Predicting TSS Reduction by Water Impoundment 1

[DeltaCascade]

Hello:

We are designing a refinery installation. Supply water is from river which is high in total suspended solids (85 ppm TSS average, ranging from about 10 in winter to 500 or higher during spring break-up conditions or heavy rainfall). We need to get raw water TSS below about 40 ppm (eg: to use it as make-up water source for evaporative cooling water, where we will concentrate the solids up to about 200 ppm TSS maximum).

We will hold the river water in a raw water pond with 3 to 10 day residence time. We need to determine what TSS reduction we can expect from a 3 day impoundment. The answer will determine if we also need the expense of a clarifier or filter installation. So, the question, as i see it, is:

Can you recommend procedure to predict total suspended solids reduction from impounding the water? We can run these tests on bench scale with river water samples.

I'm having a mental block (to say the least) and sure appreciate your help. Does a standard procedure come to mind?

Thank you.

 

[BobPE]

Delta:

There are three regeimes of settling that can occur in the situation you have. The regeim greatly depends upon the water and the particle makeup. This is a very complicated problem that unfortunately, you have to get right the first time. I would immediately assume that you will need a clarifier to get to the levels that you are stating for final quality. If the particle makeup varies greatly from season to season, a filter may be needed also. Three to ten days may seem like a lot of time but in fact with the varying levels you have, it is not going to be the only mechanism that will permit the settling of solids.

To get a grip on the problem you will have to do several column settling tests to see what you have in the water and how it behaves. For more info on these tests you can go to Theory and Practice of Water and Wastewater Treatment by Droste. Even then, this is an art that you may want to sub out because of the consequences of getting it wrong. Then you are going to have to look at chemical addition (most power plants I have designed use alum) to see its interaction on the particles. From this you can develop the necessary settling curves that I think you are desiring in order to determine the right way to proceed.

Hope I was of some help....

Bob

 

[DeltaCascade]

Thank you, Bob. Column settling tests! That set me on the right track. We'll pursue it for our river water (it's a sandy river subject to wide seasonal level fluctuation).

Reviewing texts (AWWA's Water Quality & Treatment, Metcalf & Eddy's Wastewater Manual), i now see what you mean on settling curves. We had one particle size test result on similar water available and used this to estimate settling rates for different size ranges (settling curve). We assumed a particle density (1.2 - 1.9 sg) and shape (spherical), and type 1 unhindered settling. But of course this is just guestimating as we don't know our particle density or shape, or if it is true type 1 unhindered settling, so column settling tests would be the ticket.
These helpful tests will be recommended.

A reference describing column settling testing was found, but, as you say, it must be more of an art than a science in that there appears to be no authoratitive standard (yet?). Standard Methods for the Examination of Water & Wastewater defines a "settleable solids test" although not in itself applicable to generating settling rate curves. The column settling test reference is "A.E. Zanoni & MW Blomquuist, Column Settling Tests for Flocculant Suspensions", Proc. Am. Soc. Civil Eng., vol 101 (EE3), 1975, pg 309)

Tx for refering Drost, too.

Cheers

 

[dicksewerrat]

There may be some help from the 'Stormwater ' experts in the other forum. Settling ponds are a way to 'clean' storm water before it is sent to our pristine rivers and lakes. I only constructed what they designed so I can't tell too much. But getting samples from your water source and using settling col. tests is where you have to start. Unfortunately you will have to sample for a fairly long time or make some assumptions that may not be valid. Such as spring run-off particle sizes.

 

[DeltaCascade]

Good idea, thank you.

Funny, it is the suspended solids in the river water coming into our "pristine" cooling towers that we are concerned with (chuckle). In any event, extensive sampling program in parrallel with column settling tests is the way we will go. Tx for the confirmation.

Hopefully, bulk of the river water suspended solids during the seasons of high TSS will be quick to settle (<3 days, like if it is mostly sand or large particles), so that we can avoid cost of clarification and/or filtration and thereby minimize life cycle cost of the cooling system make-up wate treatment. Settling curves will be constructed, and economics of raw water use analyzed based upon that.

Thanks all!

 

[ckmoied]

You may also consult Metcalf & Eddy's Wastewater Engineering, Pages 596-597 as a practical example. Though they apply to the design of wastewater clarifiers, but can also suit to your problem.

Regards

Khurram Moied

 

[ConsultUS]

You have a nice Rock and Roll situation, and are about to get into a mess if you do not look for all the forest and continue looking into the trees
I have experienced the same situations before and the first time made a mess, it was painfull to correct it.
Once I went trought the learning pains I never made the same mistakes again.
Let me discrive my mistakes.
1.-Water inlet design on the river its most important
2.-Pump selection is important or else you erode them very fast.
3.-How much solids are you going to collect, how are you going to clean them, are you designing a settling location of easy cleaning.
4.-Do you have to empy the basins to clean the solids , if this is so how will you operate.
5.-Now let us go to the trees
6.-Do you have fisshes on the water, they plug pumps and strainers quite nice.
7.-You must have particle dimention analisis any filter manufacturer wil do that free for you.
8.-You must look to historical records 50 year or better for fishical locations of facilities or else you might have to place your instalation on a barge at ocational storm conditions.
Good look .
Also hiring a Fortune teller helps

 

[DeltaCascade]

Tx ConsultUs Thee ole crystal ball is getting polished up pretty good.

1.-River water intake design - yes, am working with the civil engineers. We hope to have high water intake for spring run off as well as just a low level (below ice) intake for winter (when the water is low in TSS anyhow).
2.-Pump selection is important or else you erode them very fast - hadn't thought of that. Tx.
3.-Solids will settle in a 1 Mm3+ pond designed by the civil engineers. Colunmn settling tests will help determine how much will settle there.
4.-Likely most soilids will settle in a presettling compartment.
5./6.- We will have specially designed fish-screens as required by environmental legislation (in recent years).
7.-We plan not to filter, which is my original concern for use of high TSS water (at least in spring and summer) for cooling tower make-up. Our option is to clarify +/or filter, at added capital expense.
8.- Capable consultants have done a &quot;big&quot; study to locate best inlet point and design of intake proceeds now.
Tx, again//

 

[ConsultUS]

Halo Deltacascade.
looks like you work a little on sundays also.

Allow me to insist on the convenience to look into the historical flood records.
ASK THE GERMANS ABOUT UNEXPECTED increments in river levels.

Once you do that , I remind you to ,look for a Fortune teller or purchase insurance, and use generous paramethers of design. Gloval clima warming is going to continue, and weather wil be an unpredictabe factor.
By best of looks