About Fecal Coliform Testing

[eps1lon]

Hi,
Recently i have sent a water sample to the lab. The lab conducted the Fecal Coliform test by membrane filtration technique. The result of the test was Negative(no golden/green sheen found) but it was mentioned that some bacteria was present & the agar color had been changed to pink. So, what can we conclude from the result? Is the water is safe?

 

[IRstuff]

Are the pink actual colonies?

https://www.scienceprofonline.com/m...tial-selective-bacterial-growth-medium-2.html

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[bimr]

If Coliform bacteria (sometimes reported as Total Coliform) are found in your water, it is an indication that disease-causing bacteria could get in the water system the same way.

Investigate the water system for problems to determine the source of bacteria. Fix the problem, then shock chlorinate. Test the water again before using the water.

If the water system was not disinfected after recent work on the water system, this may be your source of bacteria. Shock chlorinate your water system and test the water again.

The water sample may have been contaminated when it was collected. Common problems include: (a) A hose, aerator screen, filter or other attachment on a faucet. (b) Accidentally touching the inside of the lid or the top of the bottle. (c) Not running the water 35 minutes before collecting it. Carefully collect another sample and retest. Use rubbing alcohol on a clean paper towel to wipe the faucet before letting the water run for 3-5 minutes.

Make sure there is no way for surface water to enter your drinking water system.

 

[eps1lon]

@bimr Yes, You're right. What should be the chlorine concentration for shock chlorinating? And How how long the chlorinated water should be kept in the system?

 

[bimr]

What type of system? Well or whatever?

 

[eps1lon]

We use an elevated Reservoir to store water & from the reservoir water is distributed through Pipes

 

[bimr]

It should be part of your project specification.

Something like this:

Proper and effective shock-chlorination procedure requires:
1. A dosage of 50 to 200 ppm of free chlorine evenly distributed throughout the piping and fixtures.
2. Testing of the residual to verify that the levels are present at the fixtures and hose bib or valves sections.
3. Contact time with the piping, undisturbed for 12 hours.
4. Retesting of the chlorine residual after 12 hours.

If the chlorine residual is less than 10 ppm after 12 hours, repeat the entire procedure above. If the beginning dose is 50 to 100 ppm and the remaining residual after 12 hours is less than 10 ppm, this indicates severe bio-fouling or large amounts of dirt or slime present.

 

[eps1lon]

Thank you bimr for your recommendation. We normally use 30ppm of chlorine dosage & maintain a contact time of 12h. I'll give a try according to your recommendation.