Role of Nano-Fe3O4 for enhancing nitrate removal in microbial electrolytic cells: Characterizations and microbial patterns of cathodic biofilm

Performance and mechanism of nano Fe-Al bimetallic oxide enhanced constructed wetlands for the treatment of Cr(VI)-contaminated wastewater

Enhancing the synergistic interactions between substrates and microorganisms in constructed wetlands (CWs) represents a promising approach for treating heavy metal-contaminated wastewater. Multifunctional nanomaterials may play a significant role in this process. However, their impacts and mechanisms in this context remain unclear. In this study, artificial zeolite spheres loaded with Fe-Al double metal oxide (Fe-Al-NBMO) were synthesized and utilized in the CW to treat Cr(VI)-contaminated wastewater. Adsorption experiments demonstrated that the adsorption capacity of Fe-Al-NBMO loaded substrate for Cr(VI) was 988.43 mg/kg at an initial concentration of 30 mg/L, 361, and 37 times higher than that of gravel and carrier, respectively. The CW experiment indicated that the Cr(VI) effluent concentration in CW-ZL with Fe-Al-NBMO substrate did not exceed the integrated wastewater discharge standard (GB8978-1996) (0.5 mg/L) at an influent concentration of 50 mg/L. The introduction of the Fe-Al-NBMO substrate promoted microbial growth and increase the Extracellular Polymeric Substances (EPS) and other metabolite contents, thereby enhancing the microbial adsorption of Cr(VI). Furthermore, the removal performance of Cr(VI) was enhanced by the increase in resistant microorganisms (Hyphomicrobium and Rhodopseudomonas) and functional genes. Notably, metaproteomic analysis revealed that the elevated abundance of NADH-quinone oxidoreductase (nuoB, nuoC, nuoD, nuoE, nuoF, and nuoG), reductive coenzymes (fbp, ALDO, mcrA, and cdhC), metabolic pathways of sulfur (Cysp), and glutathione transferase (GsiB, frmA, and gfa) contributed to Cr(VI) removal. Our results provide a robust strategy for treating Cr(VI)-contaminated wastewater by CWs with Fe-Al-NBMO loaded substrate.

Sustained energy generation from unusable waste steel through microbial assisted fuel cell systems

In the present study, a novel green energy generation process assisted with Microbial Fuel Cell (MFC) principle for generation of electricity from used or wasted steel is explored. Through a unique approach, unused and other steel waste are recast by simple re-melting with a flexible wide composition for generation of green energy. A microbial-assisted electron transfer derived from the degradation of the steel material is utilized for production of green energy in a microbial galvanic reactor system. A. ferrooxidans acts as biocatalysts, facilitating the oxidization of ferrous ion (Fe2+) to ferric ion (Fe3+). The reaction takes place on the biofilm matrix which results in oxidised reactive zones that endorses further degradation or dissolution of Fe anode. This consequently results in achieving the highest power density as high as 4.92 ± 0.03 mW/cm2 at a current density of 0.01 ± 9 mA/cm2. The total cost of the unusable steel anode and other accessories are roughly estimated to be 7.94 $/m2 and 178.54 $/m2 and the gain from unit power generation is estimated to be 3.79 $/W, assuming continuous operation of 4.92 ± 0.03 mW/cm2. The present study presents a potent methodology/strategy for the generation of sustainable bioenergy from low-cost, unusable steel materials, which cannot be anyway used as such in other battery systems, say iron air cells/batteries.

Multi-dimensional perspectives into the pervasive role of microbial extracellular polymeric substances in electron transport processes

During the process of biological treatment, most microorganisms are encapsulated in extracellular polymeric substances (EPS), which protect the cell from adverse environments and aid in microbial attachment. Microorganisms utilize extracellular electron transfer (EET) for energy and information interchange with other cells and the outside environment. Understanding the role of steric EPS in EET is critical for studying microbiology and utilizing microorganisms in biogeochemical processes, pollutant transformation, and bioenergy generation. However, the current study shows that understanding the roles of EPS in the EET processes still needs a great deal of research. In view of recent research, this work aims to systematically summarize the production and functional group composition of microbial EPS. Additionally, EET pathways and the role of EPS in EET processes are detailed. Then factors impacting EET processes in EPS are then discussed, with a focus on the spatial structure and composition of EPS, conductive materials and environmental pollution, including antibiotics, pH and minerals. Finally, strategies to enhance EET, as well as current challenges and future prospects are outlined in detail. This review offers novel insights into the roles of EPS in biological electron transport and the application of microorganisms in pollutant transformation.

Review of cathodic electroactive bacteria: Species, properties, applications and electron transfer mechanisms

Cathodic electroactive bacteria (C-EAB) which are capable of accepting electrons from solid electrodes provide fresh avenues for pollutant removal, biosensor design, and electrosynthesis. This review systematically summarized the burgeoning applications of the C-EAB over the past decade, including 1) removal of nitrate, aromatic derivatives, and metal ions; 2) biosensing based on biocathode; 3) electrosynthesis of CH4, H2, organic carbon, NH3, and protein. In addition, the mechanisms of electron transfer by the C-EAB are also classified and summarized. Extracellular electron transfer and interspecies electron transfer have been introduced, and the electron transport mechanism of typical C-EAB, such as Shewanella oneidensis MR-1, has been combed in detail. By bringing to light this cutting-edge area of the C-EAB, this review aims to stimulate more interest and research on not only exploring great potential applications of these electron-accepting bacteria, but also developing steady and scalable processes harnessing biocathodes.

Potential mechanisms of propionate degradation and methanogenesis in anaerobic digestion coupled with microbial electrolysis cell system: Importance of biocathode

Microbial electrolysis cells (MEC) have the potential for enhancing the efficiency of anaerobic digestion (AD). In this study, microbiological and metabolic pathways in the biocathode of anaerobic digestion coupled with microbial electrolysis cells system (AD-MEC) were revealed to separate bioanode. The biocathode efficiently degraded 90 % propionate within 48 h, leading to a methane production rate of 3222 mL·m-2·d-1. The protein and heme-rich cathodic biofilm enhanced redox capacity and facilitated interspecies electron transfer. Key acid-degrading bacteria, including Dechloromonas agitata, Ignavibacteriales bacterium UTCHB2, and Syntrophobacter fumaroxidans, along with functional proteins such as cytochrome c and e-pili, established mutualistic relationships with Methanothrix soehngenii. This synergy facilitated a multi-pathway metabolic process that converted acetate and CO2 into methane. The study sheds light on the intricate microbial dynamics within the biocathode, suggesting promising prospects for the scalable integration of AD-MEC and its potential in sustainable energy production.