Spectroscopic and Microscopic Characterization of Microbial Biofouling on Aircraft Fuel Tanks.

Avoiding microbial contamination and biofilm formation on the surfaces of aircraft fuel tanks is a major challenge in the aviation industry. The inevitable presence of water in fuel systems and nutrients provided by the fuel makes an ideal environment for bacteria, fungi, and yeast to grow. Understanding how microbes grow on different fuel tank materials is the first step to control biofilm formation in aviation fuel systems. In this study, biofilms of Pseudomonas putida, a model Gram-negative bacterium previously found in aircraft fuel tanks, were characterized on aluminum 7075-T6 surfaces, which is an alloy used by the aviation industry due to favorable properties including high strength and fatigue resistance. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) showed that extracellular polymeric substances (EPS) produced by P. putida were important components of biofilms with a likely role in biofilm stability and adhesion to the surfaces. EDX analysis showed that the proportion of phosphorus with respect to nitrogen is higher in the EPS than in the bacterial cells. Additionally, different morphologies in biofilm formation were observed in the fuel phase compared to the water phase. Micro-Fourier transform infrared spectroscopy (micro-FTIR) analysis suggested that phosphoryl and carboxyl functional groups are fundamental for the irreversible attachment between the EPS of bacteria and the aluminum surface, by the formation of hydrogen bonds and inner-sphere complexes between the macromolecules and the aluminum surface. Based on the hypothesis that nucleic acids (particularly DNA) are an important component of EPS in P. putida biofilms, the impact of degrading extracellular DNA was tested. Treatment with the enzyme DNase I affected both water and fuel phase biofilms─with the cell structure disrupted in the aqueous phase, but cells remained attached to the aluminum coupons.

Microstructural architecture and mechanical properties of empowered cellulose-based aerogel composites via TEMPO-free oxidation.

This paper describes the development of cellulose-based aerogel composites enhanced via a new refinement process. The behaviour and microstructure of treated cellulose aerogel composites are examined including, how the constituents interact and contribute to the overall aerogel composite mechanism. The various forms of cellulose such as treated microcrystalline cellulose (MCT), nanofibrillated cellulose (NFC) and nanocrystalline cellulose (NCC) are also compared. Treated cellulose/Polyvinyl alcohol (PVA) aerogel composites show reinforced microstructural systems that enhance the mechanical property of the aerogels. The specific modulus of treated cellulose aerogels could be increased five-fold compared to the stiffness of untreated cellulose aerogels, reaching specific moduli of 21 kNm/kg. The specific strength of treated cellulose aerogels was also increased by four folds at 1.7 kNm/kg. These results provide insight into the understanding of the morphology and structure of treated cellulose-based aerogel composites.

Experimental Study of the Post-Fire Mechanical and Material Response of Cold-Worked Austenitic Stainless Steel Reinforcing Bar.

This paper is concerned with the behaviour of stainless steel reinforcing bar following exposure to elevated temperatures from a fire, followed by subsequent cooling. Stainless steel-reinforced concrete is an increasingly popular solution for structural applications which require corrosion resistance, excellent mechanical properties, and long life cycles with little maintenance. In addition, although stainless steel reinforcement has a higher initial cost compared with traditional carbon steel bars, the overall life cycle costs are likely to be quite similar, owing to the lack of maintenance required for stainless steel materials. There is no information available in the literature on the post-fire properties of austenitic stainless steel reinforcement, although these data are essential for any engineer who wishes to study the structural integrity of a reinforced concrete component or system following a fire. Accordingly, this paper presents a detailed discussion and analysis from the results of a series of laboratory experiments on three grades of austenitic stainless steel reinforcement following various levels of temperature exposure and also different cooling rates. Both the mechanical and metallurgical properties are examined, and the behaviour is compared to that of B500B carbon steel reinforcement. It is shown that the stainless steel bars retained their mechanical properties under the majority of the scenarios examined and to a greater degree than traditional materials. This is important for the rehabilitation and salvage of existing reinforced concrete structures following a fire and also to avoid unnecessary demolition and replacement.

Operation of a modified anaerobic baffled reactor coupled with a membrane bioreactor for the treatment of municipal wastewater in Taiwan.

A modified anaerobic baffled reactor (ABR) combined with a submerged membrane bioreactor (MBR) was applied to treat municipal wastewater. The performance of this process was examined in terms of the removal of organic matter, suspended solids, turbidity and nitrogen. The raw wastewater was fed to the 105 L ABR and then the treated effluent was driven to a 58 L MBR equipped with a submerged hollow fibre ultrafiltration membrane module. The integrated modified ABR-MBR process resulted in the complete removal of total suspended solids (TSS) and in very high chemical oxygen demand (COD) removal (93.3 ± 3.8%). Furthermore, the recycling of mixed liquor from the MBR to the modified ABR resulted in some denitrification occurring in the first compartment of the ABR, resulting in 53 ± 6% removal of nitrogen by the integrated process. The membrane flux was stable and above 20 L/m2h. Membrane examination at the nanoscale indicated the deposition of small particles on the surface of the membranes.

Fabrication and characterization of a biodegradable Mg-2Zn-0.5Ca/1ß-TCP composite.

A biodegradable magnesium matrix and beta-tricalcium phosphate (ß-TCP) particles reinforced composite Mg-2Zn-0.5Ca/1beta-TCP (wt.%) was fabricated for biomedical applications by the novel route of combined high shear solidification (HSS) and equal channel angular extrusion (ECAE). The as-cast composite obtained by HSS showed a fine and equiaxed grain structure with globally uniformly distributed ß-TCP particles in aggregates of 2-25 µm in size. The ECAE processing at 300 °C resulted in further microstructural refinement and the improvement of ß-TCP particle distribution. During ECAE, the ß-TCP aggregates were broken into smaller ones or individual particles, forming a dispersion in the matrix. Such fabricated composite exhibited enhanced hardness and in vitro corrosion resistance. The enhanced hardness was attributed to both the addition of ß-TCP particles and grain refinement while the development of a Ca-P rich surface layer from ß-TCP during corrosion was responsible for the improvement in corrosion resistance. The composite was characterized in terms of microstructural evolution during fabrication, mechanical properties and electrochemical performance during polarization and immersion tests in a simulated body fluid. Discussions are made on the benefits of both HSS and ECAE and the mechanisms responsible for the enhanced corrosion resistance.