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In recent years, (bio)electrochemical systems (B)ES have emerged as an energy efficient alternative for the recovery of TAN (total ammonia nitrogen, including ammonia and ammonium) from wastewater. In these systems, TAN is removed or concentrated from the wastewater under the influence of an electrical current and transported to the cathode. Subsequently, it can be removed or recovered through stripping, chemisorption, or forward osmosis. A crucial parameter that determines the energy required to recover TAN is the load ratio: the ratio between TAN loading and applied current. For electrochemical TAN recovery, an energy input is required, while in bioelectrochemical recovery, electric energy can be recovered together with TAN. Bioelectrochemical recovery relies on the microbial oxidation of COD for the production of electrons, which drives TAN transport. Here, the state-of-the-art of (bio)electrochemical TAN recovery is described, the performance of (B)ES for TAN recovery is analyzed, the potential of different wastewaters for BES-based TAN recovery is evaluated, the microorganisms found on bioanodes that treat wastewater high in TAN are reported, and the toxic effect of the typical conditions in such systems (e.g., high pH, TAN, and salt concentrations) are described. For future application, toxicity effects for electrochemically active bacteria need better understanding, and the technologies need to be demonstrated on larger scale.

The assessment of water quality is critical to implement preventive and emergency interventions aimed to limit/avoid environmental contamination and human exposure to toxic compounds. While established high-resolution techniques allow quantitative and qualitative determination of contaminants, their widespread application is not feasible due to cost, time, and need for trained personnel. In this context, the development of easy-to-implement approaches for preliminary detection of contaminants is of the utmost importance. Herein, a portable self-powered microbial electrochemical sensor enabling online monitoring of Cr(VI) is reported. The biosensor employs a bio-inspired redox mediating system to allow extracellular electron transfer between a bacterial isolate from chromium-contaminated environments and the electrode, providing a clear response to Cr(VI) presence. The biosensor shows good linearity (R2 = 0.983) and a limit of detection of 2.4 mg L−1 Cr(VI), with a sensitivity of 0.31 ± 0.02 μA cm−2 mgCr(VI)−1 L. The presented microbial bioanode architecture enhanced biosensor performance thanks to the improved “electrical wiring” between biological entities and the abiotic electrode surface. This approach could be easily implemented in engineered electrode surfaces, such as paper-based multi-anodes that maximize bacterial colonization, further improving biosensor response.

In recent years, microbial fuel cell (MFC) has been regarded as a promising technology for dye wastewater treatment. Compared with traditional anaerobic reactors, MFC has better decolorization effect while producing electricity simultaneously. In this paper, a double-chamber MFC with the sponge anode modified by polyaniline and chitosan-NCNTs was employed for simultaneous azo dye decolorization and bioelectricity generation. The influence of dye concentration, co-substrate concentration, and operating temperature on the performance of MFC with the modified anodes were studied. The results showed that a high decolorization efficiency (98.41%) and maximum power density (2816.67 mW m−3) of MFC equipped with modified bioanodes were achieved due to the biocompatibility and bioelectrocatalysis of modified material. And the biomass on the modified anode’s surface was increased by 1.47 times. Additionally, microbial community analysis revealed that the modification of polyaniline and chitosan-NCNTs improved the selective enrichment of specific communities and the main microorganism was the electroactive and decolorizing bacteria Enterobacter (62.84%). Therefore, the composite anode is capable of fully utilizing the synergistic role of various materials, leading to superior performance of dye decolorization in MFCs. This work provided a strategy for the research on the recovery of biomass energy and decolorization in wastewater treatment.

This study investigated a system which simultaneously produced electricity and stored energy in the MFC integrated MnO 2 -modified capacitive bioanode. Compared to the noncapacitive anode, the maximum power density of MFC with MnO 2 -modified bioanode reached 16.47 W m −3 , which was 3.5 times higher than that of the bare anode (4.71 W m −3 ). During the charging-discharging experiment, the MFC with a capacitance bioanode has a higher average peak current density of 5.06 mA cm −2 and 36 times larger than that with the bare bioanode. With the capacitive electrode, it is possible to let the MFC at the same time for production and storage of renewable electricity. Then two different operations (intermittent operation and continuous operation) of the MFC with a capacitive bioanode were studied to degrade Cr (VI) in cathode chamber. Results showed that the Cr (VI) removal rates of intermittent operation are much higher than that of continuous operation under the same time in the closed circuit state. This is due to the good ability of storing and releasing electron of the biological capacitor with MnO 2 modified material. And this study showed that MFC with a capacitive bioanode is better adapted to treat heavy metal pollutants by intermittent mode.

The decrease in the electrochemical activity of multi‐species microbial anodes in bioelectrochemical systems is the main bottleneck to overcome for bringing these technologies one‐step closer to the industrialization stage. In this study, microsized stainless steel electrodes were implemented to investigate the distinctive electrochemical behavior of salt marsh electroactive biofilms (EABs). Four main temporal stages of biocolonization and electrochemical activity were thoroughly described. Maximum biofilm growth rate, high viability and high extracellular protein matrix content favored the increasing electrochemical activity of the EAB up to its maximum current peak. Then, when gradual fall in current became irreversible, biofilm growth rate decreased together with dead cells accumulation and an increase for extracellular polysaccharides. In addition, analyses of microbial populations showed a shift from Marinobacterium spp. to Desulfuromonas spp. These findings suggest a chemical and microbial temporal evolution of the EAB, which can be directly correlated to the electrochemical performance of the bioanode. Typical electrochemical behaviour (middle graph) of microbial anodes is investigated when salt marsh electroactive biofilms (EABs) were formed on stainless steel microelectrodes. Maximum current dropped by more than 50 % after the peak. The main results found for before (phases I and II) the maximum current peak and after (phases III and IV) were summarized at both sides of the graph.

This study aimed to develop anode with improved performance for potential use in energy applications, particularly in bio-photovoltaic applications. The study comprises the chemical synthesis of a conducting nanocomposite based on reduced graphene oxide and polypyrrole (rGO/PPy) by incorporating PPy into the rGO sheets along with the addition of an aerogel synthesis phase to improve the composite's overall characteristics. A comparative electrochemical analysis was conducted on cyanobacteria (Nostoc sp.) immobilised ITO-PET and modified rGO/PPy/ITO-PET anodes to investigate the photocurrent output of both. The rGO/PPy nanocomposite was further used to develop a cyanobacteria immobilised biofuel cell anode, and the electrochemical characterization of the fabricated bio-anode (rGO/PPy/ITO-PET) was carried out in a lab-made rudimentary electrochemical cell for the bio-electrocatalytic photolysis of water (light) and oxidation of stored organic matter (night). The results show that the modified bio-anode, for the bio-electrocatalytic reaction in the photo-bio-electrochemical cell configuration, attained a maximum current density of 0.132 mA cm-2 in light, and 0.069 mA cm-2 in dark at 0.0 V, and 0.375 mA cm-2 in light, and 0.207 mA cm-2 in dark at an applied voltage of 1.45 V. Therefore, the electrocatalytic photolysis and oxidation of organic materials were accomplished by the proposed bio-anode via the direct electron transfer mechanism. The amperometric photocurrent response of the developed bio-electrode remained relatively stable for approximately 10 days in the rudimentary designed bio-electrochemical cell. The study demonstrates the potential of rGO/PPy/ITO-PET based bio-electrode for possible application in developing the bio-photovoltaic cells for energy generation.

ObjectiveThe construction of a novel bioanode based on l-proline oxidation using a cascade reaction pathway comprised of thermostable dehydrogenases.ResultsA novel multi-enzymatic cascade pathway, containing four kinds of dehydrogenases from thermophiles (dye-linked l-proline dehydrogenase, nicotinamide adenine dinucleotide (NAD)-dependent Δ1-pyrroline-5-carboxylate dehydrogenase, NAD-dependent l-glutamate dehydrogenase and dye-linked NADH dehydrogenase), was designed for the generation of six-electrons from one molecule of l-proline. The current density of the four-dehydrogenase-immobilized electrode, with a voltage of + 450 mV (relative to that of Ag/AgCl), was 226.8 μA/cm2 in the presence of 10 mM l-proline and 0.5 mM ferrocene carboxylate at 50 °C. This value was 4.2-fold higher than that of a similar electrode containing a single dehydrogenase. In addition, about 54% of the initial current in the multi-enzyme cascade bioanode was maintained even after 15 days.ConclusionsEfficient deep oxidation of l-proline by multiple-enzyme cascade reactions was achieved in our designed electrode. The multi-enzyme cascade bioanode, which was built using thermophilic dehydrogenases, showed high durability at room temperature. The long-term stability of the bioanode indicates that it shows great potential for applications as a long-lived enzymatic fuel cell.

Self-powered immunosensors (SPIs) based on enzymatic biofuel cell (EBFC) have low sensitivity and poor stability due to the high impedance of the immune sandwich and the vulnerability of enzymes to environmental factors. Here, we applied the Faraday cage-type sensing mode on a hybrid biofuel cell (HBFC)-based SPI for the first time, which exhibited high sensitivity and stability. Cytokeratin 19 fragment (CYFRA 21-1) was used as a model analyte. Au nanoparticle-reduced graphene oxide (Au-rGO) composite was used as the supporting matrix for immunoprobe immobilized with detection antibody and glucose dehydrogenase (GDH), also the builder for Faraday cage structure on the bioanode in the presence of antigen. After the combination of immunoprobe, antigen, and the antibody on the bioanode, the Faraday cage was constructed in case the AuNP-rGO was applied as a conductive cage for electron transfer from GDH to the bioanode without passing through the poorly conductive protein. With the assistance of the Faraday cage structure, the impedance of the bioanode decreased significantly from 4000 to 300 Ω, representing a decline of over 90%. The sensitivity of the SPI, defined as the changes of open circuit voltage (OCV) per unit concentration of the CYFRA 21-1, was 68 mV [log (ng mL −1 )] −1 . In addition, Fe-N-C was used as an inorganic cathode material to replace enzyme for oxygen reduction reaction (ORR), which endowed the sensor with 4-week long-term stability. This work demonstrates a novel sensing platform with high sensitivity and stability, bringing the concept of hybrid biofuel cell-based self-powered sensor. Graphical Abstract

Bioelectrochemical anaerobic ammonium oxidation (anammox) systems allow eco-friendly removal of nitrogen from reject wastewater coming from biogas processing as the anammox bacteria have previously shown to have c-type cytochromes acting in the extracellular electron transport (EET) mechanism between the bacteria and electrode. The anammoxosome compartment present in anammox bacteria features a highly curved membrane and contains tubular structures along with electron-dense particles that contain iron, which could enhance the process of EET and enhance nitrogen removal by properly applied potentials. In this study, nitrogen removal was investigated in the electrostimulated anammox nitrogen removal (EANR) cells operated comparatively at open circuit and at applied potentials of − 300 mV, − 500 mV, and − 700 mV vs. Ag/AgCl. At peak performance (at − 700 mV vs. Ag/AgCl), the EANR showed up to 140% higher specific nitrogen removal rate (11.2 ± 0.3 g N/m 2 /day) compared to the control reactors without applied potential (8.3 ± 0.2 g N/m 2 /day). The microbial community on the cathode with the applied potential had a higher relative proportion of unclassified Candidatus Brocadia (7.5%) compared to inoculum (> 0.01%), in contrast to cathode without potential (0.74%) and control (0.2%). The EANR system demonstrated to achieve ammonium and nitrite removal efficiencies of 91% and 53%, respectively, during a 24-h test cycle from an initial TN concentration of ~ 100 mg N/L. After 150 h, it achieved complete removal of all nitrogen compounds, reaching a 100% removal efficiency. The EANR would be very useful in the establishment of field-scale bilateral anammox-bioelectrochemical technology combining microbial fuel cell bioanodes and EANR biocathodes for wastewater treatment.

The focus of this study is to develop a high-performance anode material for microbial fuel cells (MFCs). PEDOT:PSS and nitrogen-modified MXene were combined to create a hydrogel composite material called PPNM, which was drop-cast onto carbon felt (CF) as the MFCs anode. The PPNM exhibited a higher peak power density of 4.78 W m−2, an increase of 332% compared to the CF anode. It is worth noting that the PPNM Hydrogel maintains its rough and porous structure, providing favorable sites for bacterial colonization. The introduction of N-MXene has improved the electrochemical performance of the hydrogel, particularly impacting the mediated electron transfer process. Microbial community analysis revealed the presence of more electrochemically active species on the PPNM anode. These findings highlight the potential of PPNM hydrogel and pave the way for similar strategies in achieving high-performance anodes in MFCs.