Civil and Environmental Engineering Answers

 A perfectly mixed aeration pond with no recycle (return line) serves as the biological reactor for a small community. The pond receives 30 m3/d of influent with a BOD5 of 350 mg/L that must be reduced to 20 mg/L before discharge. It has been found that the kinetics constant for the system are Ks = 100 mg/L BOD5, kd = 0.10 d-1, um = 1.6 d-1, and Y is 0.60 mg BOD5.

 A)What must the hydraulic detention time be in the aeration pond?

 B) What mass of microbes will be produced in the pond each day?

A block project up an inclined plane at 20 degrees with horizontal and the block has 

an initial velocity of 6 m/s. If the coefficient of kinetic friction is 0.25, how far will the 

block go up the plane?

Two vessels, A and B each of volume 4m3 are connected by a tube of negligible volume. Vessel 

A contains air at 0.8MPa, 1050C, while vessel B contains air at 0.45MPa, 2250C. When A is allowed 

to mix with B and assuming the mixing to be complete and adiabatic, determine (a) the final 

pressure and temperature of air after mixing, (b) the amount of entropy generation and (c) the 

irreversibilities in the process. Take, T0=300C