Anaerobic treatment of municipal wastewater at ambient temperature: Analysis of archaeal community structure and recovery of dissolved methane

Anaerobic treatment is an attractive option for the biological treatment of municipal wastewater. In this study, municipal wastewater was anaerobically treated with a bench-scale upflow anaerobic sludge blanket (UASB) reactor at temperatures from 6 to 31 °C for 18 months to investigate total chemical oxygen demand (COD) removal efficiency, archaeal community structure, and dissolved methane (D-CH₄) recovery efficiency. The COD removal efficiency was more than 50% in summer and below 40% in winter with no evolution of biogas. Analysis of the archaeal community structures of the granular sludge from the UASB using 16S rRNA gene-cloning indicated that after microorganisms had adapted to low temperatures, the archaeal community had a lower diversity and the relative abundance of acetoclastic methanogens decreased together with an increase in hydrogenotrophic methanogens. D-CH₄, which was detected in the UASB effluent throughout the operation, could be collected with a degassing membrane. The ratio of the collection to recovery rates was 60% in summer and 100% in winter. For anaerobic treatment of municipal wastewater at lower temperatures, hydrogenotrophic methanogens play an important role in COD removal and D-CH₄ can be collected to reduce greenhouse gas emissions and avoid wastage of energy resources.     

Nitrogen removal in a single-chamber microbial fuel cell with nitrifying biofilm enriched at the air cathode

Nitrogen removal is needed in microbial fuel cells (MFCs) for the treatment of most waste streams. Current designs couple biological denitrification with side-stream or combined nitrification sustained by upstream or direct aeration, which negates some of the energy-saving benefits of MFC technology. To achieve simultaneous nitrification and denitrification, without extra energy input for aeration, the air cathode of a single-chamber MFC was pre-enriched with a nitrifying biofilm. Diethylamine-functionalized polymer (DEA) was used as the Pt catalyst binder on the cathode to improve the differential nitrifying biofilm establishment. With pre-enriched nitrifying biofilm, MFCs with the DEA binder had an ammonia removal efficiency of up to 96.8% and a maximum power density of 900 ± 25 mW/m², compared to 90.7% and 945 ± 42 mW/m² with a Nafion binder. A control with Nafion that lacked nitrifier pre-enrichment removed less ammonia and had lower power production (54.5% initially, 750 mW/m²). The nitrifying biofilm MFCs had lower Coulombic efficiencies (up to 27%) than the control reactor (up to 36%). The maximum total nitrogen removal efficiency reached 93.9% for MFCs with the DEA binder. The DEA binder accelerated nitrifier biofilm enrichment on the cathode, and enhanced system stability. These results demonstrated that with proper cathode pre-enrichment it is possible to simultaneously remove organics and ammonia in a single-chamber MFC without supplemental aeration.     

Synthesis and electrochromic properties of a highly water-soluble hyperbranched polymer viologen

A highly water-soluble hyperbranched polymer with viologen units (HB-1) was synthesized for application to electrochromic (EC) display. Electrochemical and spectroscopic properties of HB-1 were evaluated by absorption spectra and cyclic voltammetry. They were compared with those of a low molecular weight viologen molecule (1). We fabricated a simple EC window by a thin (300-500 nm) solid film of HB-1 and an electrolyte solution to demonstrate the EC behavior. By successively applying opposite bias voltages to it, reversible color changes between colorless and purple were observed with good contrast, whereas blue color was observed for 1 upon reduction. The colored state in HB-1 was ascribed to the generation of radical cation dimer species of viologen units due to high local concentrations in HB-1. When the bias was turned off after achieving the colored state, no fading was observed in the EC window. This result indicates that the radical cation dimer species of HB-1 in solid films were stable against disproportionation or reaction with oxygen even though no active protection was made in this EC window. Since the present EC device has such a memory effect, bias voltage is needed in writing and erasing processes alone, which is very useful in practical applications.     

Investigation on sensitivity of a polymer/carbon nanotube composite strain sensor

Extensive numerical simulation and experimental measurements have been conducted to understand the effects of processing parameters and material properties on sensor sensitivity in polymer/carbon nanotube (CNT) composite sensors. The numerical simulation was based on an improved three-dimensional statistical resistor network model incorporating the tunneling effect between the neighbouring nanotubes, and a fiber reorientation model. The behaviors of a sensor subjected to both tensile and compressive strains were investigated. Both numerical and experimental results indicate that a higher tunneling resistance or higher ratio of the tunneling resistance to the total resistance of the sensor leads to a higher sensor sensitivity. Processing conditions and material properties, such as weight fraction, diameter and conductivity of CNTs, curing temperature, mixing rate and barrier height of polymer matrix all play a role in determining the sensor sensitivity.     

Investigation of ionic polymer cathode binders for microbial fuel cells

Microbial fuel cell (MFC) air cathodes examined here were made using poly(phenylsulfone) (Radel^®) binders sulfonated to various ion exchange capacities (IECs). We examined the effect of increasing the IEC of poly(phenylsulfone) Radel binders from 0 to 2.54 meq/g on cathode performance using linear sweep voltammetry (LSV), impedance, and single chamber air-cathode MFC tests. Unsulfonated Radel, which is a non-ionic, hydrophobic polymer, showed the highest current in LSV tests and the lowest charge transfer resistance. Increasing the binder IEC resulted in a decreased current response in LSV tests and an increased charge transfer resistance from 8 to 23 Ω. It is proposed that the presence of sulfonate groups in the cathode binder impeded the oxygen reduction activity of the cathodes by adsorption of the sulfonate to catalytic sites and by impeding proton diffusion to the catalyst surface. The unsulfonated Radel binder produced the most stable performance, and eventually the highest power density, in MFCs operated over 20 cycles (55 days). These results suggest that the use of a non-ionic binder is advantageous in an MFC cathode to facilitate charge transfer and stable performance in the neutral pH conditions found in MFCs.     

Molecular dynamics studies on the structures of polymer electrolyte membranes and diffusion mechanism of protons and small molecules

We performed a series of molecular dynamics (MD) simulations on Nafion^® membranes containing various quantities of H₂O and CH₃OH. The simulations afforded diverse nanoscale phase-separated structures, such as clusters, channels, and cluster–channels. The calculated cluster–channel structure qualitatively agrees with the experimental results of X-ray diffraction studies. We also investigated the diffusion mechanisms for H₂O, protons, CH₃OH, H₂, and O₂ in these membranes. To reproduce the hopping transfer of protons, we employed a semi-classical MD approach using the empirical valence bond method. The estimated diffusion coefficients of H₂O and proton in the membranes significantly depended on the H₂O content, and these values showed qualitatively good agreement with the experimental results. The diffusion coefficient of proton in H₂O-rich membranes was much larger than that of H₂O, and the proton mainly formed H₅O₂⁺ complex. Furthermore, the simulation results indicate that the majority of CH₃OH permeates through the H₂O clusters, and the majority of H₂ and O₂ permeates through the hydrophobic region of the membrane.     

Molecular structure and gene analysis of Ce3+ -induced methanol dehydrogenase of Bradyrhizobium sp. MAFF211645

The molecular structure and nucleotide sequence of Ce(3+)-induced methanol dehydrogenase (MDH) of Bradyrhizobium sp. MAFF211645 were investigated. The addition of 30 μM Ce(3+) to 1/10 nutrient broth containing 0.5% methanol remarkably increased MDH activity. Furthermore, La(3+) increased MDH activity, but other heavier rare earth and metal elements did not have the same effect. MDH increased by Ce(3+) was purified by sequential column chromatography, and the purified MDH migrated as a single band with an apparent molecular weight of 68 kDa on SDS-PAGE. The apparent molecular weight of native MDH was estimated to be 108,000 by gel chromatography. The MDH was comprised of two identical subunits. N-terminal 23-amino acid sequence, 1-NDELHKMAQNPKDWVMPAGDYAN-23, of the purified MDH exhibited 91.3% identity to that of the MDH large subunit-like protein encoded by mxaF' of Bradyrhizobium japonicum USDA110. Nucleotide sequencing of the MDH gene of strain MAFF211645 yielded a deduced amino acid sequence comprising 601 amino acid residues, an N-terminal signal peptide, and a mature MDH comprising 578 amino acid residues with a predicted molecular mass of 62,918 Da. Further analysis of the deduced amino acid sequence of mature MDH revealed that the functional amino acids in its active site, such as two adjacent Cys residues, and bacterial quinoprotein signatures 1 and 2 were conserved. These results indicate that Ce(3+)-induced MDH encoded by mxaF' may be involved in methanol metabolism in Bradyrhizobium sp. MAFF211645.     

Recent advances in nanofibrous assemblies based on β‐sheet‐forming peptides for biomedical applications

Amyloid fibrils are supramolecular polymers with β‐sheet‐rich structures formed by polymerization of protein/peptide with intermolecular interaction. Amyloid fibrils have been miscast as toxic villains since they have historically been studied as pathogens associated with serious diseases, including Alzheimer's and Parkinson's disease. However, recent studies on their toxicity and formation mechanism and discovery of their functionality in nature correct the misconception and strongly facilitate the possible use of β‐sheet‐forming peptides in designing novel nanomaterials. Self‐assembly based on β‐sheet‐forming peptides can provide highly ordered nanostructures under certain conditions. Therefore, ingenious design of the building block peptides allows the construction of nano‐assemblies, which contain large quantities of bio‐functional molecules, including drugs and bioactive peptides, and exhibit unique properties, such as assembly or disassembly in response to external stimulus or specific molecules. These properties provide a novel strategy for the creation of innovative nanomaterials, especially for biomedical applications. Here, we describe recent progress in the biomedical application of fibrous assemblies based on β‐sheet‐forming peptides, such as the suppression of aberrant protein aggregation, controlled release, tissue engineering and other applications. This review focuses not only on the function of the nanofibrous assemblies but also on the functions of component molecules, namely amyloidogenic peptides. © 2016 Society of Chemical Industry     

Suction performance and internal flow of a 2-bladed helical inducer with inlet asymmetric plate

It has been found in our past studies that the installation of asymmetric plate at the inlet of inducer is effective for the suppression of cavitation surge phenomenon.In the present study,the suction performance of 2-bladed helical inducer with an inlet asymmetric plate is experimentally investigated.It is observed that the suction performance in large flow rate conditions is not significantly influenced by the asymmetric plate,whereas the head of inducer with the asymmetric plate increases just before the head breakdown in partial flow conditions.To understand the mechanism of this additional head,the flow measurements and the numerical simulations are carried out.It is found that the circumferential component of absolute velocity at the exit of inducer slightly increases with the development of cavitation in both cases with and without the inlet asymmetric plate,indicating the increase of the theoretical head.The theoretical head increase with the inlet asymmetric plate is also confirmed by the unsteady numerical simulations,suggesting that the additional head is achieved through the increase of the theoretical head with the change of the exiting flow from the inducer associated with some amount of cavitation.