Maifanite-amended pyrite biofilter for efficient autotrophic denitrification of low-C/N mariculture tailwater: mechanistic insights into microbial nitrogen–sulfur–iron coupling

Abstract

Mariculture tailwater, characterized by high nitrate (NO₃⁻-N) and a low carbon to nitrogen (C/N) ratio, presents a significant challenge for coastal environment protection. To address this, we developed a hybrid carrier biofilter combining pyrite and maifanite (PM) to enhance nitrogen removal performance. The PM biofilter achieved 88.98% total nitrogen (TN) removal—34.99% higher than that of a pyrite-only system. No secondary pollutants such as dissolved iron were produced during the treatment process. This enhancement was associated with synergistic effects, such as increased microbial biomass and activity, enhanced hydrophilicity and specific surface area of carriers, and elevated secretion of extracellular polymeric substance (EPS), particularly tryptophan-like proteins and humic acid-like organics. Additionally, the enriched microbial communities and functional genes associated with nitrogen, sulfur, and iron metabolism further supported key biogeochemical pathways in the PM. These findings highlight the PM biofilter as a promising strategy for low C/N ratio mariculture tailwater treatment and coastal environmental management.

Graphical abstract

Keywords

Biofilter / Mariculture tailwater / Low C/N ratio / Pyrite autotrophic denitrification / Maifanite

Highlight

	● A pyrite and maifanite (PM) biofilter significantly improved 34.99% of TN removal.
	● The PM provided adequate electron donors as higher microbial biomass and activity.
	● EPS content enhanced with the addition of maifanite.
	● N-S-Fe-related denitrifiers were enriched remarkably in the biofilter PM.
	● Increasing N-S-Fe genes ensured electron donor supply in the biofilter PM.

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