de Glossar

Optimized Quality of Drinking Water by Measurement of Turbidity and UV-Absorption

Turbidity and UV-absorption are two important parameters to ensure the quality of drinking water. At AquaPro in Berne SIGRIST presents its actual instruments to measure these parameters.

Turbidity is caused in water by mineral or organic solid particles. Studies have shown that there is a clear correlation between turbidity and the number of bacteria in a water sample. The dangers posed by these germs are made even worse by the fact that they can cling to solid particles and thus survive disinfection with chlorine, chlorine dioxide, UV irradiation or ozone. For these reasons, new guidelines call for limits below 0.2 FNU and continuous monitoring of turbidity in drinking water treatment. This requires exact, high resolution analyzers.

In early 2006 the new AquaScat family has been launched onto the market setting a new standard with its maintenance free construction. The flagship is the AquaScat WTM with a measuring span of 0 to 4000 FNU, a resolution of 0.001 FNU, non-contact measurement and automatic adjustment on demand. Also the version HT shows a non-contact setup. With a reduced resolution of 0.1 FNU and the same span it is primarily thought for higher turbidities e.g. in raw water applications. The scope is completed with the AquaScat P with a closed flow cell for measurement under pressure. This version has advantages for samples with high gas content or to optimise the sample flow. With this selection, the AquaScat can cover all applications in potable water treatment form really dirty river water with more than 2000 FNU down to best filtrated pure water with 0.015 FNU. Main difference to the previous model WTM500 besides the increased measuring span is the integration of keypad and display as well as the significantly reduced weight and volume of the instrument.

The UV-absorption at 254 nm reacts on humic substances, but detects also other organic compounds as oils, aromats, solvents, etc. These substances have to be removed e.g. by active charcoal filtration. Studies have shown that, for most applications, a linear correlation exists between the UV-absorption and DOC (dissolved organic carbon) values. This means that UV absorption measurement provides a continuous on-line indication for trend analysis of the DOC figure without time-consuming laboratory checks. Additional applications are in monitoring of ozonisation and active charcoal filtration, to survey a sufficient disinfection and reduction of organic material. A continuous monitoring of raw and treated water allows an optimized control of the treatment and ensures a constant quality of the drinking water.

The ColorPlus is built to accommodate up to three different light sources in the UV and VIS ranges. Depending on the required wavelength, a mercury bulb (UV light) or up to three LED's (VIS light) are installed. The ColorPlus can be calibrated in E/m, Hazen, EBC etc. A combined UV absorption/ Hazen color measurement is possible, too. Like all SIGRIST process instruments, the ColorPlus exhibits the high measuring stability and accuracy afforded by the dual beam measuring method.

The scope is completed by particle counters and oil trace analyzers, which can also help to ensure the quality of the potable water.

Products: AquaScat WTM | AquaScat P | AquaScat HT | ColorPlus bypass | ColorPlus in-line | OilGuard

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René Gehri
Water, Beverages & Food, Industrial Processes
Pascal Schärer
Traffic & Environment

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