Question 1 - Compare the cell concentration that will be present after 24 h through batch growth on a non-growth limiting concentration of acetate for the following four cases, assuming that Y is the only variable between the organisms. The initial cell concentration in all cases is 10 mg/l. Assume other constants of interest are q^{^} = 12 mg acetate/mg VSS_a-d, K = 2 mg/l, and b = 0.1/d.

(a) Y = 0.6 mg VSS_a/mg acetate (aerobic growth)

(b) Y = 0.45 mg VSS_a/mg acetate (denitrification)

(c) Y = 0.06 mg VSS_a/mg acetate (sulfate reduction)

(d) Y = 0.04 VSS_a/mg acetate (methane fermentation)

Question 2 - A CSTR reactor is used for treatment of 50 m³/d of wastewater with COD_b of 10,000 mg/l by methane fermentation. Assume Y = 0.04 mg VSS_a/mg BOD_L, q^{^} = 8 mg BOD_L/per VSS_a-d, K = 200 mgBOD_L/l, and b = 0.05/d.

What reactor detention time will result in the maximum BOD_L removal per day per unit volume of reactor? (You may find it useful to use a spreadsheet or programmable calculator, as a trial and error solution is likely to be needed). Show a graph of BOD_L removal per day per unit reactor volume versus reactor detention time.