CO2 removal from biogas improved stable treatment of low-alkalinity municipal wastewater using anaerobic membrane bioreactor

This study addressed a less-reported issue: the insufficient alkalinity encountered when anaerobic membrane bioreactors (AnMBRs) are used to treat municipal wastewater (MWW). In the present study, a 20-L AnMBR was initiated at an MWW treatment plant. During the initial startup, a continuous decrease in pH was observed. Through the analyses of the balance between HCO₃^–/CO₂ in the biogas and alkalinity in the reactor, the cause of pH instability was determined to be that the alkalinity could not balance the acidity induced by the continuous dissolution of CO₂ from biogas in the liquid phase. Therefore, this study employed the in-situ removal of CO₂ from biogas using soda lime to reduce the CO₂ partial pressure, thereby achieving stable control of the pH in the reactor. This study provides valuable experience and technical support for anaerobic processes for treating low-alkalinity MWW in the future applications.