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

[Display omitted] • AnMBR was used to treat real municipal wastewater. • CO 2 % was reduced to balance with the alkalinity in carbonate equilibrium system. • Successful pH control was accomplished by in-situ CO 2 removal. • Biogas upgradation, pH control and reduction of GHG were realized in the AnMBR. 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 HCO 3 –/CO 2 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 CO 2 from biogas in the liquid phase. Therefore, this study employed the in-situ removal of CO 2 from biogas using soda lime to reduce the CO 2 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. [ABSTRACT FROM AUTHOR]