Highly enriched anammox within anoxic biofilms by reducing suspended sludge biomass in a real-sewage A2/O process

This study proposes a novel strategy of stably enriching anammox in mainstream, based on the compet-itive difference to NO2-; between anoxic biofilms and suspended sludge. A modified anaerobic-anoxic-oxic (A(2)/O) process run for 500 days with actual municipal wastewater. Microbial analysis revealed that anoxic-carrier biofilms had a significantly higher abundance of anammox (qPCR: 0.74%-4.34%) than sus-pended sludge (P < 0.001). Batch tests showed that anammox within anoxic-carrier biofilms contributed to significant nitrogen removal, coupled with partial-denitrification (NO3-+ NO2-). The anammox genus, Ca. Brocadia, was highly enriched when suspended sludge was accidentally lost. Further batch tests found that reducing suspended biomass helped anammox enrichment in anoxic-carrier biofilms, because the suspended sludge had strong NO2- competition (NO2--+ N-2 ) with anammox (increased nirK). Metage-nomic sequencing revealed that Ca. Brocadia dominates in the anoxic-carrier biofilms, and is the most important narG contributor to NO3-+ NO2-, which could have promoted the competition of NO2- with heterotrophic bacteria. For this A(2)/O process, the low effluent total nitrogen (8.9 mg +/- 1.0 mg N/L) was attributed to partial-denitrification coupling with anammox, demonstrating that this process is applica-ble to the general influent N-concentration range (30 mg-50 mg NH4+-N/L) of municipal wastewater treatment plants (WWTPs). Based on the special competitive preference of anammox for NO2,- this study provides a promising and practical alternative for enriching anammox bacteria in municipal WWTPs. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study proposes a novel strategy for stably enriching anammox in mainstream by utilizing competitive differences between anoxic biofilms and suspended sludge. Experimental results showed that anammox was significantly more abundant in anoxic-carrier biofilms compared to suspended sludge, and batch tests confirmed the effectiveness of anammox for nitrogen removal. Overall, this study demonstrates a promising and practical alternative for enriching anammox bacteria in municipal wastewater treatment plants.