CIVL 456: Wastewater Treatment

Homework #7- Fall 1996

Due Date: 23 October 1996

Problem 1
Design a fixed film system for CBOD removal using the Modified-Velz equation based on the following criteria:
Flow = 6 mgd
Influent CBOD = 220 mg/L
Requisite effluent CBOD = 20 mg/L
System depth = 25 ft
Media = 60-deg crossflow
Media specific surface area = 32 sq.ft./cu.ft.
Critical wastewater temperatures: 5 deg C (sustained low for January)
Removal rate coefficient: 0.06 sq.ft./cu.ft.-day
Recycle ratio = (0.2)
Hydraulic residence constant (n) = 0.7
Based on an assumption that you would design two parrallel units to handle this full flow, determine the necessary diameter.

Problem 2
Based on your previously determined diameter, calculate the hydraulic and organic loading rates for this same design, and compare them to the `conventional' design criteria discussed in class and in your book.

Last Modified: 18 October 1996; alleman@ce.ecn.purdue.edu