coagulation environmental microbiology.pptx

environmental microbiology

1. Coagulation is a water treatment process that destabilizes suspended particles in water, causing them to clump together. To prepare water for subsequent filtration by making the suspended particles easier to remove. Settling velocities of various sizes particle 1

2. Charge system in a colloidal suspension which shows the reduction of thickness in diffused layer Electrical Double layer of charged colloid (Ryan and Elimelech  1996 ) 2

3. The force field between colloids of like charge is governed by a combination of attractive and repulsive forces, including:  Van der Waals forces Electrostatic forces Repulsive interaction between similarly charged electrical double layers  Attractive depletion force Repulsive electrostatic force force field between colloids of like charge 3

4. Coagulation theory The four types of coagulation systems are:  ionic-layer compression Adsorption and charge neutralization sweep flocculation interparticle bridging 4

5. Ionic-layer compression An example of ionic layer compression occurs in nature when a turbid stream flows into the ocean. There the ion content of the water increases drastically and coagulation and settling occur. Ionic-layer compression: reduction of thickness and net force 5

6. Adsorption and charge neutralization Adsorption and charge neutralization are key processes in water treatment. Adsorption removes contaminants by trapping them on a solid surface, while charge neutralization reduces the repulsive forces between particles, allowing them to clump together and settle out. Together, they effectively remove impurities and enhance water clarity and quality. 6

7. Sweep coagulation The last product formed in the hydrolysis of alum is aluminum hydroxide, Al(OH) 3 . The Al(OH) 3 , forms in amorphous, gelatinous flocs that are heavier than water and settle by gravity. Colloids may become entrapped in a floc as it is formed, or they may become enmeshed by its "sticky" surface as the flocs settle. The process by which colloids are swept from suspension in this manner is known as sweep coagulation. 7

8. Interparticle Bridging Interparticle bridging is a process in water treatment where large molecules, like polymers, bind multiple particles together, forming bridges. These bridges create larger aggregates or flocs by connecting suspended particles. This enhances the settling and removal of contaminants, improving the efficiency of water clarification processes. Interparticle Bridging with polymers 8

9. Jar Test for Optimum Coagulant Dosage Jar test determines the optimum coagulant dosage for water treatment. By adding different coagulant amounts to water samples in jars, we observe floc formation, settling rates, and clarity. This process identifies the most effective dosage for removing suspended particles, improving water quality, and optimizing chemical usage and costs. 9

10. Result of jar test at increasing turbidities Coagulant Dosage as function of turbidity 10

11. Rapid Mixing Rapid mixing in coagulation is the initial phase where chemicals (coagulants) are quickly and uniformly dispersed in water. This process ensures that the coagulants interact effectively with impurities, forming small particles or flocs. Effective rapid mixing is crucial for subsequent coagulation and flocculation stages in water treatment. Typical Rapid mixing tanks 11

12. Flocculation Flocculation is a water treatment process where small particles, or flocs, aggregate into larger clusters or "flocs" due to the addition of flocculants. This phase follows coagulation and involves slow mixing to promote the formation and growth of these flocs, which are then easier to remove. flocculation process relies on turbulence to promote collisions. Velocity gradients are also a convenient way of measuring this turbulence. Time is an important factor, and the design parameter for flocculation is Gt, a dimen - sionless number. Values of Gt from 10 4 to 10 5 are commonly used, with t ranging from 10 to 30 min. Large G values with short times tend to produce small, dense flocs, while low G values and long times produce larger, lighter flocs. Since large, dense flocs are more easily removed in the settling basin, it may be advan - tageous to vary the G values over the length of the flocculation basin. The small, dense flocs produced at high G values subsequently combine into larger flocs at the lower G values. 12

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14. We know Substituting the value of P in above equation, we get 14

15. Clariflocculator A clariflocculator is a combined unit used in water treatment that integrates both flocculation and clarification processes. It mixes coagulants with water to form flocs, then allows these flocs to settle out as clear water rises to the surface, optimizing space and efficiency in water purification systems. 15

16. Softening Softening is a water treatment process that removes or reduces hardness caused by calcium and magnesium ions. Softened water improves the effectiveness of soaps and detergents and prevents scale buildup in pipes and appliances. Different method involved in softening of water are Chemical Precipitation, Ion Exchange , Recarbonation etc. 16