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Combined Centrate flows / TSS
Posted: Thursday, October 24, 2013 7:56 PM
Joined: 10/24/2013
Posts: 1



I am updating an existing excel spreadsheet and have come across an issue that seems simple, but I cannot wrap my head around.


I have 2 centrifuges on-line. They are fed by one digester, but they are at 2 different flows. I can only sample at the end of a common Centrate line. I need to determine: Lbs/day coming from the centrifuges, and percent removal efficiency per centrifuge. I know there is no way to figure actual efficiency per centrifuge, I just need the estimated there efficiency per centrifuge for other formulas in the spreadsheet.   


Here is the latest data gathered:


Digested sludge % T.S. = 2.07%

Centrifuge #1 flow = 110 gpm  

Centrifuge #2 flow = 115 gpm 

Composite Centrate = 1606 mg/L


For Lbs, would I need to; combine the flows (225 gpm), convert to MGD then just perform a Lbs formula like so? 

(.324MGD)(8.34)(1606 mg/L)= 4339.67 Lbs 


For % efficiency, would I perform the formula this way:

2.07% / 100 * 1000000 - 1606 mg/L / 20700 * 100 = 92.24%


Would 92.24% represent the estimated efficiency PER centrifuge? I understand that one centrifuge may be performing poorly, but is being "hidden" due to the exceptional performance off the other centrifuge.


Like I said, these problems seem simple. I may just be over thinking it.


Thank you in advance!   

Posted: Thursday, November 14, 2013 6:23 PM
Joined: 11/14/2013
Posts: 1

I thought I would come back onto the forum to explain what conclusion I came to. (This is "Nick" by the way, my previous account became inaccessible for one reason or another.)


First: I was (for now) able to abandon the idea of individual centrifuge performance which made this problem much easier to fix. Taking out the variable of differing centrifuge flows allows for a simple "in-out" formula to be used when calculating multiple centrifuges performances at once.


Second: Finding how many lbs are coming out of the centrifuges has been more difficult. We have come to the conclusion that the centrifuges do not run consistently enough for grab sampling alone to provide us with accurate data. There are talks of adding meters on each centrifuges centrate lines, that will provide us with (hopefully) the most accurate measuring possible.


If your agency is considering installing centrifuges, be sure to take this view into consideration. It may seem to be an over-the-top way of operating, but the savings could be huge when optimizing for polymer usage. Speaking from experience.