You and your team have decided to build an aerated lagoon to treat the waste generated by a local village in a developing country. You estimate that the influent flow rate will be around 25 m3 /d and the BOD5 roughly 300 mg/L. To avoid impacting the river that will receive the effluent, the BOD5 must be reduced to 20 mg/L. Based on your experimental lab work, you have determined the following microbial kinetic parameters:

Ks = 100 mg-BOD5/L kd = 0.1 d-1 µm = 1.6 d-1 Y = 0.6 mg-VSS/mg-BOD5

(a) To meet the effluent BOD5 limit, what must the hydraulic retention time (HRT) be in the lagoon?

(b) What mass of microbes will be produced in the lagoon each day? How could this be problematic for the operation of the lagoon?