Source: Radio New Zealand
The sensors are flushable, battery-free and no bigger than a cigarette lighter. Supplied
Auckland’s beachgoers well know the frustration of being told to keep out of the water after heavy rain due to wastewater overflow, but researchers at Auckland University have been piloting flushable sensors designed to detect underground sewer faults.
The sensors are about the size of a USB stick, made from plant plastic and use ultra-high radio frequency to allow them to be detected as they move through the networks.
With some 8000 to 9000 sewer pipes under Aucklanders’ feet, the sensors can help find misconnections, where wastewater pipes are wrongly connected to stormwater or where there’s a blockages in sewer pipes causing an overflow.
Two field trials have already been completed with Auckland Council and Watercare in Browns Bay.
Dr Wei-Qin Zhuang is the project’s lead researcher based at the university’s Civil and Environmental Engineering Department.
He said he wanted to find ways to remove nitrate from waterways safely without the creation of significant greenhouse gas emissions.
He also wanted to look at water quality to detect indicator micro organisms in waterways and drinking water, he said.
There was discussion to identify the water problems specific to Auckland and consider how to use research to mitigate them, he said.
Problems identified included the overflow of the city’s sewer systems, as well as misconnections, Zhuang said.
The research team tried to come up with solutions to identify where there were misconnections on the basis it was less challenging than trying to deal with the overflow issue, he said.
“We developed this UHF-RFID [ultra-high radio frequency identification] based censors to identify illegal connections and we also found that it can be used to identify blockages of our pipes.”
Setting up the test in a stormwater utility hole. Wei-Qin Zhuang
They did not want the censors to be intrusive to avoid having to visit a house and install a bunch of devices to detect the issues, he said.
“So initially we were trying to develop something that can be flushed through our toilet bowls without clogging the pipes, the sewer lateral, and we purposely looked for small devices that has the size that is small enough to be flushed.”
They designed the censors to ensure they could be flushed and then could float on the water “so their sensitivities won’t be compromised by water,” he said.
“After they’ve been flushed into the sewer lateral, they’ll be washed and they’ll flow with the water flow and then get into the sewer mains and then we can install detectors at manholes to detect these censors.”
The censor sends out an ultra-high radio frequency which is then picked up at the various sites, Zhuang said.
“So you flush your censors through toilet bowls and then supposedly all the censors need to go through the sewer manhole, but if we catch some of the censors in the stormwater manhole then we instantly know that which household has a misconnection.”
Blockages can be detected when the censor takes much longer than expected to reach a certain point, he said.
“Then authorities can send CCTV cameras down pipes and see whether the blockage is severe or has just started building up.”
The first generation of the censors could be collected and then composted, while the second generation of the censors dissolve in water after two hours so it did not worsen the blockage situation, he said.
That provided a one hour window to use the censor to detect if there had been a blockage, he said.
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand
