Natural pyrite-enhanced co-culture system for simultaneous nitrate and ammonium removal under low C/N conditions: Mechanistic insights and real wastewater application.

This study investigates how natural pyrite (FeS2) systematically enhances mixed nitrogen removal (NO3--N: NH4+-N = 3:7) in a bacterial co-culture system consisting of Klebsiella oxytoca, Saccharomyces cerevisiae, and Bacillus sp. Although these strains possess intrinsic nitrogen conversion capacities, their performance is severely constrained under practical wastewater conditions featuring multiple nitrogen species and low carbon-to-nitrogen (C/N) ratios. The introduction of pyrite markedly improved nitrogen removal, particularly ammonium elimination. Kinetic analyses demonstrated that pyrite effectively alleviated dual substrate inhibition caused by elevated NH4+-N and NO3--N concentrations, while thermodynamic evaluation revealed that pyrite reduced the apparent activation energy, thereby facilitating nitrogen conversion. Mechanistically, iron speciation and electrochemical analyses jointly confirmed that pyrite establishes a mineral-microbe-mediator coupled electron transfer network, in which microbially driven Fe(II)/Fe(III) redox cycling and enhanced secretion of flavinlike mediators and extracellular polymeric substances synergistically promote interspecies electron transfer and metabolic activity. Application tests using industrial, landscape, and agricultural wastewaters further verified the robustness and operational stability of the pyrite-assisted systems, highlighting its practical potential as a sustainable amendment for low C/N nitrogen-contaminated wastewater treatment.