Oxidation Reduction Potential
ORP Ranges Important in Wastewater
Treatment Operations
ORP Ranges (Broad) for Wastewater Processes
Anaerobic
(Reductive)
Aerobic
(Oxidative)
Anoxic
Activated Sludge
Nitrification
Denitrification
Methanogenesis
-200 mV
0 mV
+200 mV
ORP Ranges for Wastewater Processes
Anaerobic
(Reductive)
Aerobic
(Oxidative)
Anoxic
Activated Sludge
Nitrification
Denitrification
Methanogenesis
-200 mV
-150
mV
-100
mV
0 mV
+100
mV
+150
mV
+200 mV
ORP Ranges for Various Wastewater Processes
Anaerobic
(Reductive)
Aerobic
(Oxidative)
Anoxic
Solids will clump, float, and carryover in the secondary clarifier
Activated Sludge
Biological Phosphorus Removal
Sulfide (H2S) Formation
Denitrification
Acid Formation
Biological Phosphorus
Release
Nitrification
Methane Production
-400
mV
-300
mV
-250
mV
-200
mV
-150
mV
-100
mV
-50
mV
0 mV
+50
mV
+100
mV
+150
mV
+200
mV
+250
mV
+300
mV
+350
mV
Biochemical Reaction
ORP, mV
Nitrification
+100 to +350
COD degradation with free molecular oxygen
+50 to +250
Biological phosphorus removal
+25 to +250
Denitrification
+50 to -50
Sulfide (H2S) formation
-50 to -250
Biological phosphorus release
-100 to -250
Acid formation (fermentation)
-100 to -225
Methane production
-175 to -400