Question

(2 points) A perfectly mixed aeration pond with no recycle serves as the biological reactor for a small community. The pond receives 30 m3 /d of influent with a BOD of 350 mg/L that must be reduced to 20 mg/L before discharge. It has been found that the kinetic constants for this system are: Ks = 100 mg BOD/L, kd = 0.10 day-1 , μm = 1.6 day-1 , Y = 0.60 mg SS/mg BOD. Assume Xo = 0. a. What must the hydraulic retention time (θ = V/Q) be in the aeration pond? b. What mass of microbes will be produced in the pond each day?

Answer 1

a) t = 165 days

b) 9.9 kg/day

Step-by-step explanation:

Given data:

final lelvel of BOD is 20 mg/l

Ks = 100 mg BOD/L,

kd = 0.10 day-1 ,

μm = 1.6 day-1 ,

Y = 0.60 mg SS/mg BOD

a) we know that

`c_(out) = (c_(in))/(1 + kt)`

`20 = (350)/(1 + 0.1 t)`

solving for t

t = 165 days

b) mass of microbes
`= Q(mlD) × C(mg/l)`

`= 30* 10^(-3) (350-20) = 9.9 kg/day`