Cleaning of semi full potable water storeage tanks. 2

[idratherbefishing]

Hello all.

I am in need of cleaning several inground potable water storage tanks. The tanks are in the 10,- 15,000 Gal range. Mostly constructed out of masonry and are serving as domestic water storage. The tanks are typically rectangular and have an average depth of 10'

The goal is to remove the sediment from the bottom and walls of the tank and then UV treat the water and return it to the tank.

We are considering using a commercial grade sand filter and pump rated for 280GPM, and then a UV system sized equally. We are planning to remove the water from the tank and reject the water to the same tank. By returning the water with high flow rate we plan on lifting the sediment into the solution and then remove the sediment back to the sand filter.

The aim is to keep as much water as possible, and to return the water as clean as possible. Water is at a premium

I believe that by moving the water several times through the filter, much how a swimming pool system is done, then I will be able to remove all the debris from the tank.

Is my thinking correct or am I missing a flaw.

The construction of the rig will be capitally high, plannning on using this for several year.

Any and all input is welcome! - Thanks.

 

[gr2vessels]

First, I also think that a bad day of fishing is better than any day in the office (except the pay-day).
If possible, I would use a 50-60% (why not a 100% temporary one) transfer tank during the cleaning process. I would also use that water to wash with high pressure jets the wals, and use submerged jets of returning water to stir the bottom deposits and keep them in suspension all the time. You will not remove everything, but depending on your hardware, you should be able to get >95% of suspended contaminants.
gr2vessels

 

[idratherbefishing]

Thanks gr2vessels,

Typically the process has been to remove all the water and then try and shift this around. This has proved costly over the years

 

[racookpe1978]

I don't think your 280 gpm/10,000 gal pump-to-tank ratio is large enough.

Two values: A fixed 280 gpm discharge isn't large enough to "stir" the sediment - you'll need a second (or third) pump discharge continuously and randomly aimed around and at the walls and corners of a flat-walled tank to keep the sediment suspended while the first sucks the dirty fluid from near the bottom drain point.

(Have you figured out to clean the drain pipe and "gunk" stuck down there above the cutout drain valve?)

Second value: I've got to relearn my half-life equations (vpl sighs, resigns herself to teaching that subject yet again!) but you need to consider that the "perfectly suspended solids" are getting filtered out at constant rate from an ever-diminishing level of pollution. With only a small percent of total fluid going through the filter each pass, you need 5 to 6 half lives of the original concentration (cleanup) rate to get a "good enough" final sample.

your sand filter supplier should be able to give to you "fill up" rates and tell you what capacity is needed before the filter needs replacement.

280 gpm x 60 min/hr = 16800 gal per hour. About 1 "tank" flowing per hour is what you expect?

 

[idratherbefishing]

That is close to what I am expecting.

We are aware that it will take several passes of water through the filter to ensure a good sameple.

I will research the half life, or do a search here.

Where do you think the flow rate range should be to ensure proper suspension of sediment. I was planning to put the return water to the side walls of the tank and then the suction in the center as this would be where the majority of the sediment would accumilate.

Thoughts?

 

[1gibson]

I'm sure there is a reason, but what is stopping you from using one of the many commercially available swimming pool cleaners?

Little water powered two wheeled thing with a filter, and a long spout/tail that stirs up any sediment.

Perhaps in conjunction with your initial idea, maybe pull the filters in the pool cleaner so it's only purpose is to stir up sediment. I doubt filter is fine enough, or high enough capacity, for more than XX minutes of operation in a dirty tank.

 

[gerhardl]

How to try to look at it from another angle:

a) Cheapest possible pumping/transport unit: - >lowest possible pumping capacity.

b) Cheapest intermediate water storage: Rubber sacks? Renting tank capacity (tankers? / military? / civil catastrophy equipment?) other smaller containers, but many?

c) Cheapest tank cleaning and removal of bottom sludge: Manual? Construction of manholes? Construction of sludge draining bottom valves? Ships-tank cleaning equipment rented? etc.

d) Cheapest desinfectation of tanks: chlorine? UV? Other?

e) Cheapest cleaning of water: centrifuge, sand filter, coal filter, 'swimming pool equipment' as 1gibson suggested (put me to the thought of differed equipment and methodes), UV at lowest possible capacity?


I do not think you will get a satisfactory result by your suggested methode, to many 'uncertainity' factors. Think also about structural changes investment as cost over time, maybe cheapest in the 'long run' if the process is repetitive.

Should absolutely include UV to avoid (girardia? -spelling?) or similar not cleanable by chloride.

 

[racookpe1978]

Well, he's looking at a problem with "sediment" in the bottom - so I'm assuming that the first requirement of the flow needs to be high enough/vigorous enough/fast enough to lift that stuff up and around.

But, my experience is with turbine oil flushes - but then, my limit (or my problem) is getting the very, very small suspended particle in the long, small diameter, twisted and intricate power plant oil supply and seal oil piping runs to break loose and release stuck particles. Sediment in the big tanks is only a very, very minor part of the problem, and can be wiped down before we fill the tank with clean oil.

Mechanically, if your cleaning schedule allows, you can even try getting down in the bottom and scoop up (shovel and lift bucket!) the stuff first. Fire hose the remnants into one corner, then scoop that corner out again. That will probably reduce cleaning time by the first 4x tank exchange times, and pay for itself by eliminating several filter changes. Does require emptying that one tank though.

 

[idratherbefishing]

Thanks all for the input,

Traditionally these tanks have been drained and then are refilled at great expense for the water.

There is no easy way to do a hard thing, just trying to find a more effective/progressive way of carrying this out.

Going to try and carry this out on a small scale first before going the whole nine yards.

 

[dicksewerrat]

How about using a standard pump to remove slowly, so as to minimize turbulence, all but 6 inches of water. Put removed water into a food grade tanker. Bring in a sewer jet truck, properly sanitized, to suck out some more water and jpressure jet wash the walls and floor. Treat the water in the tanker as you suggested. Save the last 6 inches of dirty water in the jet/vac for the next tank. If too much for the jet/vac truck, put in a portable water tank. Repeat process. Once a few of the tanks are cleaned, clean up the 'dirty water' and return to the clean tanks. Keep rotating thru the system till done.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com