ThOD calculation step by step
Theoretical oxygen demand (thod) calculation
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1. STEP 1 : Gather data for theoretical oxygen demand calculation
2. STEP 2 : Calculate the ThOD
Environment protection is now a priority and water effluents form factories must be controlled to make sure they do not carry too much organic material. When introducing a new component in a factory, it can be interesting to understand what will be the oxygen demand in the effluents in case the component is released. This page explains how to calculate the theoretical oxygen demand for a component of known formula.
1. STEP 1 : Gather data for theoretical oxygen demand
calculation
In order to calculate the theoretical Oxygen Demand (ThOD), a chemical formula of the component must be determined as well as the reactions that are implied in the biodegradation of the material. The following example is the one of glycine.
Carbonaceous oxygen demand :
CH2(NH2)COOH + 3/2 O2 -> NH3+2 CO2+H2O
Nitrogenous oxygen demand :
NH3 + 3/2 O2 -> HNO2+H2O
HNO2+1/2 O2 -> HNO3
that can be simplified as : NH3 + 2 O2 -> HNO3 + H2O
2. STEP 2 : Calculate the ThOD
The theoretical oxygen demand can then be calculated from the equations above. It can be seen that for every mole of glycine, there will be a consumption of 3/2 + 2 = 7/2 = 3.5 moles of O2.
Considering that the molecular weight of O2 is 16*2 = 32 g/mol, the mass of oxygen to be consumed to degrade one mole of glycine can be calculated :
ThOD = 3.5 moles of O2/mole of glycine
ThOD = 3.5 * 32 g of O2/mole of glycine
ThOD = 11 g of O2/mole of glycine
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