CE 40340 – Wastewater Design
Homework No. 5
Due February 25, 2009
Problem 1 – Steady state CSTR with active and inert biomass
For the following chemostat, tabulate the following effluent parameters for θx = 1, 5, and
30 days: S, Xa, and Xi, dissolved BODL, dissolved COD, particulate BODL and
particulate COD, and particulate N and P. Use the following data:
qmax = 16 g/gVSSa-d
Y = 0.5 gVSSa/g
K = 5 mg/L
b = 0.15 1/d
fd = 0.8
Xio = 25 mgVSSi/L (assume it contains the same P or N fraction as Xa)
So = 500 mgCOD/L (totally biodegradable)
Problem 2 - Nitrification in a Chemostat
Nitrification is carried out by two distinct groups of aerobic bacteria: ammonium
oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). BOD oxidation is carried
out by heterotrophic bacteria. In conventional wastewater treatment, nitrification
typically is carried out concurrently with aerobic BOD oxidation. You wish to develop
set of mass balance equations for BOD oxidation and nitrification in a CSTR. The
components to be modeled include:
Component
1 NH4+
2 NO23 NO34 BOD
5 Xa for AOB
6 Xa for NOB
7 Xa for Heterotrophs
8 Xi
Description
Ammonium concentration
Nitrite concentration
Nitrate concentration
BOD concentration
Active biomass concentration for AOB
Active biomass concentration for NOB
Active biomass concentration for heterotrophs
Inert biomass concentration (from decay)
Symbol
N4
N2
N3
BOD
XaAOB
XaNOB
XaHET
Xi
a) Write the mass balance equations for each of the eight components
b) Write a process matrix for the transformations
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Problem 3 – BioWin (from last week)
A wastewater is treated in an aerobic CSTR. The hydraulic detention time is 2 days and
the following kinetic parameters apply:
qmax = 15 gCOD/gVSS-d
Y = 0.6 gVSSa/gCOD
K = 12 mgCOD/L
b = 0.15 1/d
The initial conditions in the tank are So = 1000 mgCOD/L and Xao = 30 mgVSS/L,
Solve using BioWin. Use a steady state run. Assume S is COD, use defaults for other
influent parameters. Use any combination of Q and V to provide the required HRT.
What is the effluent dissolved COD? And the total COD? How do these change if the
HRT is increased to 20 days?
Problem 4 – BioWin
Set up a two-tank BioWin reactor configuration as follows:
COD Influent
CSTR 1
CSTR 2
Effluent
Sludge Wasting
Note that the first “tee” on the left is a mixer, while the two on the right are splitters. The
COD influent has the following data:
Name
Flow
Total COD mgCOD/L
Total Kjeldahl Nitrogen mgN/L
Total P mgP/L
Nitrate N mgN/L
pH
Alkalinity mmol/L
Inorganic S.S. mgTSS/L
Calcium mg/L
Magnesium mg/L
Value
4000.0000
500.0000
40.0000
10.0000
0
7.3000
6.0000
45.0000
80.0000
15.0000
2
Dissolved oxygen mg/L
0
The wastewater fractions are as follows:
Name
COD – soluble and particulate, biodegradable and non-biodegradable
Fbs - Readily biodegradable (including Acetate) [gCOD/g of total COD]
(1-Fbs) - Particulate COD
Fac - Acetate [gCOD/g of readily biodegradable COD]
(1-Fac) - Readily degradable COD from propionate and complex organics
Fxsp - Non-colloidal slowly biodegradable [gCOD/g of slowly degradable COD]
(1-Fxsp) – Colloidal slowly biodegradable COD
Fus - Unbiodegradable soluble [gCOD/g of total COD]
Fup - Unbiodegradable particulate [gCOD/g of total COD]
TKN – organic and inorganic, soluble and particulate
Fna - Ammonia [gNH3-N/gTKN]
(1-Fna) – organic N [gOrganicN/gTKN]
Fnox - Particulate organic nitrogen [gN/g Organic N]
Fnus - Soluble unbiodegradable TKN [gN/gTKN]
FupN - N:COD ratio for unbiodegradable part. COD [gN/gCOD]
Phosphate
Fpo4 - Phosphate [gPO4-P/gTP]
FupP - P:COD ratio for influent unbiodegradable part. COD
0.16000 0.27000
0.15000 0.15
0.75000 0.5000
0.05000 0.06
0.13000 0.13000
0.66000 0.66000
0.50000 0.50000
0.02000 0.015
0.03500 0.03500
[gP/gCOD]
Biomass
FZbh - Non-poly-P heterotrophs [gCOD/g of total COD]
FZbm - Anoxic methanol utilizers [gCOD/g of total COD]
FZaob - Ammonia oxidizers [gCOD/g of total COD]
FZnob - Nitrite oxidizers [gCOD/g of total COD]
FZamob - Anaerobic ammonia oxidizers [gCOD/g of total COD]
FZbp - PAOs [gCOD/g of total COD]
FZbpa - Propionic acetogens [gCOD/g of total COD]
FZbam - Acetoclastic methanogens [gCOD/g of total COD]
FZbhm - H2-utilizing methanogens [gCOD/g of total COD]
Default Value
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
0.50000 0.50000
0.01100 0.01100
0.0008
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
1.0000E-4
Problem 5 – CSTR
Model two CSTRs in series:






Set the influent flow rate to 4000 m3/d.
Set the tank volumes for CSTR 1 and CSTR 2 to 1000 m3 each
For each CSTR, set the DO set point to 2 mg/L
Set the side stream flow rates for both splitters to zero (no recycle or
recirculation)
Set the clarifier removal to zero percent (as if we had no clarifier)
Set the clarifier underflow to zero
a) What is the SRT?
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b) Using the Album, make a table with the following influent and effluent data:
 Ammonia
 Nitrate
 Nitrite
 Filtered TKN
 Total N
 Total P
 TSS
 Total COD
 Filtered COD
 Carbonaceous BOD
Discuss the results.
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