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Water turbidity

Turbidity is one of the organoleptic indicators of the water which characterizes a decrease in the transparency of the water if finely dispersed organic and inorganic impurities are present in it. The most common pollutants that cause water turbidity are sand, clay, various carbonates (water like milk), sludge formed by phytoplankton and zooplankton (yellow-green water with an unpleasant smell).

In the framework of this article we will consider the topic of water turbidity, what are the consequences of using turbid water on a daily basis as well as possible solutions to this problem.

HOW TO DETERMINE WATER TURBIDITY?

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In order to find out the turbidity of the water, analysis in the laboratory is usually carried out. Previously turbidity was determined with a kaolin suspension and expressed in grams of kaolin per liter, however, nowadays a polymer-formazin solution is used and it is expressed in the indicator of turbidity units per liter of water or NTU (nephelometric turbidity units).

Special devices or nephelometers are also available for determining the water turbidity.

REGULATORY INDICATORS

The World Health Organization has determined a maximum turbidity value for drinking water: 5 NTU . On the other hand, in Latvia, MK regulations No. 547Mandatory safety and quality requirements for drinking water, monitoring and control procedures/Dzeramā ūdens obligātās nekaitīguma un kvalitātes prasības, monitoringa un kontroles kārtība” determines that water turbidity must be within 0.3 -1 NTU.

CHARACTERIZATION OF WATER ACCORDING TO ITS ORIGIN

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Groundwater may have different degrees of turbidity. It is more pronounced during periods of floods and mud, as well as in cases where untreated sewage is discharged. In addition to high turbidity such waters are also recognized by increased color and odor.

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For well water its quality is mainly determined by the depth of the well bore. The first reason for the decrease in water transparency for well water may be the increased content of clay and sand particles that enter the water during the pumping process. The second factor is the increased content of iron and manganese in the water. In this case the turbidity appears after the water is pumped out when the iron changes from the soluble divalent form to the trivalent form.

​Although tap water usually has relatively high transparency, it often has increased NTU indicator. This is explained by the fact that water is not always completely purified in treatment plants and, when moving through pipes, it washes away biological pollution from the surface of the pipes.

CONSEQUENCES OF USING TURBID WATER

Cloudy water is not recommended for consumption as it indicates microbiological contamination of the water. Water with a turbidity of more than 1 NTU cannot be disinfected by ultraviolet light and for its purification it is necessary to increase the amount of chemical disinfectants.

Regarding the use of turbid water for industrial and domestic purposes, it should be taken into account that particles can clog the small nozzles of irrigation systems, accelerate the wear of ball valves, pipe fittings and leave dirty marks on surfaces.

HOW TO REDUCE WATER TURBIDITY?

Today there are many devices available for the water purification from mechanical particles. When choosing the most suitable type of mechanical filter, factors such as the amount of insoluble impurities, water consumption, as well as the area for the installation of filtration equipment must be taken into account.

CARTRIDGE FILTERS

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Cartridge filters are plastic flask-type filters with a replaceable cartridge made of polypropylene installed inside. Depending on the original pore size, particles larger than 1, 5, 10 or 20 microns can be removed. Such devices are intended for use in apartments and houses with medium water turbidity. They are also used for additional purification before membrane systems.

WASHABLE FILTERS

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Flushable filters have a cylindrical body, inside there is a special filtering element (metal mesh). The size of the particles to be removed is determined by the size of the holes in the filter element construction. Usually it is 90 – 100 microns. Depending on the size and productivity, they can be used in both domestic and industrial settings.

REFILLABLE FILTERS

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Refillable column-type filters consist of polymer corrosion-resistant housing with an automatic water supply valve. The column is filled with filter material (inert materials such as quartz sand, clinoptiolite, etc.). Depending on the grain size of the material holes are formed between them to allow particles of a certain size to pass through. Such filters are able to retain sand, clay, silt particles with a size of 10 microns or more. These solutions are used for very cloudy water both at home and in factories.

DISC FILTERS

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Disc filters have a metal or plastic body, inside there are discs made of polymer material. On their surface grooves of a certain size are embedded, when the discs are compressed they form a filtration body. Such devices can trap particles of 50 μm or more in size. In general, the size of the particles is controlled by the filter settings or the degree of disk compression. This is an excellent solution for preparing water for irrigation systems.

ULTRAFILTRATION

Ultrafiltration is another effective way to reduce the content of mechanical particles. It is used in large industrial water treatment plants for centralized water supply systems or industrial wastewater treatment.

Read also: The smell and taste of the water.

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