Compost-derived humic and fulvic acid coupling with Shewanella oneidensis MR-1 for the bioreduction of Cr(Ⅵ)

Abstract

The compost-derived humic acids (HA) and fulvic acids (FA) contain abundant active functional groups with strong redox capacity, which can function as an electron shuttles for promoting the reduction of heavy metals, thus changing the form of the pollutants in the environment and reducing their toxicity. Therefore, in this study, UV–Vis, FTIR, 3D-EEM, electrochemical analysis were applied to study the spectral characteristics and electron transfer capacity (ETC) of HA and FA. Upon analysis, the results showed an increasing trend of ETC and humification degree (SUVA254) for both HA and FA during composting. However, the aromatic degree (SUVA280) of HA was higher than FA. After 7 days of culture, 37.95% of Cr (Ⅵ) was reduced by Shewanella oneidensis MR-1 (MR-1) alone. Whereas, only if HA or FA existed, the diminution of Cr (Ⅵ) reached 37.43% and 40.55%, respectively. However, the removal rate of Cr (Ⅵ) by HA/MR-1 and FA/MR-1 increased to 95.82% and 93.84% respectively. It indicated that HA and FA acted as electron shuttles, mediating the transfer of electrons between MR-1 and the final electron acceptor, effectively facilitating the bioreduction of Cr (Ⅵ) to Cr (Ⅲ) and also determined via correlation analysis. This study suggested compost-derived HA and FA coupling with MR-1 exhibited excellent performance for the bioreduction of Cr (Ⅵ) to Cr (Ⅲ).