Process Reaction  Redox potential (Eh in mV) 
Aerobic: O2 + 4e + 4H+ → 2H2O 600 ~ 400
Anaerobic:    
Denitrification 2NO3+ 10e + 12H+ → N2 + 6H2O 500 ~ 200
Manganese IV reduction MnO2 + 2e + 4H+ → Mn2+ + 2H2O 400 ~ 200
Iron III reduction Fe(OH)3 + e + 3H+ → Fe2+ + 3H2O 300 ~ 100
Sulfate reduction SO42− + 8e +10H+ → H2S + 4H2O 0 ~ −150
Fermentation 2CH2O → CO2 + CH4 −150 ~ −220
Source: Wikipedia, the free encyclopedia [6]
Table 3: The decreasing biological breakdown rate as function of the redox potential.