Kamal Tawfiq

Bacillus anthracis and Bacillus subtilis spore surface properties and transport

Effective decontamination of environments contaminated by Bacillus spores remains a significant challenge since Bacillus spores are highly resistant to killing and could plausibly adhere to many non-biological as well as biological surfaces. Decontamination of Bacillus spores can be significantly improved if the chemical basis of spore adherence is understood. In this research, we investigated the surface adhesive properties of Bacillus subtilis and Bacillus anthracis spores. The spore thermodynamic properties obtained from contact angle measurements indicated that both species were monopolar with a preponderance of electron-donating potential. This was also the case for spores of both species missing their outer layers, due to mutation. Transport of wild type and mutant spores of these two species was further analyzed in silica sand under unsaturated water conditions. A two-region solute transport model was used to simulate the spore transport with the assumption that the spore retention occurred within the immobile region only. Bacillus spore adhesion to the porous media was related to the interactions between the spores and the porous media. Our data indicated that spore surface structures played important roles in spore surface properties, since mutant spores missing outer layers had different surface thermodynamic and transport properties as compared to wild type spores. The changes in surface thermodynamic properties were further evidenced by infrared spectroscopy analysis.

Power generation and nitrogen removal of landfill leachate using microbial fuel cell technology

Microbial fuel cell (MFC) technology has been practised in the treatment of landfill leachate. However, it is a big challenge for the usage of MFCs to treat landfill leachate with high ammonium conTENT. The purpose of this study was to design and test two MFC reactors, i.e. an ammonium oxidation/MFC reactor and an MFC/Anammox reactor for the treatment of landfill leachate with high ammonium conTENT in terms of power generation and nitrogen removal. Using the ammonium oxidation/MFC reactor, the landfill leachate collected from Leon County Landfill of Northwest Florida generated a power density of 8 mW/m2 together with 92% of nitrogen removal. For the MFC/Anammox reactor, a power density of 12 mW/m2 was achieved with 94% of nitrogen removal. Compared with the ammonium oxidation/MFC reactor, 50% more energy was generated because in the MFC/Anammox Reactor, nitrite served as the electron acceptor; while in the Ammonium Oxidation/MFC reactor, nitrate served as the electron acceptor. In this research, power generation was also found to be directly linked to the microbial species that were involved in organic decomposition, i.e. the greater the microbial concentration, the more the power generated.

Microbial Biofouling: A Mechanistic Investigation

Microbial biofouling is important in a variety of applications including reverse osmosis membranes and in-situ bioremediation. The initial microbial adhesion plays the key role in microbial biofouling on abiotic surfaces, which can be explained in terms of microbial surface properties. This research investigated the interactions of three indigenous bacteria with the porous medium of silica sand and their corresponding initial attachment. Traditional and extended DLVO forces were calculated based on independently measured bacterial and medium surface thermodynamic properties and were related to bacterial attachment observations. Lifshitz–van der Waals, electrostatic and Lewis acid/base forces were found to be strongly dependent on the separation distance between bacteria and the medium surface. It was concluded that the electrostatic force served as the barrier preventing the bacterial strains from getting close to the medium. Once the bacterial strains overcame the barrier with the aid of hydrodynamic forces, Lifshitz–van der Waals force and electrostatic force dropped while Lewis acid/base force increased with the decrease of separation distance. Consequently, Lewis acid/base force became the dominating force controlling bacterial adhesion.

Permeability of Concrete Subjected to Cyclic Loading

The effect of microcracking development and propagation on the permeability of concrete was investigated in this study. Large numbers of single-edge-notched beams as well as unnotched beams were prepared in the laboratory and in the field from different concrete mixes and subjected to dynamic loading at various stress ratios. During the cyclic loading, stress-strain and air permeability measurements were simultaneously recorded using strain gauges and the poroscope apparatus. Obtained strain and the air permeability measurements were used to evaluate the deterioration of concrete during crack initiation and further propagation. After fatigue testing, other sets of samples were cored from the fractured beams for water permeability testing. Results from these samples were used to correlate with the air permeability as well as with the compressive strength of the beams. Findings indicated that at the first stage of cyclic loading the beam samples exhibited large strains along with a rapid deterioration in th...

Bacterial interactions and transport in geological formation of alumino-silica clays.

Bacterial transport in the subsurface is controlled by their interactions with the surrounding environment, which are determined by the surface properties of the geological formation and bacterial surfaces. In this research, surface thermodynamic properties of Escherichia coli and the geological formation of alumino-silica clays were characterized based on contact angle measurements, which were utilized to quantify the distance-dependent interactions between E. coli and the geological formation according to the traditional and extended Derjaguin, Landau, Verwey and Overbeek (DLVO) theory. E. coli attachment to alumino-silica clays was evaluated in laboratory columns under saturated and steady-state flow conditions. E. coli deposition coefficient and desorption coefficient were simulated using convection-dispersion transport models against E. coli breakthrough curves, which were then linked to interactions between E. coli and the geological formation. It was discovered that E. coli deposition was controlled by the long-ranged electrostatic interaction and E. coli desorption was attributed to the short-ranged Lifshitz-van der Waals and Lewis acid-base interactions. E. coli transport in three layers of different alumino-silica clays was further examined and the breakthrough curve was simulated using E. coli deposition coefficient and desorption coefficient obtained from their individual column experiments. The well-fitted simulation confirmed that E. coli transport observations were interaction-dependent phenomena between E. coli and the geological formation.

Bacterial deposition in unsaturated porous media as related to surface properties

Transport of Escherichia coli, Pseudomonas fluorescens and Bacillus subtilis in silica sand under water-unsaturated conditions was investigated using column experiments. It was hypothesised that bacterial deposition was due to their interactions within the pore environment, which was a function of their surface physicochemical properties as well as pore water chemistry. Surface thermodynamic properties of these bacterial strains were measured independently by means of contact angle measurements under different water saturation conditions using variable lawn moisture contents. Bacterial interactions with the liquid-gas interface and the porous media were calculated based on their surface properties and were related to their transport observations.

Electropolishing of surfaces: theory and applications

Electropolishing is the electrochemical process to remove the metallic material from the workpiece, in order to obtain a smoother metal surface. It has found vast engineering applications in many fields, such as food, medical, pharmaceutical and semiconductor industries. This review is aimed to provide the readership with insightful understanding of the electropolishing process, from the fundamental aspects as well as from the application aspects. The general aspects of electropolishing, including its definition, the classic setup, the fundamentals behind it and methods used to evaluate the electropolishing finishes are reviewed here. Various electropolishing theories, be them quantitative or qualitative are briefly discussed. Based on those theories, important parameters evolved in the electropolishing process are enumerated. Many microscopic technologies are used to evaluate the electropolishing surface finishes. This includes optical microscope, electron microscope and atomic force microscope. Some key features of electropolishing are briefly outlined in the end.

Escherichia coli growth and transport in the presence of nanosilver under variable growth conditions.

Nanosilver (silver nanoparticles) has the ability to anchor to the bacterial cell membrane and subsequently penetrate it, thereby causing structural changes (i.e. permeability) in the cell membrane and death of the cell. The bacterial responses to the presence of nanosilver usually vary depending on the concentration of nanosilver particles, exposure time and the bacterial physiological stage. Since bacterial anabolism dependents upon a stoichiometric ratio of carbon and inorganic elements (nutrients), the macronutrient ratio, i.e. carbon to nitrogen ratio (C/N) thus plays an important role of bacterial responses to the exposure of nanosilver. This study investigated the responses of Escherichia coli to the exposure of nanosilver under variable growth conditions. It was discovered that E. coli grown under different growth conditions had different responses to the presence of nanosilver. E. coli had least resistance to the toxicity of nanosilver when cultured under carbon-limited conditions. However, the presence of rhamnolipid, a commonly utilized biosurfactant for soil remediation increased the resistance of E. coli to nanosilver. The transport of E. coli cultured under carbon-limited conditions was further studied in silica sand columns. E. coli adsorption in silica sand increased when cultured in the presence of nanosilver. On the contrary, E. coli adsorption in silica sand was significantly reduced when cultured in the presence of rhamnolipid.

Laboratory investigation of polyethylene sheeting as a friction reducer in deep foundation

Abstract A testing program was undertaken in which the effectiveness of polyethylene sheeting in mitigating downdrag in cohesionless soils was investigated using a direct shear apparatus and a rod shear test. A large number of concrete blocks were prepared in the laboratory and furnished with various arrangements of polyethylene sheets. These arrangements included samples with one or two sheets with fixed or free boundary conditions. The concrete-polyethylene-soil samples were tested in the laboratory under different temperatures and shearing rates. Based on the parameters used in this investigation, the obtained results demonstrated that the polyethylene sheets can be used as a friction reducer in piles. Using single layer of polyethylene sheeting reduced the skin friction by 62–67% depending on the soil type. The best arrangement was found in the two free 0·15 mm polyethylene sheets. This setup increased the effectiveness of the sheets to 77%. Lubricating the two sheet arrangement with mineral oil improved the effectiveness to 98%. Considering the effect of the shearing rate and the temperature on the behaviour of the lubricated sheets, a formula is suggested

Effect of Construction Induced Vibrations on Green Concrete in Drilled Shafts

This study was concerned with vibrations induced during drilled shaft construction on green concrete in adjacent drilled shafts. To characterize the types of vibrations, a full-scale field test was conducted using a 0.9-m (3-ft)-diameter steel casing vibrated at a peak particle velocity (ppv) of 250 mm/s (10 in./s) to various depths in a sandy soil layer. In addition to the steel casing, the peak particle velocities were recorded at different distances and depths from the vibration source. Empirical relationships from measurements were developed to predict the velocity values on the surface and in the ground along the penetration depth of the steel casing. Laboratory tests were conducted on two groups of green concrete samples to determine the effect of ppv and curing time on concrete properties. These tests showed a 10% reduction in the 28-day compressive strength for samples subjected to continuous vibration at ppv of 50 mm/s (2 in./s) for a duration ranging from the initial to the final setting time. O...