Catalytic reduction of NACs by nano Fe3O4/quinone composites in the presence of a novel marine exoelectrogenic bacterium under hypersaline conditions

Bioremediation of N-substituted aromatic compounds (NACs) has attracted a substantial amount of interest due to its cost effectiveness and environmental friendliness. However, the slow anaerobic NACs' reduction rate and the large amount of salt in wastewater are bottlenecks for biotechnology applications. In this study, a novel marine strain, Shewanella sp. CNZ-1, capable of reducing NACs under hypersaline conditions was isolated. To enhance the NACs reduction rate, two Fe3O4/quinone nanocomposites were first prepared via a mild covalent chemical reaction. SEM-EDX, FTIR, XRD, XPS, TG and VSM analyses were performed to illustrate the reaction process. The catalytic results showed that Fe3O4/2-carboxyl-anthraquinone (Fe3O4@COOHQ) exhibited a better catalytic performance in typical NACs bioreduction compared to Fe3O4/1,4-diamino-anthraquinone in the presence of strain CNZ-1. The NC reduction rates were approximately 2.2- to 6.5-fold higher than those lacking Fe3O4@COOHQ at 2-11% NaCl. The highest NC removal rate of 79.4 mg per h per g cell was achieved at 3% NaCl. The increased NC reduction rate is mainly due to the fact that Fe3O4@COOHQ could increase the NC reduction activity of cell membrane proteins containing dominant NC reductases. These findings indicate that strain CNZ-1 and Fe3O4@COOHQ could be used in designing a bioreactor for enhancing the treatment of NACcontaining wastewater containing a high concentration of salts.