CVEN 5534: Wastewater Treatment

Spring 2008

Assignment 2: Due Thursday, Feb. 7

1. Bacterial denitrification is carried out by heterotrophic bacteria using acetate (CH3COO-) as the

electron donor and nitrate (NO3-) as the electron acceptor. The molar stoichiometry for the

respiration (energy generating) part of the bacteria metabolism is:

5CH3COO- + 8NO3-  10HCO3- + 3OH- + 4N2 + 1H2O

a) Write the mass-basis stoichiometry for denitrification and show that mass conservation is

satisfied.

b) Write the COD-basis stoichiometry for dentirification and show that COD is conserved.

c) What is the oxygen equivalent of nitrate-nitrogen (g-O2/g-NO3-N)?

2. Given the stoichiometric relations you found in problem 1 and a denitrification rate of 20 mg-

NO3-N/L-hr:

a) What is the acetate consumption rate, as mg-CH3COO-/L-hr and as mg-COD/L-hr?

b) What is the rate of alkalinity generated, as mg-CaCO3/L-hr?

3. Methane production by a strain of Archaea growing on acetate follows this stoichiometry:

1CH3COO- + 0.03CO2 + 0.02NH4+ + 0.92H2O  0.95CH4 + 0.02C5H7NO2 + 0.98HCO3-

a) Write the mass-basis stoichiometry for methane production and show that mass

conservation is satisfied.

b) Write the COD-basis stoichiometry for methane production and show that COD is

conserved.

c) If acetate is consumed in an anaerobic digester at a rate of 500 kg-CH3COO-/d, at a

temperature of 35 oC and a pressure of 1 atm, what is the rate of methane (CH4)

production in m3/day, assuming the stoichiometry given above?

d) What is the rate of volatile suspended solids generation (kg-VSS/day,) assuming 1 g

C5H7NO2 = 1 g VSS (volatile suspended solids)?