment facilities. This collaborative research project has focused on the development of a new class of photonic humidity sensors with specialised, tailored coatings designed specifically to operate under highly biofouling and corrosive conditions. As a result of this successful research Sydney Water will implement these sensors in sewer locations and the findings will contribute to the future design of sewers.”

Fibre optic sensing projects in the pipeline

Not content with her success in Australia, Dr Alwis is now working closer to home and is partnering with the Scottish Association for Marine Science (SAMS) to help find the optimal growing conditions for kelp, or seaweed.

“They want to measure salinity, water temperature and water pressure because this is grown in the sea. Again, however, they have similar issues with traditional electrical systems. This is a huge problem so we are going to put together a grid of optical fibres and monitor the salinity in real time.”

Plans are also afoot to monitor humidity in the harsh conditions of the Arctic Ocean and Dr Alwis is also in talks with Network Rail to create a nerve system of optical sensors that can be used on railway bridges in place of hundreds of traditional electrical strain gauges.

“The challenge is exciting. Sydney Water so far has been exciting and I can’t wait to see what happens with the kelp farm and the Arctic projects. I love the sheer excitement of trying it out and seeing if it works. Optical fibre sensing technology is still at laboratory level. It’s not very widely used but I believe it will take up within the next 10 years or so. We’re trying to be at the forefront.” 

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