[erukus]

I am trying to work out the theoretical oxygen demand of a waste  through
converting the g/l or mass percents.  

I have been looking at the following:

To determine ThOD the general formulae for carbohydrates (C6H12O5), proteins
(C5H7O2N) and lipids (C57H104O4) were used. In order to fully oxidize CnHaObNc you
need n+a/4-b/2-3/4c mols of O2.

The amount of moles of each group of chemical components in a given mass was calculated,
from there the amount of moles of O2 needed for full oxidization.

Then it was multiplied by 32 g/mol to get the COD in grams.
Hence, the theoretical COD per unit mass of CnHaObNc can be quickly calculated by:

Equation  ThOD = 8·(4n+a-2b-3c)/(12n+a+16b+14c) gCOD/ g CnHaObNc

What I am confused about is what the (n, a, b, c) variables represent, do I simply
insert n=6 a=12 b=5 c=0 for hydrocarbons, or does it depend on the amount of
hydrocarbon I have, my understanding is that the variables would not change for
hydrocarbons regardless of the mass of it? can anyone clarify this.