Water Recirculation - Drinking Water Storage Tanks

[marc5000]

I have a question regarding water recirculation. Let me explain the circumstances and maybe someone has a solution or suggestion.

We'll be getting our potable water from the municipality but it's likely going to be of questionable quality so we'll be treating incoming water via osmosis and chlorine. We'll be storing the treated water in storage tanks and based on the use of the occupants the retention of the water in the tanks will likely be approximately two weeks. Currently, the water network has not been designed with recirculation.

Questions:

1) With a retention time of two weeks is recirculation justified? Does anyone know of any sources of info?

2) Normally how long can treated water be stored before residual chlorine levels deplete to below acceptable levels?

 

[eddieng27]

Wow. That would be poor potable water quality if you have to retreat it via osmosis ... hope you're not paying much for it. Seem as though the original purveyor should improve their treatment. Water age is not necessarily a direct link to seriously degraded quality, but it's an indicator of potential problems. AWWA has a good publication out (a decade or so ago) that discusses circulating water in tanks. Since you have an existing tank, retrofitting it for better circulation is at least somewhat problematic and might not prevent quality degradation. It sounds like your system is rather small, but EPA is requiring water providers to study water quality in the distribution system. Modeling water quality is tricky and first requires a functioning and rather accurate hydraulic model that has been satisfactorily calibrated to reflect the conditions within your system. Then you will need to create another scenario for your system to model the water quality. In order to calibrate the hydraulic model to adequately predict quality, you will need to choose a series of sampling points and evaluate the results and adjust the model with those parameters. I highly suggest that you solicit the assistance of a qualified engineer to help you in this endeavor.

 

[bimr]

A storage time of 2-3 days would probably be the ideal. You have much more than that.

You proably want to maintain a free chlorine residual of at least 0.2 to 0.4 mg/l to maintain bacteriological control of the water supply. You probably can not maintain the residual without a recirculation system.

A small pumped recirculation system with a chlorine booster is probably the most reasonable approach.

Here is a study that may help:

http://www.research.cecs.ucf.edu/dr...ine_dissipation_in_DS_Jorge_Arevalo_ACE04.pdf

 

[quark]

Why can't you fill your tank with enough capacity to cater for 2 to 3 days only?