Natural mackinawite-based elimination of vanadium and ammonium from wastewater in autotrophic biosystem

Vanadium (V) production results in significant amounts of wastewater, which often co-contains considerable ammonium (NH₄⁺) after being used as precipitants. Both pentavalent V [V(V)] and NH₄⁺ can be removed independently through biological process. However, internal interactive biotechnology for one-step elimination of V(V) and NH₄⁺ remains an enigma. In this study, we proposed biologically removing V(V) and NH₄⁺ simultaneously with natural mineral mackinawite as electron donor and its oxidation products as electron acceptors. Our bioreactor achieved a V(V) removal efficiency of 99.5 ± 0.22 % and an NH₄⁺-N removal capacity of 49.5 ± 0.40 g/m³·d. V(V) was reduced to tetravalent V precipitates, while mackinawite was bio-oxidized to Fe(III) and sulfate. Metagenomic binning analysis indicated Sulfurivermis sp. mediated mackinawite oxidation and V(V) reduction. Putative Pseudomonas sp. conducted NH₄⁺ assimilation, anaerobic ammonium oxidation coupled to Fe(III) reduction (Feammox), and denitrification, achieving complete NH₄⁺-N removal. Real-time qPCR validated the upregulation of functional genes involved in V(V) reduction and nitrogen metabolisms, with improved functional enzyme activities. Cytochrome c, nicotinamide adenine dinucleotide, and extracellular polymeric substances promoted electron transfer, facilitating the elimination of both V(V) and NH₄⁺-N from wastewater. This study offers a novel and sustainable biological strategy for one-step treating V industrial wastewater.