Biological Oxygen Demand Lecture and explanation.

1. Bio chemical Oxygen Demand
⚫It is a measure of the amount of
“reduced” organic and inorganic matter
in a water
⚫Relates to oxygen consumption in a
river or lake as a result of a pollution
discharge
⚫Measured in several ways
◦ BOD - Biochemical Oxygen Demand
◦ COD - Chemical Oxygen Demand
◦ ThOD - Theoretical Oxygen Demand

2. Theoretical Oxygen Demand
C6H12O6 + 6O2 = 6CO2 + 6H2O
Oxygen Demand
6moles*32g/mole Oxygen/1mole*180g/mole
= 1.06 O2 / Glucose
If glucose concentration is 360 mg/L THOD is
1.06 * 360 mg/L = 384 mg/L Oxygen

3. BOD: A Bioassay
BOD
Bottle
Briefly, the BOD test employs a
bacterial seed to catalyze the
oxidation of 300 mL of full-strength or
diluted wastewater. The strength of
the un-diluted wastewater is then
determined from the dilution factor
and the difference between the initial
D.O. and the final D.O.
BODt  DOi  DOf

4. BOD with Dilution
BODt =
DOi - DOf
 Vs 
 Vb
 
Where
BODt = biochemical oxygen demand at t days, [mg/L]
DOi = initial dissolved oxygen in the sample bottle,
[mg/L]
DOf
Vb
Vs
= final dissolved oxygen in the sample bottle, [mg/L]
= sample bottle volume, usually 300 or 250 mL, [mL]
= sample volume, [mL]
When BOD>8mg/L

5. BOD - loss of biodegradable organic
matter (oxygen demand)
Lo
Lt
L
or
BOD
remaining
Time
Lo-Lt = BODt
BOD
Bottle
BOD
Bottle
BOD
Bottle
BOD
Bottle
BOD
Bottle

6. BOD
CBOD
NBOD
y
or
BOD
(mg/L)
Time
L=oxidizable carbonaceous material remaining to be oxidized
BODt  yt  Lo  Lt

7. BOD Modeling
"L" is modelled as a simple 1st order decay:
dt
dL
 k L
1
o
L  L ek t
1
Which leads to:
We get: k t
BODt  yt  Lo (1 e )
1
BODt  yt  Lo  Lt
And combining with:

8. NBOD Nitrogeneous BOD (NBOD)
3 2 2 2
NH 1.5O 
N

i
t
r
o

s
o
m

o

n
a
s
NO
 H O  H
Nitrobacter
2 2 3
1
2
 
NO  O  NO
2 moles oxygen/1 mole of ammonia
4.57 grams oxygen/gram ammonia-nitrogen
Inorganic NH3, NO3
- NO2
-
Organic Proteins, Amino acids
TKN = Ammonia-N + Organic Nitrogen

9. COD: A chemical test
The chemical oxygen demand
(COD) of a waste is measured in
terms of the amount of potassium
dichromate (K2Cr2O7) reduced by the
sample during 2 hr of reflux in a
medium of boiling, 50% H2SO4 and in
the presence of a Ag2SO4 catalyst.

10. ⚫TDS: used as a measure of inorganic salt
S
co
on
li
te
d
n
s
t:in
sd
ig
rin
n
ki
in
fi
g
cw
aa
n
te
c
re
s and natural
waters
⚫TSS: used to assess clarifier performance
⚫VSS: used to estimate bacterial
populations in wastewater treatment
systems

11. Solids Analysis
Total Solids
Total Dissolved Solids
TDS
TS
Total Suspended Solids
TSS
FSS
VSS
Fixed S.S.
Volatile S.S.
Filtration
filtrate retained matter
ignition

12. Filtration for Solids Analysis
3. Start
suction pump
2. Pour
Sample
1. Weigh new
filter and insert
4. Remove filter
and re-weigh
6. Divide this by the
Volume filtered and you get TSS
5. Measure
Change in
Weight
Suction Flask & Filter Holder

13. ⚫Bio chemical oxygen
demand can be
checked using titration
of that water
⚫Different fluids are
titrated to check BOD
of that fluid

14. RESULT OF TITRATION OF DIFFERENT FLUIDS
NAME OF
FLUID
INITIAL
VOLUME
FINAL
VOLUME
CHANGE
IN
VOLUME
BOD

15. THANK YOU