Performance and mechanisms of a microbial-earthworm ecofilter for removing organic matter and nitrogen from synthetic domestic wastewater

► A combination of soil with sawdust and wormcast facilitate OM and NH3-N reduction. ► Higher diverse community of AOB and Nitrospira in soil layers than other layers. ► Positive correlation between AOB biodiversity and decreasing NH3-N concentration. ► Soil plays a major role in COD removal and nitrogen conversion. ► The dominant AOB microbial compositions belong to uncertain AOB genus.