Biofabrication of nanomaterials is currently constrained by a low production efficiency and poor controllability on product quality compared to chemical synthetic routes. In this work, we show an attractive new biosynthesis system to break these limitations. A directed production of selenium-containing nanoparticles in Shewanella oneidensis MR-1 cells, with fine-tuned composition and subcellular synthetic location, was achieved by modifying the extracellular electron transfer chain. By taking advantage of its untapped intracellular detoxification and synthetic power, we obtained high-purity, uniform-sized cadmium selenide nanoparticles in the cytoplasm, with the production rates and fluorescent intensities far exceeding the state-of-the-art biosystems. These findings may fundamentally change our perception of nanomaterial biosynthesis process and lead to the development of fine-controllable nanoparticles biosynthesis technologies.

The production of volatile fatty acids (VFAs) from wastewater is considered as another promising way, in addition to methane (CH4) production, to utilize wastewater resources. To simplify or even circumvent the downstream separation and purification steps, selective production of a specific VFA is highly desirable. In this study, we report a continuous, selective co-production of acetate and CH4 during the anaerobic wastewater treatment under mesophilic (35 ± 1 °C) and acidic (5.0) conditions. At a stable stage, acetate accounted for 66% of the liquid-phase products, whereas CH4 accounted for 41% of the gaseous products. A consistent microbial community distribution was observed, where Clostridium, Bacteroides, and hydrogenotrophic methanogens were enriched at pH 5.0, creating a low hydrogen (H2) partial pressure environment to favor the selective acetate production. In contrast, the reactor performance deteriorated at pH 4.0 due to the suppression of microbial activities. This study demonstrates the feasibility of diverting the anaerobic fermentation pathway towards the selective co-production of acetate and CH4via adjusting the wastewater pH and may provide implications for optimizing anaerobic wastewater treatment processes for improved resource recovery.

Excitation of TiO2 for visible light absorption by surface complexation with antenna organic molecules is an effective strategy to improve its solar utilization efficiency for photocatalytic application, but the existing antenna molecules are mostly toxic and environmentally-aggressive, severely limiting their practical application. In this study, we tested the potential of zwitterionic buffers (Good's buffers) as an environmentally-benign alternative. The addition of Good's buffers significantly enhanced methyl orange (MO) photodegradation by TiO2 under visible light, but the enhancement degree varied with the different buffer types, buffer concentration and solution pH. The presence of 4-(2-hydroxyerhyl) piperazine-1-erhanesulfonic acid (HEPES) as a typical Good's buffer led to over 90% MO removal within 180 min, whereas only slight MO removal was observed in the TiO2 alone system during the same period. Such an induced visible light photocatalytic activity was attributed to a complexation between the conjugate acid structured buffer molecule and TiO2, which favors a ligand-to-metal charge transfer (LMCT). The LMCT activity was strongly dependent on the molecule structure, especially the states of hydroxyl and amino groups of Good's buffers. The pH buffering ability of the buffers also contributed to the efficient MO photodegradation. This study suggests a great potential of Good's buffers as both “green” antenna molecules and pH buffer for strengthening TiO2-based photocatalytic remediation processes.

•WO3 nanorods-modified carbon paper was used as the anode of MFC.•WO3 nanorods suppressed biofilm growth on the electrode surface.•Sustained electron transfer from cells to electrode via riboflavin was achieved.•C–WO3 nanorods enable stable and efficient EET process in long-time operation.Carbon materials are widely used as electrodes for bioelectrochemical systems (BES). However, a thick biofilm tends to grow on the electrode surface during continuous operation, resulting in constrained transport of electrons and nutrients at the cell-electrode interface. In this work, we tackled this problem by adopting a WO3-nanorods modified carbon electrode (C–WO3 nanorods), which completely suppressed the biofilm growth of Shewanella Oneidensis MR-1. Moreover, the C–WO3 nanorods exhibited high electric conductivity and strong response to riboflavin. These two factors together make it possible for the C–WO3 nanorods to maintain a sustained, efficient process of electron transfer from the MR-1 planktonic cells. As a consequence, the microbial fuel cells with C–WO3 nanorods anode showed more stable performance than the pure carbon paper and WO3-nanoparticles systems in prolonged operation. This work suggests that WO3 nanorods have the potential to be used as a robust and biofouling-resistant electrode material for practical bioelectrochemical applications.

•Azobenzene was reduced to aniline at the cathode of an acetate-fueled MFC.•Aniline was degraded at the bioanode of a single-chamber MFC.•Cathodic reduction of azobenzene was coupled with anodic oxidation of aniline.•Self-driven, complete mineralization of azobenzene in an MFC was accomplished.Bioelectrochemical systems have been intensively studied as a promising technology for wastewater treatment and environment remediation. Coupling of the anodic and cathodic electrochemical reactions allows an enhanced degradation of recalcitrant organics, but external power supply is usually needed to overcome the thermodynamic barrier. In this work, we report a self-driven degradation of azobenzene in a microbial fuel cell (MFC), where the cathodic reduction of azobenzene was effectively coupled with the anodic oxidation of its reduction degradation intermediate (i.e., aniline). The anodic degradation rate of aniline, as the sole carbon source, was significantly higher than that under open-circuit conditions, suggesting a considerable bioelectrochemical oxidation of aniline. Output voltages up to 8 mV were obtained in the MFC. However, a shift of cathodic electron acceptor from oxygen to azobenzene resulted in a decreased aniline degradation rate and output voltage. The present work may provide valuable implications for development of sustainable bioelectrochemical technologies for environmental remediation.

•PFOS was degraded by photochemical process in environmental matrices.•pH buffering ability of the environmental matrices contributed to this process.•Phenol and ammonia benefited PFOS photodegradation.•Humic acid and relatively low ionic strength had negative influence.Effective photodegradation of perfluorooctane sulfonate (PFOS), an environmentally-ubiquitous persistent organic pollutant, in simple aqueous solution has been previously demonstrated. However, photocatalyst usually needs to be added and its application in complicated aquatic environment has not been reported so far. Here, we investigated the photodegradation of PFOS in environmental matrices, including municipal wastewater treatment plant (WWTP) effluent and lake water, and without adding any photocatalyst. A moderate PFOS degradation in the WWTP effluent and lake water was observed, with pseudo-first-order decomposition rate constants of 0.10 ± 0.02 h−1 and 0.16 ± 0.01 h−1 respectively. A further investigation using artificial water solution suggest that the weak alkaline pH and the presence of some dissolved organic matters (e.g., phenol and ammonia) might be important factor accounting for the efficient PFOS decomposition in environmental matrices, while humic acid and the relatively low ionic strength posed negative impacts. This study demonstrates the feasibility of eliminating PFOS pollution by photodegradation approach and may have implications for wastewater deep treatment and environmental remediation.

Zero-Valent Iron nanoparticles (nZVI) have been extensively applied for the reduction of various recalcitrant organic contaminants, but their reactivity usually declines over time due to the formation of passive iron oxides. In this study we observed a sustained reactivity of nZVI for the dechlorination of carbon tetrachloride (CT) in water during several consecutive reaction cycles. The dechlorination rate constants increased substantially in Cycle 2, then remained at a high level over several consecutive cycles, and ultimately declined in Cycle 7. In the entire process, the solution pH increased only slightly from 7.0 to 7.8, which was different from other unbuffered nZVI reduction systems reported before. Characterization of the particle surface morphology and composition revealed an important role of Fe oxyhydroxide formation in self-buffering the solution pH and sustaining a high nZVI reactivity. Our study provides new knowledge on the nZVI dechlorination process and may offer implications for extending the lifetime of nZVI in wastewater treatment and environmental remediation applications.

Microbial fuel cells (MFCs) have emerged as a promising technology for wastewater treatment with concomitant energy production but the performance is usually limited by low microbial activities. This has spurred intensive research interest for microbial enhancement. This study demonstrated an interesting stimulation effect of a static magnetic field (MF) on sludge-inoculated MFCs and explored into the mechanisms. The implementation of a 100-mT MF accelerated the reactor startup and led to increased electricity generation. Under the MF exposure, the activation loss of the MFC was decreased, but there was no increased secretion of redox mediators. Thus, the MF effect was mainly due to enhanced bioelectrochemical activities of anodic microorganisms, which are likely attributed to the oxidative stress and magnetohydrodynamic effects under an MF exposure. This work implies that weak MF may be applied as a simple and effective approach to stimulate microbial activities for various bioelectrochemical energy production and decontamination applications.

Bioelectrochemical systems (BESs), in which microorganisms are utilized as a self-regenerable catalyst at the anode of an electrochemical cell to directly extract electrical energy from organic matter, have been widely recognized as a promising technology for energy-efficient wastewater treatment or even for net energy generation. However, currently BES performance is constrained by poor cathode reaction kinetics. Thus, there is a strong impetus to improve the cathodic catalysis performance through proper selection and design of catalysts. This review introduces the fundamentals and current development status of various cathodic catalysts (including electrocatalysts, photoelectrocatalysts and bioelectrocatalysts) in BES, identifies their limitations and influential factors, compares their catalytic performances in terms of catalytic efficiency, stability, selectivity, etc., and discusses the possible optimization strategies and future research directions. Special focus is given on the analysis of how the catalytic performance of different catalysts can be improved by fine tuning their physicochemical or physiological properties.

Dissimilatory metal-reducing bacteria play an important role in environmental bioremediation, and their extracellular electron transfer (EET) and pollutant reduction process can be affected by various redox-active substances. While it is generally thought that these substances usually only accelerate the EET rate, here we discover that the electron flow route within Shewanella oneidensis MR-1 cells can also be altered by the introduction of carbon nanotubes (CNTs). Addition of 0.5% (w/v) CNTs in the cell-immobilized alginate beads led to a shift of intracellular nitrobenzene (NB) reduction to extracellular reaction and a 74% improvement in NB reduction efficiency. This work provides the first evidence that the electron flow route of microorganisms can be altered by CNTs. It broadens our view about the possible environmental consequence of CNTs from a microbial extracellular respiration perspective and may lead to an improved understanding of microbial respiration and improve the practical application of bioremediation processes.

Effective monitoring and diagnosis of anaerobic digestion processes is a great challenge for anaerobic digestion reactors, which limits their stable operation. In this work, an online monitoring and alert system for upflow anaerobic sludge blanket (UASB) reactors is developed on the basis of a set of novel evaluating indexes. The two indexes, i.e., stability index S and auxiliary index a, which incorporate both gas- and liquid-phase parameters for UASB, enable a quantitative and comprehensive evaluation of reactor status. A series of shock tests is conducted to evaluate the response of the monitoring and alert system to organic overloading, hydraulic, temperature, and toxicant shocks. The results show that this system enables an accurate and rapid monitoring and diagnosis of the reactor status, and offers reliable early warnings on the potential risks. As the core of this system, the evaluating indexes are demonstrated to be of high accuracy and sensitivity in process evaluation and good adaptability to the artificial intelligence and automated control apparatus. This online monitoring and alert system presents a valuable effort to promote the automated monitoring and control of anaerobic digestion process, and holds a high promise for application.

In this study, the H2 production and chemical oxygen demand (COD) removal performances of a thermophilic upflow anaerobic sludge blanket (UASB) reactor with online monitoring system were investigated. The online monitoring system enabled a rapid monitoring and timely control of the process. As a consequence, high operating stability was achieved despite of the varied hydraulic retention time (HRT) during 310-day operation. The COD efficiency remained at above 98%, and the hydrogen yield fluctuated slightly within the range of 2.42–3.06 mol H2 mol−1 sucrose. Thermophilic H2-producing granules were successfully cultivated in this reactor, which showed better physical and microbial properties than floc sludge and higher H2 production rate than mesophilic granules. An analysis of the microbial growth kinetics further demonstrated a possibly higher synthesis and metabolism activity of microbes in the thermophilic granule state.Highlights► Long-term operating stability of a thermophilic UASB reactor. ► An online monitoring system for process monitoring and control. ► Higher COD removal and hydrogen production compared to mesophilic system. ► Good stability under HRT variation during 310-d operation.

•Electrogenic activities of many bacteria were affected by uncouplers.•The uncoupler effects were concentration-dependent and varied with bacterial species.•Adding 50 μg/L TCS or DNP improved power generation of MFC.•Bacterial activity was significantly inhibited at 400 μg/L TCS or DNP.Low energy efficiency, usually limited by insufficient electrogenic activities of anodic bacteria, is currently one of the critical hurdles for application of microbial fuel cells (MFCs) in wastewater treatment. The presence of uncouplers was recently found to ease such a limitation, but the universality of this approach for different uncoupling compounds and bacterial species remain unclear. In this study, the impacts of two uncouplers, 3,3′,4′,5-tetrachlorosalicylanilide and 2,4-dinitrophenol, on the electrogenic performances of a number of electrochemically-active bacteria were investigated by WO3 probe and MFC tests. Although the influential degree varied for different uncouplers and bacteria, similar uncoupler impacts were observed: low-concentration promotion and high-concentration inhibition, suggesting that uncoupler regulation on microbial electrogenic activity is a universal phenomenon. This study underscores an untapped important role of uncouplers in regulating microbial electrogenic activities and implies a promising chemical route to strengthen the performance of bioelectrochemical systems.Download high-res image (189KB)Download full-size image

•FeS nanoparticles was biosynthesized by Shewanella putrefaciens CN32.•Biogenic FeS significantly accelerated CT bioreduction by 8 times.•Biogenic FeS showed much higher dechlorination activity than abiotic FeS.Dissimilatory metal reducing bacteria (DMRB) widely exist in the subsurface environment and are involved in various contaminant degradation and element geochemical cycling processes. Recent studies suggest that DMRB can biosynthesize metal nanoparticles during metal reduction, but it is unclear yet how such biogenic nanomaterials would affect their decontamination behaviors. In this study, we found that the dechlorination rates of carbon tetrachloride (CT) by Shewanella putrefaciens CN32 was significantly increased by 8 times with the formation of biogenic ferrous sulfide (FeS) nanoparticles. The pasteurized biogenic FeS enabled 5 times faster dechlorination than abiotic FeS that had larger sizes and irregular structure, confirming a significant contribution of the biogenic FeS to CT bioreduction resulting from its good dispersion and relatively high dechlorination activity. This study highlights a potentially important role of biosynthesized nanoparticles in environmental bioremediation.Download high-res image (158KB)Download full-size image

•A novel approach coupling pollutant degradation and nanomaterial biosynthesis.•NGB and thiosulfate were efficiently reduced by Shewanella oneidensis MR-1.•The reduction products, Fe2+ and H2S, reacted to form FeS nanoparticles.•FeS nanoparticles were synthesized both extracellularly and at inside the cells.•Mtr respiratory pathway was essential in the biosynthesis process.Biogenetic nanomaterials have attracted growing interests in recent years attributed to their “green” synthesis nature, but expensive precursors are typically needed. On the other hand, release of hazardous intermediates during contaminant biodegradation/conversion is usually encountered in wastewater treatment processes. This study reports an effective coupling of both processes in one simple system to overcome the individual limitations. By using Shewanella oneidensis MR-1 as the inoculum, the Fe2+ ions released from naphthol green B (NGB) bioreduction and H2S from thiosulfate reduction were utilized in-situ to generate ferrous sulfide (FeS) nanoparticles, with an average size of ∼30 nm. In addition, we discovered for the first time that FeS nanoparticles could be synthesized both extracellarly and intracellularly by this strain, and identified the essential role of the Mtr respiratory pathway in the biosynthesis process. This study deepens our understanding of the bioconversion behaviors of metal-complex dyes, and may provide implications for development of sustainable nanomaterial fabrication processes.Download high-res image (160KB)Download full-size image

The production of volatile fatty acids (VFAs) from wastewater is considered as another promising way, in addition to methane (CH4) production, to utilize wastewater resources. To simplify or even circumvent the downstream separation and purification steps, selective production of a specific VFA is highly desirable. In this study, we report a continuous, selective co-production of acetate and CH4 during the anaerobic wastewater treatment under mesophilic (35 ± 1 °C) and acidic (5.0) conditions. At a stable stage, acetate accounted for 66% of the liquid-phase products, whereas CH4 accounted for 41% of the gaseous products. A consistent microbial community distribution was observed, where Clostridium, Bacteroides, and hydrogenotrophic methanogens were enriched at pH 5.0, creating a low hydrogen (H2) partial pressure environment to favor the selective acetate production. In contrast, the reactor performance deteriorated at pH 4.0 due to the suppression of microbial activities. This study demonstrates the feasibility of diverting the anaerobic fermentation pathway towards the selective co-production of acetate and CH4via adjusting the wastewater pH and may provide implications for optimizing anaerobic wastewater treatment processes for improved resource recovery.

Bioelectrochemical systems (BESs), in which microorganisms are utilized as a self-regenerable catalyst at the anode of an electrochemical cell to directly extract electrical energy from organic matter, have been widely recognized as a promising technology for energy-efficient wastewater treatment or even for net energy generation. However, currently BES performance is constrained by poor cathode reaction kinetics. Thus, there is a strong impetus to improve the cathodic catalysis performance through proper selection and design of catalysts. This review introduces the fundamentals and current development status of various cathodic catalysts (including electrocatalysts, photoelectrocatalysts and bioelectrocatalysts) in BES, identifies their limitations and influential factors, compares their catalytic performances in terms of catalytic efficiency, stability, selectivity, etc., and discusses the possible optimization strategies and future research directions. Special focus is given on the analysis of how the catalytic performance of different catalysts can be improved by fine tuning their physicochemical or physiological properties.