## Problems

11.1. What would be the approximate dry weight of the cells in 1.0 L of medium containing 106 cells/mL if they are 1.0-p.m-diameter cocci?

11.2. One rod-shaped bacterium has a diameter of 0.5 mm and a length of 1.5 mm, and another is 1.0 x 3.0 mm. (a) Assuming that they have equal densities, what is the ratio (smaller/larger) of their mass? (b) What is the ratio of their surface area/ volume ratios?

11.3. If the minimum doubling time of E. coli in a particular system is 20 minutes, what is its maximum growth rate in units of (a) h-1; (b) day-1?

11.4. Given the Monod coefficients for heterotrophs and for nitrifiers below, find the substrate concentrations (mg/L of COD and NH3-N, respectively) that result in a growth rate of 0.1 day-1. Use the following maximum growth rate coefficients and the Monod half-rate coefficients (from the International Water Association's Activated Sludge Model No.1):

For heterotrophs : p,max H = 6.0 day-1 KS = 20.0mgCOD/L For autotrophs : M-max A =

11.5. Given the two-substrate growth model and coefficients for the activated sludge process given below, compute the growth rate at a substrate concentration (S) of 5.0 mg/L and dissolved oxygen (DO) concentration (SO) of 0.3 mg/L. What would the growth rate be if the DO term were excluded?

From Activated Sludge Model No.1: For aerobic heterotrophic growth, _ Ss__So mg = mrnax , hKS + SsKO , H + SO

KS = 20.0mg/L (Monod coefficient for COD) KO H = 0.20 mg/L (Monod coefficient for DO) mmax H = 6.0 day-1 (maximum growth rate)