Measuring the BOD and COD Value, and Calculation of the BOD/COD Ratio

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  • Topic: Water pollution, Biochemical oxygen demand, Wastewater
  • Pages : 4 (1332 words )
  • Download(s) : 134
  • Published : March 20, 2012
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Discussion
Before discussing the results of the BOD and COD tests carried out, it is vital to know the different between both tests. The BOD is the measure of the dissolved oxygen which is done with a DO meter. Dissolved oxygen (DO) is the amount of oxygen present in the water sample. Whereas BOD is a calculation and it is the amount of oxygen that would be consumed in 5days by the bacteria. However in this experiment, BOD is the difference of the dissolved oxygen after 7 days. COD on the other hand measures the microorganisms’ chemical oxidation instead of the biochemical oxidation like BOD. So this is the reason for the tenuous relationship between COD and BOD. These tests do not have a direct relationship but one can be obtained empirically by performing the test a number of times. Keeping this in mind we can now analyze the results obtained in this lab which are 136.2 mg/L and 365.2 mg/L for the BOD7 and COD values respectively. The BOD/COD ratio is 0.373. Knowing that the BOD/COD wastewater ratio should be approximately 0.5, the percent yield obtained is 75% so there are definitely different sources of errors that affected the ratio which will be mentioned and elaborated on in this discussion. Additionally, this ratio makes it possible to presume that the tested sample is from industrial wastewater. This wastewater can be cleaned by making it undergo chemical treatment. This ratio can be categorized in the acceptable zone hence primary treatment would be the best way of treating this water sample. One of the conditions for the BOD test is that it has to be incubated in the dark to avoid photosynthesis. In other words, to avoid algae growth; this will consume the oxygen in the water and as a result increase the BOD values. This test must also be carried out at constant temperature, at 20⁰ C being that this test consists of microorganisms whose activity has a direct relationship with temperature increase. This part of the lab was taken care of by the lab...
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