Self Assessment Quiz

Q13.1 Waste Water Treatment
6 million lit/day seawage of a campus of 20000 population water with COD of 200mg/L is to be treated. The growth parameters are µm = 0.3/day and Ks = 10 mg/L. river discharge norms desire near primary water quality for drinking purposes of COD less than 10 mg/L. Estimate the size of the vessel needed. Take concentration factor as B = 0.3.

Q13.2. Natural Selection
Organism 1 with specific growth rate µm = 0.5/hr and Ks = 50g/L and organism 2 with µm= 0.3/hr and Ks = 10g/L. the yield coefficient 0.5 g cell/g substrate for both organisms.

Q13.2.1. Organism 2 is growing at steady state in a chemostat with feed entering at 100 g/L and leaving at 80 g/L. suddenly an infection due to organism 1 occurs. Explain what happens. Determine the steady state composition of the system.

Q13.2.2. Organism 1 is growing at steady state in a chemostat with feed entering at 100 g/L and leaving at 30 g/L. Suddenly an infection due to organism 2 occurs. Explain what happens. Determine the steady state composition of the system.

Q13.2.3. How would you use the above phenomena to manage infections in a process and in daily life.

Q13.3. Alcohol via fermentation
Kinetics of alcohol production using saccharomyces cerevisiae can be given as

Where µm = 0.5/hr, k = 0.17 lit/g, Ks = 2.2 g/L, Yx = 0.08 gcell/g substrate, Yp = 0.4 g alcohol/g substrate, YCO2 = 0.48 g CO2/substrate. Take S0 = 100 g/L

Q13.3.1. Estimate time need to get 90% conversion in a batch equipment.

Q13.3.2. What is the dilution rate needed for 90% conversion in a chemostat.

Q13.3.3. What is the dilution rate needed for 90% conversion in an IMR given cell loading is 30% per volume reactor. Take €s = 0.4 and €g = 0.1.

Q13.3.4. Fermentation alcohol industries typically dilute molasses (500g sugar /L ) to 100 g/L why ?

Q13.3.5. Cell recycle seem to produce little benefit fermentation alcohol but recycles are routine in waste treatment. Why ?

Q13.3.6. Saccharomyces is a fungi. But alcohol via bacteria zymomonas mobilis without higher rates is well known but not used in process industries ? Why ?

Q13.4. Biomethanation
The stoichiometry of rate limiting step and specific growth rate  in  biomethanation is given as

CH3COOH + 0.032 NH3 =  0.032 C5H7NO2 + 0.92 CH4 + 0.92 CO2 + 0.096 H2O

Where Ks = 0.0333 mmol/L and Ki = 0.667 mmol/L and µm = 0.4/day, pKa =4.5 and operating
pH = 6.8   and HS is unionized acid ( HS = H+ + S-  ) herein taken as acetic acid.

Q13.4.1. A dairy waste water  of 3000 cum /d with 6000 mg/L (100 mol/L) COD is to be treated in a chemostat (CSTR). Estimate size and outputs to be expected.