Turbidity
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Turbidity is the cloudiness or
Turbidity (or haze) is also applied to transparent solids such as glass or plastic. In plastic production, haze is defined as the percentage of light that is deflected more than 2.5° from the incoming light direction.[1]
Causes and effects
Turbidity in open water may be caused by growth of
In drinking water, the higher the turbidity level, the higher the risk that people may develop
In water bodies such as
For many mangrove areas, high turbidity is needed in order to support certain species, such as to protect juvenile fish from predators. For most mangroves along the eastern coast of Australia, in particular Moreton Bay, turbidity levels as high as 600 Nephelometric Turbidity Units (NTU) are needed for proper ecosystem health.[citation needed]
Measurement
The measurement of turbidity is a key test of both
There are several practical ways of checking water quality, the most direct being some measure of attenuation (that is, reduction in strength) of light as it passes through a sample column of water.[7] The alternatively used Jackson Candle method (units: Jackson Turbidity Unit or JTU) is essentially the inverse measure of the length of a column of water needed to completely obscure a candle flame viewed through it. The more water needed (the longer the water column), the clearer the water. Of course water alone produces some attenuation, and any substances dissolved in the water that produce color can attenuate some wavelengths. Modern instruments do not use candles, but this approach of attenuation of a light beam through a column of water should be calibrated and reported in JTUs.[7]
The propensity of particles to scatter a light beam focused on them is now considered a more meaningful measure of turbidity in water. Turbidity measured this way uses an instrument called a nephelometer with the detector set up to the side of the light beam. More light reaches the detector if there are many small particles scattering the source beam than if there are few. The units of turbidity from a calibrated nephelometer can be either NTU or FTU, depending on the standard method used. To some extent, how much light reflects for a given amount of particulates is dependent upon properties of the particles like their shape, color, and reflectivity. For this reason (and the reason that heavier particles settle quickly and do not contribute to a turbidity reading), a correlation between turbidity and total suspended solids (TSS) is somewhat unusual for each location or situation.[7]
Turbidity in lakes, reservoirs, channels, and the ocean can be measured using a
An additional device, which may help measuring turbidity in shallow waters is the turbidity tube.[9][8] The turbidity tube condenses water in a graded tube which allows determination of turbidity based on a contrast disk in its bottom, being analogous to the Secchi disk.
Turbidity in air, which causes solar attenuation, is used as a measure of pollution. To model the attenuation of beam irradiance, several turbidity parameters have been introduced, including the Linke turbidity factor (TL).[10][11]
Standards and test methods
Drinking water standards
Governments have set standards on the allowable turbidity in drinking water. In the United States, public water systems that use conventional or direct filtration methods must not have a turbidity higher than 1.0 NTU at the plant outlet and all samples for turbidity must be less than or equal to 0.3 NTU for at least 95 percent of the samples in any month. Systems that use filtration other than the conventional or direct filtration must follow state limits, which must include turbidity at no time exceeding 5 NTU. Many drinking water utilities strive to achieve levels as low as 0.1 NTU.[12] The European turbidity standard is 4 NTU.[13]
Ambient water standards
United States
The US Environmental Protection Agency (EPA) has published water quality criteria for turbidity.[14] These criteria are scientific assessments of the effects of turbidity, which are used by states to develop water quality standards for water bodies. (States may also publish their own criteria.) Some states have promulgated water quality standards for turbidity, including:
- Louisiana. 25, 50 or 150 NTU, or background plus 10 percent, depending on the water body.[15]
- Vermont. 10 NTU or 25 NTU, depending on water body classification.[16]
- Washington. 5 NTU over background (when background is 50 NTU or less), or 10 percent increase when background is over 50 NTU.[17]
Analytical methods
Published analytical test methods for turbidity include:
- ISO 7027 "Water Quality: Determination of Turbidity" [18]
- US EPA Method No. 180.1, "Turbidity"[19]
- "Standard Methods", No. 2130B.[20]
Treatment
Turbidity is commonly treated using a settling or filtration process, or both settling and filtration. Depending on the application,
Reagents
There are a number of
The dosing process must also be considered when using reagents as the flocs may be broken apart by excessive mixing.
See also
- McFarland standards – Scale for turbidity measurement - reference for microbiological analysis
- Ocean optics
- Transparency and translucency – Property of an object or substance to transmit light with minimal scattering
- Water clarity
- Water quality
References
- ^ Thermallaminatingfilms.com. Haze technical definition Archived August 22, 2015, at the Wayback Machine
- ^ National Management Measures to Control Nonpoint Source Pollution from Urban Areas (Report). Washington, D.C.: U.S. Environmental Protection Agency (EPA). November 2005. EPA 841-B-05-004. Chapters 7-8.
- PMID 17888154.
- ^ Stevenson, J. Court; Piper, Catherine B.; Confer, Nedra (1979). "Decline of Submerged Plants in Chesapeake Bay". Annapolis, MD: U.S. Fish and Wildlife Service. Archived from the original on 2019-04-28.
- ^ "Sediments". Annapolis, MD: Chesapeake Bay Program. 2009-08-06. Archived from the original on 2011-09-27.
- S2CID 111183462.
- ^ a b c "Measuring Turbidity, TSS, and Water Clarity". Fairborn, OH: Fondriest Environmental, Inc. Retrieved 1 February 2021.
- ^ a b Myre, E, Shaw, R. The Turbidity Tube: Simple and Accurate Measurement of Turbidity in the Field. "The Turbidity Tube"[dead link]
- ^ Waterwatch Australia, Module 4 - physical and chemical parameters "Methods Turbidity"[dead link]
- ^ HelioClim (Center for Energy and Processes). Paris, France. "Linke Turbidity Factor." Archived 2011-07-23 at the Wayback Machine
- ..
- ^ "National Primary Drinking Water Regulations". EPA. 2022-01-26.
- ^ "What are the drinking water standards?" (PDF). London: Drinking Water Inspectorate (UK). June 2017. Archived from the original (PDF) on 2020-11-11.
- ^ Quality Criteria for Water (PDF) (Report). EPA. 1986. EPA 440/5-86-001. (Commonly known as the "Gold Book.").
- ^ Louisiana Department of Environmental Quality. Baton Rouge, Louisiana."Surface Water Quality Standards." Louisiana Administrative Code (LAC). Title 33, Part IX, Chapter 11. August 6, 2007.
- ^ Vermont Water Resources Board. Montpelier, Vermont. "Vermont Water Quality Standards." Archived 2013-12-31 at the Wayback Machine January 25, 2006.
- ^ Washington Department of Ecology. Olympia, Washington."Water Quality Standards for Surface Waters of the State of Washington." Washington Administrative Code (WAC). Chapter 173-201A. November 18, 1997.
- ^ International Organization for Standardization. Geneva, Switzerland. "ISO 7027-1:2016 Water quality – Determination of turbidity – Part 1: Quantitative Methods." 2016 and "ISO 7027-2:2019 Water quality – Determination of turbidity – Part 2: Semi-quantitative methods for the assessment of transparency of waters." 2019.
- ^ EPA. Environmental Monitoring Systems Laboratory. Cincinnati, Ohio. "Method 180.1: Determination of Turbidity by Nephelometry; Revision 2.0." August 1993.
- ISBN 978-0-87553-047-5. Also available on CD-ROM and onlineby subscription.
- ^ Water Treatment, Grade 1. Denver, CO, USA: American Water Works Association. 2016.
- ^ Darshan Singh Sarai (2006). Water Treatment Made Simple For Operators. John Wiley.
- ^ Earth Systems, Clear Solutions newsletter - Focus on Turbidity [1] 2003.
External links
- Water on the Web: "Turbidity" (University of Minnesota, Duluth and Lake Superior College)
- "Turbidity and Water" United States Geological Survey (USGS)
- USGS field manual on measuring turbidity
- Water Quality - Stormwater, Washington State