REAL TIME MONITORING FOR CROSS CONNECTION DETECTION

Asoka Jayaratne 1, Les Richards

2, Ravi Vivekanantham

2, Jessica Yeung

3, Tim Muster

4, Melissa Toifl

4

1. Yarra Valley Water, Melbourne, VIC, Australia

2. Hawk Measurement Systems, Melbourne, VIC, Australia

3. Smart Water Fund, Melbourne, VIC, Australia

4. CSIRO Land & Water Flagship, Melbourne, VIC, Australia ABSTRACT Reliable and rapid means of detecting unintentional cross connections between the recycled and potable water systems is essential to prevent public health incidents and reputational damage. Two types of low cost prototype cross connection detection devices were developed during a Smart Water Fund sponsored research project, using electrical conductivity (EC) as the parameter. Sensor performances were independently verified at CSIRO during the second stage of this project. Six insertion probes and four miniaturised devices are being field tested in live recycled water networks in Melbourne at Yarra Valley Water and South East Water. This paper discusses the outcomes of the initial trial, development, manufacturing, testing, installation and performance monitoring of the two prototype devices. The paper further highlights how real time EC monitoring will accurately and immediately detect potential cross connections in a water supply network. INTRODUCTION The risk of cross-connections between the recycled and potable water systems has been highlighted as a potential threat to the integrity of dual-reticulation schemes. There is a growing need for a reliable and rapid means of detecting unintentional cross connections so that they can be corrected quickly, preventing a public health incident and reputational damage. In 2008, Water Research Australia (then CRC for Water Quality and Treatment) coordinated an investigation to identify water quality parameters that might be used to indicate the presence of a cross connection. The investigation recommended EC as the preferred indicator. In 2012 the Smart Water Fund sponsored the next phase of the research in collaboration with Yarra Valley Water, South East Water, Hawk Measurement Systems (Australian Small to Medium Enterprise) and CSIRO, to develop an advanced self-powered EC sensor, to be trialed in the distribution network and at the customer interface. A new inline EC sensor technology capable of detecting very small changes in water chemistry

was developed and trialed at Yarra Valley Water’s Brushy Creek Recycled Water Treatment Plant. Building on the success of this initial trial, two types of prototype sensor devices were subsequently developed by Hawk Measurement Systems and independently tested at CSIRO during the second stage of this project;

(a) an insertion probe for installation into water mains with ability to hot tap to avoid interruptions to water utility operation, and

(b) a low cost miniaturised device to be installed inline at the customer interface and/or within customer properties.

The miniaturised device features an environmentally sustainable self-powered function, using thermal electric harvesting, solar photovoltaic (PV) and other technologies and has been designed with ultra-low power consumption. The platform developed is also sized with the capacity to house multiple sensors (not limited to just cross connection detection) and currently additionally monitors temperature and water flow rate. Six insertion probes and four miniaturised devices are being field tested in live dual-reticulation networks in Melbourne at both Yarra Valley Water and South East Water. The devices are located in strategic locations across the network, in pairs, in both drinking and recycled water assets from the source all the way to the customer interface (the water meter). This research is part of the overall water industry move to intelligent networks and digital metering. This research complements a project led by CSIRO, funded by the Australian Water Recycling Centre of Excellence and the Smart Water Fund, to develop a secondary indicator for detecting cross connections (e.g. fluorescence) across a broader range of recycled water in the future. It is anticipated this technology will integrate into the sensor platform developed as part of this project. SENSOR DEVELOPMENT AND TESTING Parameter selection EC is one of few parameters (in addition to fluorescence and UV absorption) that have been determined to be potentially useful in detecting contamination of potable water by non-potable water. Any such cross-connection could be partial

or full, therefore the detection method must be able to detect a low concentration of recycled water in potable water consistent with small amounts of recycled water ‘bleeding’ into the potable water system. The conductivity of potable water supplies can vary significantly across different areas of Australia, and lie typically in the range 50 – 500 µS/cm. Potable water in metropolitan Melbourne, the site of the present study, tends to be at the lower end of this range and is typically 50 - 150 µS/cm. Conductivity of recycled water can be anywhere from 450 – 750 µS/cm. Trial sensor development Hawk Measurement Systems was tasked with developing a system which demonstrated accuracy, sensitivity, stability and robustness in monitoring EC over a long term test at Yarra Valley Water’s Brushy Creek Recycled Water Treatment Plant, under live water conditions. The project hurdle requirement was to the ability to detect a minimum of 10% change in conductivity. The resultant trial system was designed to be able to detect minute changes, and tests demonstrated it is actually capable of identifying as little as 2% changes in conductivity. Hawk Measurement Systems developed a 4-probe stainless steel EC sensor with very high accuracy in the critical measurement range. Electronic hardware was designed to compensate for temperature, long term drifts, voltage fluctuations and probe operational conditions. Stainless steel was chosen as the sensing probe material. It offered longer lasting probe life and an increased stability measurement over a long time frame, and had a good compatibility with both recycled and potable water. To test the functionality of the sensor, Hawk Measurement Systems also developed an automated accurate mixing system of potable and recycled water under real time plant operating conditions. Dedicated software was designed and programmed utilising the Hawk Measurement Systems Link data logger to control the sequence of recycled water and potable water mixing. This program logged the data from two EC sensors; one measuring the potable supply and the other recycled water. The system outperformed the initial sensitivity target of 10% by a factor of 5. Preliminary trial for proof of concept The inline EC sensor was trialled over a period of six months in a controlled environment within the Brushy Creek recycled water treatment plant (Figure 1 and Figure 2). A deliberate cross connection (with appropriate backflow prevention) between the potable and recycled water supply was

established at the Brushy Creek Treatment Plant to facilitate mixing recycled water with drinking water at varying ratios from 2% to 10%. The mixing trials were performed up to four times a day and were remotely controlled. EC data recorded by the data logger was validated by field EC measurements over the trial period.

Figure 1 Cross connection test equipment

schematic

Figure 2 Cross connection test equipment set up

(EC sensors circled)

The advanced EC sensors successfully detected cross connections down to 2% of recycled water in potable water (Figure 3). The sensors also detected the natural variation in EC in both drinking and recycled water.

Figure 3 EC (µS/cm) data for different

recycled/potable mixing ratios Prototype development Following the preliminary trials, Hawk Measurement Systems was commissioned to develop:

(a) an insertion probe for installation into water mains with ability to hot tap to avoid interruptions to water utility operation, and

(b) a miniaturised version of the inline sensor with the ability to self power and communicate with the same or better specifications than the initial trials.

The project originally envisioned the inline sensor small enough to be installed inside the customer properties “under the kitchen sink”. Project partners later agreed to change the direction to develop the sensor to be installed at the customer water meter due to imparacticalities in managing household installations, though small enough that future applications within household plumbing was still possible. Importantly, the inline prototype was developed with a low cost objective coupled with fit for purpose accuracy and reliability, such that it is possible for future large scale residential roll out of real time monitoring of water networks. Consequently the design and manufacture of the device is inherently different to higher cost commercially available EC sensors for industrial applications. During the development stage, the electronic hardware was redesigned to achieve higher accuracy and resolution to allow reliable EC measurment. The design incorporated three of the latest power harvesting technologies – thermoelectric, microturbine and solar PV. Thermoelectric harvesting was utilised to harvest energy from the temperature difference between the water and the external environment. The unit was able to harvest power from a temperature difference of +/- 1°C or greater. Turbine technology

allowed energy harvesting from the water flow, and solar PV cell allowed energy harvesting from sunlight. All harvested energy is stored in a battery backup system to run the sensor electronics and communication. The platform is sized and designed to have surplus energy to allow for future additional sensors. This includes integrating the fluorescence sensor technology investigated by CSIRO to develop a more robust system, which could detect cross connections in waters with unstable EC or where EC differences are negligible. By utilising the latest power saving technology, the entire system has a very low energy footprint. The hardware allows for multi-sensor input and has the ability to send the data over a communication network. Adjusting for temperature was a critical aspect of the design in order to improve the accuracy of EC readings. Temperature can affect EC by up to 2% per 1°C if it is not correctly compensated for. Factors with the potential to influence the accuracy of temperature measurment include the sensor housing and external environmental temperature. A fast-acting temperature sensor with minimal interference from external temperature was incorporated, as well as increased electronic hardware resolution to achieve enhanced compensated EC reading. Independent laboratory testing Laboratory testing was carried out in replicate by CSIRO, in the presence of a staff member from Hawk Measurement Systems who operated the software and ensured correct connection and orientation of the sensor system prior to testing. The accuracy of the reference conductivity meter was checked against conductivity standards (Lab Serv/Pronalysis brand, 10 µS/cm, 84 µS/cm and 1413 µS/cm) prior to commencing testing each day. The results from the calibration checks are presented in Table 1.

Table 1 Comparison of conductivity standards and reference EC meter reading for the 3 separate

testing periods

EC Standard (µS/cm)

Conductivity readings - reference EC meter (µS/cm)

22/04/14 24/04/14 01/05/14

10 10 9.9 10 84 83.9 84.1 84

1413 1413 1413 1413 As the proposed starting EC range for the testing was lower than that of the tap water on the CSIRO Clayton site, de-ionised water was used (0.1-0.2 µS/cm). The conductivity of the water was increased in the following indicative increments for each of the tests:

• 5 µS/cm increments from the starting conductivity (0.1-0.2 µS/cm) to 100 µS/cm,

• 10 µS/cm increments to 200 µS/cm, • 25 µS/cm increments to 700 µS/cm, and • 50 µS/cm increments to 2000 µS/cm

Comparative EC readings of the sensor and meter are presented in Figure 4. The EC sensor readings were found to replicate those of the reference meter and stabilised quickly- in most cases stable readings were recorded within 15-20 seconds. Readings in high conductivity solutions took longer to stabilise, however, in comparison to the reference EC instrument, the sensor stabilised quicker in all conditions. Temperature readings were recorded on the sensor output and observed visually on the reference instrument and found to be consistent to within 0.3°C. The deviations from the reference EC meter readings were found to decrease from 4% (at a conductivity of approx 15 µS/cm) to less than 2% over a conductivity range of 25 to 750 µS/cm. From this conductivity, the sensor readings began to deviate away from the reference EC meter readings again and the error increased to 3.9% over the conductivity range of 750-2000 µS/cm. This is acceptable, given the expected range in EC for potable and recycled water of 50 – 750 µS/cm.

Figure 4 Electrical conductivity of sensor B

compared to the reference EC instrument (Test 3) Endurance testing The devices were further pressure tested in a pipe test loop (Figure 5) at Hawk Measurement Systems to simulate field conditions. The device successfully passed the test criteria with a safety factor of 1.2.

Figure 5 Pressure testing arrangement for EC

probe and miniaturised device (circled) Manufacturing and smart water networks The final design of the sensor device is low cost, highly reliable and compact (the size of an existing water meter). It will be injection moulded, with the ability to add additional sensors like fluorescence, chlorine and other water quality parameters. It also has an input for water and totaliser capability. All data, including the meter reading will be available over the smart network utilising either an existing or proprietary network. The system will have the ability to detect leaks via flow rate and acoustic sensor to “hear” evidence of leaks. A holistic system will reduce the cost per measurement by exploiting shared electronics, housing, being self-powering and by using a single smart network connection therefore significantly reducing the cost of installation and data management. The project user requirements included a target cost of $50-100 per EC device and $300 for a self-powered platform that would support multiple sensors. Based on the final design of the devices it is able to achieve these unit costs assuming a large scale roll out. In addition to the miniaturised inline sensor version, the insertion probe was also developed for the installation into water mains in the distribution system for baseline monitoring of the source water quality to recognise if cross connection has occurred downstream. The manufacture of the insertion probe would be a higher unit cost to the miniature inline device, given the durability requirements operating under high pressure conditions and generally smaller quantities of installation expected. The system outputs are currently communicated over SCADA however other protocols such as ZigBee and longer range options are also being explored based on current trends of smart metering technology. The devices will be in sleep mode to conserve power and awaken when data needs to be transmitted. This is particularly important with increasing quantities of live monitoring devices being installed in the field which is leading to increasing power consumption.

Installation Six insertion probes and four miniaturised devices were installed in strategic locations (Figure 6) across the network, in pairs, in both drinking and recycled water assets from the source all the way to the customer interface. Insertion probes are housed in below ground concrete pits (Figure 7) whilst the miniaturised devices are installed above ground at the customer meter (Figure 8). The devices are connected to the existing telemetry (SCADA) system.

Figure 6 Schematic of sensor installation locations

in the distribution system

Figure 7 Insertion probe inserted into a reticulation

main (circled)

Figure 8 Miniaturised devices installed on potable and recycled water pipes at a customer property

(circled)

PERFORMANCE ASSESSMENT Data collection and analysis

The inline sensors are currently being monitored via the SCADA system to assess performance over an 18 month period. The data will be assessed to understand natural and seasonal variations, and to establish appropriate alarms to alert operational staff of potential cross connections. The recycled water network is currently supplied with drinking water due to upgrades to the recycled water treatment plant. Field testing within the supply system allowed minor assembly defects to be picked up and fixed (Figure 9).

Figure 9 Abnormal EC variations in drinking water main (blue) and recycled water main (purple) from

22 Sept – 22 October 2014 The potable water and the recycled water networks are both currently supplied from two different sources. The recycled water plant was not operational at the time. The sensors successfully detected the switch over to different drinking water sources. Figure 9 and Figure 10 shows clearly that the drinking water supplied via the recycled water network has a much higher EC (80 – 150 µS/cm µS/cm, sourced from Melbourne’s Winneke treatment plant) than the water supplied via the potable water network which is sourced from Melbourne’s Silvan reservoir (45 – 75 µS/cm).

Figure 10 - Accurate detection of EC variations in two drinking water sources (purple line - drinking

water back up supply in recycled water main) This proves the sensors would be capable of successfully detecting variations and potential cross conections when recycled water supply (with a much higher EC of 750 µS/cm) is restored. Field validation Extensive field validation of the sensors using hand held EC meters will be undertaken upon restoration of the recycled water scheme. Allowing for natural variations in potable water EC, SCADA alarms (operational and critical) will be estabished over the

RW main EC range : 80-100

DW main EC range : 65-75

18 month trial period to immediately detect potential cross connections. CONCLUSION The sensitive EC devices are capable of accurately and immediately detecting cross connections. Installing paired EC sensors at strategic locations in the water distribution network will enable operational staff to immediately detect and rectify cross connections in the distribution system. Proactive detection of cross connections will prevent public health incidents and reputational damage to the water utility. Additionally, as the water industry move towards smart water networks, the design of this online cross connection detection device has considered the most cost effective approach, with integrated communication, multi-sensor housing, low power consumption and self-powering mechanisms. ACKNOWLEDGEMENTS The authors would like to acknowledge the support and contributions made to the project and paper by the following people;

• Andrew Forster-Night, South East Water

• Roger O’Halloran, Salamander

Technologies (ex CSIRO)

• Mark Beaton, Lend Lease

• Vivek Kataria and Colin Prohasky, Hawk

Measurement Systems

This project is funded by the Smart Water Fund. Further information on this project can be found on the website, updated with the latest research outcomes:

http://clearwater.asn.au/resource-library/smart-water-fund-projects/cross-connection-detection-sensor-projects.php

REFERENCES

Best, M., Muster, Trinchi,T.H., Toifl, M., Gould, S. and O’Halloran, R. (2015). An inline sensor to detect cross-connections between potable and recycled water systems in real-time. Proceedings of Ozwater 15.

Hambly, A. (2012). Fluorescence as a portable tool for cross-connection detection within dual reticulation systems. PhD Thesis, University of New South Wales, Sydney, Australia.

O’Halloran, R. and Toifl, M. (2008). Detection of cross connection to potable water distribution systems - Stage 1: Development of contamination signatures,Water for a Healthy Country Flagship Report. CSIRO, Melbourne, Australia.

O’Halloran, R.,Toifl, M., Taylor, R. and Winnel, M. (2010). Detection of cross connection to potable water distribution systems - Stage 2: Field trials of recommended detection Water

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Storey, M.V., Deere, D., Davison, A., Tam, T. and Lovell, A.J. (2007). Risk Management and cross-connection detection of a dual reticulation system. 3rd Australian Water Association Conference on Water Reuse and Recycling, July 16th -18th. University of New South Wales, Sydney, Australia.

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