Ligands regulate the application of Fe(III)-ligands on Se(IV) bioreduction: Electron transfer, metabolism activity and EPS secretion

Ligands influence the performance of Fe(III) on pollutant biotreatment by affecting the properties of Fe(III), but few studies focused on the effect and mechanism for Fe(III)-ligands on Se(IV) bioreduction. Results showed that 5 mM Fe(III)-ligands (ethylenediaminetetraacetic acid ferric sodium salt (Fe(III)EDTA) and ferric citrate (Fe(III) Cit)) could accelerate 4-5 times of Se(IV) bioreduction rate by accelerating electron transfer rate, improving metabolism activity and enhancing extracellular polymeric substances (EPS) secretion, while the performance of Fe(III)Cit and Fe(III)EDTA to accelerate Se(IV) bioreduction was influenced by ligands. Cyclic voltammetry (CV) results showed that the specific capacitance in BK + Fe(III)EDTA was 64.43% higher than BK + Fe(III)Cit. But, the adenosine triphosphate (ATP) in BK + Fe(III)Cit was 67.29 % higher than BK + Fe(III)EDTA. Meanwhile, electron transport system activity (ETSA), reduced coenzyme I (NADH) and cytochrome c contents in BK + Fe (III)Cit were also higher than those in BK + Fe(III)EDTA. EPS analysis showed that Fe(III)EDTA led to decreased aromatic protein content in EPS, while Fe(III)Cit could enhance aromatic protein content in EPS. This study provided a new insight and valuable mechanism for Fe(III)-ligands to regulate Se(IV) bioreduction.