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Theoretical oxygen demand

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ThOD (Theoretical Oxygen Demand) 
                                                                            .

                    This is the calculated amount of oxygen required to oxidise a compound to its final oxidation products. However, there

are some differences between standard methods that can influence the results obtained: for example, some calculations assume that nitrogen

released from organics is generated as ammonia, whereas others allow for ammonia oxidation to nitrate. Therefore in expressing results, the

calculation assumptions should always be stated. 

 Inorder to determine the  ThOD for glycine (CH2 (NH2 )COOH)  using the following assumptions: 

     1. In the first step, the organic carbon and nitrogen are  converted to carbon dioxide (CO2 ) and 
         ammonia  (NH3 ), respectively.

     2.  In the second and third steps, the ammonia is  oxidized sequentially to nitrite and nitrate. 

     3.  The ThOD is the sum of the oxygen required for all  three steps. 

 We can calculate by following steps:

     1. Write balanced reaction for the carbonaceous oxygen demand.

            CH2(NH2)COOH + 1.502 ----->NH3 + 2CO2 + H2 0

     2.  Write balanced reactions for the nitrogenous oxygen demand.

                 NH3 + 1.502 -----> HNO2 + H20

                 HNO2 + 0.5O2 -----> HNO3

                NH3 + 2O2 -----> HNO3 + H2O

     3.  Determine the ThOD. 



       ThOD     = (1.5 + 2) mol O2/mol glycine

                = 3.5 mol O2/mol glycine X 32 g/mol O2 X 43 g/mol glycine

                = 2.6 g O2/g glycine
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