CE 60330 – Environmental Biotechnology
Homework No. 4
Due October 10, 2007
1. An industry uses a CSTR to treat its wastewater. The HRT θ = 5 days, and the kinetic
parameters are as follows:
qmax = 18 gCOD/gVSS-d
Y = 0.7 gVSSa/CODg
K = 10 mgCOD/L
b = 0.25 1/d
fd = 0.9
Xvo = 40 mg/L
Xao = 0 mg/L
Assume SMPs can be disregarded, Q = 3785 m3/day, and So = 1000 mgCOD/L
(totally biodegradable). Assume input COD is completely biodegradable.
a) If the influent contains 15 mgN/L and 6 mgP/L, compute the effluent N and P in
mg/L of wastewater flow.
b) Calculate the excess (or required) N and P amounts in kg/day.
c) Qualitatively, how would you expect the above results to change if θ were
increased to 10 days, or decreased to 2 days?
2. (a) Using the pseudoanalytical method, calculate the flux, biofilm thickness, and
biofilm accumulation for the following conditions:
S = 0.5 mg/L
L = 0.01 cm
K = 10 mg/L
Xf = 40 mga/cm3
qmax =8 mgs/mga-d
b’ = 0.1 1/d
D = 0.8 cm2/d
Df = 0.64 cm2/d
Y=0.5 mga/mgs
(b) How would the results change if the substrate concentration S doubled to 1 mg/L?
And if S dropped to 0.3 mg/L?
(c) How would the results in (a) change if L increased to 0.4 cm?
3. You have been asked to design a completely mixed biofilm reactor. The kinetic
parameters are as follows:
L = 0.01 cm
K = 10 mg/L
Xf = 10 mga/cm3
qmax =12 mgs/mga-d
b’ = 0.1 1/d
D = 1 cm2/d
Df = 0.75 cm2/d
Y=0.5 mga/mgs
The input concentration is 200 mg/L and you seek 95% removal at steady state.
The flowrate is 1000 L/day, and the reactor volume is 100 L.
(a) Determine the required surface are in m2.
(b) How would the solution change if the reactor volume was decreased to 50 L?
(c) How would the solution change if the input substrate increased to 400 mg/L
and the influent flowrate decreased to 500 L/day?