4.6 Equation (4.11) is used in the design and operation of activated sludge waste- water treatment processes. The term (dX/dt)NG/X is equal to SRT, where SRT is the solids retention time that represents the average unit of time that the microorganisms remain in the system. The substrate utilization rate (dS/dt), is equal to Q(S; Se)/V for a completely mixed reactor. Dividing both sides of Equation (4.11) by X, the microorganism concentration, results in the following equation: SRT (days) 2.94 5.13 7.15 10.5 1 SRT Q (gallons/day) 20 20 20 20 = Y Q[Si Sel XV - A plot of 1/SRT versus Q(S; - Se)/(XV) yields a slope equal to Y, the yield coefficient, and the endogenous decay coefficient (ka) as the Y-intercept. Determine the magnitude and units for Y and ka, given the following data collected on a continuous-flow activated sludge bench-scale unit. - ka V (gallons) X (mg/L) 20 4165 20 6566 20 8966 20 10781 S; (mg/L) 2462 2406 2383 2436 Se (mg/L) 546 305 224 172