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The course of coagulation using all types of coagulants is strongly influenced by water temperature.
To get the same effect at a low temperature of the coagulant dose was necessary to increase by almost half. When reducing the turbidity of the water affects the temperature effect to a lesser degree.
In some cases, treatment coagulants few cloudy colored water for good flocculate advisable to increase the turbidity of water. This can be done artificially cloudy water by adding to it a suspension of clay, the dose which is selected experimentally.
A similar result can be achieved by recycling previously precipitate, i.e., pumping sludge from septic tanks or clarifiers from coming in to clean up the water.
As a coagulant, as mentioned above, is also used iron salts. When dissolved in water, sulphate, ferrous iron dissociates with the formation of ferrous iron cations, which participate in ion exchange with cations adsorbed layer of colloidal particles of dirt, and excess of iron sulfate is hydrolyzed.
In case of insufficient water pH or lack of dissolved oxygen in water, iron may remain in the water, leaving the sewage treatment plant. To create a specified pH value of water in all cases, the natural water purification must alkalize water, while the application of aluminum sulfate alkalinization produced only during periods of insufficient alkalinity.
With a lack of dissolved oxygen in water, iron can be oxidized by chlorination.
The disadvantage of ferrous sulphate as coagulant is a need to raise water pH alkalinization and providing conditions for the oxidation of ferrous iron.
Ferric chloride, ferric iron sulfate and chlorinated copperas may be used without alkalizing water if the pH after adding a coagulant is not below 5-5.5.
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