Biochemical Oxygen Demand

Incoming wastewater, with BOD5 equal to about 200 mg/l, is treated in a well-run secondary treatment plant that removes 90 percent of the BOD. You are to run a five-day BOD test with a standard 300-ml bottle, using a mixture of treated sewage and dilution water (no seed).
Assume the initial DO is 9.2 mg/l.
Thus we have: BOD5 = 200 mg/l; 90% efficient removal; initial DO = 9.2 mg/l
The general relation between BOD5, DOi, DOf and P is:
BOD5= (DOi-DOf)/P

a) Roughly what maximum volume of treated wastewater should you put in the bottle if you want to have at least 2.0 mg/l of DO at the end of the test (filling the rest of the bottle with water)?
b) If you make the mixture half water and half treated wastewater, what DO would you expect after five days?
c) What would be the remaining BOD after five days have elapsed?
d) Estimate the reaction rate constant k per day.