Chlorine is the most commonly used water disinfectant used in the water industry today. Chlorine present in water binds with bacteria leaving only a part of the original chlorine (the free chlorine) to continue its disinfection action. Free Chlorine reacts with ammonium ions and organic compounds to form chlorine compounds known as combined chlorine. Combined chlorine and free chlorine taken together are known as Total Chlorine.
There are a number of ways of testing for Chlorine, but all rely on DPD standard chemistry, which is by measuring the colour developed in a water sample after adding a DPD reagent to the sample.
Chemical Test Kit The most basic method of testing is to use a colour comparison chemical test kit, whereby the operator compares the colour developed within the sample to a colour chart or coloured cube. Colour Wheel Comparator A step up from this in terms of accuracy is to use a colour wheel comparator, which provides a better resolution and resulting accuracy, but still depends on the operators visual interpretation of the colour seen. Colorimeter or Photometer The most accurate way of measuring the colour is to use an electronic version of the operators eye, and these are known as photometers or colorimeters. These shine a fixed wavelength light through the sample and then the meter measures the amount of light that has been absorbed - from this the meter can very accurately (to 0.01mg/l) measure the chlorine present and provide a digital readout of the result. Hanna Instruments manufacture all 3 types of test method to allow you to choose the best solution to fit your budget and application.
Turbidity Testing
Turbidity in liquids is caused by the presence of un-dissolved but finely dispersed matter. The unit of measure adopted by the ISO Standard is the FNU (Formazine Nephelometric Unit), and by the EPA the NTU (Nephelometric Turbidity Unit). FTU and NTU units are the same ie: 1 FTU = 1 NTU.
In waste water treatment, monitoring the turbidity levels can determine if the different stages of the process, particularly in the filtration and purification stages, are completed correctly.
In drinking water Turbidity is one of the most important parameters to determine water quality, and very low levels are expected and are impossible to detect without using a meter (higher Turbidity levels can be detected using manual tubes and the naked eye).
