CE 311 Environmental Engineering I
Dr. Kauser Jahan, P.E.
Fall 2012
Assignment # 2
DUE DATE: Monday September 17, 2012
1. Problem 2-5
2. Problem 2-11
3. A gravity thickener is used in numerous water and wastewater treatment plants. The device
separates solids from liquid usually water by taking advantage of the fact that the solids are
denser than water. Suppose a thickener in a wastewater plant receives influent at a
suspended solids of 5000 mg/L at 40 m3/hr. The thickener in a steady state mode generates a
solids concentration of 30 mg/L at a flowrate of 30 m 3/hr in the effluent stream. What is the
solids concentration in mg/L in the underflow?
No reactions are occurring in the thickener.
Effluent
Influent
Underflow
4. Landis Sewerage Authority discharges treated wastewater into the Delaware River.
The plant flowrate is 100 gal/min. The discharge to the river contains 40 mg/L of
suspended solids. The river has a number of discharges upstream of the LSA plant.
The upstream river flow is 1.0 MGD with 8 mg/L of suspended solids.
a) Draw a mass balance flowchart for the problem.
b) What is the downstream river flow in GPM and the downstream suspended solids
concentration in mg/L?
a) The allowable suspended solids concentration downstream is 5 mg/L as imposed
by the regulatory agency. The plant engineer claims that LSA is NOT violating the
downstream allowable suspended solids concentration. Is he correct in making
this statement? Justify with calculations whether the engineer is correct.