Bimetallic catalysts as electrocatalytic cathode materials for the oxygen reduction reaction in microbial fuel cell:A review

Microbial fuel cell(MFC) is one synchronous power generation device for wastewater treatment that takes into account environmental and energy issues, exhibiting promising potential. Sluggish oxygen reduction reaction(ORR) kinetics on the cathode remains by far the most critical bottleneck hindering the practical application of MFC. An ideal cathode catalyst should possess excellent ORR activity, stability, and costeffectiveness, experiments have demonstrated that bimetallic catalysts are one of the most promising ORR catalysts currently. Based on this, this review mainly analyzes the reaction mechanism(ORR mechanisms, synergistic effects), advantages(combined with characterization technologies), and typical synthesis methods of bimetallic catalysts, focusing on the application effects of early Pt-M(M = Fe, Co, and Ni) alloys to bifunctional catalysts in MFC, pointing out that the main existing challenges remain economic analysis, long-term durability and large-scale application, and looking forward to this. At last, the research trend of bimetallic catalysts suitable for MFC is evaluated, and it is considered that the development and research of metal-organic framework(MOF)-based bimetallic catalysts are still worth focusing on in the future, intending to provide a reference for MFC to achieve energy-efficient wastewater treatment.

Microbial synthesis of N, P co-doped carbon supported PtCu catalysts for oxygen reduction reaction

Developing highly efficient and stable platinum-based electrocatalyst for oxygen reduction reaction(ORR) is critical to expediting commercialization of fuel cells.Herein,several PtCu alloy nanocatalysts supported on N,P co-doped carbon(PtCu/NPC) were prepared by microbial-sorption and carbonization-reduction.Among them,PtCu/NPC-700 ℃ exhibits excellent catalytic performance for ORR with a mass activity of 0.895 A mg_(pt)^(-1)(@0.9 V) which is 8.29 folds of commercial Pt/C.Additionally,the ECSA and MA of PtCu/NPC-700℃ only decrease by 14.2% and 18.7% respectively,while Pt/C decreases by 35.2% and 52.8% after 10,000 cycles of ADT test.Moreover,the PtCu/NPC-700℃ catalyst emanates a maximum power density of 715 mW cm^(-2) and only 11.1% loss of maximum power density after 10,000 ADTs in single-cell test,indicating PtCu/NPC-700℃ also manifests higher activity and durability in actual single-cell operation than Pt/C.This research provides an easy and novel strategy for developing highly active and durable Pt-based alloy catalyst.

Sustainable biochar as an electrocatalysts for the oxygen reduction reaction in microbial fuel cells

Microbial fuel cells(MFCs)have gained remarkable attention as a novel wastewater treatment that simultaneously generates electricity.The low activity of the oxygen reduction reaction(ORR)remains one of the most critical bottlenecks limiting the development of MFCs.To date,although research on biochar as an electrocatalyst in MFCs has made tremendous progress,further improvements are needed to make it economically practical.Recently,biochars have been considered to be ORR electrocatalysts with developmental potential.In this review,the ORR mechanism and the essential requirements of ORR catalysts in MFC applications are introduced.Moreover,the focus is to highlight the material selection,properties,and preparation of biochar electrocatalysts,as well as the evaluation and measurement of biochar electrodes.Additionally,in order to provide comprehensive information on the specific applications of biochars in the field of MFCs,their applications as electrocatalysts,are then discussed in detail,including the uses of nitrogen-doped biochar and other heteroatom-doped biochars as electrocatalysts,poisoning tests for biochar catalysts,and the cost estimation of biochar catalysts.Finally,profound insights into the current challenges and clear directions for future perspectives and research are concluded.

Nitrogen and Sulfur Co-doped Porous Carbon Derived from ZIF-8 as Oxygen Reduction Reaction Catalyst for Microbial Fuel Cells

Nitrogen and sulfur co-doped porous nanocarbon (ZIF-C-N-S) catalyst was successfully synthesized derived from ZIF-8 and thiourea precursors.The electrochemical measurements indicate that the as-obtained ZIF-C-N-S catalyst exhibits higher electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline electrolyte and superior durability-longer than commercial Pt/C catalyst.The enhancment of electrocatalytic activity mainly be come from the open pore structure,large specific surface area as well as the synergistic effect resulted from the co-doping of N and S atoms.In addition,the ZIF-C-N-S catalyst is also used as the air cathode catalyst in the microbial fuel cell (MFC) device.The maximum power density and stable output voltage of ZIF-C-N-S based MFC are 1315 mW/m2 and 0.48 V,respectively,which is better than that of Pt/C based MFC.

A Comprehensive Review on Oxygen Reduction Reaction in Microbial Fuel Cells

The focus of microbial fuel cell research in recent years has been on the development of materials,microbes,and transfer of charges in the system,resulting in a substantial improvement in current density and improved power generation.The cathode is generally recognized as the limiting factor due to its high-distance proton transfer,slow oxygen reduction reaction(ORR),and expensive materials.The heterogeneous reaction determines power gen-eration in MFC.This comprehensive review describes-recent advancements in the development of cathode mate-rials and catalysts associated with ORR.The recent studies indicated the utilization of different metal oxides,the ferrite-based catalyst to overcome this bottleneck.These studies conclude that some cathode materials,in parti-cular,graphene-based conductive polymer composites with non-precious metal catalysts provide substantial ben-efits for sustainable development in the field of MFCs.Furthermore,it also highlights the potentiality to replace the conventional platinum air cathode for the large-scale production of the next generation of MFCs.It was evi-dent from the experiments that cathode catalyst needs to be blended with conductive carbon materials to make cathode conductive and efficient for ORR.This review discusses various antifouling strategies for cathode biofoul-ing and its effect on the MFC performance.Moreover,it also depicts cost estimations of various catalysts essential for further scale-up of MFC technology.

Influences of Microbial Oxidation/Reduction on Mineral Transformation in Sulfide Tailings and Environmental Consequence in Shizishan Cu-Au Mine, Tongling, Eastern China

Mining activities have created great wealth, but they have also discharged large quantities of tailings. As an important source of heavy metal contamination, sulfide tailings are usually disposed of in open-air impoundments and thus are exposed to microbial oxidation. Microbial activities greatly enhance sulfide oxidation and result in the release of heavy metals and the precipitation of iron (oxy) hydroxides and sulfates. These secondary minerals in turn influence the mobility of dissolved metals and play important roles in the natural attenuation of heavy metals. Elucidating the microbe–mineral interactions in tailings will improve our understanding of the environmental consequence of mining activities.

Quality enhancement and microbial reduction of mung bean(Vigna radiata)sprouts by non-thermal plasma pretreatment of seeds

Mung bean(Vigna radiata)sprouts are widely consumed worldwide due to their high nutritional value.However,the low yield and microbial contamination of mung bean sprouts seriously reduces their economic value.This study investigates the effects of non-thermal plasma on the quality and microbial reduction of mung bean sprouts by pretreatment of seeds in water for different times(0,1,3 and 6 min).The quality results showed that short-time plasma treatment(1 and 3 min)promoted seed germination and seedling growth,whereas long-time plasma treatment(6 min)had inhibitory effects.Plasma also had a similar dose effects on the total flavonoid and phenolic contents of mung bean sprouts.The microbiological results showed that plasma treatment achieved a reduction of native microorganisms ranging from 0.54 to 7.09 log for fungi and 0.29 to 6.80 log for bacteria at 96 h incubation.Meanwhile,plasma treatment could also efficiently inactivate artificially inoculated Salmonella typhimurium(1.83–6.22 log)and yeast(0.53–3.19 log)on mung bean seeds.The results of seed coat permeability tests and scanning electron microscopy showed that plasma could damage the seed coat structure,consequently increasing the electrical conductivity of mung bean seeds.The physicochemical analysis of plasma-treated water showed that plasma generated various long-and short-lived active species[nitric oxide radicals(NO·),hydroxyl radicals(·OH),singlet oxygen(1O2),hydrogen peroxide(H_(2)O_(2)),nitrate(NO_(3)^(-)),and nitrite(NO_(2)^(-))]in water,thus the oxidizability,acidity and conductivity of plasma-treated water were all increased in a treatment timedependent manner.The result for mimicked chemical mixtures confirmed the synergistic effect of activity of H_(2)O_(2),NO_(3)^(-)and NO_(2)^(-)on bacterial inactivation and plant growth promotion.Taken together,these results imply that plasma pretreatment of mung bean seeds in water with moderate oxidizability and acidity is an effective method to improve the yield of mung bean sprouts and reduce microbial contamination.

PREPARATION OF ENANTIOMERICALLY PURE SYN-4,5-DIHYDROXY CARBOXYLIC ACID LACTONES BY MICROBIAL REDUCTION

Enantiomerically pure syn-4,5-dihydroxy carboxylic acid lactones were prepared by microbial reduction of acyl lactones with resting cell of Aspergillus niger.

Microbially-mediated formation of Ca-Fe carbonates during dissimilatory ferrihydrite reduction:Implications for the origin of sedimentary ankerite

The origin of sedimentary dolomite has become a long-standing problem in the Earth Sciences.Some carbonate minerals like ankerite have the same crystal structure as dolomite,hence their genesis may provide clues to help solving the dolomite problem.The purpose of this study was to probe whether microbial activity can be involved in the formation of ankerite.Bio-carbonation experiments associated with microbial iron reduction were performed in batch systems with various concentrations of Ca^(2+)(0–20 mmol/L),with a marine iron-reducing bacterium Shewanella piezotolerans WP3 as the reaction mediator,and with lactate and ferrihydrite as the respective electron donor and acceptor.Our biomineralization data showed that Ca-amendments expedited microbially-mediated ferrihydrite reduction by enhancing the adhesion between WP3 cells and ferrihydrite particles.After bioreduction,siderite occurred as the principal secondary mineral in the Ca-free systems.Instead,Ca-Fe carbonates were formed when Ca^(2+)ions were present.The CaCO_(3) content of microbially-induced Ca-Fe carbonates was positively correlated with the initial Ca2+concentration.The Ca-Fe carbonate phase produced in the 20 mmol/L Ca-amended biosystems had a chemical formula of Ca_(0.8)Fe_(1.2)(CO_(3))_(2),which is close to the theoretical composition of ankerite.This ankeritelike phase was nanometric in size and spherical,Ca-Fe disordered,and structurally defective.Our simulated diagenesis experiments further demonstrated that the resulting ankerite-like phase could be converted into ordered ankerite under hydrothermal conditions.We introduced the term“proto-ankerite”to define the Ca-Fe phases that possess near-ankerite stoichiometry but disordered cation arrangement.On the basis of the present study,we proposed herein that microbial activity is an important contributor to the genesis of sedimentary ankerite by providing the metastable Ca-Fe carbonate precursors.

In-situ sludge reduction based on Mn^(2+)-catalytic ozonation conditioning:Feasibility study and microbial mechanisms

To improve the sludge conditioning efficiency without increasing the ozone dose,an in-situ sludge reduction process based on Mn^(2+)-catalytic ozonation conditioning was proposed.Using ozone conditioning alone as a control,a lab-scale sequencing batch reactor coupled with ozonated sludge recycle was evaluated for its operating performance at an ozone dose of 75 mg O_(3)/g VSS and 1.5 mmol/L Mn^(2+)addition.The results showed a 39.4%reduction in MLSS and an observed sludge yield of 0.236 kg MLSS/kg COD for the O_(3)+Mn^(2+)group compared to the O_(3)group (15.3%and 0.292 kg MLSS/kg COD),accompanied by better COD,NH_(4)^(+)-N,TN and TP removal,improved effluent SS and limited impact on excess sludge properties.Subsequently,activity tests,BIOLOG ECO microplates and 16S rRNA sequencing were applied to elucidate the changing mechanisms of Mn^(2+)-catalytic ozonation related to microbial action:(1) Dehydrogenase activity reached a higher peak.(2) Microbial utilization of total carbon sources had an elevated effect,up to approximately 18%,and metabolic levels of six carbon sources were also increased,especially for sugars and amino acids most pronounced.(3) The abundance of Defluviicoccus under the phylum Proteobacteria was enhanced to 12.0%and dominated in the sludge,they had strong hydrolytic activity and metabolic capacity.Denitrifying bacteria of the genus Ferruginibacter also showed an abundance of 7.6%,they contributed to the solubilization and reduction of sludge biomass.These results could guide researchers to further reduce ozonation conditioning costs,improve sludge management and provide theoretical support.

Phylogenetic analysis and arsenate reduction effect of the arsenic-reducing bacteria enriched from contaminated soils at an abandoned smelter site

Microbial reduction of As(V)(i.e.,arsenate)plays an important role in arsenic(As)mobilization in aqueous environment.In this study,we investigated As(V)reduction characteristics of the bacteria enriched from the arsenic-contaminated soil at an abandoned smelter site.It was found that As(V)was completely reduced to As(III)(i.e.,arsenite)in 21 h.After 3-d incubation,a yellow solid was precipitated and the concentration of As(III)decreased sharply.After 150 h incubation,ca.65%of soluble arsenic was removed fro...

Dissimilatory reduction of Fe^III (EDTA) with microorganisms in the system of nitric oxide removal from the flue gas by metal chelate absorption

In the system of nitric oxide removal from the flue gas by metal chelate absorption, it is an obstacle that ferrous absorbents are easily oxidized by oxygen in the flue gas to ferric counterparts, which are not capable of binding NO. By adding iron metal or electrochemical method, Fe III (EDTA) can be reduced to Fe II (EDTA). However, there are various drawbacks associated with these techniques. The dissimilatory reduction of Fe III (EDTA) with microorganisms in the system of nitric oxide removal by metal chelate absorption was investigated. Ammonium salt instead of nitrate was used as the nitrogen source, as nitrates inhibited the reduction of Fe III due to the competition between the two electron acceptors. Supplemental glucose and lactate stimulated the formation of Fe II more than ethanol as the carbon sources. The microorganisms cultured at 50℃ were not very sensitive to the other experimental temperature, the reduction percentage of Fe III varied little with the temperature range of 30—50℃. Concentrated Na 2CO 3 solution was added to adjust the solution pH to an optimal pH range of 6—7 The overall results revealed that the dissimilatory ferric reducing microorganisms present in the mix culture are probably neutrophilic, moderately thermophilic Fe III reducers.

Reduction of Nitrate to Ammonium in Selected Paddy Soils of China *1

Three paddy soils were examined for their capacities of dissimilatory reduction of nitrate to ammonium (DRNA). 15 N labelled KNO 3 was added at the rate of 100 mg N kg -1 . Either glucose or rice straw powder was incorporated at the rate of 1.0 or 2.0 mg C kg -1 respectively. Three treatments were designed to keep the soil saturated with water: A) a 2 cm water layer on soil surface (with beaker mouth open); B) a 2 cm water layer and a 1 cm liquid paraffin layer (with beaker mouth open); and C) water saturated under O 2 free Ar atmosphere. The soils were incubated at 28 oC for 5 days. There was almost no 15 N labelled NH + 4 N detected in Treatment A. However, there was 1.4 to 3.4 mg N kg -1 15 N labelled NH + 4 N in Treatment B and 2.1 to 13.8 mg N kg -1 in Treatment C. Glucose was more effective than straw powder in ammonium production. Because there was sufficient amount of non labelled NH + 4 N in the original soils, 15 N labelled NH + 4 N produced as such should be the result of dissimilatory reduction. Studies on microbial population showed that there were plenty of bacteria responsible for DRNA process (DRNA bacteria) in the soils examined, indicating that number of DRNA bacteria was not a limiting factor for ammonium production. However, DRNA bacteria were inferior in number to denitrifiers. DRNA process in soil suspension seemed to start after 5 days of incubation. Glycerol and sodium succinate, though both are readily available carbon sources to organisms,did not facilitate DRNA process. DRNA occurred only when glucose was available and at the C/NO 3 - N ratio of over 12. It seemed that both availability and quality of the carbon sources affected DRNA.

Characterization of Fe/N-doped graphene as air-cathode catalyst in microbial fuel cells

This work proposed a simple and efficient approach for synthesis of durable and efficient non-precious metal oxygen reduction reaction（ORR） electro-catalysts in MFCs. The rod-like carbon nanotubes（CNTs）were formed on the Fe–N/SLG sheets after a carbonization process. The maximum power density of1210 ± 23 m W·mobtained with Fe–N/SLG catalyst in an MFC was 10.7% higher than that of Pt/C catalyst(1080 ± 20 mW ·m) under the same condition. The results of RDE test show that the ORR electron transfer number of Fe–N/SLG was 3.91 ± 0.02, which suggested that ORR catalysis proceeds through a four-electron pathway. The whole time of the synthesis of electro-catalysts is about 10 h, making the research take a solid step in the MFC expansion due to its low-cost, high efficiency and favorable electrochemical performance. Besides, we compared the electrochemical properties of catalysts using SLG, high conductivity graphene（HCG, a kind of multilayer graphene） and high activity graphene（HAG, a kind of GO） under the same conditions, providing a solution for optimal selection of cathode catalyst in MFCs.The morphology, crystalline structure, elemental composition and ORR activity of these three kinds of Fe–N/C catalysts were characterized. Their ORR activities were compared with commercial Pt/C catalyst.It demonstrates that this kind of Fe–N/SLG can be a type of promising highly efficient catalyst and could enhance ORR performance of MFCs.

Microbial Processes in Stratified Lake Doroninskoe(Transbaikal Region)

In recent decades,meromictic ponds attract the attention of researchers in different directions,because here the character of the physical,chemical and biological processes differ from those of typical mixing waters(Kuznetsov,1970;Hutchinson,1969).In Transbaikalia widely distributed soda and salt lakes with different salinity.Notable among them is Lake Doroninskoye,which has a pronounced stratification for a

Cathode catalyst prepared from bacterial cellulose for ethanol fermentation stillage treatment in microbial fuel cell

Bacterial cellulose doped with P and Cu was used as a catalyst for a microbial fuel cell(MFC) cathode,which was then used to treat ethanol fermentation stillage from food waste.Corresponding output power,coulombic efficiency(CE),and biological toxicity were detected.Through a series of characterization experiments,the addition of the cathode catalyst was found to improve catalytic activity and accelerate the consumption of the substrate.The resulting maximum output power was 572.16 mW·m^(-2).CE and the removal rate of chemical oxygen demand(COD) in the fermentation stillage by P-Cu-BC reached 26% and 64.5%,respectively.The rate of biotoxicity removal by MFC treatment reached 84.7%.The aim of this study was apply a novel catalyst for MFC and optimize the treatment efficiency of fermentation stillage.

Preliminary Study on the Effective Microbial Supplementation of Feed on the Infection of Salmonella in Two Lymph Nodes of Beef Cattle in Eastern Ethiopia

A double-blinded randomized controlled field trial based on parallel group design was conducted from January, 2018 to July, 2018 in Chercher Oda-Bultum Farmers Union beef Farm. The present study was conducted to evaluate the roll of effective microbial supplementation to feed on the infection of Salmonella in the mesenteric and sub-iliac lymph nodes of beef cattle. In order to undertake the study, 130 beef cattle kept by the farm were used to establish a cohort. The study animals were randomly assigned to the treatment group (n = 100) and control group (n = 30). The feed of treatment group was mixed with EM at dose of 5× 1010 cfu/day/head for 90, 100 and 115 days while that of the control group was mixed with molasses, which acts as placebo. Both the treatment and control were slaughtered and two lymph nodes were collected from each animal under strict sterile condition and processed for the isolation and identification of Salmonella using standard procedure. The occurrence of Salmonella was 70% (CI = 51% - 85%) in control group while it was 33% (CI = 24% - 43%) in treatment group. The difference in the proportion of Salmonella infection in the two group was significant (x2 = 13.01;p = 0.000). The relative risk of Salmonella isolation in the control was 2.12 (1.41 - 3.20) compared to treatment group. The absolute and relative risk reduction in the treatment were 37% (CI = 17% - 57%) and 53% (CI = 29% - 69%), respectively. This preliminary study indicated that effective microbial supplementation of beef cattle feed reduced the occurrences of Salmonella in the lymph node of beef cattle, thereby potentially minimizing the economic and public health impacts of Salmonella infection. Then, it was recommended to use EM as prevention and control option in Salmonella carriage in cattle.

Microbial reduction of graphene oxide and its application in microbial fuel cells and biophotovoltaics

Despite more than a decade of study,there are still significant obstacles to overcome before graphene can be successfully produced on a large scale for commercial use.Chemical oxidation of graphite to produce graphene oxide(GO),followed by a subsequent reduction process to synthesize reduced graphene oxide(rGO),is considered the most practical method for mass production.Microorganisms,which are abundant in nature and inexpensive,are one of the potential green reductants for rGO synthesis.However,there is no recent review discussing the reported microbial reduction of GO in detail.To address this,we present a comprehensive review on the reduction of GO by a range of microorganisms and compared their efficacies and reaction conditions.Also,presented were the mechanisms by which microorganisms reduce GO.We also reviewed the recent advancements in using microbially reduced GO as the anode and cathode material in the microbial fuel cell(MFC)and algal biophotovoltaics(BPV),as well as the challenges and future directions in microbial fuel cell research.

化肥减量配施微生物菌肥对膜下滴灌红花生长发育及产量的影响

【目的】研究化肥减量配施微生物菌肥对膜下滴灌红花生长发育及产量的影响。【方法】2020~2021年在新疆塔城地区裕民县设置2年定位施肥试验,采用裂区试验设计,设6个处理:(1)对照CK:不施肥;(2)CF:复合肥20 kg/667m^(2);(3)OF:微生物菌肥20 kg/667m^(2);(4)CF+25M:化肥15 kg/667m^(2)(化肥减量25%)+微生物菌肥5 kg/667m^(2);(5)CF+37.5M:化肥12.5 kg/667m^(2)(化肥减量37.5%)+微生物菌肥7.5 kg/667m^(2);(6)CF+50M:化肥10 kg/667m^(2)(化肥减量50%)+微生物菌肥10 kg/667m^(2)。研究不同施肥处理对红花农艺性状、干物质积累与分配和产量形成的影响。【结果】处理CF+25M和CF+37.5M有利于红花的生长发育,可以显著增加红花株高、分枝数、叶片数和叶绿素含量等,并能促进红花干物质积累,调节干物质分配,协调改善红花产量构成因素,从而增加红花花丝和籽粒产量。其中以CF+37.5M处理下红花综合性状表现最优,其单株果球数、千粒重、花丝产量和籽粒产量分别比CF处理显著提高了87.85%、12.29%、11.42%和15.78%,同时株高、根长和叶绿素含量亦均达到最高水平。【结论】化肥减量配施微生物菌肥CF+37.5M:化肥12.5 kg/667m^(2)(化肥减量37.5%)+微生物菌肥7.5 kg/667m^(2)最优,能有效降低化肥施用量,促进红花生长发育,从而提高肥料利用率。

微生物菌肥对结球生菜产量和品质的影响

针对京郊结球生菜生产中化肥用量偏多的问题,以北京地区春大棚结球生菜为研究对象,通过设置常规施肥(T1)、减氮施肥(T2)和微生物菌肥部分替代化肥(T3)3个处理,探究微生物菌肥部分替代化肥对结球生菜产量和品质的影响。结果表明,与常规施肥相比,减氮施肥阻碍了结球生菜的生长,降低了产量,而微生物菌肥部分替代化肥促进了结球生菜的生长,显著提升了结球生菜的单株质量和产量,改善了结球生菜的品质,显著降低了硝酸盐含量,提升维生素C含量。T3处理投入养分最少,但是N肥偏生产力达到了730.92 kg/kg,较T1提高了57.17%。因此,施加微生物菌肥,不仅能减少化肥投入,而且能够提升结球生菜的产量和品质,可以作为京郊结球生菜生产中推荐施肥的措施之一。