Question

 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?

Answer 1

Given data:

Final lelvel of BOD is $20 mg/l$

$K_s = 100 mg BOD/L,$

$k_d = 0.10 day^{-1} ,$

$μm = 1.6 day^{-1} ,$

$Y = 0.60 mg SS/mg BOD$

a) we know that $C_{out}=\frac{C_{in}}{1+kt}$

$20=\frac{350}{1+0.1*t} \implies t = 165$

solving for t

$t = 165 days$

b) mass of microbes 

$Q(mlD)AC(mg/l)$

$3*10^{-3}(350-20)=9.9kg/day$