# Interpolation ?

1. Apr 2, 2009

### Stacyg

Interpolation ???

A treatment plant consists of a primary sedimentation tank followed by a trickling filter that removes 80% of the influent BOD. The flow is then directed to a constructed marsh system that has an influent target BOD concentration of 30 mg/l before being discharged to a small stream.

Using the following table of % BOD removal to overflow rate and calculate the dimensions of a circular sedimentation tank suitable for the imposed flow with a detention time of 1.5 hours. Assume BOD and flow of wastewater entering the plant to be 214.245 mg/l and 848 kL/day.
BOD Removal % 22.0 31.5 33.5 35.5 36.5 37.5
Overflow rate m3/m2/day 100 50 40 30 25 20

How do I find the value of overflow rate when the BOD removal percentage is 80% from this table?
Do I use interpolation ? I'm not sure on how to use interpolation.

Thanks Stacy.

2. Apr 2, 2009

### lanedance

Re: Interpolation ???

hi stac
2 questions
- first, do you have any ideas how to do it?
- 2nd are you sure its 80% BOD removal? this is a very large extrapolation of the table... could it be calculate BOD rate by interpolating from a given overflow rate?

3. Apr 2, 2009

### Stacyg

Re: Interpolation ???

I know how to answer the question, just not how to find the overflow rate at 80% BOD.
The question is exactly what I have written so i have to find the overflow rate at 80% BOD.
Thanks Stacy