Water and Wastewater.com Help Forums - Determining A RAS Rate for A Package Plant

kimmy

YaBB Newbies

Offline

I love Water and
Wastewater.com

Posts: 49

Company or Organization: wsacc

Determining A RAS Rate for A Package Plant
Mar 30^th, 2012, 10:34am

Hello all.

I have a .150MGD package plant. Two sides are online, each receiving a flow of 50gpm thru the aeration basins. This week my MLSS ran very high, >4000. We reseeded the plant yesterday due to all sorts of stuff that has gone wrong over the last month. I have attached a spreadsheet containing MLSS/RAS and settlometer date. I would like to get help determining what my return rates should be. Right now I am fluctuating between 75 and 77%. I would welcome any input from anyone who would like to help out. Also, I am merely a HS graduate. So, its ok to talk to me like I'm brand new at this. I am still in the learning process. Thanks.

Back to top

IP Logged

kimmy YaBB Newbies Offline I love Water and Wastewater.com Posts: 49 Company or Organization: wsacc	Re: Determining A RAS Rate for A Package Plant Reply #1 - Mar 30^th, 2012, 11:08am Let me correct 1 thing. I am actually getting 35gpm down each side. Not 50gpm.
Back to top	IP Logged

The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: Determining A RAS Rate for A Package Plant Reply #2 - Mar 30^th, 2012, 11:11am Use a return rate that keeps your desired sludge blanket level in the clarifier. (the lower the better). Are you setting your RAS rate automatically based on the influent or manually?
Back to top	IP Logged

grrun

God Member

Offline

WaterandWastewa
ter.Com is the best!

Posts: 3526
Pekin, IL
Gender: male

Company or Organization: Freelance Environmental Engine

Re: Determining A RAS Rate for A Package Plant
Reply #3 - Mar 30^th, 2012, 12:04pm

The RAS rate should be high enough to prevent denitrification in the clarifier. My opinion is that you need to track sludge age to promote a strategy for consistent wasting (search for sludge age in the upper right hand corner of this page). Reseeding may get you restarted again, but you need to consistently waste sludge.

grrun

Back to top

IP Logged

Eric Raj

God Member

Offline

As long as it flows,
I'll treat it!

Posts: 518

Gender: male

Company or Organization: City of Bedford

Re: Determining A RAS Rate for A Package Plant
Reply #4 - Mar 30^th, 2012, 12:05pm

I did not see any attachement, so here goes with what you posted. If you return 60% of your flow back to aeration, then you would be returning about 21 gpm to each side of RAS. I would use this as my starting point. Blanket depths need to be measured, MLSS levels need to be measured, as do RAS levels. Track your SVI calc from settleometer reading. Your SVI ought to track somewhere between 80-120. Watch the direction of the trending numbers in order to determine if you have changed something properly or not. Overall treatment efficiency provides the final grade of course.

You have not given us any design numbers for MLSS blanket depths, etc.. What is your wasting rate from the system?

~Eric

Back to top

IP Logged