Turnover and water quality for EST

[PEorl]

Does anyone know a rule of thumb on a reasonable turnover rate for an elevated storage tank to maintain water quality? Is one day sufficient? Does the entire tank need to empty? Any info would be appreciated. I looked through previous threads and didn't see anything on this. Thanks.

 

[coloeng]

It really depends on a number of factors such as;
Water temperature- the warmer the water the quicker your disinfectent will disipate and the water quality degrade. If you are in an area where the water stays colder, you may not have to turnover the water as often.
Disinfectant residual- the higher your residual at the tank the longer you can leave it in without having to refresh it, or if you redisinfect at or near the tank, you may not have to turn it over as often.
Water's propensity to form DBPs- If your water and disinfectant combine to form disinfectant by-products readily, you may need to turnover your tank more often.

Because each system is unique, there is no hard and fast rule on how often a tank should turnover.

 

[jammer45]

As with most engineering questions, this one is not that straight forward. It depends upon the quality of the water being stored and the issues that might arise if it is stored too long. Long storage can lead to loss of chlorine residual, which is bad, but can also lead to development of disinfection by-products, which is also bad. Neither of these is a given for all waters. A one day turnover would be a very conservative design and would avoid quality issues but is rarely seen in water storage tanks. It is also rare to totally empty a water storage tank on a regular basis. There are, however, several ways to improve mixing of water as it is introduced into the tank or stored in the tank to improve water quality performance by avoiding stagnant areas from developing.

 

[PEorl]

Thanks for your reponses. I am doing some extended period simulation modeling and was trying to determine what would be reasonable on turnover, but was guessing no easy answer.