Anaerobic bioreduction of elemental sulfur improves bioavailability of Fe (III) oxides for bioremediation

Sulfur cycle process accelerates microbial fuel cells driven denitrification system: Low sulfate yield and enrichment of functional microorganisms

The denitrification of dual-chamber microbial fuel cells cathodic chamber driven by sulfur powder has the advantages of economy, efficient and pollution-free. However, the low electron utilization of anodic chamber (ACE) and high sulfate (SO42-) production limit its application. Therefore, the cooperation of calcined pyrite (CP) and γ-FeOOH was proposed to solve the above bottleneck problems (S-CP-γ-FeOOH). The results showed that after adding CP and γ-FeOOH to S system, the nitrate removal rate (NRR) changed from 20.39 ± 0.37 % to 94.11 ± 1.40 %; ACE increased from 11.10 ± 0.76 % to 61.05 ± 7.82 %; and SO42- content decreased by 61.26 %. CP and γ-FeOOH promoted the intra/extracellular electron transfer process. SO42- was reduced to sulfur compounds after γ-FeOOH was added, which improved the electron generation efficiency of the anodic chamber. The addition of CP and γ-FeOOH not only enriched sulfur-oxidizing bacteria and enhanced their metabolic activity, but γ-FeOOH also promoted sulfate-reducing bacteria, all of which improved NRR.

Dual-purpose elemental sulfur for capturing and accelerating biodegradation of petroleum hydrocarbons in anaerobic environment

Hydrophobic organic pollutants in aqueous environments are challenging to biodegrade due to limited contact between microorganisms, the pollutants and the electron acceptor, particularly under anaerobic or anoxic conditions. Here, we propose a novel strategy that uses inexpensive, dual-function elemental sulfur (S0) to enhance biodegradation. Using petroleum hydrocarbons as the target pollutants, we demonstrated that hydrophobic and nonpolar S° can concentrate hydrocarbons while simultaneously serving as an electron acceptor to enrich hydrocarbon-degrading bacteria. The permeable reactive barrier filled with S0 effectively removed petroleum hydrocarbons. In addition to rapid adsorption, we discovered, for the first time, that petroleum hydrocarbons underwent efficient biodegradation through the reduction of S0. Specifically, n-alkanes were degraded by 80 % to 90 % and polycyclic aromatic hydrocarbons by 40 % to 95 %. These degradation rates were 17 % to 30 % and 26 % to 43 % higher, respectively, compared to those observed without S0. Consecutive subcultures combined with untargeted metabolomics analysis revealed that bacteria capable of dissimilatory sulfur reduction enhanced the fermentation process. These bacteria provided electrons to the metabolic network, which facilitated the mineralization of petroleum hydrocarbons. Our findings highlight the significant potential of S° for removing hydrophobic organic pollutants in oxygen-free environments, demonstrate the feasibility of integrating adsorption, biodegradation, and electron supply to enhance pollutant removal.

Enhanced Stability and Detection Range of Microbial Electrochemical Biotoxicity Sensor by Polydopamine Encapsulation

With the rapid development of modern industry, it is urgently needed to measure the biotoxicity of complex chemicals. Microbial electrochemical biotoxicity sensors are an attractive technology; however, their application is usually limited by their stability and reusability after measurements. Here, we improve their performance by encapsulating the electroactive biofilm with polydopamine (PDA), and we evaluate the improvement by different concentrations of heavy metal ions (Cu2+, Ag+, and Fe3+) in terms of inhibition ratio (IR) and durability. Results indicate that the PDA-encapsulated sensor exhibits a more significant detection concentration than the control group, with a 3-fold increase for Cu2+ and a 1.5-fold increase for Ag+. Moreover, it achieves 15 more continuous toxicity tests than the control group, maintaining high electrochemical activity even after continuous toxicity impacts. Images from a confocal laser scanning microscope reveal that the PDA encapsulation protects the activity of the electroactive biofilm. The study, thus, demonstrates that PDA encapsulation is efficacious in improving the performance of microbial electrochemical biotoxicity sensors, which can extend its application to more complex media.

Reduction of S0 deposited on electroactive biofilm under an oxidative potential

The inevitable deposition of S⁰ on the electroactive biofilm (EAB) via anodic sulfide oxidation affects the stability of bioelectrochemical systems (BESs) when an accidental discharge of sulfide occurred, leading to the inhibition of electroacitivity, because the potential of anode (e.g., 0 V versus Ag/AgCl) is ~500 mV more positive than the redox potential of S^2-/S⁰. Here we found that S⁰ deposited on the EAB can be spontaneously reduced under this oxidative potential independent of microbial community variation, leading to a self-recovery of electroactivity (> 100 % in current density) with biofilm thickening (~210 μm). Transcriptomics of pure culture indicated that Geobacter highly expressed genes involving in S⁰ metabolism, which had an additional benefit to improve the viability (25 % - 36 %) of bacterial cells in biofilm distant from the anode and the cellular metabolic activity via electron shuttle pair of S⁰/S^2-(S_x^2-). Our findings highlighted the importance of spatially heterogeneous metabolism to its stability when EABs encountered with the problem of S⁰ deposition, and that in turn improved the electroactivity of EABs.