The Challenge:
With the introduction of dual-reticulation schemes in Australia, the risk of cross-connections between the recycled and potable water systems has been highlighted as a potential threat to the development of recycled water projects. There is a need for a reliable means of detecting unintentional cross connections so that they can be corrected quickly, preventing a public health incident and reputational damage. The water industry and public require protection and a means to monitor water quality at the distribution point and at the household in real time. This will enable cross connections to be identified and corrected in a timely manner.
The solution developed needs to be low cost in order for it to be economically viable for use at the household level. Previous research on the range of parameters that can be utilised to detect the presence of recycled water in potable water has indictaed that the two strongest indicators were electrical conductivity and UV absorbance and UV fluorescence. Each of these detect different characteristics of recycled water. Smart Water Fund invested in two concurrent research projects to develop and test the use of the parameters as cross-connection indicators.
The Projects:
Project 1 – Electrical Conductivity (Hawk Measurement Systems)
The first project led by ‘Hawk Measurement Systems’ developed a miniaturised low cost high accuracy electrical conductivity (EC) sensor with software to detect cross connections. The electrical conductivity of recycled water is typically much higher than potable water, therefore an online sensor monitoring this water quality parameter is useful to alert the water utilities to potential cross connections. The platform housing the sensor is self-powered in an environmentally friednly way. The platform developed also has the capacity to house multiple sensors (not limited to just cross connection detection) and can additionally monitor temperature and water flow rate. The EC sensor device itself is small enough to be accommodated at the household water meter as well as being installed across the water supply networks.
Project 2 – Fluorescence (CSIRO & AWRCoE)
The second project was led by ‘CSIRO’, funded by the Australian Water Recycling Centre of Excellence and Smart Water Fund, developed a small scale low cost sensor using UV absorbance and UV fluorescence for detecting cross-connections. Amino acids and proteins from wastewater provide characteristic spectroscopic responses by absorbing or fluorescing when exposed to UV light at particular wavelengths. This technique is more experimental compared to electrical conductivity and required significant research effort into issues such as sensor stability, temperature compensation, calibration drift and fouling resistance to reliably detect cross connection. Once the technology is stable, the sensor will be adapted and miniaturised to a small scale sensor, and likely integrated with the EC sensor and platform developed as part of the first project.
The Outcomes:
Project 1
The EC project developed and field tested insertion probes and miniaturised devices in live dual-reticulation networks in Melbourne. Results from the trials confirm the EC devices are capable of accurately and quickly detecting cross-connections and small variations in source water quality. Installing EC sensors at strategic locations across the water distribution network will enable operational staff to immediately detect and rectify cross-connections. Proactive detection of cross-connections in future will prevent public health incidents and reputational damage to water utilities. Extended monitoring of the sensor devices over a longer period will be necessary to further assess the measurement accuracy and performance due to seasonal variations in water quality and to check calibration requirements.
Project 2
UV fluorescence was found to offer superior sensitivity as opposed to UV absorbance, and furthermore, offered improved affordability. The final UV fluorescence prototype was able to detect cross-connections of under 1% recycled water in potable water supply. The fluorescence detectors were demonstrated to work effectively in two field trials. These were conducted on sites of varying water quality at Brushy Creek (Yarra Valley Water) and Surbiton Park (Western Water). The fluorescence prototype has been demonstrated to provide an excellence means of differentiating water quality over long periods of time at low cost, although the ultimate accuracy of the device is highly dependent upon an effective means of ongoing calibration. Commercialisation opportunities are currently being explored.
