The city of Ten Sleep proposes to use Crater Lake for its water supply. The plan

Question

The city of Ten Sleep proposes to use Crater Lake for its water supply. The plan is to treat 3,500 m'/d by direct filtration. The first customer is adjacent to the plant. The raw water analysis is shown below. The city council is concerned about safety and the lack of skilled operating personnel. The available space at the site is restricted. 1. Determine the total removal/inactivation required. 2. Determine the credits for physical removal. 3. Determine the credits required for inactivation by disinfection. 4. Select the primary disinfectant. 5. Determine the required Ct to achieve the required inactivation for the design con- ditions (pH, temperature) Crater Lake water analysis Constituent Concentration Raw Water TOC Bromide Turbidity Giardia cysts Virus Cryptosporidium oocysts Treated Water Turbidity pH Temperature Not detected

Explanation / Answer

1. a) At least 99.9% (3-log) removal and/ or inactivation of Giardia lambia cysts

b) At least 99.9% (4-log) removal and/ or inactivation of viruses

c) At least 99% (2-log) removal of cryptosporidium

2. Maximum logs of credits for physical removal

a) Cryptosporidium = >2

b) Giardia = 2

c) Viruses = 1

3. Minimum logs of inactivation needed by disinfection

a) Giardia =1

b) Viruses = 3

4. Select CHLORINE as the primary disinfectant

5. Ct value required for pH=7.5 and temp= 5 and for 1cyst/100L is 175.

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