Electroactive microorganisms synthesizing iron sulfide nanoparticles for enhanced hexavalent chromium removal in microbial fuel cells

• Published in: The Science of the total environment 2023-09, Vol.889, p.164311-164311, Article 164311
• Main Authors: Fan, Mengjie, Zhuang, Xinglei, Gao, Zhen, Lv, Zuopeng, Dong, Weiliang, Xin, Fengxue, Chen, Yingwen, Jia, Honghua, Wu, Xiayuan
• Format: Article
• Language: English
• Subjects: Biocathode; Cr6+ removal; Hybridized electrode biofilm; Microbial fuel cell; Nano-FeS biosynthesis
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.164311

Microbial fuel cells (MFCs) have been considered a promising technology for Cr6+ removal, but they are limited by Cr6+-reducing biocathodes with low extracellular electron transfer (EET) and poor microbial activity. In this study, three kinds of nano-FeS hybridized electrode biofilms, obtained through synchronous biosynthesis (Sy-FeS), sequential biosynthesis (Se-FeS) and cathode biosynthesis (Ca-FeS), were applied as biocathodes for Cr6+ removal in MFCs. The Ca-FeS biocathode exhibited the best performance due to the superior properties of biogenic nano-FeS (e.g., more synthetic amount, smaller particle size, better dispersion). The MFC with the Ca-FeS biocathode achieved the highest power density (42.08 ± 1.42 mW/m2) and Cr6+ removal efficiency (99.18 ± 0.1 %), which were 1.42 and 2.08 times as high as those of the MFC with the normal biocathode, respectively. The synergistic effects of nano-FeS and microorganisms enhanced the bioelectrochemical reduction of Cr6+, first realizing deep reduction of Cr6+ to Cr0 in biocathode MFCs. This significantly alleviated the cathode passivation caused by Cr3+ deposition. In addition, the hybridized nano-FeS as “armor” layers protected the microbes from toxic attack by Cr6+, improving the biofilm physiological activity and extracellular polymeric substances (EPS) secretion. The hybridized nano-FeS as “electron bridges” facilitated the microbial community to form a balanced, stable and syntrophic ecological structure. This study proposes a novel strategy through the cathode in-situ biosynthesis of nanomaterials to fabricate hybridized electrode biofilms with enhanced EET and microbial activity for toxic pollutant treatment in bioelectrochemical systems. [Display omitted] •MFC cathode synthesis of nano-FeS produced a superior hybridized electrode biofilm.•The Ca-FeS biocathode had the best electrochemical and Cr6+ removal performance.•Nano-FeS hybridized biocathodes first realized the deep reduction of Cr6+ to Cr0.•Nano-FeS as “armor” layers protected biofilm microbes from toxic attack by Cr6+.•Nano-FeS as “electron bridges” constructed a syntrophic microbial community.