Wire-drawing process with graphite lubricant as an industrializable approach to prepare graphite coated stainless-steel anode for bioelectrochemical systems

Regulating microbial redox reactions towards enhanced removal of refractory organic nitrogen from wastewater

Biotechnology for wastewater treatment is mainstream and effective depending upon microbial redox reactions to eliminate diverse contaminants and ensure aquatic ecological health. However, refractory organic nitrogen compounds (RONCs, e.g., nitro-, azo-, amide-, and N-heterocyclic compounds) with complex structures and high toxicity inhibit microbial metabolic activity and limit the transformation of organic nitrogen to inorganic nitrogen. This will eventually result in non-compliance with nitrogen discharge standards. Numerous efforts suggested that applying exogenous electron donors or acceptors, such as solid electrodes (electrostimulation) and limited oxygen (micro-aeration), could potentially regulate microbial redox reactions and catabolic pathways, and facilitate the biotransformation of RONCs. This review provides comprehensive insights into the microbial regulation mechanisms and applications of electrostimulation and micro-aeration strategies to accelerate the biotransformation of RONCs to organic amine (amination) and inorganic ammonia (ammonification), respectively. Furthermore, a promising approach involving in-situ hybrid anaerobic biological units, coupled with electrostimulation and micro-aeration, is proposed towards engineering applications. Finally, employing cutting-edge methods including multi-omics analysis, data science driven machine learning, technology-economic analysis, and life-cycle assessment would contribute to optimizing the process design and engineering implementation. This review offers a fundamental understanding and inspiration for novel research in the enhanced biotechnology towards RONCs elimination.

Synergistic effect of electrotrophic perchlorate reducing microorganisms and chemically modified electrodes for enhancing bioelectrochemical perchlorate removal

Perchlorate has been described as an emerging pollutant that compromises water sources and human health. In this study, a new electrotrophic perchlorate reducing microorganism (EPRM) isolated from the Atacama Desert, Dechloromonas sp. CS-1, was evaluated for perchlorate removal in water in a bioelectrochemical reactor (BER) with a chemically modified electrode. BERs were operated for 17 days under batch mode conditions with an applied potential of -500 mV vs. Ag/AgCl. Surface analysis (i.e., SEM, XPS, FT-IR, RAMAN spectroscopy) on the modified electrode demonstrated heterogeneous transformation of the carbon fibers with the incorporation of nitrogen functional groups and the oxidation of the carbonaceous material. The BERs with the modified electrode and the presence of the EAM reached high cathodic efficiency (90.79 ± 9.157%) and removal rate (0.34 ± 0.007 mol m-3-day) compared with both control conditions. The observed catalytic enhancement of CS-1 was confirmed by a reduction in the charge transfer resistance obtained by electrochemical impedance spectroscopy (EIS). Finally, an electrochemical kinetic study revealed an eight-electron perchlorate bioreduction reaction at -638.33 ± 24.132 mV vs. Ag/AgCl. Therefore, our results show the synergistic effect of EPRM and chemically modified electrodes on perchlorate removal in a BER.

Microbial-Inspired Surface Patterning for Selective Bacterial Actions for Enhanced Performance in Microbial Fuel Cells

The performance of any bio-electrochemical system is dependent on the efficiency of electrode-microbial interactions. Surface properties play a focal role in bacterial attachment and biofilm formation on the electrodes. In addition to electrode surface properties, selective bacterial adhesion onto the electrode surface is mandatory to mitigate energy loss due to undesired bacterial interactions on the electrode surface. In the present study, microbial-patterned graphite scaffolds are developed for selective bacterial-electrode interactions. A power density as high as 1105 mW/m² is achieved with mG-E (a graphite electrode patterned with Escherichia coli), which is about 3 times higher than that of the pristine graphite electrode (370 mW/m²). Initial mechanical pre-treatment of the graphite electrode, followed by bacterial patterning, results in the formation of a unique cobblestone topography with a tuned surface area of 127.12 m²/g. This provides suitable morphology with enhanced active sites for selective bacterial intercalation in graphite layers. This cannot be otherwise achieved by any mechanical or other means. A unique methodology of symbolic regression is adopted to validate a genetic algorithm suitable for predicting a perfect correlation between surface characteristics and electrochemical characteristics with a minimum root-mean-square error of 0.08. The bacterial intercalation onto the graphite electrode causes protuberance of the graphite layers that reduces the surface potential and resistance, leading to high electron transfer. The study presents a unique bacterial-inspired surface patterning on the anode, which is critical for the performance of a microbial fuel cell.

Fabrication of Pd/Sludge-biochar electrode with high electrochemical activity on reductive degradation of 4-chlorophenol in wastewater

Effective treatment and utilization of sludge contribute to achieve conventional carbon emission reduction and resource recovery, which is of great significance to realize carbon neutralization of WWTPs. Sludge carbonization derived biochar has attracted more interest because of high potential as catalytic materials. Therein, sludge-derived electrode exhibits a promising potential in the case of sludge utilization for electrocatalysis, however, electrocatalytic performance of the already reported sludge-derived electrode is unsatisfactory due to insufficient active sites. In this study, an efficient Pd/sludge-biochar loaded foam nickel (Pd-SAC@Ni) was successfully fabricated using simple pyrolysis and solidification method, and exhibited remarkable electrocatalytic performance for 4-chlorophenol (4-CP) degradation. Furthermore, the morphology, element distribution and crystal composition were characterized by SEM, EDS, XPS and XRD. The Pd-SAC@Ni electrode exhibited superior electrocatalytic performance than Ni, SAC@Ni, Pd-Ni electrodes. The reduction rate of 98.9% was achieved at current density of 5 mA cm^-2, 4-CP concentration of 0.8 mM and initial pH of 7.0. Also, Pd-SAC@Ni electrode showed desirable reusability and achieved 98% of 4-CP removal after multiple runs of experiments. Moreover, the active hydrogen species (H*) generation capacity of electrodes was determined using tert-butanol (TBA) as trapping agent. The mechanism analysis demonstrated that direct reduction process and indirect reduction process both involved in the 4-CP degradation process, and their contribution were 19.5% and 80.5%, respectively. Then, the intermediates formed in the electrochemical degradation of 4-CP were revealed by HPLC and the plausible degradation pathway was proposed. This study provides a cost-effective approach for preparing sludge biochar electrode, and explored a novel way to promote resourceful utilization of sludge for carbon neutrality.

Advances in cathode designs and reactor configurations of microbial electrosynthesis systems to facilitate gas electro-fermentation

In gas fermentation, a range of chemolithoautotrophs fix single-carbon (C1) gases (CO₂ and CO) when H₂ or other reductants are available. Microbial electrosynthesis (MES) enables CO₂ reduction by generating H₂ or reducing equivalents with the sole input of renewable electricity. A combined approach as gas electro-fermentation is attractive for the sustainable production of biofuels and biochemicals utilizing C1 gases. Various platform compounds such as acetate, butyrate, caproate, ethanol, butanol and bioplastics can be produced. However, technological challenges pertaining to the microbe-material interactions such as poor gas-liquid mass transfer, low biomass and biofilm coverage on cathode, low productivities still exist. We are presenting a review on latest developments in MES focusing on the configuration and design of cathodes that can address the challenges and support the gas electro-fermentation. Overall, the opportunities for advancing CO and CO₂-based biochemicals and biofuels production in MES with suitable cathode/reactor design are prospected.

Shape Analysis of the Elastic Deformation Region throughout the Axi-Symmetric Wire Drawing Process of ETP Grade Copper

The wire drawing process is commonly perceived as one of the best studied metal forming processes in almost every aspect; however, when considering elastic deformation, researchers usually focus on the uniaxial tensile forces after the material exits the drawing die and not the elastic deformation region before entering the drawing die, even though it may have a significant impact on the strength parameters and the nature of metal flow inside the drawing die. The aim of this research is to theoretically and experimentally identify the deformation in the elastic region and to further link the shape of this region and the values of stress occurring in it with the geometrical parameters of the drawing process and assess its impact on its strength parameters. In order to achieve the assumed goals, numerical analyses using the finite element method and experimental research on the drawing process in laboratory conditions were carried out using Vickers hardness tests and resistance strain gauges measuring deformation in stationary and non-stationary conditions. The obtained results indicate that the shape and the extent of the region of elastic deformations generated in the material before the plastic deformation region during the drawing process depends on the applied deformation coefficient and stationarity of the process.