Scum Pumping

[workingweekends]

Hello,

I am trying to size a scum pump but I am unable to find much information on scum generation per overflow rate, or any other similar standards. Most existing thread discuss pump selection and disposal.

Thank you in advance

 

[ashtree]

You may have to provide more information.
Can we assume that you are pumping scum off the top of a settling tank given that you mention overflow rates?
If this is linked to an activated sludge plant the quantity of scum is not linked to overflow rates but more to the population of norcardia or other types of scum forming bacteria. In turn the rate of scum formation is then linked to things like aeration intensity , and plant configuration as well as the presence of or absence of a number of substances in the wastewater.
The reason there are no references to scum formation and overflow rates is because there is little direct relationship.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Have never seen any correlation of scum generation to flow rate.

Many times the scum pumping operation is a batch process.

 

[workingweekends]

More information:

Scum to be skimmed off the top of clarifier

Secondary Treatment Parameters:
Facility influent 0.25 (mgd)
BOD 190 (mg/L)
SRT 20 (days)
Temp 60 (F)
MLSS 2526 (mg/L)
WAS 247 (lb/day)
NH3 0.37 (mg/L)
NO3+NO2 28.42 (mg/L)
DO 2.19 (mg/L)
Brush Aerators 20 (HP)

 

[ashtree]

I agree with bimr above.

Just to get a bit of understanding about your plant and how it is operating do you know what your SVI is? What is your design flow?

Have you tried shortening your SRT a little to see if you can reduce your scum?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[workingweekends]

The information provided is from the proposed process model. We would like to replace the existing 35' clarifier with a new 65' to account for seasonal I/I.

The I/I associated with seasonal changes ranges considerably, 0.25 mgd during the summer, historical peaks of 2.7 mgd during the winter.

For the proposed design SVI would be about 400 (ml/gm) during low flows, and 225 for historical high flows.

 

[ashtree]

So i am guessing that this is onnly theoretical scum you are dealing with then.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[workingweekends]

Yes

 

[ashtree]

Are those peaks due to storm water infiltration or is that your daily load during the winter time?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[workingweekends]

There is a significant amount of infiltration and inflow within the collection system during high lake levels. The high lake levels last almost the entire winter and produce daily flows near 0.8 mgd. There is substantial infiltration as a result of precipitation events with a return interval greater than 5y years as well.

 

[ashtree]

With your 65 foot sed tank you are going to have quite low overflow rates and risk all that going septic. That will make things worse for you.
Without knowing all your circumstances i would suggest that you dont have enough aeration capacity which in turn causes problems with the scum formation which is what you are trying to pump away.
You may well need some more settling capacity but maybe you should duplicate what you have already to give you some back up capacity and redundancy and allow one tank off line during the low season.
Then perhaps spend the rest of the money dealing with the infiltration issue and getting more aeration capacity


Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

One would think that it would be more practical to reduce the I/I than try to treat it. If the I/I is 10 times the treatment capacity in the summer, that means the wastewater will be diluted by 90% which will be too dilute strength to treat in a mechanical plant.