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Homework Coagulation and Flocculation
Instructions: Answer the questions inline below. Save the document with your last name in the file name. Submit the assignment through WebCT. See the instructions on the course website ().
1. Which type of water is likely to require coagulation and flocculation?
2. What types of impurities are removed by coagulation and flocculation?
3. What are examples of colloidal solids?
4. What is the difference between coagulation and flocculation?
5. What is the most frequently used coagulant? Give name and chemical formula.
6. Define alkalinity.
7. What is the (a) typical mixing time, and (b) minimum detention time for flocculation?
8. What is the advantage of having vertically suspended flocculation paddles rather than horizontal ones?
9. What is the most important consideration in controlling the success of the coagulation-flocculation process?
10. How does proper coagulation procedure help insure adequate disinfection?
11. What water quality parameters are measured (with meters or with lab tests) to monitor the coagulation-flocculation process?
12. What would you look for when visually observing the performance of a coagulation-flocculation process?
13. What could cause the performance of coagulation-flocculation systems to vary over the course of a day?
14. How do you calculate detention time?
15. A water treatment plant has a total daily flow-through of 2.8 MGD, or 2,800,000 gallons/day. The flocculation basin has 3 sections, but its total length is 48’ long. It is 10’ deep and 15’ wide. Calculate the detention time in minutes.
16. Give the definition of a jar test, including (a) why it is done, and (b) roughly how it is done.
17. When you apply jar test results to calculate the lbs/day of alum needed, what conversion factor do you need to use when going from mg/L of coagulant when your flow is in MGD?
18. You have just performed a series of jar tests, and your results indicate that the best dosage is 11 mg/L of alum. How many lbs/day do you need to deliver to the system if your water flow is 2.9 MGD?
19. Why do you have to be sure that you add enough alum (or other trivalent salt)?
20. Are cationic polymers or anionic polymers more likely to be the primary coagulant?
For the next few questions, refer to your chemistry text by Sarai.
21. Why are trivalents salts, such as of aluminum or iron, used to create a precipitate floc, instead of monovalent or bivalent salts?
22. Adding a trivalent salt is one way to precipitate colloids (cause flocculation). List two other methods.