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Will Furnass

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Turbidity as a concentration
Jul 24^th, 2012, 8:25am

I am currently looking at discolouration in potable water distribution networks and am working with models that aim to predict how bulk water turbidity increases due to the erosion of material that is bound to pipe walls.

The maths behind the models treat turbidity as a concentration. Is this appropriate? I.e. if 1m^3 of water with a turbidity of 2.0NTU is instantaneously mixed with 1m^3 of water with a turbidity of 1.0NTU is the turbidity of the resulting 2m^3 going to be 1.5NTU?

Cheers,

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Will Furnass
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Pennine Water Group
Department of Civil and Structural Engineering
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A4YB YaBB Newbies Offline I love Water and Wastewater.com Posts: 30 Company or Organization: awzi	Re: Turbidity as a concentration Reply #1 - Jul 24^th, 2012, 8:33am Id imagine that it is possible, but why dont you make some standard solutions with different turbidity's (NTUs) and then mix them 1on1 and 1:2, 1:3, 1:4 and plot your graph and see how linear it is?
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David S. Senior Member Offline I have nothing clever to say here. Posts: 373 Gender: Company or Organization: Environmental Express	Re: Turbidity as a concentration Reply #2 - Jul 24^th, 2012, 11:02am Yes, turbidity is appropriately expressed in concentrations and can be diluted like most other parameters. Be aware that turbid is not the same as colored. Turbidity is the measure of the light dispersing properties of the fluid and suspended material.
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Will Furnass

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Re: Turbidity as a concentration
Reply #3 - Jul 24^th, 2012, 11:04am

I think I've found an answer to my question in a US Geological Survey book [1]. The USGS seem to suggest that a value in NTU is effectively a concentration:

"For a 40 NTU standard, dilute 10.00 mL of the 400 NTU stock
suspension to 100 mL with turbidity-free water (sample or deionized
water passed through a filter media of ≤ 0.2 μm)."

Cheers,

Will

[1] Wilde, F.D., ed., 2005, Field measurements: U.S. Geological Survey
Techniques of Water-Resources Investigations, book 9, chap. A6, with
sec. 6.7, accessed 2012-07-24, at
http://water.usgs.gov/owq/FieldManual/Chapter6/6.7_contents.html.

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BendelBoy Senior Member Offline Free the STOAT Posts: 317 Gender: Company or Organization: wrc plc	Re: Turbidity as a concentration Reply #4 - Aug 1^st, 2012, 7:05am Turbidity is not a concentration. But for low values, as should occur with drinking water, it will behave that way.
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H2O_Tech

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Re: Turbidity as a concentration
Reply #5 - Aug 1^st, 2012, 11:55am

Good feedback so far and here's a couple links to some papers we've produced on turbidity:

http://www.hach.com/quick.search-quick.search.jsa?keywords=lit7061 Turbidity Science by Michael J. Sadar

http://www.hach.com/quick.search-quick.search.jsa?keywords=lit7063 Turbidimeter Instrument Comparison:
Low-level Sample Measurements by Michael J. Sadar

The dilution recipe is merely how to make a 40 NTU standard from a 400 NTU stock...its still just turbidity, not concentration.

As was stated, color is a whole different type of interference in a turbidity reading that is really measuring scatter of light via suspended particles.

Hope the links provide some insight.

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sobisch God Member Offline Posts: 1777 Gender: Company or Organization: L.U.M. GmbH	Re: Turbidity as a concentration Reply #6 - Aug 2^nd, 2012, 1:19am Maybe for the case in question turbidity might be misleading. The equation only holds if chemical composition and particle size distribution is exactly the same. Kind regards T. Sobisch
Back to top	T. Sobisch for@appliedcolloidssurfactants.info http://AppliedColloidsSurfactants.blogspot.com http://www.AppliedColloidsSurfactants.info http://www.lum-gmbh.com IP Logged