A series of completely-mixed flow reactor configuration is to be considered for reducing the influent substrate concentration from 100 mg/L to 15 mg/L at a design flow rate of 5 million gallons per day (MGD). Assume that substrate removal follows first-order kinetics and the first-order rate constant k is 8.0 d-1. Determine the reactor volume (ft3) required for three ideal complete-mix flow reactors in series at steady state.

Amixture of slurry and mud is to be pumped through a horizontal pipe of diameter 500 mm. the fluid behaves as a bingham plastic with a yield stress of 30 pa and viscosity 0.04 pa. s. describe the effects of the shear stress through a transverse section of the pipe by plotting the variation in shear stress and velocity profile: (i) just before the slurry starts to move (ii) as the slurry flows when the pressure gradient is double that in part (i)