A classmate of yours is having a hard time with the concepts of Theoretical Oxyg

Question

A classmate of yours is having a hard time with the concepts of Theoretical Oxygen Demand (ThOD), Carbonaceous Biochemical Oxygen Demand (CBOD), and Nitrogenous Biochemical Oxygen Demand (NBOD) and is coming to you for help. Before even solving any problems or calculating any of these parameters, how would you explain to your classmate what all these terms mean? Be as explicit as possible. For example, how do these terms relate to each other, how do they depend on the particular organic compound considered, and exactly what do the units used to measure them mean.

Now that your classmate understands the general concept of ThOD, CBOD, and NBOD, he/she is beginning to solve specific problems. However, she/he is still puzzled by a particular aspect of the calculations and asks you the following question: “I sort of vaguely remember the instructor saying that if you want to calculate the NBOD for a compound, you need to calculate some sort of ‘theoretical N concentration’ in solution first. However, I don’t remember him ever calculating a corresponding C concentration in solution to calculate the CBOD. How come? Shouldn’t we? Is there a difference in how we handle C and N? Should there be a difference? Why or why not? Please help!!” Well, how would you answer this legitimate question that your good friend has? Needless to say, you want to be as clear and helpful as possible.

Explanation / Answer

Amount of oxygen required for oxidation of ammonia and nitrite contaminants in wastewater is called Nitrogenous Biochemical Oxygen Demand (NBOD; mg/L). Biological organisms in a body of waste water reacts with dissolved oxygen, the amount of oxygen reacted with biological organisms is called Carbonaceous Biochemical Oxygen Demand (CBOD; mg/L). Total required amount of oxygen (NBOD and CBOD) in above both processes is called theoretical oxygen demand (ThOD; mg/L), on the other hand we can say that ThOD is needed to oxidize a compound into its final oxidation products. For NBOD calculation, N is required for oxidation of ammonia and nitrite, but not C. Biological organisms reacts with oxygen and produce ammonia, carbon dioxide and water.

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