Carbon Dioxide and Sewage

There are plenty of sites on the internet describing your problem. You may want to contact someone with hands on experience with CO2 and alkaline sewage and Praxair would be good. It would also be helpful to know the actual alkalinty as CaCO3 in mg/L.

It can be done but that will depend on what is raising your pH level. For limewater you need 2 moles of CO₂ for one mole of lime so as to precipitate the calcium out as insoluble CaCO₃. Too much will cause the calcium to redissolve as highly soluble CaHCO₃. For soda or potash you need to neutralize them first and then keep adding CO₂ to lower the pH.