Integrated Wet Air Oxidation and Biological Treatment of Polyethylene Glycol-Containing Wastewaters

The treatment of a model wastewater containing polyethylene glycol (PEG) of molecular weight 10000 in an integrated wet air oxidation–aerobic oxidation process was investigated. Partial wet air oxidation under mild operating conditions was capable of converting the original polymer to lower molecular weight compounds, such as oligomers and short-chain organic acids. The effect of molecular weight on the aerobic biodegradability of polyethylene glycol was assessed by performing shake flasks experiments with various polyethylene glycols in a molecular weight range from 200–35000 and it was found that biodegradability generally decreased with increasing molecular weight. Aqueous solutions of PEG 10000 were subjected to continuous wet air oxidation at a temperature of 423 K and a residence time of 30 min and the oxidised effluents were then subjected to subsequent continuous aerobic oxidation at residence times varying between 0·5 and 4 days. Simultaneously, continuous aerobic oxidation experiments on solutions of PEG 10000 were performed and used to compare the efficiency of the integrated treatment process with that of the direct biological treatment. Partial pretreatment by wet air oxidation under mild operating conditions resulted in effluents whose biodegradation rates were significantly higher than those of the original, unoxidised wastewater, as assessed by total organic carbon (TOC) removal rates. The original wastewater was practically non-biodegradable at a 0·5-day residence time with direct biological treatment, while an 80% TOC removal was achieved when biological treatment was coupled with a preceding wet air oxidation step. Conversely, with a 4-day residence time for the direct biological treatment the original wastewater was only partially degradable with 60–70% TOC removal recorded; with the integrated treatment process at a 4-day residence time in the bioreactor the overall TOC removal was greater than 90%. © 1997 SCI     

Structural Basis of Microtubule Stabilization by Discodermolide

Microtubule‐stabilizing agents (MSAs) are widely used in chemotherapy. Using X‐ray crystallography we elucidated the detailed binding modes of two potent MSAs, (+)‐discodermolide (DDM) and the DDM–paclitaxel hybrid KS‐1‐199‐32, in the taxane pocket of β‐tubulin. The two compounds bind in a very similar hairpin conformation, as previously observed in solution. However, they stabilize the M‐loop of β‐tubulin differently: KS‐1‐199‐32 induces an M‐loop helical conformation that is not observed for DDM. In the context of the microtubule structure, both MSAs connect the β‐tubulin helices H6 and H7 and loop S9–S10 with the M‐loop. This is similar to the structural effects elicited by epothilone A, but distinct from paclitaxel. Together, our data reveal differential binding mechanisms of DDM and KS‐1‐199‐32 on tubulin.     

Fracture toughness enhancement of silicon carbide composites with hydrophilic-modified Tyranno® Si–Al–C fibre addition

The surface properties of Tyranno® Si–Al–C (SA) fibre (mean length: 0.7?mm) were modified from hydrophobic to hydrophilic nature by acid treatment of carbon-coated SA fibre, in order to enhance dispersibility or fracture toughness within silicon carbide (SiC) matrix. Two types of carbons, i.e. amorphous carbon and graphite carbon, were used to coat the surface of SA fibres (SA(AC) and SA(GC) fibres, respectively) by the pyrolysis of polyvinyl alcohol at 500°C for 30?min and 1800°C for 30?min, respectively. Then, carboxyl groups were formed on the SA(AC) and SA(GC) fibre surfaces through acid treatment (concentrated H₂SO₄ and HNO₃) at room temperature. Owing to the acid treatment, SA fibre could be homogeneously mixed with SiC particles in polar solvent (acetone). The fracture toughness of SiC composites containing 40 mass% of acid-treated SA(GC) fibre (PVA/SA ratio?=?2.5) hot-pressed at 1800°C for 60?min attained 8.3?MPa?m^1/2.     

The mechanism of photocure of inherently photosensitive polyimides containing a benzophenone group

The photochemistry of an appropriately substituted bisimide has been studied in solution by conventional means and time resolved laser techniques as a model for the behavior of inherently photosensitive solvent soluble polyimides, whose photochemistry are not well understood. A mechanism for the photochemical insolubilization of the polymer systems is suggested based on the results for the model system, which is confirmed by time resolved laser studies of polyimide solutions. Phosphorescence quenching rate constants for the model compound indicate that the triplet excited state is about one order of magnitude more reactive than triplet benzophenone, an increase most likely due to the inductive effect of the imide moieties.     

Simultaneous Gas Storage and Catalytic Gas Production Using Zeolites—A New Concept for Extending Lifetime Gas Delivery

Copper containing MCM-41 materials can be used to both store gaseous nitric oxide and to catalytically produce nitric oxide from nitrite. The active species for the reaction is copper (I). Addition of cysteine to the solution in contact with the material has different effects depending on how much Cu(I) is present. This is a new method of extending the lifetime of gas delivery from a gas storage material.     

Mesoporous silica–magnetite nanocomposites: Fabrication, characterisation and applications in biosciences

Template assisted fabrication of magnetic mesoporous silica–magnetite nanocomposites and their performance in binding and elution of Salmon sperm DNA has been reported. The effect of reaction pH (10–2) during the fabrication of nanocomposites has been studied. All materials fabricated at various pH were characterised by XRD, TEM, FT-IR, nitrogen adsorption and magnetic susceptibility measurements. Fabrication at neutral pH (7) in the presence of a cationic surfactant (cetyl trimethyl ammonium bromide; CTAB) produced core–shell nanocomposites of quasi spherical and rod shaped morphologies with mesoporous (pore size 3.5 nm) silica shell and rhombic magnetite core. Fabrication at alkaline pH (10) produced monolithic mesoporous silica composites with embedded magnetite nanoparticles. Fabrication at acidic pH (4 and 2) produced a biphasic mixture of rhombic magnetite and amorphous silica rods. A similar fabrication at acidic pH (2) in the absence of CTAB produced a biphasic mixture of rhombic magnetite and spherical silica nanoparticles. All materials exhibited a high value of Salmon sperm DNA binding at physiological pH whereas elution value of DNA was observed to be dependent on the extent of silica coating on magnetite nanoparticles.     

Thermochemical Reactions Between PZT and Ag/Pd Powders: Relevance to Cofiring of Multilayer Actuators

Mixtures of Ag_{1− x} Pd _x ( x =0.2, 0.3) and doped PZT ceramic powders have been heat treated in air and the resulting phase content has been analyzed by X-ray diffraction and transmission electron microscopy. Beginning around 400°C, a phase similar to PbPdO₂ is formed on the surface of the Ag_{1− x} Pd _x particles and subsequently decomposes at temperatures <700°C. Consequently, the remaining Ag_{1− x} Pd _x powder becomes significantly silver-rich while the reaction progresses. After decomposition the Pd appears to realloy and the initial Ag_{1− x} Pd _x composition is recovered. We show that the reaction is all but eliminated in a nitrogen atmosphere. The occurrence of this reaction was also investigated in PZT multilayer actuators cofired with Ag_0.7Pd_0.3 electrodes. Transmission electron microscope analysis revealed the presence of distinct crystallites at the electrode–ceramic interface, most likely nucleated from a PbO liquid phase arising from the decomposition of PbPdO₂.     

The influence of pH on particle packing in YSZ coatings electrophoretically deposited from a non-aqueous suspension

Yttria stabilized zirconia (YSZ) coatings were produced from a YSZ suspension in acetylacetone (ACAC) using electrophoretic deposition (EPD) and then sintered with substrate constraint at 1200 and 1300 °C. Before EPD, the operational pH of the suspension was adjusted by addition of acetic acid or triethanolamine (TEA) base. The effect of suspension pH on the deposition of EPD coatings was studied with respect to the suspension stability, coating density and microstructure. Results showed that the zeta potential had a high positive value on both sides of the iso-electric point (IEP). This probably resulted from the adsorption of TEA, detected by Fourier transform infrared spectroscopy. Three alkalies with different molecular structures were compared and the effect of their molecule length on the interparticle repulsion was discussed. Based on this, particle interactions were estimated for different pH suspensions. The reduced particle coagulation increased the packing density of the EPD coatings from 38% at pH 7.4 to 53% at pH 8.4. Therefore, subsequent sintering of coatings was promoted. The sinterability was evaluated by micro-hardness and microstructure. After sintering at 1200 °C, coatings made in pH 8.4 suspensions obtained a hardness of 786 MPa and had fewer big pores than coatings fabricated in pH 7.4 suspensions that had a hardness of 457 MPa.     

Studies into the swelling of gelatine films using a scanning fluid dynamic gauge

Fluid dynamic gauging (FDG) has been developed to measure both the thickness and strength (cohesive or adhesive) of a range of fouling deposits, in situ and in real time. We report the development of a scanning FDG device (sFDG) with fully automated movement and deposit thickness measurement. Thickness-time profiles can be collected for several points on the surface over the course of a single experiment. sFDG is employed here to study the cleaning kinetics of model gelatine fouling layers when contacted with aqueous solutions at different pHs and temperatures, and with a commercial dishwasher formulation containing enzymes.Solution pH is an important parameter: above ～pH 10.6 the gelatine layers swell markedly, due to protonation of the amino acids proline and hydroxyproline, and subsequent charge repulsion within the gel. An unusual behaviour (discontinuity) is reported during swelling in the commercial formulation. It is proposed that hydration of the deposit and an extent of swelling (ratio of the final to the initial deposit thickness) of ～12 is necessary before the enzymes can promote deposit removal.     

Corrosion studies of rebar in contact with saturated solution produced by leaching of Portland Type-II cement: examining the effects of chloride,carbonation and an amorphous silica additive

This study examined the effects of silica addition on electrochemical behavior of rebar in native pH 12.5 saturated solutions prepared by leaching of Portland Type-II cement, and in solutions reduced by CO₂ to pH 9. Cyclic polarizations showed that at pH 12.5 the silica additive increased the threshold concentration required for pitting from 100 to 105mM, and from 0.3 mM to 0.5 mM at pH 9. Passivation kinetic exponents were consistently larger for solutions with either pH when silica was present. The silica additive provided the passive film with generally increased resistance and lower capacitance, as confirmed by electrochemical impedance spectroscopy. Charge carrier densities calculated from Mott-Schottky plots were on the order of 1020 (cm^-3), increasing significantly after the passive film breakdown. Raman spectroscopy of rebar samples immersed in saturated cement solutions showed films predominantly composed of iron oxyhydroxides with a new shoulder attributed to amorphous silica.