Using Water Storage Reservoir as Contact Basin

[mell9401]

Does anyone have any experience or thoughts about using a large water storage reservoir to obtain the chlorine contact time for a hypochlorite disinfection system? I have been asked to look at the possibility of adding hypochorite prior to a 240,000 gallon circular water storage reservoir and then using the time that the water is in the reservoir to obtain the required contact time. I am concerned about short circuiting. This tank will be over 50 feet tall. Would adding large vertical curtain baffles inside the tank to make a more serpintine flow path do much good? Has anyone seen this done?

 

[JedClampett]

We've dealt with this problem several times, although not with a 50 ft. tall reservoir. What we've found is that any kind of curtain is susceptible to the turning forces of the water at the baffle ends. I've taken to building the ends out of concrete or CMU to avoid this. Another spot that tends to billow is where the influent pipe is perpendicular to the baffle direction. The entrance velocity will push the curtain. Also, support the curtains at the floor and ceiling.
There are companies that make spiral mixers that might be better suited for your application.
Is there a typo in you dimensions? You say the tank is 240,000 gallons, yet it is 50 ft. tall. Is that the tank elevation or height?

 

[mell9401]

Thanks for your advice. The tank is to sit on the ground and is expected to be roughly 28 feet in diamter by 52 feet or so high. I've been wary of this idea but it sounds like curtain baffles could work. Using mixers within the tank and treating the tank like a large batch reactor is also an interesting idea. I'll look into both of these options.

 

[hydrae]

I have put Hypolon (NSF-61) curtain baffles in a 30 ft dia x 20 high storage tank. Used stainless angles and hardware to support the fabric. Installation was nearly 10 years ago, still in service, without wear.
CT went from 7500 gallon equivalent to 30,000 gallon equivalent with 3 walls
The forces on the walls is not noticeable.

mixing will shorten CT, cause what counts is the first 10% and mixing will ensure that 10% will go fast to the exit.

The testing protocol I used: step change the chlorine dose. The results are set when 10% of the final change appears in the outlet. Initial residual 0.5 ppm , a step change to final residual of 1.0 ppm. time is counted when reading is 0.55 ppm.

Hydrae

 

[SteveWag]

What is the rate of flow into the tank?

Steve

 

[mell9401]

Pumping rate into the tank is to be 80 GPM to meet system MDD.

I am pushing to keep money in the budget to perform tracer testing of the finished tank and baffling so that we can determine actual CT values of the "as-built" system and then look at ways to improve the CT through the tank if necessary.

 

[dannyc1]

Hi
We proposed to build a reservior for aprox. 1,000,000 gallon of water.
the water source is a stream/river that is in the same location which will be use. I would like your assitance in the design for this project which include pumping, filtering and sterlizing/chorinating of the water for human consumption

Dannyc1

 

[kchayfie]

Dannyc1

You might find it more helpful to start a new thread and ask your question there.