CIVL 456: Wastewater Treatment

Homework #5- Fall 1996

Due Date: 4 October 1996



Part 1 Estimate the daily sludge production at the local WWTP (West Lafayette) in terms of both primary and secondary sludge. Your answers should include both a wet volume (daily)...in gallons of primary and secondary sludge per day...as well as dry mass (lbs) per day for each such source.
Part 2 Suppose that you are growing a special culture of nitrifying bacteria (i.e., notoriously slow growing lithotrophs) and that you conduct a series of chemostat tests (reactor volume = 17 liters; influent substrate concentration of 955 mg ammonia-nitrogen per liter) in order to evaluate their relative maximal specific growth rate and half-reaction constant. Seven such tests were conducted at seven different HRT's...and in each case, the effluent substrate concentration (i.e., ammonia-nitrogen) was measured once the reactor reached steady-state conditions (NOTE: after making each change in the chemostat's HRT you waited a minimum of 3 weeks in order for the tank to reach its new point of equilibrium). These results are as follows:
Test #1-HRT=0.90 days-S=26.0 mg/L
Test #2-HRT=1.00 days-S=11.6 mg/L
Test #3-HRT=2.00 days-S=2.61 mg/L
Test #4-HRT=4.00 days-S=0.66 mg/L
Test #5-HRT=8.00 days-S=0.29 mg/L
Test #6-HRT=16.0 days-S=0.14 mg/L
Test #7-HRT=0.84 days-S=955 mg/L
Washout was obviously achieved in Test #7, since the effluent ammonia-nitrogen value during this run was equal to the influent ammonia-nitrogen value (i.e., there was no substrate utilization taking place because all of the cells had been washed out of the chemostat with such a short HRT.
Using this data and the Lineweaver-Burke modeling approach, determine the apparent values for the maximum specific cell growth rate and half-reaction constant.
In addition to calculating these two values, determine the likely cell concentration which might be found within this chemostat's effluent for sixth (6th) test run at the HRT of 16 days...assuming that these bacteria have a theoretical yield of 0.05, and neglecting any cell decay or death.