Water supply service providers require many measurements to ensure safe, contaminant-free, and high quality water. Some important measurements include pH, Oxidation-reduction potential (ORP), conductivity, temperature, free chlorine, monochloramine, dissolved oxygen (DO), and turbidity.
Ryo opened describing some of the challenges:
Meeting and reporting the water quality requirements of in-country environmental agencies, coping with infrastructure issues and costs, and dealing with lack of personnel or sufficient training and experience can exacerbate points of vulnerability throughout the water distribution system.
He noted that it’s not possible to test for every possible variable and some contaminants cannot be tested for. There are reasonable precautions that suppliers can take:
The only way utilities can detect a problem in the water is to identify changes in the water composition and understand what various changes could indicate. In order to detect any change, utilities must continuously monitor on-line both the raw and processed water throughout the system to get a baseline for the normal water composition. It’s best to have baseline data for at least a year in order to understand, monitor and detect patterns.
Faced with changes from baseline, operators can:
…make informed judgments when changes beyond the normal patterns emerge that could be cause for concern. This kind of continuous, online, systematised monitoring makes up a critical early warning system that can often detect chemical or microbial risks, indicating to the plant the need for further water quality analysis at a particular point in the water system.
Ryo highlighted some of the low probability but high impact issues that continuous measurements can find:
- Early warning systems monitor pH to detect changes that impact the potential corrosion of the distribution network.
- pH is also important as it determines the solubility and biological availability.
- ORP is continuously measured to determine the level of chemical reactivity.
- Conductivity provides an indication of the total dissolved solids.
- Turbidity indicates biological growth in suspended matter.
- Free chlorine and/or monochloramine are tracked to ensure the maintenance of optimum residual disinfection levels.
- In addition, dissolved oxygen is an important indicator of whether there is a healthy environment being maintained in the water distribution network.
He shared that it’s important to place the measurements at each area of potential vulnerability in the distribution system. Wireless technologies such as IEC 62591 WirelessHART have made adding these measurements more practical [hyperlink added]:
New device adapters allow wireless to be enabled for any existing HART communications analysers. These adapters, such as the Smart Wireless THUM adapter from Emerson, can be retrofitted onto any two- or four-wire HART device and enables wireless transmission of measurement and diagnostic information.
For many water treatment plants, chlorine must measured at several points including pre-filter, filtration, and effluent water treatment stages for quality assurance requirements. Where wired analyzers are difficult to install, whereas:
…a wireless solution that includes an advanced intelligent analyser, chlorine analysis system and a wireless adaptor is a good solution since it enables the wireless transmission of measurement data and advanced diagnostic information through the WirelessHART protocol.
Ryo noted that each treatment plant is different and no “one-size-fits-all” water quality monitoring solution exists. These measurement devices must be flexible enough to meet the unique challenges of the individual plant.
By monitoring a variety of measurements throughout the water treatment and water distribution system, plants can better understand normal patterns and detect unusual and potentially dangerous changes in the water quality. Continuous, on-line water quality monitoring technologies and processes can greatly reduce the risk that contamination events will be missed, enabling plants of all sizes to better protect the water quality in the communities they serve.
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