There is no general problem with CO and CO2 in wastewater so one cannot state limit concentrations.
I also agree with Henrik Rasmus Andersen and I would like to add that the upper limits are determined by their solubility in water which depends mainly determined on the pH and the temperature of the wastewater at atmospheric conditions.
Carbon dioxide CO2 dissolves very well in (waste)water at neutral or high pH and at moderate temperature. That's why we use CO2 to neutralize alkaline wastewaters. In contrast carbon dioxide CO dissolves very little in water.
We have our reactors covered (for some technology related reasons), and we experienced CO2 levels rise while pH getting low. Maybe these had no connections, I hadn't have the proper instruments to define; anyway, the treatment efficiency was slightly worse.
Laszlo Tutor
Probably your (bio)reactors produce CO2 from the conversion of organics. When you cover the reactors, CO2 will accumulate in the headspace (gas phase).
Then, according to Henry's law, more CO2 will remain dissolved in the water. Because CO2 is acid, the pH will drop accordingly.
Dear Bruno,
These are all clear. The important is that we experienced decline in treatment, despite CO2 content is usually not considered to be relevant. As I wrote, there might be a connection; and this connection might come from the temporary bound of alkalinity.
Low pH is generally considered to be a relevant problem for bioreactors. There is no difference if it is caused by CO2 or a mineral acid.