All remediation processes come down to mass balance. How many pounds or kilograms of a contaminant exists in the subsurface, and how much of this mass can be removed by the proposed remediation system? With aerobic bioremediation, the mass balance is a function of the stoichiometry of the oxidation-reduction reactions that govern the biological utilization of a particular compound. For example, oxidation-reduction reactions for the aerobic utilization of benzene are as follows:
Oxidation Reaction: C6H6 + 12 H2O → 6 CO2 + 30 H+ + 30 e–
Reduction Reaction: 7.5 O2 + 30 H+ + 30 e- → 15 H2O
Overall Reaction: C6H6 + 7.5 O2 → 6 CO2 + 3 H2O
The O2 requirement for this reaction is that 1 mole of C6H6 requires 7.5 moles of O2. Converting to the appropriate mass ratio results in the following:
1 unit C6H6 : 7.5 x (32/78) units of O2, or 1 unit C6H6 requires 3 units of O2
Additional info on the science behind Aerobic Bioremediation can be found at the ETEC web site.