1. Course TEN-702 Industrial waste management unit-2
Lecture -12

2. Industrial Wastewater Treatment
Physical/chemical treatment
Biological treatment
Thermal treatment
Treatment needed will depend on the type and
concentration of pollutants in the wastewater

3. Rapid Mixing Used to blend chemicals and water being treated
Retention time from sec.
Mechanical mixing using vertical-shaft impeller in tank with baffles
(Source: Water Supply and Pollution Control, 5th
ed. W. Viessman, Jr. and M.J. Hammer, Harper Collins
College Publ. 1993)

4. Rapid Mixing

5. Coagulation and Flocculation
Goal: To alter the surface charge of the particles that contribute to color and turbidity so that the particles adhere to one another and are capable of settling by gravity

6. Colloids Small particles (0.001 to 1 m) Usually negatively charged
Particles repel so suspension is considered stable

7. Coagulation and Flocculation+
Coagulation (process) + +
Colloidal particles
( m)
floc
( m)

8. Coagulant Non-toxic and relatively inexpensive
Insoluble in neutral pH range - do not want high concentrations of metals left in treated water
Concentration

9. Coagulants Alum: Al2(SO4)3.14H2O Ferric chloride: FeCl3
Ferric sulfate: FeSO4
Polyelectrolytes

10. How does alum work? Al2(SO4)314H2O  2Al3++ 3SO42-+ 14H2O
2Al3+ + colloids  neutralize surface charge
2Al3+ + 6HCO3-  2Al(OH)3(s) + 6CO2
If insufficient bicarbonate is available:
Al2(SO4)314H2O  2Al(OH)3(s) + 3H2SO H2O
Optimum pH: 5.5 to 6.5
Operating pH: 5 to 8

11. Flocculation Paddle units rotate slowly, usually <1 rpm
Velocity of water: ft/sec
Detention time of at least 20 min
(Source: Water Supply and Pollution Control, 5th
ed. W. Viessman, Jr. and M.J. Hammer, Harper Collins
College Publ. 1993)

12. Flocculation

13. Assignment-4
Discuss the effects of mixing on coagulation and flocculation process in detail.

14. Thanks!
In next lecture we will discuss sedimentation and chemical treatment