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 | موضوع: 15-كتالوج اجهزة معمل تحاليل المياه والهندسة الصحية النظرى(المواد الفوسفاتية)  الإثنين يناير 24, 2011 1:49 am | |
| Chemical parameters of water
Phosphorus
Phosphorus is a nutrient required by all organisms for the basic processes of life.
Phosphorus is a natural element found in rocks, soils and organic material.
Its concentrations in clean waters is generally very low; however, phosphorus is used extensively in fertilizer and other chemicals, so it can be found in higher concentrations in areas of human activity.
Phosphorus is generally found as phosphate (PO 4 -3 ).
High levels of phosphate, along with nitrate, can overstimulate the growth of aquatic plants and algae, resulting in high dissolved oxygen consumption, causing death of fish and other aquatic organisms.
The primary sources of phosphates to surface water are detergents, fertilizers, and natural mineral deposits.
Phosphorus is a nutrient required by all organisms for the basic processes of life.
Phosphorus is a natural element found in rocks, soils and organic material.
Phosphorus clings tightly to soil particles and is used by plants, so its concentrations in clean waters is generally very low.
However, phosphorus is used extensively in fertilizer and other chemicals, so it can be found in higher concentrations in areas of human activity.
Many seemingly harmless activities added together can cause phosphorus overloads.
Phosphorus exists in water in either a particulate phase or a dissolved phase.
Particulate matter includes living and dead plankton, precipitates of phosphorus, phosphorus adsorbed to particulates, and amorphous phosphorus.
The dissolved phase includes inorganic phosphorus and organic phosphorus.
Phosphorus in natural waters is usually found in the form of phosphates (PO4-3).
Phosphates can be in inorganic form (including orthophosphates and polyphosphates), or organic form (organically-bound phosphates).
Organic phosphate is phosphate that is bound to plant or animal tissue.
Organic phosphates are formed primarily by biological processes.
They are contributed to sewage by body waste and food residues, and also may be formed from orthophosphates in biological treatment processes or by receiving water biota.
Organic phosphates may occur as a result of the breakdown of organic pesticides which contain phosphates.
They may exist in solution, as loose fragments, or in the bodies of aquatic organisms.
Inorganic phosphate is phosphate that is not associated with organic material.
Types of inorganic phosphate include orthophosphate and polyphosphates.
Orthophosphate is sometimes referred to as "reactive phosphorus.
" Orthophosphate is the most stable kind of phosphate, and is the form used by plants.
Orthophosphate is produced by natural processes and is found in sewage.
Polyphosphates (also known as metaphosphates or condensed phosphates) are strong complexing agents for some metal ions.
Polyphosphates are used for treating boiler waters and in detergents.
In water, polyphosphates are unstable and will eventually convert to orthophosphate.
Phosphates are not toxic to people or animals unless they are present in very high levels.
Digestive problems could occur from extremely high levels of phosphate.
In freshwater lakes and rivers, phosphorus is often found to be the growth-limiting nutrient, because it occurs in the least amount relative to the needs of plants.
If excessive amounts of phosphorus and nitrogen are added to the water, algae and aquatic plants can be produced in large quantities.
When these algae die, bacteria decompose them, and use up oxygen.
This process is called eutrophication.
Dissolved oxygen concentrations can drop too low for fish to breathe, leading to fish kills.
The loss of oxygen in the bottom waters can free phosphorus previously trapped in the sediments, further increasing the available phosphorus.
Phosphates do not pose a human or health risk except in very high concentrations.
It is measured in mg/L. Larger streams may react to phosphate only at levels approaching 0.1 mg/L, while small streams may react to levels of PO4-3 at levels of 0.01 mg/L or less.
In general, concentrations over 0.05 will likely have an impact while concentrations greater than 0.1 mg/L will certainly have impact on a river.
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Measurement of Phosphorus
There are several forms of phosphorus which can be measured.
Total phosphorus (TP) is a measure of all the forms of phosphorus, dissolved or particulate, that are found in a sample.
Soluble reactive phosphorus (SRP) is a measure of orthophosphate, the filterable (soluble, inorganic) fraction of phosphorus, the form directly taken up by plant cells.
Both phosphorus and orthophosphate are often measured using a colorimetric method, which means the color of treated sample reflects the concentration of the parameter.
If total phosphorus is being measured, all forms of phosphorus are converted to dissolved orthophosphate with acid, persulfate, and heat.
A chemical is then added to the water sample.
The darker the color of the sample becomes, the more phosphorus present.
This test can be done visually, comparing the treated sample to a set of reference colors.
However, it is more accurate to use an electronic colorimeter, which uses a light source and a photodetector to find the concentration based on how much light is absorbed by the sample.
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Factors Affecting Phosphorus Concentrations
Wastewater and Septic System Effluent
Domestic and industrial sewage are very important sources of phosphorus to surface water.
Organic phosphates are formed primarily by biological processes.
They are contributed to sewage by body waste and food residues. Phosphorus is essential in metabolism so is always present in animal waste.
Orthophosphates and polyphosphates can be contributed by detergents, as discussed below.
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Detergents
Orthophosphates and certain polyphosphates are major constituents of many commercial cleaning preparations.
In the 1950s and 1960s, sodium phosphate was used often as a "builder" in households detergent to increase cleaning power.
The extensive use of detergents led to major eutrophication problems, and in the 1960s efforts were made by governments, detergent manufacturers, and consumers to reduce the use of phosphates in detergents.
As a result, phosphorus concentrations in many streams and lakes decreased.
This was due to limits on the phosphate content of detergent, and also additional treatment used in waste water treatment plants to remove phosphorus.
Many states have a ban on phosphates in detergents.
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Fertilizers
Fertilizers generally contain phosphorus in the form of orthophosphate.
Phosphate is not very mobile in soil; it tends to remain attached to solid particles rather than dissolving in water.
However, if too much fertilizer is applied, the phosphates are carried into surface waters with storm runoff and also with melting snow.
Soil erosion of fertilized fields and lawns can also carry a considerable amount of particulate phosphate to streams.
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Animal Waste
Phosphorus is essential in metabolism, so is present in animal waste.
Therefore, phosphate runoff can be an issue in waters near cattle feedlots, hog farms, dairies, and barnyards.
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Development/Paved Surfaces
Development can cause soil erosion, which will release phosphorus.
If swamps and wetlands are drained for development, phosphorus that was buried can be exposed.
During the building phase, and after everything has stabilized, phosphorus concentrations in stormwater can increase because natural filters such as trees, shrubs, and puddles have been eliminated.
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Industrial Discharge
Polyphosphates are often added to water to prevent iron oxides or calcium carbonates from forming.
If this water is released to streams or lakes, polyphosphates can enter the water body, and will convert to orthophosphate.
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Phosphate Mining
Phosphate mining, concentrating, and processing are sources of phosphate to rivers in some areas.
The most common phosphorus-containing mineral is apatite (Ca5F(PO4)3).
There are no significant sources of phosphate minerals in the Boulder Creek Watershed, so this is not a problem in our area.
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Drinking Water Treatment
Small amounts of orthophosphates or certain polyphosphates are added to some water supplies during treatment.
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Forest Fires
Forest fires can cause soil erosion, which will release phosphorus bound to soil particles.
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Synthetic Materials
Organophosphates are commonly used as construction materials, flame retardant and
plasticizers.
Reduced forms of phosphorus are present in certain synthetic organic chemicals, including some that are used in insecticides.
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Water Quality Standards and Other Criteria Regarding Phosphorus
No national or state criteria have been established for concentrations of phosphorus compounds in water.
However, to control eutrophication, the EPA makes the following recommendations: total phosphate should not exceed 0.05 mg/L (as phosphorus) in a stream at a point where it enters a lake or reservoir, and should not exceed 0.1 mg/L in streams that do not discharge directly into lakes or reservoirs (Muller and Helsel, 1999).
Phosphate levels greater than 1.0 mg/L may interfere with coagulation in water treatment plants. As a result, organic particles that harbor microorganisms may not be completely removed before distribution.
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