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.
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 BlankDay 1 (Initial) 5.61 5.63 5.91After 5 days (Final) 7.36 7.87 7.81Change of DO (∆) -1.75 -2.24 -1.9Initial - Final
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.
Table 3 : Biological Oxygen Demand (BOD) mg/L and Chemical Oxygen Demand (COD) mg/L Leachate River BlankDay 1 (Initial) 5.61 5.63 5.91After 5 days (Final) 7.36 7.87 7.81Change of DO (∆) Initial - -1.75 -2.24 -1.9FinalBiological 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 DOblank ) ] / PChemical Oxygen Demand 49x100 20 x2 -(COD) mg/L =4900 =40
Question 1 : Compare the COD and BOD readings in both samples. Do you think thatthe 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.
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.
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.