How is Turbidity measured in India?
Turbidity is a measurement of how transparent water has become due to the presence of suspended particle. Turbidity is regarded as an excellent indicator of water quality. The World Health Organization specifies that the turbidity of drinking water should not exceed 5 NTU, and ideally should be less than 1 NTU.
Drinking water: Turbidity Guidelines
The following rules should be considered when it comes to drinking water supplies:
• The turbidity of drinking water should be less than 5 NTU. Users will notice if there is more than 5 NTU, and the supply may be rejected.
• Turbidity in chlorinated water should be less than 5 NTU. For chlorination to be effective, it should be less than 1 NTU. “I” is the required limit whereas “5” is the permissible limit.
Methods of measuring
1: NTUs (Nephelometric Turbidity Units) are used to measure turbidity. The nephelometer or turbidimeter, which measures the intensity of light scattered at 90 degrees as a beam of light passes through a water sample, is the instrument used to measure it.A unit that is equivalent to FTU but is measured using an EPA-approved turbidity metre.
2: JTU (Jackson Turbidity Units) was the unit of measurement in ancient times, and it was measured with a Jackson candle turbidimeter. This device is no longer in common usage.
3: Secchi Disc
Water clarity and turbidity are intricately related. The higher the turbidity in any body of water, the worse the water clarity is. The measures of the two metrics are not interchangeable, even if one is typically a predictor of the other.
In lakes, a “Secchi disc” is used to measure turbidity. This is a black and white disc that is dropped into the water on a rope. The depth to which the disc sinks before disappearing from view is kept track of. This provides a turbidity level estimate for the lake.
4: Turbidity Meter
One of the most common tools for measuring turbidity is a turbidity metre. Turbidity metres might be portable and ready for use in the field, or they can be intended for use in a laboratory. These instruments use a light source and one or more detectors to measure the light scattered by particles in water samples.
Indian Turbidity Standards
The turbidity standards are a crucial component of the measurement.
1: Formazine, a synthetic polymer with a consistent particle size, is used in the majority of current turbidity standards.
2: Hydrazine and hexamethylenetetramine are used to make the polymer. Nearly all standards organisations, including ISO, EPA, and ASBC, have adopted this chemical due to its uniformity.
A turbidity of one Formazine Turbidity Unit is equal to 1.25 mg/L hydrazine sulphate and 12.5 mg/L hexamethylenetetramine in water (FTU).
The majority of other turbidity units are based on FTUs, however the mechanism they utilise varies. There are numerous types of units, however here are a few examples:
• Nephelometric Turbidity Ratio Unit (NTRU): An EPA-based unit that calculates turbidity using the ratio approach.
• Formazine Nephelometric Units (FNU), which are equivalent to FTU but are measured in accordance with ISO 7027 requirements for metre design.
• American Society of Brewing Chemists (ASBC-FTU): The turbidity metre is designed according to ASBC standards.
In India, for measuring turbidity, Indian Standard (IS): 3025-Part-10 is followed.
When selecting a turbidity metre, it's critical to consider which method you're most likely to use. There are many various types of turbidity metres, but the two most prevalent are those that comply with (EPA 180.1) and those that comply with (ISO 7027).
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