Electricity-Driven Microbial Metabolism of Carbon and Nitrogen: A Waste-to-Resource Solution.

Electricity-driven microbial metabolism relies on the extracellular electron transfer (EET) process between microbes and electrodes and provides promise for resource recovery from wastewater and industrial discharges. Over the past decades, tremendous efforts have been dedicated to designing electrocatalysts and microbes, as well as hybrid systems to push this approach toward industrial adoption. This paper summarizes these advances in order to facilitate a better understanding of electricity-driven microbial metabolism as a sustainable waste-to-resource solution. Quantitative comparisons of microbial electrosynthesis and abiotic electrosynthesis are made, and the strategy of electrocatalyst-assisted microbial electrosynthesis is critically discussed. Nitrogen recovery processes including microbial electrochemical N2 fixation, electrocatalytic N2 reduction, dissimilatory nitrate reduction to ammonium (DNRA), and abiotic electrochemical nitrate reduction to ammonia (Abio-NRA) are systematically reviewed. Furthermore, the synchronous metabolism of carbon and nitrogen using hybrid inorganic-biological systems is discussed, including advanced physicochemical, microbial, and electrochemical characterizations involved in this field. Finally, perspectives for future trends are presented. The paper provides valuable insights on the potential contribution of electricity-driven microbial valorization of waste carbon and nitrogen toward a green and sustainable society.

Metal nanoparticles increased the lag period and shaped the microbial community in slurry-electrode microbial electrosynthesis.

Concerns about energy crisis and CO2 emission have motivated the development of microbial electrosynthesis (MES); recent studies have showed the potential of novel slurry-electrode MES. In this study, the effect of nonprecious metal nanoparticles (NPs) on the performance of slurry-electrode MES was systematically evaluated in terms of chemical production, physicochemical properties, electrochemical characterization, and microbial community. Ni and Cu NPs increased the lag period from 6 to 15 days for acetate production, while Mo NPs showed no apparent effect. However, these metal NPs slightly affected the final total acetate production (ca. 10 g L-1), Faradic efficiency (ca. 50%), net water flux across the anion exchange membrane (ca. 6 mL d-1), or electrochemical characterization of catholyte. BRH-c20a was enriched as the dominated microbe (>48%), and its relative abundance was largely affected by the addition of metal NPs. This study demonstrates that metal NPs affect the performance of biocathodes, mainly by shaping the microbial community.

Efficient production of medium chain fatty acids in microbial electrosynthesis with simultaneous bio-utilization of carbon dioxide and ethanol.

Microbial electrosynthesis (MES) is a promising technology for chemicals production driven by renewable energy. However, how the medium chain fatty acids (MCFAs) production in MES is affected by the method of chain elongation is not clear, and no direct evidence is provided yet for a simultaneous bio-utilization of CO2 and ethanol. In this study, different methods of chain elongation in MES reactors were investigated. During in-situ chain elongation, a maximum caproate concentration of 11.9 ± 0.6 g L-1 was achieved, while the C6 specificity (56.4% ± 0.5%) was much lower than that of ex-situ chain elongation (78.7% ± 1.5%). Carbon distribution and reduction degree balance indicated a simultaneous bio-utilization of CO2 and ethanol, and it was validated by the isotope tracer technique. MCFAs-forming microbes, acetogens, and electrochemically active microorganisms were enriched. This study provides fundamental insights relevant to the carbon and electron fluxes driven by electricity.

Indicators of water biotoxicity obtained from turn-off microbial electrochemical sensors.

The development of biosensors is critical to reducing potential risks associated with contamination accidents. However, the application of microbial electrochemical sensors for water biotoxicity monitoring is hampered by the lack of an indicator with high response magnitudes. In this study, microbial electrochemical sensors were fabricated with interdigitated electrode arrays (IDAs), and indicators from various electrochemical analyses were comprehensively investigated. Only the peak of cyclic voltammetry (CV) was highly linearly correlated with the commonly used current indicator during the enrichment of the electroactive biofilm. The resistance fitted from the electrochemical impedance spectroscopy (EIS) data provided a comparable and even higher inhibition ratio (IR) than the current during toxicity assessments. The differential pulse voltammetry (DPV) did not exhibit a higher sensitivity than the CV peak. However, no clear response was observed in the real-time impedance analysis for use in water biotoxicity monitoring. Most of the microbes were in the propidium iodide (PI)-permeable state after the toxicity assessments, although the current was fully recovered. This study demonstrates the potential to use EIS data as indicators of water biotoxicity using microbial electrochemical sensors.

Rechargeable microbial fuel cell based on bidirectional extracellular electron transfer.

Rechargeable microbial electrochemical systems can be used as renewable energy storage systems or as potable bioelectronics devices. In this study, a bioelectrode capable of bidirectional extracellular electron transfer was firstly introduced to construct the rechargeable microbial fuel cell (MFC). The performance of rechargeable MFC was enhanced with the increase of charge/discharge cycles, and a maximum energy efficiency of 4.5 ± 0.2% and Coulombic efficiency of 29.4 ± 4.1% were obtained. H2 was the main charge carrier, while the accumulated acetate was only about 10 mg L-1. The charge time under constant current mode largely affected the energy recovery. A decreased abundance of Mycobacteria, Geobacter, and Azospirillum, accompanied by an increase of Azonexus and Rhodococcus was observed in the rechargeable MFC, compared to control tests fueled with acetate. This study demonstrates the potential of bioelectrode for energy storage and recovery.

Micro-microbial electrochemical sensor equipped with combined bioanode and biocathode for water biotoxicity monitoring.

The development of low-cost biosensors for water monitoring is expected to reduce potential risks from contamination accidents. This study reported a novel micro-microbial electrochemical sensor using combined bioanode and biocathode as the sensing element, characterized by a sequential flowing membrane-free channel and a bilateral passive oxygen supply. A decrease in the ratio of number of bioanode to biocathode resulted in a lower power generation, whereas, achieving a similar or even higher toxic response. The voltage was affected by both the flow rate and the acetate concentration. With the increased acetate concentration, a clear trade-off was observed between the electroactivity stimulation of bioanode vs. the electroactivity maintenance of biocathode. Biosensors made good response to the injection of formaldehyde (10 µL of 0.25%, and 100 µL of 0.025%) into the inlet. A high microbial diversity was observed. This work can lead to a revolutionizing way of water monitoring using self-powered micro-biosensors.

A slurry electrode integrated with membrane electrolysis for high-performance acetate production in microbial electrosynthesis.

Microbial electrosynthesis (MES) technology employs electrotrophic microbes as biocatalysts to produce chemicals from CO2. The application of a slurry electrode can enlarge the surface area to volume ratio, and membrane electrolysis (ME) for on-line extraction can solve the problem of product inhibition. This study constructed a novel dual-chamber ME-MES integrated system equipped with a slurry electrode, and the effect of concentration of powder-activated carbon (AC) in the catholyte on chemical production was also evaluated. The integrated system amended with 5 g L-1 AC produced up to 13.4 g L-1 acetate, showing a 179% increase compared with the control group without AC (4.8 g L-1). However, further increasing the AC concentration to 10 and 20 g L-1 resulted in decreased acetate production. A high concentration of AC showed higher antimicrobial activity to methanogens, as compared to acetogens. Amending AC exacerbated the process of electroosmosis. Also, amending AC with 0 to 10 g L-1 decreased the electrochemical losses via both the membrane and electrolyte. The chemical production using H2 or the electrode as electron donors showed a similar trend when amending AC. The present study provided important information for guiding future research to construct an efficient configuration of an MES bioreactor.

Microbial electrochemical platform for the production of renewable fuels and chemicals.

The electrochemical conversion of CO2 and organic waste can combine renewable surplus electricity storage, CO2 utilization, and organic waste management. This review emphasizes the microbial electrochemical platform that merges electrochemical conversion and microbial conversion for the production of fuels and chemicals. In addition, this review examines methods to overcome limitations by the design of advanced reactor concepts, bioconversion with metabolic engineering, multiple-step catalysis, and anodic electro-oxidation reactions, among others. An in-depth discussion of trends is presented, including the interfacing of the classic carboxylate, syngas, and sugar platforms with microbial electrochemical technology. A critical assessment of microbial electrochemical biogas upgrading is also provided. Criticisms and perspectives related to electrobiorefineries and electro-fermentation for organic waste valorization are critically reviewed. The microbial electrochemical platform for the production of renewable fuels and chemicals is a recent application; thus, a number of concerns have yet to be resolved. Among the aspects to address are the increase in carbon fixation rate, production of highly valuable chemicals, response of physiological metabolism, and long-term assessment of scaled-up bioreactors. Insights into these factors may further increase the economic efficiency and sustainability of the technology.

[Analysis on variance of common pathogenic bacteria and drug resistance in children in Chengdu area from 2001 to 2006].

OBJECTIVE: To investigate the variance and drug resistance of pathogenic bacteria isolated from children with infectious diseases seen between 2001 and 2006 in Chengdu area. METHODS: A total of 2888 pathogenic bacterial strains isolated from children in Chengdu Children's Hospital from 2001 to 2006 were analyzed. Tests were performed according to the guidelines of National Committee for Clinical Laboratory Standards (NCCLS) of the United States. RESULT: (1) Of the 2888 strains, 1845 (63.9%) were Gram negative bacteria. The main pathogenic bacteria included Escherichia coli (Ec, 718 strain, 24.9%), Hemophilus (H, 476 strain, 16.5%), Streptococcus pneumoniae (Sp, 412 strain, 14.3%), Klebsiella pneumoniae (Kp, 369 strain, 12.8%), Staphylococcus aureus (Sa, 353 strain, 12.2%), Staphylococcus epidermidis (Se, 278 strain, 9.6%), Pseudomonas aeruginosa (Pa, 146 strain, 5.1%) and other non-zymocyte (Onz, 136 strain, 4.7%). (2) The common pathogens found in blood specimen were 158 strain, which included Se (78 strain, 49.4%), Ec (23 strain, 14.6%), Kp (17 strain, 10.8%), Sa (14 strain, 8.9%), Onz (14 strain, 8.9%), Sp (7 strain, 4.4%) and Pa (5 strain, 3.2%). (3) The number of common pathogens isolated from patients with lower respiratory tract infection was 2018, including Ec (441 strains, 21.9%), H (430 strains, 21.3%), Sp (368 strains, 18.2%), Kp (253 strains, 12.5%), Sa (207 strains, 10.3%), Se (149 strains, 7.3%), Pa (97 strains, 4.8%) and Onz (73 strains, 3.6%). (4) There were 120 strains of common pathogens isolated from urine specimens, including Ec (78 strains, 65%), Kp (25 strains, 20.8%), Onz (7 strains, 5.8%), Pa (5 strains, 4.2%) and Se (5 strains, 4.2%). (5) There were 497 strains of common pathogens found in pus specimens, including Ec 167 strains, (33.6%), Sa (126 strains, 25.4%), Se (46 strains, 9.3%), H (44 strains, 8.9%), Onz (37 stains, 7.4%), Kp (31 strains, 6.2%), Sp (26 strains, 5.2%) and Pa (20 strain, 4.0%). The trend of drug resistance of pathogenic bacteria to antibiotics deteriorated. The proportion of methicillin-resistant Staphylococcus aureus (MRSA) was 6.7% and the methicillin-resistant coagulase-negative Staphylococci (MRCNS) rate was 20% in 2001 - 2003. The total proportion of extended-spectrum beta-lactamase stains (ESBL(S)) in Ec and Kp was 21.8%, and the rate of beta-lactamase production stains of Hemophilus influenzae (Hi) was 19.4% in 2001 - 2003.The proportion of MRSA was 17.2% and the MRCNS rate was 70.2%, the total proportion of ESBL(S) in Ec and Kp was 43.8%, and the rate of beta-lactamase producing stains of Hi was 39.7% in 2004 - 2006. CONCLUSION: The distribution of common pathogenic bacteria seen in Chengdu Children's Hospital has changed and the trend of drug resistance of pathogenic bacteria to antibiotics deteriorated in recent three years. Regionally monitoring the changes in pathogenic bacteria and the trend of drug resistance to antibiotics is paramount in guiding the pediatric clinical treatment.