CE 40340 – Wastewater Design
Homework No. 6
Due April 8, 2009
Problem 1 - Activated Sludge Design
You are to design an activated sludge process. The influent values are:
Q = 5000 m3/d
So = 300 mgBODL/L
Xoi = 40 mgVSS/L
Xoa = 0
The following kinetic parameters were estimated from lab studies and stoichiometry:
qmax = 20 g/gVSSa-d
Y = 0.6 gVSSa/g
K = 25 mg/L
b = 0.2 1/d
fd = 0.8
The design factors are:
Safety factor = 20
MLVSS = Xa + Xi = 3,500 mgVSS/L
Xvr = Xar + Xir = 15,000 mgVSS/L
(Xa + Xi)eff = 30 mgVSS/L
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
l)
Calculate [θxmin]lim
Calculate θx design
Calculate effluent S
Calculate rate of production of active, inactive, and total VSS produced in the
reactor in kg/d
Calculate the hydraulic retention time and tank volume
Calculate Xa/(Xa+Xi). What is Xa in the reaction tank?
Calculate the sludge wasting flow rate (Qw) if the sludge is wasted from the
return line. Calculate the rate (in kg/d) of wasting of active, inactive, and total
VSS.
Calculate the required recycle flow rate (Qr) and the recycle ratio R
What is the BOD of the solids in the effluent?
Calculate the particulate N and P concentrations in the effluent in mg/L and kg/d.
If the influent P and N concentrations are 10 mgP/L and 45 mgN/L, determine the
soluble and total P and N in the effluent.
If the influent contains 5 mgDO/L and the effluent 2 mgDO/L, calculate the
required oxygen in kgO2/day.
1
Problem 2 - BioWin Exercises
Part 1 – CSTR. This should have been completed as part of Homework 5, but is copied
below for reference.
Prepare the following set up in BioWin:
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
Dissolved oxygen mg/L
Value
4000.0000
500.0000
40.0000
10.0000
0
7.3000
6.0000
45.0000
80.0000
15.0000
0
Use the following 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]
Default Value
0.16000 0.27000
0.15000 0.15
0.75000 0.5000
0.05000 0.06
0.13000 0.13000
2
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
0.66000 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]
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
From HW 5, you also should have done the following
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
From HW 5, you also should have answered the following questions:
a) What is the SRT?
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
 Carbonaceous BOD
Discuss the results. Do they seem reasonable?
3
For HW 6, you need to address Parts 2 and 3, below.
Part 2 - Activated Sludge. Using the same configuration, make the following changes:



Set the clarifier underflow to 300 m3/day
Set the clarifier removal to 100%
Set the sludge wasting split to 30 m3/d
Using the SRT calculator, for “Elements for calculation of total mass” select “CSTR 1”
and “CSTR 2. For “Wastage elements”, select “sludge wasting” and “effluent.”
Determine (a) and (b) from Part 1. What processes are taking place?
Repeat the above considering winter conditions, where the water temperature decreases
from 20 oC to 5 oC.
Repeat the above (at 5 oC) forcing the SRT to 15 days (select Project from the top menu
bar, then select Active SRT, check Control SRT, set to 15 days, then for “select SRT
control splitter” choose the splitter that you use for wasting).
Part 3 – Pre-denitrification
For the configuration in Problem 2, (temp = 20 oC, SRT = 15 days), set the recirculation
flow split to 3 times the influent flow. Set the first CSTR to un-aerated. Determine part
(b) from problem 1 and discuss results.
Plot the effluent total nitrogen as a function of recirculation rate for Qr = Q, 2Q, 3Q, 4Q,
5Q, and 6Q. Interpret results.
4