Disinfection

Question 1

How is the efficiency of a disinfectant measured?

Answer 1

Measured by the time(T) in minutes of the disinfectant’s contact in the water and the concentration(c) of the disinfectant residual in mg/L measured at the end of the contact time

Question 2

When a new well is completed, why is it necessary to disinfect the well, pump, screen, piping, and the aquifer accessed by the well?

Answer 2

All could have been contaminated during construction

Sodium hypochlorite for well and aquifer

Question 3

What are the advantages of disinfecting a well by applying chlorine through the pump column pipe rather than through the vent pipe?

Answer 3

Organic matter such as oil may be used during drilling and may end up floating on the water surface. Therefore, if the well is disinfected by injecting the chlorine solution via ventpipe, the chlorine solution should have a higher initial concentration. Less of a concentration is required using the pump column pipe.

Question 4

How would you determine if a well has been successfully disinfected?

Answer 4

If the results of a bacteriological analysis for Total coliform are NEGATIVE

Question 5

How can water mains be kept clean during construction or repair?

Answer 5

*Keep outside materials out of main being installed/repaired
*Inspect interior of all pipes for cleanliness when laid in trench
*Keep trench dry or dewatered
*Install water tight plugs on all open-ended joints

Question 6

Before a water main is disinfected, how long should the main be flushed and what flushing velocity should be used?

Answer 6

30 mins and at least 2.5ft/s

Question 7

What areas in a water main require special care for successful disinfection?

Answer 7

Fittings and valves

Air pockets should be eliminated

Question 8

List 3 forms of chlorine commonly used for disinfection

Answer 8

Chlorine Gas
Calcium Hypochlorite
Sodium Hypochlorite

Question 9

What precautions should be taken when disposing of water with a high chlorine residual?

Answer 9

Greater than 1mg/L DO NOT dispose in a manner that will cause an adverse impact on the environment
*Sanitary sewers - enough dilution/travel time so NO Cl residual when reaches treatment plants
*Storm Sewer - NO cl residual - toxic to fish and aquatic life
*Land - may be acceptable if percolation rates are high and there are no nearby wells pumping groundwater

Question 10

List the major parts of a typical hypochlorinator system

Answer 10

*Chemical solution tank for hypochlorite
*pump
*power supply
*water pump
*pressure switch
*water storage tank

Question 11

What are the 2 common methods of feeding hypochlorite to the water being disinfected?

Answer 11

1. hypochlorite solution may be pumped directly into water
2. hypochlorite solution is pumped through ejector (injector), which draws in additional water for dilution of the hypochlorite solution

Question 12

How is the rate of gas flow in a chlorinator measured?

Answer 12

The gas passes through a spring-loaded pressure regulating valve

A rotameter is used to indicate the rate of gas flow

Question 13

What is the primary advantage of vacuum system chorinators?

Answer 13

Dampens fluctuations and gives smoother operation

Primary advantage is SAFETY

Prevents chlorine from escaping into surrounding atmosphere in the event of failure

Question 14

List 2 major types of chlorine feeders

Answer 14

Hypochlorinators - feed liquid chlorine solutions

Chlorinators - feeds gaseous chlorine