2. Objectives
• To understand the difference between biochemical oxygen
demand (BOD) and chemical oxygen demand (COD).
• To understand the relationship between BOD and dissolved
oxygen (DO).
• To study the test that can be used to measured water
pollution.
• To gain awareness of the effect of water pollution to the
environment.
3. ResultS
Table 1 : Chemical Oxygen Demand (COD) mg/L
Leachate River Blank
Chemical Oxygen 49x100 20x2 0
Demand (COD) =4900 =40
Table 2 : Dissolved Oxygen (DO) mg/L
Leachate River Blank
Day 1 (Initial) 5.61 5.63 5.91
After 5 days (Final) 7.36 7.87 7.81
Change of DO (∆) -1.75 -2.24 -1.9
Initial - Final
4. Biological Oxygen Demand
BOD value in mg/L = [ (Initial DO sample - final DO sample ) –
(Initial DO blank - final DO blank ) ] / P
• P= fraction of the BOD bottle that is represented by the sample or mL
pipette divided by 300mL when a 300mL bottle is used.
5. Table 3 : Biological Oxygen Demand (BOD) mg/L
and Chemical Oxygen Demand (COD) mg/L
Leachate River Blank
Day 1 (Initial) 5.61 5.63 5.91
After 5 days (Final) 7.36 7.87 7.81
Change of DO (∆) Initial - -1.75 -2.24 -1.9
Final
Biological Oxygen Demand -1.75 -(-1.9) -2.24-(-1.9) -
(BOD) mg/L 0.01 0.5
=
= 15 = -0.68
[ (Initial DO sample -
final DO sample ) –
(Initial DO blank - final DO
blank ) ] / P
Chemical Oxygen Demand 49x100 20 x2 -
(COD) mg/L =4900 =40
6. Question 1 :
Compare the COD and BOD readings in both samples. Do you think that
the landfill leachate has polluted the nearby river? Discuss.
Yes, leachate is highly polluted and this may gives effect to the
nearby river because when the high BOD levels flow into a
river, it will accelerate bacterial growth in the river and
consume the oxygen levels in the river. The oxygen level may
decrease to levels that are lethal for most fish and many
aquatic insects.
7. Question 2 :
List the differences between BOD and COD measurements.
Biological Oxygen Demand Chemical Oxygen Demand
(BOD) (COD)
Measure the amount of food (or Measures the content of all
organic carbons) that bacteria can chemicals present in the water
oxidize. that are capable of being oxidized
by the oxidizing agent.
Slow : five days required for BOD Faster : takes just two hours to
studies. complete.
Can only be use to test water Can be use to test water from
from wastewater treatment plants industrial and domestic waste
that do not contain toxic industrial water.
wastes.
*industrial wastewater that is rich
in cyanides or heavy metal ions is
toxic to the bacteria.
8. Conclusion
• Biological Oxygen Demand (BOD) and Chemical Oxygen
Demand (COD) test can be used to test the pollution of water.
• The COD value is always higher than the BOD value because
more organic matter can be oxidized in these chemicals than
are biodegradable in the BOD test.
• Leachate are more polluted compared to river.
