Flushable “smart sensors” trialled at Browns Bay could help stop sewage reaching Auckland beaches.

A single wrong pipe connection underground can send wastewater into stormwater lines, making the water unsafe for swimming.

Two associate professors from the Department of Civil and Environmental Engineering, Dr Wei-Qin Zhuang and Dr Colin Whittaker, with a wider team, have invented biodegradable sensors that can detect misconnected or blocked pipes.

The devices use ultra-high frequency radio frequency identification (UHF-RFID).

A radio signal can be picked up and traced as a sensor moves through sewer and stormwater networks.

They are battery-free, flushable, and no bigger than a cigarette lighter.

They are made from plant-based plastic and float naturally, so they can travel through pipes while staying easier to detect.

“Each sensor carries a unique code, so we know exactly where it was released from,” says Dr Wei-Qin Zhuang.

“If it appears in the wrong pipe system, it immediately flags a faulty or illicit connection.”

The sensors are flushable, battery-free and no bigger than a cigarette lighter. Photo: Wei-Qin Zhuang

In two field trials with Auckland Council and Watercare at Browns Bay, the sensors detected an illicit connection in a newly built house.

Zhuang says each sensor costs less than a cup of coffee to produce, and the unique digital ID meant the fault could be traced back to an individual property.

The team says the sensors can also help detect blockages, including fatbergs, where congealed fat and hygiene products build up and cause overflows.

They say existing methods like dye testing, smoke testing and CCTV can be time-consuming and labour-intensive.

With about 8000–9000km of sewer pipes under Auckland, the team says the technology is designed to be affordable and scalable.

For Hibiscus Coast swimmers, faster fault-finding upstream could mean fewer surprise closures after wastewater ends up in the wrong place.

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