Eliminating non-renewable CO2 emissions from sewage treatment: An anaerobic migrating bed reactor pilot plant study

The aim of this work was to demonstrate at pilot scale a high level of energy recovery from sewage utilising a primary Anaerobic Migrating Bed Reactor (AMBR) operating at ambient temperature to convert COD to methane. The focus is the reduction in non-renewable CO2 emissions resulting from reduced energy requirements for sewage treatment. A pilot AMBR was operated on screened sewage over the period June 2003 to September 2004. The study was divided into two experimental phases. In Phase 1 the process operated at a feed rate of 10 L/h (HRT 50 h), SRT 63 days, average temperature 28 degrees C and mixing time fraction 0.05. In Phase 2 the operating parameters were 20 L/h, 26 days, 16 degrees C and 0.025. Methane production was 66% of total sewage COD in Phase 1 and 23% in Phase 2. Gas mixing of the reactor provided micro-aeration which suppressed sulphide production. Intermittent gas mixing at a useful power input of 6 W/m(3) provided satisfactory process performance in both phases. Energy consumption for mixing was about 1.5% of the energy conversion to methane in both operating phases. Comparative analysis with previously published data confirmed that methane supersaturation resulted in significant losses of methane in the effluent of anaerobic treatment systems. No cases have been reported where methane was considered to be supersaturated in the effluent. We have shown that methane supersaturation is likely to be significant and that methane losses in the effluent are likely to have been greater than previously predicted. Dissolved methane concentrations were measured at up to 2.2 times the saturation concentration relative to the mixing gas composition. However, this study has also demonstrated that despite methane supersaturation occurring, microaeration can result in significantly lower losses of methane in the effluent (< 11% in this study), and has demonstrated that anaerobic sewage treatment can genuinely provide energy recovery. The goal of demonstrating a high level of energy recovery in an ambient anaerobic bioreactor was achieved. An AMBR operating at ambient temperature can achieve up to 70% conversion of sewage COD to methane, depending on SRT and temperature. (c) 2006 Wiley Periodicals, Inc.

Characterization of titanium phosphate as electrolytes in fuel cells

Titanium phosphate is currently a promising material for proton exchange membrane fuel cells applications (PEMFC) allowing for operation at high temperature conditions. In this work, titanium phosphate was synthesized from tetra iso-propoxide (TTIP) and orthophosphoric acid (H3PO4) in different ratios by a sol gel method. High BET surface areas of 271 m(2).g(-1) were obtained for equimolar Ti:P samples whilst reduced surface areas were observed by varying the molar ratio either way. Highest proton conductivity of 5.4 x 10(-2) S.cm(-1) was measured at 20 degrees C and 93% relative humidity (RH). However, no correlation was observed between surface area and proton conductivity. High proton conductivity was directly attributed to hydrogen bonding in P-OH groups and the water molecules retained in the sample structure. The proton conductivity increased with relative humidity, indicating that the Grotthuss mechanism governed proton transport. Further, sample Ti/P with 1:9 molar ratio showed proton conductivity in the order of 10(-1) S.cm(-1) (5% RH) and similar to 1.6x10(-2) S.cm(-1) (anhydrous condition) at 200 degrees C. These proton conductivities were mainly attributed to excess acid locked into the functionalized TiP structure, thus forming ionisable protons.

Hydrogen from coal: Production and utilisation technologies

Error condition detected Although coal may be viewed as a dirty fuel due to its high greenhouse emissions when combusted, a strong case can be made for coal to be a major world source of clean H-2 energy. Apart from the fact that resources of coal will outlast oil and natural gas by centuries, there is a shift towards developing environmentally benign coal technologies, which can lead to high energy conversion efficiencies and low air pollution emissions as compared to conventional coal fired power generation plant. There are currently several world research and industrial development projects in the areas of Integrated Gasification Combined Cycles (IGCC) and Integrated Gasification Fuel Cell (IGFC) systems. In such systems, there is a need to integrate complex unit operations including gasifiers, gas separation and cleaning units, water gas shift reactors, turbines, heat exchangers, steam generators and fuel cells. IGFC systems tested in the USA, Europe and Japan employing gasifiers (Texaco, Lurgi and Eagle) and fuel cells have resulted in energy conversions at efficiency of 47.5% (HHV) which is much higher than the 30-35% efficiency of conventional coal fired power generation. Solid oxide fuel cells (SOFC) and molten carbonate fuel cells (MCFC) are the front runners in energy production from coal gases. These fuel cells can operate at high temperatures and are robust to gas poisoning impurities. IGCC and IGFC technologies are expensive and currently economically uncompetitive as compared to established and mature power generation technology. However, further efficiency and technology improvements coupled with world pressures on limitation of greenhouse gases and other gaseous pollutants could make IGCC/IGFC technically and economically viable for hydrogen production and utilisation in clean and environmentally benign energy systems. (c) 2005 Elsevier B.V. All rights reserved.

The refolding of different alpha-fetoprotein variants

The effect of glycosylation on AFP foldability was investigated by parallel quantitative and qualitative analyses of the refolding of glycosylated and nonglycosylated AFP variants. Both variants were successfully refolded by dialysis from the denatured-reduced state, attaining comparable ``refolded peak'' profiles and refolding yields as determined by reversed-phase HPLC analysis. Both refolded variants also showed comparable spectroscopic fingerprints to each other and to their native counterparts, as determined by circular dichroism spectroscopy. Inclusion body-derived AFP was also readily refolded via dilution under the same redox conditions as dialysis refolding, showing comparable circular dichroism fingerprints as native nonglycosylated AFP. Quantitative analyses of inclusion body-derived AFP showed sensitivity of AFP aggregation to proteinaceous and nonproteinaceous inclusion body contaminants, where refolding yields increased with increasing AFP purity. All of the refolded AFP variants showed positive responses in ELISA that corresponded with the attainment of a bioactive conformation. Contrary to previous reports that the denaturation of cord serum AFP is an irreversible process, these results clearly show the reversibility of AFP denaturation when refolded under a redox-controlled environment, which promotes correct oxidative disulfide shuffling. The successful refolding of inclusion body-derived AFP suggests that fatty acid binding may not be required for the attainment of a rigid AFP tertiary structure, contrary to earlier studies. The overall results from this work demonstrate that foldability of the AFP molecule from its denatured-reduced state is independent of its starting source, the presence or absence of glycosylation and fatty acids, and the refolding method used (dialysis or dilution).

Generic Technique to Generate Large Branched DNA Complexes

The inherent self-recognition properties of DNA have led to its use as a scaffold for various nanotechnology self-assembly applications, with macromolecular complexes, metallic and semiconducting nanoparticles, proteins, inter alia, being assembled onto a designed DNA scaffold. Such structures may typically comprise a number of DNA molecules organized into macromolecules. Many studies have used synthetic methods to produce the constituent DNA molecules, but this typically constrains the molecules to be no longer than around 100 base pairs (30 nm). However, applications that require larger self-assembling DNA complexes, several tens of nanometers or more, need to be generated by other techniques. Here, we present a generic technique to generate large linear, branched, and/or circular DNA macromolecular complexes. The effectiveness of this technique is demonstrated here by the use of Lambda Bacteriophage DNA as a template to generate single- and double-branched DNA structures approximately 120 nm in size.

Dilution versus dialysis - A quantitative study of the oxidative refolding of recombinant human alpha-fetoprotein

Alpha-fetoprotein (AFP) is a commercially important polypeptide with important diagnostic. physiological and immunomodulatory functions. Previous studies into the refolding of this macromolecule are contradictory. and variously suggest that AFP denaturation may be irreversible or that refolding may be achieved by reducing denaturant concentration through dilution but not dialysis. Importantly, these same previous studies do not provide quantitative metrics by which the Success of refolding, and the potential for bioprocess development. can be assessed. Moreover, these same studies do not optimize and control refolding redox potential - an important factor considering that AFP contains 32 cysteines which form 16 disulfide bonds. In this current study, a quantitative comparison of recombinant human AFP (rhAFP) refolding by dilution and dialysis is conducted under optimized redox conditions. rhAFP refolding yields were > 35% (dialysis refolding) and > 75% (dilution refolding) as assessed by RP-HPLC and ELISA, with structural Similarity to the native state confirmed by UV spectroscopy. Dialysis refolding yield was believed to be lower because the gradual reduction in denaturant concentration allowed extended conformational searching. enabling more time for undesirable interaction with other protein molecules and/or the dialysis membrane, leading to a Sub-optimal process outcome. Significant yield sensitivity to redox environment was also observed, emphasizing the importance of physicochemical optimization. This study demonstrates that very high refolding yields can be obtained, for a physiologically relevant protein, with optimized dilution refolding. The study also highlights the quantitative metrics and macromolecular physical spectroscopic 'fingerprints' required to facilitate transition from laboratory to process scale.

Mechanical properties of interfacial films formed by lysozyme self-assembly at the air-water interface

We present the first characterization of the mechanical properties of lysozyme films formed by self-assembly at the air-water interface using the Cambridge interfacial tensiometer (CIT), an apparatus capable of subjecting protein films to a much higher level of extensional strain than traditional dilatational techniques. CIT analysis, which is insensitive to surface pressure, provides a direct measure of the extensional stress-strain behavior of an interfacial film without the need to assume a mechanical model (e.g., viscoelastic), and without requiring difficult-to-test assumptions regarding low-strain material linearity. This testing method has revealed that the bulk solution pH from which assembly of an interfacial lysozyme film occurs influences the mechanical properties of the film more significantly than is suggested by the observed differences in elastic moduli or surface pressure. We have also identified a previously undescribed pH dependency in the effect of solution ionic strength on the mechanical strength of the lysozyme films formed at the air-water interface. Increasing solution ionic strength was found to increase lysozyme film strength when assembly occurred at pH 7, but it caused a decrease in film strength at pH 11, close to the pI of lysozyme. This result is discussed in terms of the significant contribution made to protein film strength by both electrostatic interactions and the hydrophobic effect. Washout experiments to remove protein from the bulk phase have shown that a small percentage of the interfacially adsorbed lysozyme molecules are reversibly adsorbed. Finally, the washout tests have probed the role played by additional adsorption to the fresh interface formed by the application of a large strain to the lysozyme film and have suggested the movement of reversibly bound lysozyme molecules from a subinterfacial layer to the interface.

Production of Enzymatically active ketosteroid isomerase following insoluble expression in Escherichia coli

Enzymatically active Delta(5)-3-ketosteroid isomerase (KSI) protein with a C-terminus his(6)-tag was produced following insoluble expression using Escherichia coli. A simple, integrated process was used to extract and purify the target protein. Chemical extraction was shown to be as effective as homogenization at releasing the inclusion body proteins from the bacteria] cells, with complete release taking less than 20 min. An expanded bed adsorption (EBA) column utilizing immobilized metal affinity chromatography (IMAC) was then used to purify the denatured KSI-(His(6)) protein directly from the chemical extract. This integrated process greatly simplifies the recovery and purification of inclusion body proteins by removing the need for mechanical cell disruption, repeated inclusion body centrifugation, and difficult clarification operations. The integrated chemical extraction and EBA process achieved a very high purity (99%) and recovery (89%) of the KSI-(His(6)), with efficient utilization of the adsorbent matrix (9.74 mg KSI-(His(6))/mL adsorbent). Following purification the protein was refolded by dilution to obtain the biologically active protein. Seventy-nine percent of the expressed KSI-(His(6)) protein was recovered as enzymatically active protein with the described extraction, purification, and refolding process. In addition to demonstrating the operation of this intensified inclusion body process, a plate-based concentration assay detecting KSI-(His(6)) is validated. The intensified process in this work requires minimal optimization for recovering novel his-tagged proteins, and further improves the economic advantage of E. coli as a host organism. (c) 2006 Wiley Periodicals, Inc.

Assembly of Human Papillomavirus Type-16 Virus-Like Particles: Multifactorial Study of Assembly and Competing Aggregation

Pentameric capsomeres of human papillomavirus capsid protein L1 expressed in Escherichia coli self-assemble into virus-like particles (VLPs) in vitro. A multifactorial experimental design was used to explore a wide range of solution conditions to optimize the assembly process. The degree of assembly was measured using an enzyme-linked immunosorbent assay, and a high-throughput turbidity assay was developed to monitor competing aggregation. The presence of zinc ions in the assembly buffer greatly increased the incidence of aggregation and had to be excluded from the experiment for meaningful analysis. Assembly of VLPs was optimal at a pH of about 6.5, calcium and sodium ions had no measurable effect, and dithiothreitol and glutathione inhibited assembly. Tryptophan fluorescence spectroscopy demonstrated that an increase in urea concentration reduced the rate of VLP formation but had no effect on the final concentration of assembled VLPs. This study demonstrates the use of the hanging-drop vapor-diffusion crystallization method to screen for conditions that promote aggregation and the use of tryptophan fluorescence spectroscopy for real-time monitoring of the assembly process.

Effect of over-doped yttrium on the microstructure, mechanical properties and thermal properties of a Zr-based metallic glass

The effects of over-doped yttrium on the microstructure, mechanical properties and thermal behaviour of an oxygen-contaminated Zr51Cu20.7Ni12Al16.3 bulk metallic glass are studied systematically. It has been found that, when yttrium doping is beyond the optimum doping, the glass-forming ability enhancement effect induced by yttrium addition decreases and the mechanical properties are adversely affected. In this study, a new phase with an orthorhombic structure (a = 0.69 nm, b = 0.75 nm and c = 0.74 nm) is identified in the yttrium over-doped alloys. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Microstructures and electrolytic properties of yttrium-doped ceria electrolytes: Dopant concentration and grain size dependences

The microstructures and electrolytic properties of YxCe1-xO2-x/2 (x = 0.10-0.25) electrolytes with average grain size in the range 90 nm-1.7 mu m were systematically investigated. Through detailed transmission electron microscopy characterization, nanosized domains were observed. The relationship of the domains, the doping level and grain sizes were determined, and their impacts on the electrolytic properties were systematically studied. It was found that the formation of domains has a negative impact on the electrolytic properties, so that electrolytic properties can be adjusted through careful control of domain formation, doping level and grain size. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Atomic composition profile change of SiGe islands during Si capping

The 6% Ge isocomposition profile change of individual SiGe islands during Si capping at 640 degrees C is investigated by atomic force microscopy combined with a selective etching procedure. The island shape transforms from a dome to a {103}-faceted pyramid at a Si capping thickness of 0.32 nm, followed by the decreasing of pyramid facet inclination with increasing Si capping layer thickness. The 6% Ge isocomposition profiles show that the island with more highly Si enriched at its one base corner before Si capping becomes to be more highly Si intermixed along pyramid base diagonals during Si capping. This Si enrichment evolution inside an island during Si capping can be attributed to the exchange of capped Si atoms that aggregated to the island by surface diffusion with Ge atoms from inside the island by both atomic surface segregation and interdiffusion rather than to the atomic interdiffusion at the interface between the island and the Si substrate. In addition, the observed Si enrichment along the island base diagonals is attempted to be explained on the basis of the elastic constant anisotropy of the Si and Ge materials in (001) plane. (c) 2006 American Institute of Physics.

Structural characteristics of GaSB / GaAs nanowire heterostructures grown by metal-organic chemical vapor deposition

Highly lattice mismatched (7.8%) GaAs/GaSb nanowire heterostructures were grown by metal-organic chemical vapor deposition and their detailed structural characteristics were determined by electron microscopy. The facts that (i) no defects have been found in GaSb and its interfaces with GaAs and (ii) the lattice mismatch between GaSb/GaAs was fully relaxed suggest that the growth of GaSb nanowires is purely governed by the thermodynamics. The authors believe that the low growth rate of GaSb nanowires leads to the equilibrium growth. (c) 2006 American Institute of Physics.