Highly selective and sensitive nitrite biocathode biosensor prepared by polarity inversion method coupled with selective removal of interfering electroactive bacteria.

Nitrite is a multipurpose marker that needs to be detected quickly and accurately, including for water pollution and human urinary tract infections. In this study, we reported a novel nitrite-reducing bacteria electrochemical biosensor based on the metronidazole-treated biocathode (MT-NBEB). The biocathode with high nitrite response sensitivity used was first prepared by polarity inversion method and then treated with metronidazole to selectively remove the interfering electroactive bacteria for selectivity improvement. MT-NBEB could detect nitrite in the range of 0.0001 mg NO2--N L-1-8 mg NO2--N L-1 within 1.7 min and maintain stable detection performance for over 50 continuous cycles with relative standard deviations < 2.4%. Besides, the response signals of MT-NBEB were not affected by the common inorganic salts (such as nitrate and ammonia) and organic matter (such as acetate). MT-NBEB successfully detected nitrite in five types of wastewaters with relative errors < 14.3%. Our study provided a feasible way to prepare highly selective and sensitive electrochemical biosensors to quickly and accurately detect nitrite in real wastewaters.

Fast and simultaneous detection of dissolved BOD and nitrite in wastewater by using bioelectrode with bidirectional extracellular electron transport.

Timely and simultaneously detecting BOD and nitrite concentrations is of great significance for curbing of water pollution and adjusting wastewater treatment strategies. However, existing BOD and nitrite biosensors cannot perform synchronous detection due to their single electroactivity and differences in detection time. This study reported a novel dual-function electrochemical biosensor (DFEB) that could perform fast, simultaneous detection of nitrite and dissolved BOD. DFEB conducted a potential-step chronoamperometry on the mixed-bacteria bioelectrode with bidirectional electron transfer ability to obtain response signals. DFEB accurately measured dissolved BOD in the range of 5 ∼ 100 mg BOD L-1 and nitrite in the range of 0.05 ∼ 16 mg NO2--N L-1 within 20 min and maintain stable performance over 200 tests. DFEB performed well in artificial wastewater, aquatic wastewater, anaerobic tank effluent and anammox effluent, with relative errors < 15.7% and 16.8% in detecting nitrite and dissolved BOD, respectively. Our study provided a feasible way to develop multifunctional biosensors for detecting pollutants with different redox properties in wastewater.

A novel, rapidly preparable and easily maintainable biocathode electrochemical biosensor for the continuous and stable detection of nitrite in water.

Nitrite is a highly toxic and pathogenic pollutant that is widely distributed in various nitrogenous wastewaters. Therefore, there is an urgent need for fast and stable nitrite detection to avoid water pollution and protect human health. In this study, we developed a novel rapidly preparable and easily maintainable biocathode electrochemical biosensor (BEB) using nitrite-reducing bacteria as the detectors to realize continuous nitrite monitoring in wastewater. The preparation of the biocathode was shortened by the polarity inversion method to less than 6 d. The BEB could detect nitrite solution samples in the range of 0.1- 16.0 mg NO2--N L-1 within 1.7 min. The BEB was also successfully used to detect nitrite in real wastewater with a relative error < 4.0% and a relative standard deviation < 5.8%. In addition, the BEB could be easily maintained by an operation mode of microbial fuel cells and stably detected nitrite for at least 150 tests. Our study provided a feasible and convenient way to develop electrochemical biosensors based on the biocathode for continuous and stable monitoring of pollutants in wastewater.

Promoting Extracellular Electron Transfer of Shewanella oneidensis MR-1 by Optimizing the Periplasmic Cytochrome c Network.

The low efficiency of extracellular electron transfer (EET) is a major bottleneck for Shewanella oneidensis MR-1 acting as an electroactive biocatalyst in bioelectrochemical systems. Although it is well established that a periplasmic c-type cytochrome (c-Cyt) network plays a critical role in regulating EET efficiency, the understanding of the network in terms of structure and electron transfer activity is obscure and partial. In this work, we attempted to systematically investigate the impacts of the network components on EET in their absence and overproduction individually in microbial fuel cell (MFC). We found that overexpression of c-Cyt CctA leads to accelerated electron transfer between CymA and the Mtr system, which function as the primary quinol oxidase and the outer-membrane (OM) electron hub in EET. In contrast, NapB, FccA, and TsdB in excess severely impaired EET, reducing EET capacity in MFC by more than 50%. Based on the results from both strategies, a series of engineered strains lacking FccA, NapB, and TsdB in combination while overproducing CctA were tested for a maximally optimized c-Cyt network. A strain depleted of all NapB, FccA, and TsdB with CctA overproduction achieved the highest maximum power density in MFCs (436.5 mW/m2), ∼3.62-fold higher than that of wild type (WT). By revealing that optimization of periplasmic c-Cyt composition is a practical strategy for improving EET efficiency, our work underscores the importance in understanding physiological and electrochemical characteristics of c-Cyts involved in EET.

Enhancing stability and resilience of electromethanogenesis system by acclimating biocathode with intermittent step-up voltage.

Electromethanogenesis (EMG) system could efficiently convert CO2 to CH4 by using excess renewable electricity. However, the fluctuation and interruption of renewable electricity will adversely affect the biocathode and therefore the CH4 production of the EMG system. In this work, a novel biocathode acclimation strategy with intermittent step-up voltage (ISUV) was proposed to improve the stability and resilience of the EMG system against the unstable input of renewable power. Compared with the intermittent application of constant voltage (IACV), the ISUV increased the rate of CH4 production by 11.7 times with the improvement of the stability and resilience by 56% and 500%, respectively. Morphology and microflora structure analysis revealed that the biofilm enriched with ISUV exhibited a compact microflora structure with high-density cells and nanowires interconnected. This study provided a novel effective strategy to regulate the biofilm structure and enhance the performance of the EMG system.

Enhancing bio-cathodic nitrate removal through anode-cathode polarity inversion together with regulating the anode electroactivity.

Bio-cathodic nitrate removal uses autotrophic nitrate-reducing bacteria as catalysts to realize the nitrate removal process and has been considered as a cost-effective way to remove nitrate contamination. However, the present bio-cathodic nitrate removal process has problems with long start-up time and low performance, which are urgently required to improve for its application. In this study, we investigated an anode-cathode polarity inversion method for rapidly cultivating high-performance nitrate-reducing bio-cathode by regulating bio-anodic bio-oxidation electroactivities under different external resistances and explored at the first time the correlation between the oxidation performance and the reduction performance of one mixed-bacteria bioelectrode. A high bio-electrochemical nitrate removal rate of 2.74 ± 0.03 gNO3--N m-2 d-1 was obtained at the bioelectrode with high bio-anodic bio-oxidation electroactivity, which was 4.0 times that of 0.69 ± 0.03 gNO3--N m-2 d-1 at the bioelectrode with low bio-oxidation electroactivity, and which was 1.3-7.9 times that of reported (0.35-2.04 gNO3--N m-2 d-1). 16S rRNA gene sequences and bacterial biomass analysis showed higher bio-cathodic nitrate removal came from higher bacterial biomass of electrogenic bacteria and nitrate-reducing bacteria. A good linear correlation between the bio-cathodic nitrate removal performance and the reversed bio-anodic bio-oxidation electroactivity was presented and likely implied that electrogenic biofilm had either action as autotrophic nitrate reduction or promotion to the development of autotrophic nitrate removal system. This study provided a novel strategy not only to rapidly cultivate high-performance bio-cathode but also to possibly develop the bio-cathode with specific functions for substance synthesis and pollutant detection.

High electrochemical activity of a Ti/SnO2-Sb electrode electrodeposited using deep eutectic solvent.

Electrodeposition is an economical and efficient way to prepare Ti/SnO2-Sb electrode for electrochemical oxidizing pollutants in wastewater. The solvent used for electrodeposition has a great effect on electrode performance. The conventional Ti/SnO2-Sb electrode electrodeposited using aqueous solvent has poor electrochemical activity and short service life. In this study, a Ti/SnO2-Sb electrode was prepared via electrodeposition using a deep eutectic solvent (DES). This new Ti/SnO2-Sb-DES electrode performed a rate constant of 0.571 h-1 for methylene blue decolorization and long accelerated service life of 12.9 h (100 mA cm-2; 0.5 M H2SO4), which were 1.7 times and 3.2 times as high as that of the electrode prepared in aqueous solvent, respectively. The enhanced properties were related to the 1.3 times increased electrochemically active surface area of Ti/SnO2-Sb-DES electrode which had a rough, multilayer and uniform surface structure packed with nano-sized coating particles. In conclusion, this study developed a facile, green and efficient pathway to prepare Ti/SnO2-Sb electrode with high performance.

Combination of plasma oxidation process with microbial fuel cell for mineralizing methylene blue with high energy efficiency.

Plasma advanced oxidation process (PAOP) has great ability to break recalcitrant pollutants into small molecular compounds but suffers from poor performance and low energy efficiency for mineralizing dyeing pollutants. Combining advanced oxidation process with biodegradation process is an effective strategy to improve mineralization performance and reduce cost. In this study, a combined process using PAOP as pre-treatment followed by microbial fuel cell (MFC) treatment was investigated to mineralize methylene blue (MB). The PAOP could degrade MB by 97.7%, but only mineralize MB by 23.2% under the discharge power of 35 W for 10 min. Besides, BOD5/COD ratio of MB solution raised from 0.04 to 0.38 while inhibition on E. coli growth decreased from 85.5% to 28.3%. The following MFC process increased MB mineralization percentage to 63.0% with a maximum output power density of 519 mW m-2. The combined process achieved a mineralization energy consumption of 0.143 KWh gTOC-1 which was only 41.8% of that of PAOP. FT-IR, UV-vis and pH variation demonstrated that PAOP could break the aromatic and heterocyclic structures in MB molecule to form organic acids. Possible degradation pathways of MB were accordingly proposed based on LC-MS, GC-MS, and density functional theory calculation.

Enhancement of the denitrification activity by exoelectrogens in single-chamber air cathode microbial fuel cells.

Single-chamber microbial fuel cells (MFCs) can efficiently treat wastewater containing nitrate, probably because the interaction between exoelectrogens and denitrifying bacteria may enhance the denitrification activity of MFCs. In this study, the denitrification of nitrate with a wide range of concentrations was investigated by using single-chamber air cathode MFCs. The maximum average denitrification rate of the MFCs inoculated and operated under closed-circuit conditions (Group N-CC) was up to 12.2 ±â€¯0.6 kg NO3--N m-3 d-1 at a high nitrate concentration of 2000 mg NO3-N L-1, which was 74.3% higher than that of the MFCs inoculated and operated under open-circuit conditions and which was significantly higher than those of other MFC systems and many traditional bioreactors. The high denitrification activity of the MFCs of Group N-CC was attributed to the significant reduction of nitrite accumulation through the possible bioelectrochemical nitrite reduction by exoelectrogens that were only enriched at the anodes of the MFCs of Group N-CC. In addition, the MFCs of Group N-CC showed good stability (over 3.5 years) and low apparent activation energy (34.0 kJ mol-1) of the denitrification, indicating the good coexistence of exoelectrogens (Geobacter) and denitrifying bacteria (Thauera) with high performance on denitrification during the long-term operation.