coagulation and flocculation
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The document discusses coagulation, which is a process used in water treatment plants to remove fine particles from water. Coagulants such as aluminum sulfate, ferric chloride, and polymers are added to water to combine fine particles together and form larger clumps or flocs that are then removed by sedimentation. Common coagulants include aluminum sulfate, ferrous sulfate, chlorinated copperas, and magnesium carbonate. Aluminum sulfate is the most widely used coagulant. The coagulation process occurs in basins containing chambers for inlet, coagulant feeding and mixing, flocculation, sludge removal, and clear water collection.
![CHLORINATED COPPERAS
Hydrated Ferrous Sulphate FeSO4.7H2O is traditionally referred to as Copperas. It has too high
solubility to act as satisfactory coagulant . It is therefore, first oxidized to Ferric Sulphate
[Fe2(SO4)3] and Ferric Chloride (FeCl3) by mixing its solution with a feed from chlorinator the
.6FeSO4.7H2O + 3Cl22Fe (SO4)3+ 2 FeCl3+ 7H2OFe2(SO4)3and FeCl3, produced instantaneously
are called chlorinated Copperas .
.Fe2(SO4)3effective pH 4 to 7 and >9FeCl3. it is effective over pH value 3.5 to 6.5 and >8.5The
combination has therefore proved to be very effective coagulant for treating low pH water](https://image.slidesharecdn.com/7-170819222604/85/coagulation-and-flocculation-9-320.jpg)
coagulation and flocculation
- 2. COAGULATION The very fine suspended particles and the colloidal matter present in water can not be settled in plain sedimentation tank. So they need special treatment to remove, for this purpose certain chemicals compound called coagulants are added to water, which on thorough mixing form a gelatinous precipitated called folc. The process of addition and mixing of chemicals is called coagulation. In addition to removing turbidity from water , coagulation and flocculation is beneficial. In other ways the process to remove many bacteria which are suspended in the water and can be used to remove color from water. The coagulation before sedimentation is almost universally adapted in all the major water treatment pant and is followed by rapid sand filtration.
- 4. COMMON COAGULANTS The coagulants like aluminum sulphate (Alum), ferrous sulphate etc carry positive charge and attract negatively charged colloidal particles of clay, turbidity, and color. Thus helping in the removal of these impurities from water. Following are common coagulants: 1. Aluminum sulphate 2. Ferrous sulphate 3. Chlorinated copperas 4. Magnesium carbonate 5. Poly electrolytes 6. Ferric chloride 7. Sodium aluminate etc
- 5. ALUMINUM SULPHATE This is most common and universal coagulant used in water works. Its chemical composition is Al2(SO4)3.18H2O. It requires the presence of alkalinity in water to form flux. Many water have bicarbonate alkalinity naturally in them. When dissolved in water aluminum sulphate tends to hydrolyze into aluminum hydrolyze as is evident from following reactions Al2(SO4)3 18H2O+3Ca (HCO3)= 2Al( OH3)+3CaSO4+18H2O+6CO2 If Natural alkalinity in water is insufficient to react with alum , lime is also added to water to form calcium hydrodoide Ca(OH)2 Or hydrated lime which reacts with Alum as follows Al2(SO4)3 18H2O+3Ca(OH)2=2Al( OH3)+3CaSO4+18 H2O
- 6. ALUMINUM SULPHATE Sometimes sodium carbonate known as soda ash is added to form alkalinity the resulting reactions are Al2(So4)3 18H2o+3Na2co2 = 2Al(OH)2+3NaSo4+3cO2+18H2O though soda ash does not cause hardness , it is expensive than lime and is found to be effective when ph value of water varies from 6.5 t0 8.5. Its dose depends upon turbidity , color , taste, ph value and temperature of water . The dose of alum varies between 10 t0 30mg per dm3 of water . Alum is preferred over other coagulants because it reduces taste and odour etc effectively. It is cheap and floc formed is quite tough to be broken easily. It produce crystal clear water. The main disadvantage of alum is that it is difficult to dewater sludge formed.
- 8. FERROUS SULPHATE Ferrous or copperas can react with naturally calcium carbonate and alkalinity in water but this is very much delayed one , hence lime is used with ferrous sulphate and the following reactions take place. Fe(SO4) 7H2O+ Ca (OH)2= Fe(OH)2+ Caso4+ 7H2O The ferrous hydroxide is satisfactory gelatinous floc , which is heavier than one formed by Alum. The effective Ph range for this is 8.5 and above. Ferrous sulphate is not suitable for soft colored water.
- 9. CHLORINATED COPPERAS Hydrated Ferrous Sulphate FeSO4.7H2O is traditionally referred to as Copperas. It has too high solubility to act as satisfactory coagulant . It is therefore, first oxidized to Ferric Sulphate [Fe2(SO4)3] and Ferric Chloride (FeCl3) by mixing its solution with a feed from chlorinator the .6FeSO4.7H2O + 3Cl22Fe (SO4)3+ 2 FeCl3+ 7H2OFe2(SO4)3and FeCl3, produced instantaneously are called chlorinated Copperas . .Fe2(SO4)3effective pH 4 to 7 and >9FeCl3. it is effective over pH value 3.5 to 6.5 and >8.5The combination has therefore proved to be very effective coagulant for treating low pH water
- 10. Polyelectrolytes: These are mostly used to assist the flocculation process and are often called flocculation aids. They are polymeric organic compounds of long polymer chains that act to enmesh particles in the water. Polyelectrolytes can be cationic (carrying a positive charge), anionic (carrying a negative charge) or non-ionic (carrying no net charge). This coagulant removes both temporary and permanent hardness and is effective for Ph range of 6 t0 8.5 naturally available in water. Ferric chloride: (FeCl3) is commonly used as a coagulant. When added to water, the ion precipitates as ferric hydroxide (Fe(OH)3) and the hydroxide flocs enmesh the colloidal particles in the same way as the aluminium hydroxide flocs do. The optimum pH for precipitation of iron is not as critical as with aluminium and pH values of between 5 and 8 give good precipitation.
- 11. POLYMERS : Polymers long-chained, high-molecular-weight, organic chemicals--are becoming more widely used, especially as coagulant aids together with the regular inorganic coagulants. Anionic (negatively charged) polymers are often used with metal coagulants. Low-to-medium weight, positively charged (cationic) polymers may be used alone or in combination with the aluminum and iron type coagulants to attract the suspended solids and neutralize their surface charge. The manufacturer can produce a wide range of products that meet a variety of source-water conditions by controlling the amount and type of charge and relative molecular weight of the polymer. Polymers are effective over a wider pH range than inorganic coagulants. They can be applied at lower doses, and they do not consume alkalinity.
- 12. CHAMBERS OF COAGULANT BASIN Inlet chamber: water is allowed to enter coagulant tank through it. Feeding device: the selected coagulant is added to water by feeding device. Mixing device: there are many types of Mixing device. A suitable one is adapted for mixing operation. Generally the device consist of paddles , which are rotated by deriving unit. The paddles go on rotating continuously and coagulant are mixed in this way. Flocculation chamber: in this chamber the mixture of water and coagulant is detained for some period or it is allowed to flow in very low velocity so that the floc may be formed and get settled down by arresting the suspended particles . Thus sludge is deposited at bottom of coagulant chambers.
- 13. CHAMBERS OF COAGULANT BASIN Sludge removal: at the time of removal the sludge is agitated by scrappers fixed with rotating arms which are operated by deriving unit. The sludge is taken off through the sludge removal pipe by opening the valve. Collection of clear water: the clear water from top is collected in a draw off chamber from where it is taken to the next unit through the outlet pipe.