Oxygen Reduction Reaction with Manganese Oxide Nanospheres in Microbial Fuel Cells.

Operating microbial fuel cells (MFCs) under extreme pH conditions offers a substantial benefit. Acidic conditions suppress the growth of undesirable methanogens and increase redox potential for oxygen reduction reactions (ORRs), and alkaline conditions increase the electrocatalytic activity. However, operating any fuel cells, including MFCs, is difficult under such extreme pH conditions. Here, we demonstrate a pH-universal ORR ink based on hollow nanospheres of manganese oxide (h-Mn3O4) anchored with multiwalled carbon nanotubes (MWCNTs) on planar and porous forms of carbon electrodes in MFCs (pH = 3-11). Nanospheres of h-Mn3O4 (diameter ∼ 31 nm, shell thickness ∼ 7 nm) on a glassy carbon electrode yielded a highly reproducible ORR activity at pH 3 and 10, based on rotating disk electrode (RDE) tests. A phenomenal ORR performance and long-term stability (∼106 days) of the ink were also observed with four different porous cathodes (carbon cloth, carbon nanofoam paper, reticulated vitreous carbon, and graphite felt) in MFCs. The ink reduced the charge transfer resistance (R ct) to the ORR by 100-fold and 45-fold under the alkaline and acidic conditions, respectively. The current study promotes ORR activity and subsequently the MFC operations under a wide range of pH conditions, including acidic and basic conditions.

Enhanced biohydrogen production with low graphene oxide content using thermophilic bioreactors.

Modern society envisions hydrogen (H2) fuel to drive the transportation, industrial, and domestic sectors. Here, we explore use of graphene oxide nanoparticles (GO NPs) for greatly enhancing bio-H2 production by a consortium based on Thermoanaerobacterium thermosaccharolyticum spp. Thermophilic batch bioreactors were set up at 60 OC and initial pH of 8.5 to assess the effects of GO NPs supplements on biohydrogen production. Under optimal GO NPs loading of 10 mg/L, the supplemented system yielded âˆ¼ 300% higher H2 yield (6.78 mol H2/mol sucrose) than control. Such an optimized system offered 73% H2 purity and 85% conversion efficiency by promoted the desirable acetate fermentation pathway. Miseq Illumina sequencing tests revealed that the optimal levels of GO NPs did not alter the microbial composition of consortium.

Electricity from methane by Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b.

Given the difficulties valorizing methane (CH4) via catalytic routes, this study explores use of CH4-oxidizing bacteria ("methanotrophs") for generating electricity directly from CH4. A preconditioned methanotrophic biofilm on 3D nickel foam with reduced graphene oxide (rGO/Ni) was used as the anode in two-compartment microbial fuel cells (MFCs). This study demonstrates a proof of concept for turning CH4 into electricity by two model methanotrophs including Methylosinus trichosposium OB3b and Methylococcus capsulatus (Bath). Both OB3b (205 mW.m-2) and Bath (110 mW.m-2) strains yielded a higher electricity from CH4 when grown on rGO/Ni compared to graphite felt electrodes. Based on electrochemistry tests, molecular dynamics simulations, genome annotations and interaction analysis, a mechanistic understanding of reasons behind enhanced performance of methanotrophs grown on rGO/Ni are presented.

Anaerobic wastewater treatment and reuse enabled by thermophilic bioprocessing integrated with a bioelectrochemical/ultrafiltration module.

The current study aimed to develop an anaerobic wastewater treatment and reuse module enabled by thermophilic bioprocessing, a microbial fuel cell (MFC) and ultrafiltration (UF) treatment. A previously unexplored consortium based on Thermoanaerobacterium thermosaccharolyticum and Arcobacter sp. was used to remove ~73% of chemical oxygen demand (COD) from wastewater under anaerobic conditions (CODi = 200 mg/L). The subsequent MFC and UF treatment removed the COD remnants to meet the secondary treatment standards and reuse criteria. The energy efficiency of polyethersulfone UF membranes was improved by modifying their surfaces with coatings based on self-polymerized dopamine, mixtures of dopamine and poly(2-dimethylamino) ethyl methacrylate methyl, and dopamine analog norepinephrine. The resulting hydrophilic, anti-fouling layers were found to reduce interactions between rejected species and the membrane surface. Finally, this study presents a comparative treatment performance and energy efficiency of the wastewater treatment and reuse modules arranged in six different configurations.

Hexagonal Boron Nitride for Sulfur Corrosion Inhibition.

Corrosion by sulfur compounds is a long-standing challenge in many engineering applications. Specifically, designing a coating that protects metals from both abiotic and biotic forms of sulfur corrosion remains an elusive goal. Here we report that atomically thin layers (∼4) of hexagonal boron nitride (hBN) act as a protective coating to inhibit corrosion of the underlying copper (Cu) surfaces (∼6-7-fold lower corrosion than bare Cu) in abiotic (sulfuric acid and sodium sulfide) and biotic (sulfate-reducing bacteria medium) environments. The corrosion resistance of hBN is attributed to its outstanding barrier properties to the corrosive species in diverse environments of sulfur compounds. Increasing the number of atomic layers did not necessarily improve the corrosion protection mechanisms. Instead, multilayers of hBN were found to upregulate the adhesion genes in Desulfovibrio alaskensis G20 cells, promote cell adhesion and biofilm growth, and lower the protection against biogenic sulfide attack when compared to the few layers of hBN. Our findings confirm hBN as the thinnest coating to resist diverse forms of sulfur corrosion.

Electricity from methanol using indigenous methylotrophs from hydraulic fracturing flowback water.

Methanol solvents that are used in hydraulic fracturing often return back to the surface in the form of recalcitrant flowback water. Here, the indigenous methylotrophic bacteria from flowback water were enriched and used to generate electricity from methanol in a two-compartment microbial fuel cell (CH3OH-MFC). An identical MFC based on a tryptone-yeast extract (TY-MFC) was used as a control. CH3OH-MFC yielded a 2.7-fold thicker biofilm dominated by electrogenic species (81%) and higher power density (76 mW/m2) compared with TY-MFC (50 mW/m2). Illumina MiSeq sequencing of the 16S rRNA gene in TY-MFC revealed classes from Actinobacteria, Bacteroidia and γ-proteobacteria. The CH3OH-MFC yielded α-proteobacteria, ß-proteobacteria, γ-proteobacteria and Bacteroidia, with a dominant fraction of Rhodobacter sphaeroides (~29%). We discuss the potential pathways used by R. sphaeroides to maintain syntrophic cooperation with other bacterial and archaeal members to sustain CH3OH oxidation. Finally, we establish that a pure culture of R. sphaeroides 2.4.1 generates electricity directly from methanol.

Extremophiles for microbial-electrochemistry applications: A critical review.

Extremophiles, notably archaea and bacteria, offer a good platform for treating industrial waste streams that were previously perceived as hostile to the model organisms in microbial electrochemical systems (MESs). Here we present a critical overview of the fundamental and applied biology aspects of halophiles and thermophiles in MESs. The current study suggests that extremophiles enable the MES operations under a seemingly harsh conditions imposed by the physical (pressure, radiation, and temperature) and geochemical extremes (oxygen levels, pH, and salinity). We highlight a need to identify the underpinning mechanisms that define the exceptional electrocatalytic performance of extremophiles in MESs.