Unveiling organic loading shock-resistant mechanism in a pilot-scale moving bed biofilm reactor-assisted dual-anaerobic-anoxic/oxic system for effective municipal wastewater treatment

[Display omitted] •Effluent from bioreactor were influenced by organic loading shock.•High biomass and bacterial diversity were obtained by adding biocarriers.•Effective removal of carbon, nitrogen and phosphorus was established.•Coexistence of aerobic and anoxic micro-environments stimulated the SNDPR pathway.•D-A2MBBR showed high stability under OLR fluctuations (417.9–812.0 g COD m−3 d−1). Microbial biomass and activity are frequently subjected to organic loading shock (OLS) from decentralized municipal wastewater. A hybrid moving bed biofilm reactor-assisted dual-anaerobic-anoxic/oxic system (D-A2MBBR) was established by integrating dual-anaerobic-anoxic/oxic with moving bed biofilm reactor to resist OLS for stable nutrients removal. The D-A2MBBR achieved 91.57% of chemical oxygen demand, 93.33% of ammonia-nitrogen, 80.20% of total nitrogen and 92.68% of total phosphorus removal, respectively, under the fluctuation of organic loading rate from 417.9 to 812.0 g COD m−3 d−1. The 16S rRNA gene sequencing revealed that Gemmobacter (7.28%) was identified as dominating anoxic denitrifying genus in oxic chamber, confirming the coexistence of aerobic and anaerobic/anoxic micro-environments. This circumstance boosted simultaneous nitrification-denitrification and phosphorus removal and the microbial community evolution inside the multilayer biocarrier-attached biofilms. In general, the D-A2MBBR was able to provide unique, cooperative and robust bacterial consortia to form a buffer against OLS, and ensuring effluent stability.