Page 273 - Water and wastewater engineering

6-50 WATER AND WASTEWATER ENGINEERING

4. Sketch a particle showing the charge of the Helmholtz layer and the diffuse layer.

5. Sketch the family of zeta potential curves under the influence of increasing ionic
strength.
6. Sketch the family of zeta potential curves under the influence of increasing cationic
charge of a coagulant.
7. Explain the Schulze-Hardy rule and why it is seldom achieved in natural waters.
8. Explain the physics of coagulation using the four mechanisms of coagulation.

9. Explain why the jar test is conducted in two steps.
10. Explain the purpose of enhanced coagulation and select appropriate coagulant(s) from
a list.
11. Given a set of chemicals chosen for coagulation, select the order of addition.
12. In terms of the physics of coagulation, explain the difference between adsorption/
destabilization and sweep coagulation.
13. From a list of mixing devices select appropriate mixers for either adsorption/
destabilization or sweep coagulation.
With the use of this text, you should be able to do the following:

14. Estimate the alkalinity consumed by the addition of alum or ferric chloride to water
with varying amounts of alkalinity including no alkalinity.

15. Estimate the pH from the addition of coagulant given the alkalinity.
16. Given the alkalinity, estimate the amount of base to neutralize an excess of coagulant
over the available alkalinity.

17. Determine the optimum dose of coagulant from jar test data.
18. Select the appropriate coagulant and mixer system from jar test data.
19. Design an in-line blender, a static mixer, and a mechanical mixer in a stirred tank.

20. Design a baffle wall for a flocculation tank.
21. Design a vertical turbine mixer for flocculation or a paddle flocculator.

6-10 PROBLEMS
6-1. What is the “exact” alkalinity of a water that contains 0.6580 mg/L of bicarbonate, as
the ion, at a pH of 5.66? No carbonate is present.
6-2. Calculate the “approximate” alkalinity (in mg/L as CaCO 3 ) of a water containing 120
mg/L of bicarbonate ion and 15 mg/L of carbonate ion.
6-3. Calculate the “exact” alkalinity of the water in Problem 6-2 if the pH is 9.43.