Solving sewer network issues with smart sensors

7 Dec 2021

This article is printed in the November/December edition of Water 

Two Auckland university researchers have joined with international partners to develop a revolutionary biodegradable sensor for detecting blocked sewage pipes, using a similar technique to how we might find missing car keys.

Setting up the test in a stormwater utility hole

Sewer systems are one of the most important parts of urban infrastructure. However, rapidly growing populations, ageing

infrastructure issues, and extreme climate change events are stressing facilities of urban networks.

As a result, drainage networks have seen an increasing number of fatberg formations, blockages, and raw sewage overflows. A fatberg is a very large mass of solid waste in a sewage system, consisting especially of congealed fat and personal hygiene products flushed down the toilet.

Moreover, like blockages, illicit or cross-connections can happen in several ways, with different environmentally damaging outcomes. Sewer cross-connections to the stormwater pipes are more problematic, as this releases human waste containing pathogens to receiving water bodies, such as marine or freshwater.

Alternatively, an illicit connection from stormwater to sewer can significantly increase wastewater volumes to the wastewater treatment plants (WWTPs) during rainy days. Stormwater, which Solving sewer network issues
with smart sensors is otherwise much less polluted than raw sewage, is then treated
as raw sewage, incurring additional costs, labour, and overflow risks at the WWTPs. So, detecting illicit or cross-connections is an important task.

At present, there are only a few options for identifying blockages, illicit/cross-connections, or structural deteriorations. Techniques such as dye testing, smoke testing, or CCTV visualisation exist, but they can be time-consuming and labour-intensive.

To better address sewer blockage and illicit connection,researchers from across three institutions came together to develop a suite of flushable ultra-high frequency identification (UHFRFID) sensors.

RFID technology, especially the ultra-high frequency kind (865-928 MHz), has been widely used in many industries and large-scale Internet of Things (IoT) applications, due to its simple architecture,real-time sensing capability, and versatile detection ranges.

To better address sewer blockage and illicit connections, researchers from across three institutions came together to develop a suite of flushable ultra-high frequency identifications(UFID-RFID) sensors

There are a number of benefits of using UHF-RFID sensors in sewer systems. They are battery-free, have a long lifespan, are small in size, and low in cost. The UHF-RFID-based sensors used in the study cost under two dollars.
Each sensor has a unique serial number and a microchip that can store information, such as property names, street numbers and asset information. By properly using RFID technology, it is possible to precisely determine illicit or cross-connections specifically to a toilet bowl or gully trap of a household.

In their study, RFID-sensors were tested with various environmentally-friendly polymer materials to ensure sensors
remained buoyant or floating on wastewater surfaces throughout their travel time in the sewer network. The research team finally landed on 3D-printed polylactic acid (PLA) structures that ensured substantial detecting ranges by allowing sensors to always align in the required direction in a sewer system. PLA is a biodegradable material that is compostable.
The team has also been developing completely biodegradable RFID sensors that do not create additional solid loadings to the sewer environment.

The finished sensors are designed to be small enough (each of them no larger than a cigarette lighter) and flushable via
a toilet bowl or directly released through a gully trap, creating WATER NEW ZEALAND SMART SENSORS a ‘non-invasive’ method.

The team conducted field trials with Auckland Council’s Healthy Waters department, Watercare, and Tonkin+Taylor.
With all the additional costs on top of the UHF-RFID sensors, such as antennas, RFID readers, computing power, and labour, the trials led to an estimated gross cost of $21 per property, with plenty of room for cost reduction.
Additionally, these sensors can be used to obtain hydraulic information of sewer networks, providing real-time input to
hydraulic models that predict scenarios like blockages.

They can also be used as digital tracers to provide network remapping solutions and buried property drainage directions in a cost-effective and efficient manner. When used in conjunction with GIS, it will be a high-throughput method of updating dated network records and confirming newly completed land developments.

The research is very exciting, partially because of the speed of the research. So far, the sensors have gone from an idea to successful field trials and real-life applications within a couple of years.
The team is poised to develop more IoT sensors to digitalise Three Waters Networks, for a more sustainable, resilient, and clean future.

Dr Wei-Qin Zhuang (middle) and the Tonkin + Taylor team in the field trial.

The project is led by Drs Wei-Qin Zhuang and Colin Whittaker at the University of Auckland and Dr Ray Zhong at the University of Hong Kong. The project team also includes environmental engineering Ph.D. candidates Sundra Tatiparthi (also Three Waters engineer at Babbage Consultants) and Yashika De Costa (also environmental engineer at PDP Consultants), and two researchers from the University of Queensland, Dr Shihu Hu and Professor Zhiguo Yuan. All are co-authors in a recently published journal article in Water Research (Tatiparthi et al., 2021)
detailing results from field-trials with more ongoing studies.

For collaboration or more information, email Wei-Qin Zhuang (