Flocculation

Flocculation

1. Flocculation Flocculation is a process of down stream processing, falls in the category of isolation of insolubles . Various stages of processing occur after the completion of fermentation or bioconversion stage is known as downstream processing.

2. Flocculation Aggregation of micro flocs . C ells, are kept apart in a suspension via electrostatic repulsion, due to negative charges on their surface. One key area for flocculation is within centrifugations by density differences. Fast and well defined separation due to Larger aggregation of cells-diameter

3. Larger flakes __ block filters__ cake formation. Flocculating agents: ionic compounds such as aluminium sulfate and ferric chloride. Fitting of cells is difficult due to varing shape__high molecular weight polymer bridges used.

4. Bridge flocculation The polymers act to form bridges between different particles, one part of the polymer becomes attached to one or several adsorption sites and the other part extends into t he bulk solution. The extended loops and tails can be adsorbed by other particles thus forming bridges between particles.

5. Rate of aggregation The rate of aggregation will depend on followings: probability of collisions between particles, probability of attachment during such collisions probability of detachment of particles from the aggregates subsequently.

6. Example Flocculation in dirty water Some organic particles and some inorganic Turbidity

7. Flocculation mechanism: Principle: Removal of Hydrophobic Colloids from the Aqueous Phase.

8. Flocculation mechanism: Flocculants, with their very high molecular weights (long monomer chain ) and their charge content, fix the destabilized particles and aggregates along the polymer chain. During the flocculation step, an increase in the size of the particles present in the water phase resulting in the formation of flocs . The type of bonds between the destabilized particles and the flocculant are mainly ionic bonds and hydrogen bonds.

9. Flocculation mechanism:

10. Flocculants: Amongst the 800 different flocculants of the FLOPAM™ Range, two main categories of flocculants can be distinguished: 1 - Anionic and Non-Ionic flocculants that bring negative (-) charges to the media. 2 - Cationic flocculants that bring positive (+) charges to the media.

11. Conti……… ● Anionic flocculant  for mineral particles Acrylamide + Acrylic Acid + Caustic  Anionic polyacrylamide A nionic charge (-) ● Cationic flocculant  for organic particles Acrylamide + Chloro-methylated monomer  Cationic polyacrylamide C ationic charge(+)

12. FACTORS AFFECTING FLOCCULATION Several factors can affect flocculation, primarily polymer type ionic strength pH S lurry solids F locculant dilution Molecular weight Process conditions.

13. Conti……. These factors, individually and collectively, have a great influence on the type of flocculant that will provide optimum performance, its optimum dose, and addition points.

14. pH As the pH of the system ranges from 0 to 14, the choice of flocculant ranges from nonionic to highly anionic. At a pH of 4 and below, nonionic polymers show the greatest activity

15. MOLECULAR WEIGHT Higher molecular weight flocculants are generally more viscous and are not easily distributed through the slurry. Since adsorption is very rapid and usually irreversible, a loss in activity results.

16. SLURRY SOLIDS When a fully activated flocculant is added to a slurry adsorption takes place rapidly. It is important that the flocculant is well dispersed throughout the slurry. when the particle size decreases and the solids concentration increases, flocculant demand increases.

17. FLOCCULANT DILUTION A significant improvement in performance can be achieved by changing the dilution at which the flocculant is added to the slurry. By diluting it, the distribution of the flocculant in the slurry improves, thereby improving performance.

18. Applications Waste water management. Harvesting of micro algae to produce Biofuel. Brewing of Beer. Removing inorganic particles from waste streams etc. Simplicity and cost-effectiveness Separates many kind of particles from water Enhances filtration process Uses abundant and low cost chemical

19. Disadvantages Input of chemicals required. Qualified personnel required for design (e.g. construction of chambers and dosage of chemicals) and system maintenance. Relatively time consuming process