A novel electrochemical sensor based on autotropic and heterotrophic nitrifying biofilm for trichloroacetic acid toxicity monitoring.

Trichloroacetic acid (TCA), a toxic substance produced in the disinfection process of wastewater treatment plants, will accumulate in the receiving water. The detection of TCA in the water can achieve the purpose of early warning. However, currently there are few reports on microbial sensors used for TCA detection, and the characteristics of their microbial communities are still unclear. In this work, a toxicity monitoring microbial system (TMMS) with nitrifying biofilm as a sensing element and cathode oxygen reduction as a current signal was successfully constructed for TCA detection. The current and nitrification rate showed a linear relationship with low TCA concentration from 0 to 50 µg/L (R2current = 0.9892, R2nitrification = 0.9860), and high concentration range from 50 to 5000 µg/L (R2current = 0.9883, R2nitrification = 0.9721). High-throughput sequencing revealed that the TMMS was composed of autotrophic/heterotrophic nitrifying and denitrifying microorganisms. Further analysis via symbiotic relationship network demonstrated that Arenimonas and Hyphomicrobium were the core nodes for maintaining interaction between autotropic and heterotrophic nitrifying bacteria. Kyoto Encyclopedia of Genes and Genomes analysis showed that after adding TCA to TMMS, the carbon metabolism and the abundance of the tricarboxylic acid cycle pathway were reduced, and the activity of microorganisms was inhibited. TCA stress caused a low abundance of nitrifying and denitrifying functional enzymes, resulting in low oxygen consumption in the nitrification process, but more oxygen supply for cathode oxygen reduction. This work explored a novel sensor combined with electrochemistry and autotrophic/heterotrophic nitrification, which provided a new insight into the development of microbial monitoring of toxic substances.

Effect of air-exposed biocathode on the performance of a Thauera-dominated membraneless single-chamber microbial fuel cell (SCMFC).

To investigate the effect of air-exposed biocathode (AEB) on the performance of single-chamber microbial fuel cell (SCMFC), wastewater quality, bioelectrochemical characteristics and the electrode biofilms were researched. It was demonstrated that exposing the biocathode to air was beneficial to nitrogen removal and current generation. In Test 1 of 95% AEB, removal rates of ammonia, total nitrogen (TN) and chemical oxygen demand (COD) reached 99.34%±0.11%, 99.34%±0.10% and 90.79%±0.12%, respectively. The nitrogen removal loading rates were 36.38gN/m3/day. Meanwhile, current density and power density obtained at 0.7A/m3 and 104mW/m3 respectively. Further experiments on open-circuit (Test 2) and carbon source (Test 3) indicated that this high performance could be attributed to simultaneous biological nitrification/denitrification and aerobic denitrification, as well as bioelectrochemical denitrification. Results of community analysis demonstrated that both microbial community structures on the surface of the cathode and in the liquid of the chamber were different. The percentage of Thauera, identified as denitrifying bacteria, maintained at a high level of over 50% in water, but decreased gradually in the AEB. Moreover, the genus Nitrosomonas, Alishewanella, Arcobacter and Rheinheimera were significantly enriched in the AEB, which might contribute to both enhancement of nitrogen removal and electricity generation.

Enhanced methane production in an anaerobic digestion and microbial electrolysis cell coupled system with co-cultivation of Geobacter and Methanosarcina.

The anaerobic digestion (AD) and microbial electrolysis cell (MEC) coupled system has been proved to be a promising process for biomethane production. In this paper, it was found that by co-cultivating Geobacter with Methanosarcina in an AD-MEC coupled system, methane yield was further increased by 24.1%, achieving to 360.2 mL/g-COD, which was comparable to the theoretical methane yield of an anaerobic digester. With the presence of Geobacter, the maximum chemical oxygen demand (COD) removal rate (216.8 mg COD/(L·hr)) and current density (304.3A/m(3)) were both increased by 1.3 and 1.8 fold compared to the previous study without Geobacter, resulting in overall energy efficiency reaching up to 74.6%. Community analysis demonstrated that Geobacter and Methanosarcina could coexist together in the biofilm, and the electrochemical activities of both were confirmed by cyclic voltammetry. Our study observed that the carbon dioxide content in total gas generated from the AD reactor with Geobacter was only half of that generated from the same reactor without Geobacter, suggesting that Methanosarcina may obtain the electron transferred from Geobacter for the reduction of carbon dioxide to methane. Taken together, Geobacter not only can improve the performance of the MEC system, but also can enhance methane production.

Deciphering the differentiated performance on electricity generation and COD degradation by Rhodopseudomonas-dominated bioanode in light or dark.

Anoxygenic phototrophic bacteria is a promising catalyst for constructing bioanode, but the mixed culture with non-photosynthetic bacteria is inevitable in an open environment application. In this study, a Rhodopseudomonas-dominated mixed culture with other electrogenic bacteria was investigated for deciphering the differentiated performance on electricity generation in light or dark conditions. The kinetic study showed that reaction rate of OM degradation was 9 times higher than that under dark condition, demonstrating that OM degradation was enhanced by photosynthesis. However, CE under light condition was lower. It indicated that part of OM was used to provide hydrogen donors for the fixation of CO2 or hydrogen production in photosynthesis, decreasing the OM used for electron transfer. In addition, higher COD concentration was not conducive to electricity generation. EIS analysis demonstrated that higher OM concentration would increase Rct to hinder the transfer of electrons from bacteria to the electrode. Indirect and direct electron transfer were revealed by CV analysis for light and dark biofilm, respectively, and nanowires were also observed by SEM graphs, further revealing the differentiate performance. Microbial community analysis demonstrated Rhodopseudomonas was dominated in light and decreased in dark, but Geobacter increased apparently from light to dark, resulting in different power generation performance. The findings revealed the differentiated performance on electricity generation and pollutant removal by mixed culture of phototrophic bacteria in light or dark, which will improve the power generation from photo-microbial fuel cells.

Enhanced Microbial Protein Production from CO2 and Air by a MoS2 Catalyzed Bioelectrochemical System.

Carbon dioxide can be relatively easily reduced to organic matter in a bioelectrochemical system (BES). However, due to insufficient reduction force from in-situ hydrogen evolution, it is difficult for nitrogen reduction. In this study, MoS2 was firstly used as an electrocatalyst for the simultaneous reduction of CO2 and N2 to produce microbial protein (MP) in a BES. Cell dry weight (CDW) could reach 0.81±0.04 g/L after 14 d operation at -0.7 V (vs. RHE), which was 108±3 % higher than that from non-catalyst control group (0.39±0.01 g/L). The produced protein had a better amino acid profile in the BES than that in a direct hydrogen system (DHS), particularly for proline (Pro). Besides, MoS2 promoted the growth of bacterial cell on an electrode and improved the biofilm extracellular electron transfer (EET) by microscopic observation and electrochemical characterization of MoS2 biocathode. The composition of the microbial community and the relative abundance of functional enzymes revealed that MoS2 as an electrocatalyst was beneficial for enriching Xanthobacter and enhancing CO2 and N2 reduction by electrical energy. These results demonstrated that an efficient strategy to improve MP production of BES is to use MoS2 as an electrocatalyst to shift amino acid profile and microbial community.

The research progress, hotspots, challenges and outlooks of solid-phase denitrification process.

Nitrogen pollution is one of the main reasons for water eutrophication. The difficulty of nitrogen removal in low-carbon wastewater poses a huge potential threat to the ecological environment and human health. As a clean biological nitrogen removal process, solid-phase denitrification (SPD) was proposed for long-term operation of low-carbon wastewater. In this paper, the progress, hotspots, and challenges of the SPD process based on different solid carbon sources (SCSs) are reviewed. Compared with synthetic SCS and natural SCS, blended SCSs have more application potential and have achieved pilot-scale application. Differences in SCSs will lead to changes in the enrichment of hydrolytic microorganisms and hydrolytic genes, which indirectly affect denitrification performance. Moreover, the denitrification performance of the SPD process is also affected by the physical and chemical properties of SCSs, pH of wastewater, hydraulic retention time, filling ratio, and temperature. In addition, the strengthening of the SPD process is an inevitable trend. The strengthening measures including SCSs modification and coupled electrochemical technology are regarded as the current research hotspots. It is worth noting that the outbreak of the COVID-19 epidemic has led to the increase of disinfection by-products and antibiotics in wastewater, which makes the SPD process face challenges. Finally, this review proposes prospects to provide a theoretical basis for promoting the efficient application of the SPD process and coping with the challenge of the COVID-19 epidemic.

Coupling mixotrophic denitrification and electroactive anodic nitrification by nitrate addition for promoting current generation and nitrogen removal.

Nitrate promotes anodic denitrification and fasts organic matter removal in microbial fuel cells (MFCs). However, it suffers from poor total nitrogen (TN) removal and current recovery. In this study, some novel electroactive nitrifying/denitrifying bacteria (ENDB) were introduced in a single chambered air-cathode MFC to investigate the performance of this device and the microbial community shift by adding nitrate. Results showed a similar disturbance in current output by adding nitrate during a short-term operation. However, a stable and reproducible current increase was achieved in the continuous experiment. A maximum current of 0.76 A m-3 and a maximum TN removal of >99 % were accomplished. The corresponding corrected coulombic efficiency was approximately 18 %. Under repeatable batches, a sharp decrease in chemical oxygen demand (COD) with feeding nitrate confirmed the temporary competition on electron donors through heterotrophic denitrification. The later current increase and nitrite detection occurring without metabolized COD could be considered evidence of electroactive anodic nitrification. The ENDB biofilm successfully coupled mixotrophic denitrification and electroactive anodic nitrification. It eventually promoted TN removal. In the process, genera Pseudoxanthomonas, Thauera, and Pseudomonas were enriched in the anodic ENDB biofilms. Cyclic voltammetry data confirmed the promotion of the electron transfer process by biofilms. The bacterial function predication revealed that the genes related to nitrogen removal and electron transfer were upregulated. Therefore, mixotrophic denitrification and electroactive anodic nitrification processes facilitated power recovery with the high efficiency of pollutant removal, finally ensuring water body security.

Innovative electrochemical biosensor with nitrifying biofilm and nitrite oxidation signal for comprehensive toxicity detection in Tuojiang River.

Water toxicity detection, as a valuable supplement to conventional water quality measurement, is an important method for evaluating water environmental quality standards. However, the toxicity of composite pollutants is more complicated due to their mixture effects. This study developed a novel, rapid and interference-resistant detection method for water toxicity based on an electrochemical biosensor using peak current from nitrite oxidation as a signal. Toxicants could weaken the characteristic peak current of nitrite to indicate the magnitude of toxicity. The proof-of-concept study was first conducted using a synthetic water sample containing trichloroacetic acid (TCAA), and then the results were compared with those of the traditional toxicity colorimetric method (CCK-8 kit) and laser confocal microscopy (CLSM). The accuracy of the biosensor was further verified with water samples containing individual pollutants such as Cd2+ (50-150 µg/L), Cr6+ (20-80 µg/L) mixture, triclosan (TCS; 0.1-1.0 µg/L) and TCAA (10-80 µg/L), or a mixture of the above. The viability of the sensor was further validated with the actual water sample from the Tuojiang River. The results demonstrated that although the concentration of a single conventional pollutant in water did not exceed the discharge standard for surface water, the comprehensive toxicity of natural water should not be ignored. This method could be a beneficial supplement to conventional water quality detection to understand the characteristics of the water, and thus contribute to the next stage of water treatment.

Evaluation and optimization of ecological landscape pattern for urban agglomeration in the Pearl River Delta, China.

The evaluation and optimization of landscape ecological pattern has important implications for the accurate improvement of forest quality and high-quality urban development in the Pearl River Delta urban agglomeration. Based on the "one map" data and digital elevation model data of forest resource management in 2021, we evaluated and optimized landscape ecological pattern of the Pearl River Delta urban agglomeration by morphological spatial pattern analysis and minimum cumulative resistance model. The results showed that there were 435861 patches in the Pearl River Delta urban agglomeration that could be used as ecological source area, covering an area of 7346.60 km2 and accounting for 13.4% of the Pearl River Delta area. Thirty patches were selected as the ecological source area of the study area by using the area and patch importance index, covering an area of 2792.59 km2 and accounting for 5.1% of the Pearl River Delta area. The overall natural environment of the Pearl River Delta urban agglomeration was excellent. The ecological resistance level was small. The peripheral ecological resistance was low. The core ecological resistance was high. There was still a large room for adjustment of stand types and landscape patterns, which should be optimized by adjusting the composition and spatial distribution of tree species. The ecological network of the Pearl River Delta urban agglomeration was optimized with 30 ecological sources, 103 key ecological corridors, and 95 ecological nodes. The improvement rates of the optimized probability of connectivity index and integral index of connectivity index were 297.5% and 695.1%, respectively. The optimization results could effectively connect the ecological sources and spread the ecological service functions of ecological sources.

Deciphering three-dimensional bioanode configuration for augmenting power generation and nitrogen removal in air-cathode microbial fuel cells.

In this study, the engineering-oriented three-dimensional (3D) bioanode concept was applied, demonstrating that spiral-stairs-like/rolled carbon felt (SCF/RCF) configurations achieved good performances in air-cathode microbial fuel cells (ACMFCs). With the 3D anodes, ACMFCs generated significantly higher power densities of 1535 mW/m3 (SCF) and 1800 mW/m3 (RCF), compared with that of a traditional flat carbon felt anode (FCF, 315 mW/m3). The coulombic efficiency of 15.39 % at SCF anode and 14.34 % at RCF anode also is higher than the 7.93 % at FCF anode. The 3D anode ACMFCs exhibited favorable removal of chemical oxygen demand (96 % of SCF and RCF) and total nitrogen (97 % of SCF, 99 % of RCF). Further results show that three-dimensional anode structures could enrich more electrode surface biomass and diversify the biofilm microbial communities for promoting bioelectroactivity, denitrification, and nitrification. These results demonstrate that three-dimensional anodes with active biofilm is a promising strategy for creating scalable MFCs-based wastewater treatment system.

Dissimilatory nitrate reduction by Pseudomonas alcaliphila with an electrode as the sole electron donor.

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were considered two alternative pathways of dissimilatory nitrate reduction. In this study, we firstly reported that both denitrification and DNRA occurred in Pseudomonas alcaliphila strain MBR with an electrode as the sole electron donor in a double chamber bio-electrochemical system (BES). The initial concentration of nitrate appeared as a factor determining the type of nitrate reduction with electrode as the sole electron donor at the same potential (-500 mV). As the initial concentration of nitrate increased, the fraction of nitrate reduced through denitrification also increased. While nitrite (1.38 ± 0.04 mM) was used as electron acceptor instead of nitrate, the electrons recovery via DNRA and denitrification were 43.06 ± 1.02% and 50.51 ± 1.37%, respectively. The electrochemical activities and surface topography of the working electrode catalyzed by strain MBR were evaluated by cyclic voltammetry and scanning electron microscopy. The results suggested that cells of strain MBR were adhered to the electrode, playing the role of electron transfer media for nitrate and nitrite reduction. Thus, for the first time, the results that DNRA and denitrification occurred simultaneously were confirmed by powering the strain with electricity. The study further expanded the range of metabolic reactions and had potential value for the recognization of dissimilatory nitrate reduction in various ecosystems.

Aerobic bioreduction of nickel(II) to elemental nickel with concomitant biomineralization.

Although microorganisms have the potential to reduce metals, products with elementary forms are unusual. In the present study, a strain of Pseudomonas sp. MBR was tested for its ability to reduce metal ions to their elementary forms coupled to biomineralization under aerobic conditions. The Pseudomonas sp. MBR strain was able to reduce metals such as Fe(III), Mn(II), Cu(II), Ni(II), Cd(II), Co(II), Al(III), Se(IV), and Te(IV) as electron acceptors to elementary forms using citrate, lactate, pyruvate, succinate, malate, glucose, or ethanol as electron donors. Growth and reduction during biomineralization occurred within the pH range of 6.0 to 11.0 and temperature range of 4 to 40 °C, with an optimum growth temperature of 28 °C. The resistance of Ni(II) varied from 0.5 to 5 mM. Ni(II) reduction was still observed when nitrate was present in addition to oxygen as a potential electron acceptor. The Ni(II) reduction efficiency was related with the molar ratio of the electron donor to Ni(II). Unlike other dissimilatory metal-reducing bacteria, which oxidizes organic matter with Fe(III) or Mn(IV) as the sole electron acceptor coupled to energy production under facultative anaerobic conditions, this strain used oxygen as an electron acceptor combined with metal reduction. The aerobic metal reduction may relate to a co-metabolic reduction. Transmission electron microscopy images demonstrated that the cells had the ability to accumulate heavy metals, and that the detoxicity mechanism was intracellular metal reduction. These results suggested that the use of Pseudomonas sp. MBR could be promising for toxic heavy metal bioremediation and biological metallurgy.

Visual signal sensor coupling to nitrification for sustainable monitoring of trichloroacetaldehyde and the response mechanisms.

In this work, a toxicity monitoring microbial system (TMMS) with a nitrifying biofilm as a sensing element and cathode oxygen reduction as an electrical signal was successfully constructed for trichloroacetaldehyde (TCAL) detection. The current and nitrification rate showed a linear relationship with TCAL concentration from 0 to 100 µg/L (R2current = 0.9892, R2nitrification = 0.9858), indicating that the target substrate concentration can be directly obtained from an electrical signal without further sample concentration. High-throughput sequencing revealed that the TMMS was composed of autotrophic/heterotrophic nitrifying and denitrifying microorganisms. Further analysis via a symbiotic relationship network demonstrated that unclassified_Comamonadaceae and unclassified_Xanthobacteraceae were the core nodes for maintaining the interaction between autotropic and heterotrophic nitrifying bacteria. Kyoto Encyclopedia of Genes and Genomes analysis showed that the electron transfer process primarily relied on ferredoxin and cytochromes under TCAL stress, and the abundance of functional enzymes involved in the process of nitrification was decreased, resulting in changes in electrical signal output. This work explored a visual signal sensor combined with electrochemistry and autotrophic/heterotrophic nitrification, which provided new insights into recognition and response mechanisms for microbial monitoring of toxic substances.

Rapid detection of nitrite based on nitrite-oxidizing bacteria biosensor and its application in surface water monitoring.

Timely and sensitive detection of nitrite is of great significance for human health protection and water pollution treatment. However, many biosensors can only determine the comprehensive toxicity of the water, and there are few electroactive biofilm (EAB) sensors for the specific detection of pollutants. Biofilms formed by bacteria with specific functions can improve the specificity of nitrite identification by biosensors. This study developed a novel, rapidly responding, high sensitivity (958.6 µAµM-1cm-2), wide detection range and anti-interference electrochemical biosensor based on electroactive nitrite-oxidizing bacteria. The biosensor could accurately detect nitrite in the range of 0.3-100 mg/L within 3 min by the cyclic voltammetry (CV) method. The bioelectrode could perform stable detection of nitrite over 200 cycles. The specificity of the biosensor for detecting nitrite was demonstrated by the presence of nitrite oxidizing bacteria (NOB) and nitrite oxidase enzyme (NXR) on the electrode biofilm. The biosensor performed well in wetlands and rivers, with an RSD <14.8% in the detection of nitrite at low concentrations, and further revealed the nitrification occurrence. Our study provided a feasible way for the development of a highly sensitive, rapidly responding and stable electrochemical biosensor, which also exhibited potential applications for long-term detection of nitrite and assessment of ecological function in surface water (rivers, lakes, wetlands, marshes, etc.).

A high-sensitive and durable electrochemical sensor based on Geobacter-dominated biofilms for heavy metal toxicity detection.

A highly sensitive electrochemical sensor for detecting low concentrations of heavy metals (Cd2+, Ni2+, Pb2+ and Cu2+) based on Geobacter-dominated biofilms was developed. The biosensor showed a high sensitivity for the determination of Cd2+ (109.7 µAµM-1cm-2) and the determination of Pb2+ (161.7 µAµM-1cm-2). The performance of three fitting models for biosensor response to heavy metal toxicity was investigated based on the relationship between total coulomb yield and heavy metal concentration. The full-area model (Equation a) provided the best fit, and the response times tended to be the fastest based on the peak current model (Equation c). Recovery methods were proposed to ensure the electrical activity of the biofilm for long-term monitoring. 16S rRNA gene sequence analysis showed that the most dominant genus in the anodic biofilm was Geobacter (44.1%-45.8%), indicating a stable community structure after continuous toxicity shock for 22 days. The confocal laser scanning microscope (CLSM) further proved the restorable and reusability of the biosensor. Thanks to the thin and electrically active Geobacter-dominated biofilms, it could be a good alternative biosensor for groundwater analysis etc. The results of this study contribute to the development of a highly sensitive and accurate biosensor with long-term usage towards on-site monitoring of heavy metals at low concentrations, improving the test performance of the biosensor for practical application.

A novel electrochemical sensor based on nitrite-oxidizing bacteria for highly specific and sensitive detection of nitrites.

Real-time nitrite control in water is necessary for environmental safety and human health, and has triggered the research and development of novel detection methods. Previous studies have made great progress on enzyme-free and enzyme electrochemical sensors. However, enzyme-free sensors have low selectivity and a complex preparation process, and enzyme sensors have short lifetimes, and these issues need to be addressed. In this work, we proposed for the first time a highly specific and sensitive biofilm sensor based on nitrite-oxidizing bacteria (NOB) for the bio-electrochemical detection of nitrite in water. The mechanism of nitrite detection was attributed to the competition of oxygen between aerobic respiration of the NOB and the cathode oxygen reduction on the carbon felt electrode, resulting in a decrease in current. This decrease in current (ΔI) had a linear relationship with the nitrite concentration in the range of 0.1 to 1 mg L-1 and 1 to 10 mg L-1, which was corresponding to the sensitivities of 48.62 and 2.24 µA mM-1 cm-2, respectively. And the limit of detection (LOD) was calculated to be 0.033 mg L-1 (2.39 µM) with a signal-to-noise ratio of 3. Moreover, several common interfering ions had no effect on the nitrite detection owing to the functional microbial species (NOB) and weakly electrochemical behavior of electrode at the low potential of -0.1 V, showing high specificity for nitrite detection of biofilm sensor. Therefore, the actual nitrified wastewater was well detected by the biofilm sensor. In addition, allylthiourea (ATU) took good effect on the resistance of the influence of ammonia oxidizing bacteria (AOB) in the biofilm sensor, maintaining the high selectivity of biofilm sensor in case the biofilm sensor was fouled with AOB. The biofilm sensor in our work showed good selectivity, sensitivity and stability in long-term detection.

Aerobic biocathodes with potential regulation for ammonia oxidation with concomitant cathodic oxygen reduction and their microbial communities.

Aerobic biocathodes are effective construct for the simultaneous nitrification and denitrification, but the disturbance of cathodic oxygen reduction on ammonia oxidation and denitrification remains unclear. In this study, we revealed the oxygen reduction peak at -0.4 V (versus silver/silver chloride) by cyclic voltammetry analysis at a cathode without a biofilm. The reduction peak, however, showed a right shift from -0.4 to -0.3 V for the biocathode, indicating that the aerobic biocathode could simultaneously perform traditional nitrification and cathode oxygen reduction. Therefore, different electrode potentials ranging from -0.5 to -0.1 V were designed for regulating the ammonia oxidation rate, and the results showed that the highest oxidation rate reached 3.08 mg/h/L at a potential of -0.2 V under a low-aeration rate of 5 mL/min. High-throughput sequencing showed that Nitrosomonas and Rhodococcus were the dominant nitrogen removal genera in the biocathode, and the abundance of Devosia was related to the interactions between the aeration rate and the electrode potential. Furthermore, the amoC and hao genes responded to aeration and electrode potential regulation, and -0.2 V was more suitable for promoting the denitrification process under low-aeration conditions. Therefore, these findings provided new insights on cathodic potential control for ammonia oxidation and nitrogen removal as well as for the regulation of microbial communities.

Microbial electrochemical driven anaerobic ammonium oxidation coupling to denitrification in a single-chamber stainless steel reactor for simultaneous nitrogen and carbon removal.

Anodic ammonium oxidation mainly focuses on autotrophic process, and the removal combined with organic matter oxidation is still unclear in microbial electrolysis cell (MEC). Here, a stainless-steel tank is constructed as an MEC for anaerobic ammonium oxidation and organic matter removal. Results show that MEC increases ammonium oxidation from 3.83 ± 2.51% to 32.90 ± 3.39%, and the organic matter removal rises from 75.69 ± 0.59% to 92.12 ± 0.57%, and the energy consumption is only 0.80 ± 0.09 kWh kg-1N, indicating an energy-efficient approach for simultaneous ammonium and carbon removal. Cyclic voltammetry reveals two pairs of oxidative peaks (-0.4 V and + 0.6 V) which demonstrate the electrochemical activity of biofilms for organic matter and ammonium oxidation, respectively. 16S rRNA gene analysis clarifies the anodic biofilm mainly enriched by the genus of Azoarcus, Hydrogenophaga and Paracoccus. Further analysis indicates that anodic potential controls the community succession of heterotrophic and hydrogenotrophic denitrifying bacteria, and then regulates the nitrogen and carbon removal processes, which extend the insights of anodic anaerobic ammonium oxidation coupling to denitrification under organic conditions.

Improving electroautotrophic ammonium production from nitrogen gas by simultaneous carbon dioxide fixation in a dual-chamber microbial electrolysis cell.

Microbial electrosynthesis is a promising technology for high-value added products generation from organic and inorganic waste. In this work, autotrophic dual-chamber microbial electrolysis cells (MECs) were set up for N2 fixation at -0.9 V vs Ag/AgCl (sat. KCl) cathodic potential under ambient conditions. Higher NH4+ production yield (average value of 0.35 µmol h-1 cm-2, normalized to cathode surface area) and higher faradaic efficiency (FE, 20.25%) were obtained with intermittent addition of N2 and CO2, while the yield and FE were only 0.018 µmol h-1 cm-2 and 4.21% in the absence of CO2. Furthermore, cyclic voltammograms (CV) explained the bioelectrochemical behavior of N2 reduction was coupled with CO2 reduction in the autotrophic MECs. Microbial community analysis and functional prediction in the cathodic chamber revealed that Xanthobacter and Hydrogenophaga played as producers for N2 and CO2 fixation and Pannonibacter acting as a decomposer for converting organic nitrogen to ammonium. This work not only provided an optional bioelectrocatalytic method for N2 fixation with negative CO2-emissions but also revealed the mechanism of simultaneous fixation of N2 and CO2 via Calvin cycle in autotrophic MECs.

Integrated simultaneous nitrification/denitrification and comammox consortia as efficient biocatalysts enhance treatment of domestic wastewater in different up-flow bioelectrochemical reactors.

Simultaneous nitrification/denitrification (SND) can efficiently deplete NH4+ by using air-exposed biocathode (AEB) in bioelectrochemical reactors. However, the fluctuation of wastewater adversely affects the functional biofilms and therefore the performance. In this work, four up-flow bioelectrochemical reactors (UBERs) with some novel inocula were investigated to improve domestic wastewater treatment. The UBERs exhibited favorable removal of chemical oxygen demand (COD, 95%), NH4+-N (99%), and total nitrogen (TN, 99%). The maximum of current (2.7 A/m3), power density (136 mW/m3) and coulombic efficiency (20.5%) were obtained. Cyclic voltammetry analysis showed all the electrodes were of diversified catalytic reactions. Illumina pyrosequencing showed the predominant Ignavibacterium, Thauera, Nitrosomonas, Geminicoccus and Nitrospira were in all electrodes, contributing functional biofilms performing SND, comammox, and bioelectrochemical reactions. FAPROTAX analysis confirmed twenty-one functional groups with obvious changes related to chemoheterotrophy, respiration/oxidation/denitrification of nitrite and nitrate. Comfortingly, such novel diversified consortia in UBERs enhance the microbial metabolisms to treat domestic wastewater.