Smell, taste and turbidity are the most important indicators for the quality of potable water.
At the effluent of a waste water treatment plant, turbidity is a quantitative measure of remaining undissolved solids, indicating malfunctions within the treatment process. Turbidity can be measured relatively simple on-line with optical methods. Therefore, turbidity is extremly suitable for measuring the cleaning efficiency of wastewater treatment plants.
Turbidity is typically determined using 90 degree scattered light principle in compliance with EN ISO 7027.

Measuring principle
By the passing of optical radiation through a dispersing system, dipersed solids reduce radiation power by transforming it into another form of energy. This effect is called absorbtion. The ratio of penetrating to emitting light beams is measured as turbidity.

Factory calibration
The online-sensors from WTW are precisely factory calibrated with a “multi-point” calibration. The calibration is very stable – so further calibration is not needed. Formazine is used as a calibration standard – it is diluted to the necessary concentrations.

A continuous gravimetric analysis is not possible in waste water treatment process – therefore indirect methods like turbidity measurement are used. The concentration of suspended solids is a very important process parameter for today’s sludge treatment. Total suspended solids can be determined online using scattered light or light absorbance. Under normal conditions there is a good correlation to gravimetric analysis.
For the most important sludge characteristics, WTW has defined so called matrix types – with this stored data, even without customer specific calibration a good correlation to total suspended solids concentrations can be achieved.
However, sludges can be totally different – concerning coloration, particle size and structure. Threrefore of course a “multi-point” user calibration is possible. This can be done also with the mandatory required gravimetric determination of total suspended solids.