SIGRIST-Photometer - Process Instruments for Measuring Turbidity, Color and UV Absorption

SIGRIST process instruments have been used for 60 years to secure the quality of drinking water by measuring turbidity and other important variables. The most important parameters to be monitored with SIGRIST instruments are turbidity, color, UV absorption, DOC, and oil in water. The accuracy and reliability of SIGRIST photometers are proverbial the world over.

TURBIDITY MEASUREMENT

Turbidity is caused in water by mineral or organic solid particles. A light beam passed through the sample will be scattered by these particles. Measurement of the scattered light intensity and determination of the turbidity level therefore provides an indication of the concentration of the solid particles in the liquid.

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.

Typical applications are:

• Turbidity in raw water
• Turbidity after flocculation
• Turbidity after filtration
• Filter-back-flushing
• Turbidity after reservoir / before supply to network

ON-LINE TURBIDIMETER AQUASCAT

3 different versions of AquaScat were developed specifically for water treatment: from dirty river water down to filtrated pure water. AquaScat WTM has a measure span of 0 FNU to 4,000 FNU, a resolution of 0.001 FNU, a non-contact measurement and an automatic adjustment on demand. AquaScat HT has a resolution of 0.1 FNU, a non-contact measurement and is perfect for measurement of high turbidity (e.g. raw water). AquaScat P has a closed flow cell and is used for measurements under pressure (e.g. sample with high content of gas).

COLOR DETECTION IN WATER TREATMENT

The detection of color in water treatment is particularly important wherever surface water with high humic matter loading is treated. If the humic substances are not removed from the water right at the start with flocculation and filtration, it is possible that hazardous trihalomethanes will be formed during disinfection with chorine.

The detection of color and hence of the humic matter concentration is employed in the raw water or following flocculation for control of the flocculation process. It is also useful following filtration as a final check on the decoloration process.

UV ABSORPTION

Harmful substances may be present in water in either undissolved or dissolved form. Just as turbidity detection is used to measure the total solids content, UV absorption detection at a wavelength of 254 nm can be employed to measure the total content of dissolved organic matter.

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.

COLOR MONITOR VIS/ UV ABSORPTION MONITOR COLORPLUS

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.

For the measurement in water treatment a PVC bypass flowcell (path length of 100mm or 50mm) with compensation glass can be used. The compensation glass is used for calculating and compensating window contamination. This will prevent reading falsification and reduces the need of maintenance.

Another feature of ColorPlus is the possibility of turbidity compensation at a second wavelength, if this can disturb the absorption measurement, e.g. in raw water application.