Role of Turbidity in Drinking Water Treatment

Turbidity was initially meant as a qualitative indicator of the quality of drinking water, an indicator of the cloudiness or haziness of a stream. This is not a measure of individual particles in the water; this measures how much light reflected through the water impacts certain particles, or how much light reflects particles in the water. In an effort to add objective accuracy to the calculation for the quality of drinking water, the turbidity designs and methods of today were regimented.

The benefit of reading turbidity is not that it can precisely tell how many pathogens a sample may contain, but that it practically tells how much or how little of any reflective particles affects the sample’s visibility, even if they are undetectable with the human eye. Measures of turbidity are normally taken from multiple locations.

Intake Of Source Water

Turbidity readings of the source water may provide a clear understanding of criteria for pre-filtration treatment that may prevent filters from overloading. For WTPs which use surface water or mixed water sources where quality and turbidity can vary widely, they are of particular value.

Pre Filtration

Pre-filtration turbidity is measured using any turbidity instrument or Sigrist turbidity meter to check the efficiency of the processes of coagulation, flocculation, and clarification. An indicator of the efficacy of the filtration is to be able to compare pre and post-filtration turbidity monitoring.

Post Filtration

Compliance with regulatory requirements includes turbidity testing of individual and mixed filter effluents. Measures are made to ensure that pathogens did not do so by traditional and/or membrane filtration systems of the WTP. Ideally, this is a continuous process allowing plant operators to react quickly to potential upset conditions and to maintain compliance. In case, if you use Sigrist Aquascat, it measures turbidity of potable water according to IEC 27027 using 90+° scattered light detection in a free-falling water stream.

Monitoring the membrane banks before recombining streams also helps automate filter maintenance and cleaning measures by stream-by-stream reporting of declining output or failures. Turbid meters are often used to read backwash water’s clarity to prevent backwash procedures from running any longer than required.

Plant Effluent

At the point where water reaches the water delivery system additional turbidity readings may be taken. It can be especially relevant as different organizations manage water management and water delivery. Additional turbidity measurements may also be taken to track any changes in water quality as it passes through the system at various other points in the distribution network.

Laboratory Instruments

Lesser WTPs could use only one or two laboratory instruments for turbidity sampling due to cost constraints. Larger WTPs tend to have multiple online nephelometers for continuous monitoring of processes and use laboratory instruments for backup and process readings check. In comparing laboratory and process measurements caution must be exercised, unless the sensing technology is similar in both. Differences in methods of measurement will carry possible variables between the two readings. Physical changes in samples including particle settling can occur over time as samples are transported from the process line to the laboratory.

The author of this article has been working in a company that offers high-quality Sigrist Aquascat. In this article, he has mentioned a few roles of turbidity in drinking water treatment. Visit

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