Field measurements in Mexico with UV254Go! as part of Safe Water project.

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As part of an ongoing process improvement project, the water treatment plant wanted to optimise its disinfection process. It was known that the presence of organics caused instability in the disinfection effectiveness, by causing a shift in the Total and Free Chlorine residuals. The only way to improve the performance was to thoroughly understand the levels organic components, which was difficult due to their intermittent presence. It is well known that organics in the water can cause harmful disinfection by-products such as Trihalomethanes (THMs) and Halo-acetic Acids (HAAs). The plant measures these parameters with samples every 90 days, and includes the running averages in its annual Water Quality Report. Despite performing well, a review was undertaken to study the disinfection process to see if any improvements could be made. The first step was to identify the best means of measuring the organic presence. For regulatory compliance, samples are taken periodically and sent to a lab for analysis. This is a straightforward process, but limits the level of testing that can be done and has a cost with each sample. As the goal was process improvement, it was important to have a good volume of data and to have it quickly, so it was decided to purchase a measurement device, however any such device had to compare closely to the results that a certified laboratory would provide. There are many stages in water treatment and the conditions can differ considerably from stage to stage, therefore it was important to be able to measure at various points in the process, so having a portable solution would be a major benefit. UV254 is an excellent method of determining Natural Organic Material in the water. The Ultraviolet Absorption values (UVA) can also be used as surrogate measurements for COD, BOD, TOC & DOC, as long as they have been correctly correlated. The UV254Go!, from Photonic Measurements, was chosen because it was “really, really simple” to use, very user friendly and portable. The UV254Go!, not only measures UVT/UVA but also provides results for the surrogate parameters. In addition, all of the collected data, including surrogate values, is stored on the unit and can be transferred to a PC in Excel-compatible format. The unit was calibrated to the lab results for the COD effluent, and maintained a strong correlation against subsequent lab samples. This meant that the team could have confidence in the results and quickly adapt the disinfection process to live results. As part of the project TOC and DOC values were also measured and showed a strong correlation to the UVA values, meaning that calibration curves for TOC and DOC could be readily created and entered directly on to the Go!. Following on from these measurements the next stage is to start measuring BOD. BOD measurement is a long process, takes 5 days, uses reagents and adds additional cost. The plant intends to reduce its lab-based measurement by more than half, and use the Go! for more data, saving both time and money. A further investment in Photonic Measurements UV254 continuous measurement devices will ensure that NOM data is available throughout the year for trend analysis and process improvement


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