Biochar mediated microbial synergy in Partial nitrification–anammox systems: enhancing nitrogen removal efficiency and stability

Abstract

This study investigated the role of biochar in enhancing nitrogen removal efficiency (NRE) and stability in partial nitrification–anammox (PN/A) systems, focusing on its selective promotion of partial denitrification and maintaining the dynamic balance between AnAOB and denitrifying bacteria (DNB). The results showed that biochar enhances electron transfer, effectively reduced nitrate accumulation and significantly improved PN/A system NRE and stability. Under high ammonium conditions (800 mg/L), biochar increased NRE in the PN/A system to 83.58%, a 10% improvement over the anammox-control (A_CK). Additionally, partial denitrification contributed 8% more to total nitrogen removal in the anammox-biochar (A_BC) system. The porous structure and redox-active groups of biochar provided an ideal environment for key microorganisms, promoted microbial growth and increased specific anammox activity by approximately 1.25–1.46 times compared to A_CK, further enhancing microbial stability under fluctuating nitrogen loads. Biochar also enriched AnAOB and DNB communities, sustained their dynamic balance and improved system stability by promoting nitrogen removal related gene expression. Overall, biochar demonstrated great potential for improving PN/A system efficiency, optimizing wastewater treatment, and reducing energy consumption and emissions.

Graphical abstract

Keywords

Biochar / Partial nitrification–anammox / AnAOB / Nitrogen removal efficiency / Microbial community

Highlight

	● Biochar improves nitrogen removal efficiency and stability in PN/A systems.
	● Biochar promotes partial denitrification by accelerating electron transfer.
	● Growth and activity of AnAOB and denitrifying bacteria are stimulated by biochar.
	● Biochar enhances the synergy between AnAOB and denitrifying bacteria.

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