Water & Wastewater engineering problem (Chemical engineering)

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Construct a BOD demand curve for a sample that has a first stage rate constant K of 0.16 d-1 (base 10) and a nitrogenous rate constant Kn 0.08 d-1 (base 10). Nitrification is not significant until a period of 7.5 days has passed. The ultimate first stage BOD is 335 mg/L and the ultimate nitrogenous demand is 120 mg/L. What is the total BOD exerted at 10 days? How many complete days are required to exert at least 90% of the expected demand