Mass transfer affects reactor performance, microbial morphology, and community succession in the methane-dependent denitrification and anaerobic ammonium oxidation co-culture

Denitrifying anaerobic methane oxidation (DAMO) combining anaerobic ammonium oxidation (Anammox) process is a novel nitrogen removal technology. However, the roles of methane transfer (gas phase) and nitrogen transfer (liquid phase) in the heterogeneous process remain unclear. In this study, granular DAMO and Anammox co-cultures were inoculated from a hollow-fiber membrane bioreactor into a sequence batch reactor (SBR). Since the methane transfer became limited in SBR, the nitrate removal rate first decreased and then increased to 10 mg/(L∙day), while the ammonium removal rate did not recover and was around 2 mg/(L∙day). The activity of DAMO archaea and Anammox bacteria decreased noticeably. Furthermore, granular aggregates dispersed into small granules and ultimately became flocs with poor settleability in SBR. The content of extracellular polymeric substances decreased, especially that of proteins and humics. DAMO archaea decreased by 94.6% and Anammox bacteria decreased by 72%. In summary, the limitation of methane transfer affected DAMO and Anammox processes more notably than nitrogen transfer, resulting in lower nitrogen removal, granule disruption, and microbial community succession. [Display omitted] •CH4 transfer is more crucial than N transfer in the DAMO & Anammox co-culture.•Mass transfer limitation causes DAMO-Anammox granules disruption and bad settling.•Mass transfer affects N removal and DAMO archaea and Anammox bacteria activity.•CH4 limitation affects microbial community and decreases DAMO archaea by 94.6%.•Mass transfer impacts interactions between DAMO and Anammox microorganisms.