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This is a method of using chemicals and chemical reactions in the water treatment process.
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If the water has a high turbidity, it shows that it contains a lot of organic matter and plankton, then use alum and coagulants to condense impurities.
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Water containing a lot of metal ions (high hardness) is treated with lime, soda or ion exchange method. Water containing a lot of H2S toxins is treated by oxidation, chlorination, alum method.
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Water containing a lot of bacteria must be disinfected with compounds containing chlorine, ozone.
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Water containing Fe must be oxidized with air oxygen (to ventilate the rain rack) or use oxidants to treat...
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The low alkalinity of the water makes the coagulation process difficult, the water has a taste and smell, so it must be alkalized with ammonia (NH3). After carbonization, preliminary chlorination, then add KMnO4.
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Water with a lot of dissolved oxygen must be treated by using reducing agents to bind oxygen. These are hydrazine, sodium thisulfate…
In general, chemical treatment methods are often highly productive and effective.
3. Biological treatment
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In the world today, the method of water treatment using microorganisms is being researched and has been applied in some places. In this method, some special types of microorganisms have been cultivated and introduced into the water treatment process with very small doses but with high efficiency.
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However, up to now, the research results of this method have not been widely published. Depending on the water source as raw material for different fields, people have used different methods to treat water supply for that field. Usually, people combine both mechanical and chemical methods to treat water.
1. Introduction to ultrafiltration membrane technology:
1. Introduction to ultrafiltration membrane technology:
UF membrane, also known as hollow fiber ultrafiltration membrane, the filtration process will allow water to pass from the outside to the inside of the hollow fiber thanks to the water flow pressure. This is considered an important water filtration technology used to produce highly purified water.
UF membranes are effective in removing colloids, proteins, bacteria and organic molecules larger than 0.01 microns.
2. Structure of UF ultrafiltration membrane module
UF ultrafiltration membrane is a combination of hollow fibers made of PVDF (PolyVinyliden DiFloride) material with extremely small filter pore size of 0.01 micron. The application of UF membrane in water treatment system design has brought:
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Excellent filtration performance with high and stable flux.
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The ability to remove many types of bacteria/viruses has been proven through many practical projects.
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Reasonable investment cost.
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The size of the system is compact, the structure is simple so it does not take up installation space.
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The filtration process takes place at normal temperature and low pressure so it consumes little electricity.
3. Operating principle of UF ultrafiltration membrane
UF membrane filter works on the mechanism of water molecules movement, thanks to external pressure creating a strong flow (can be called the separation process in the water stream in normal environment due to pressure). At that time, it will push chemical components, metals, impurities in water to low pressure areas or flow out with the water through the drain. Elements with size > 0.01 micron will be retained.
III. TREATMENT OF WATER CONTAMINATED WITH AMMONIUM AND NITRATE
1. Ammonium removal
1.1. Method of chlorinating water to the point of mutation
When chlorine is added to water, hypochlorite acid is produced in the water
Cl2 + H2O ⇔ HCl + HOCl
Hypochlorite acid combines with NH4+ to form Chloramine. When the water temperature is ≥200C, pH ≥7, the reaction occurs as follows:
OH- + NH4+→ NH4OH ⇔ NH3 + H2O
NH3 + HOCl → NH2Cl + H2O monochloramine
NH2Cl + HOCl → NHCl2 + H2O dichloramine
NHCl2 + HOCl → NCl3 + H2O trichloramine
The process ends after 3 minutes of gentle stirring. At the point where all the chlorine is oxidized and free chlorine appears in the water, this is called the mutation point. After removing all the NH4+ in the water, there is a large amount of residual chlorine left, which must be removed before supplying to consumers.
Remove residual chlorine in water after filtration with Natrisulfite (Na2SO3)
Na2SO3 + Cl2 + H2O → 2HCl + Na2SO4
Remove residual chlorine in water after filtration with Trionatrisulfite (Na2S2O3)
4Cl2 + Na2S2O3 + 5H2O → 2NaCl+ 6HCl + 2H2SO4
The process is complete after 15 minutes of stirring the chemicals and water evenly
1.2. Ventilation method
To remove NH4+ from water by aeration, the pH of the source water must be raised to 10.5 - 11.0 to convert 99% of NH4+ into NH3 gas dissolved in water.
Raising the pH of raw water: To raise the pH of raw water to 10.5 - 11.0, lime or caustic soda is often used. After the filter tank, acid is mixed into the water to bring the pH from 10.5 - 11.0 down to 7.5
The NH3 aeration tower is usually designed to remove ammonia gas with an input concentration of 20 - 40 mg/l, the output from the system has a remaining concentration of 1 - 2 mg/l, so the degassing efficiency of the tower must reach 90 - 95%. The NH3 degassing efficiency of the aeration tower when pH ≥11 depends a lot on the water temperature. When the water temperature increases, the speed and quantity of NH4 ions converted to NH3 increase rapidly.
1.3. Ion exchange method
To remove NH4+ from water, the method of filtering through a cationite filter tank can be applied. Through the cationite filter tank, the filter layer will retain NH4+ ions dissolved in water on the surface of the beads and add Na+ ions to the water. To remove NH4+, the pH of the source water must be kept greater than 4 and less than 8. Because when pH ≤ 4, the cationite filter beads will retain both H+ ions, reducing the efficiency of NH4+ removal. When pH > 8, a part of the NH4+ ions will convert to NH3 in the form of dissolved gas, which has no effect on the cationite beads.
1.4. Biological method
Filter the water that has been removed of iron and dirt through a slow filter tank or a rapid filter tank, blowing air continuously from bottom to top. Due to the activity of Nitrosomonas bacteria, NH4+ is oxidized into NO2- and Nitrobacter bacteria are oxidized into NO2-. The process takes place according to the equation:
NH4+ + 2O2 → NO3- + 2H+ + H2O
1.02NH4++ 1.89O2 + 2.02HCO3- → 0.21C5H7O2N + 1.0NO3- + 1.92 H2CO3 + 1.06H2O
2. Nitrate NO3 reduction
To remove nitrate, use reverse osmosis filtration, electrolysis, ion exchange in ionit filter tanks.
Conditions for applying ion exchange method
Water has residue content < 1mg/l.
The total content of NO3-, SO42- and Cl- ions available in water must be less than 250 mg/l, which is the maximum allowable Cl- ion content in drinking water. Because when filtered through anionit filter tank, SO42-, NO3- ions are retained, replaced by Cl- ions when regenerating the anionit filter tank with salt solution.