No description available.

The dissolved air flotation process experiences process stability problems that are attributed to a poor understanding of the fundamental mechanisms. A detailed review of the literature revealed that the mechanisms of flotation are fairly well understood in mineral flotation application but that the transfer of knowledge to water treatment application is poor, particularly regarding the differences between particle and floc flotation.

Interfaces of water with water-repellent, or hydrophobic, materials are relevant in numerous natural and applied contexts. Examples include lotus leaves, membranes-assisted separation processes, and oil–water emulsions. Typically, water repellence is realized with the help of hydrocarbons and perfluorocarbons. Although these materials present low adhesion to water, their interfaces with water are known to be electrically charged. Origins of the electrification of water–hydrophobe interfaces is a century-old mystery that has been intensely debated on. A number of competing hypotheses have been proposed: specific interfacial adsorption of hydroxide ions, water dipole moment, partial interfacial charge transfer, specific interfacial adsorption of protons, cryptoelectrons, bicarbonate ions, and surfactant contamination. Given the significance of these interfaces, we investigated the origin of water–hydrophobe electrification. To disentangle the role of the various factors, we studied water’s interfaces with: solid hydrophobes, e.g., polypropylene; liquid hexadecane; and gas (air). Electrical charges incurred by water droplets formed using pipettes/tubes of hydrophobic (and hydrophilic) chemical make-up were quantified via electrometers and uniform electric fields. Specifically, we interrogated the contributions of water–hydrophobe surface area, surface chemistry, and water’s ionic strength, pH and dissolved CO2 content. We deduced that common solid hydrophobes have negatively charged surfaces even in air: when a hydrophobic pipette/tube is used to draw an aliquot of water from the bulk, hydrated cations form an electrical double layer at the liquid–solid interface. For the water–hexadecane interface, we tracked interfacial tensions over time. Our investigation revealed that trace amounts of impurities are present in the oil, despite purification, which interfere with purely interfacial effects. Lastly, we applied these fundamental insights to investigate slippery liquid-impregnated surfaces (SLIPS) realized using microtextured SiO2/Si wafers and sand dollar (Dendraster excentricus) templated PDMS surfaces. Recognizing the significant activity in triboelectric nanogenerators (TENGs), we conducted a parametric study of the device output and water–hydrophobe interfacial properties; and tested whether SLIPS could be incorporated in next-generation TENGs. The findings reported in this thesis address some long-standing questions on the spontaneous electrification of water–hydrophobe interfaces, and they should aid the rational development of practical applications such as SLIPS, TENGs, and beyond.

No description available.

Surface active agents have been successfully employed in numerous industrial, agricultural and biomedical applications for decades. Trisiloxane surfactants in particular have proved to be exceptionally effective as wetting enhancers; hence the name ‘superspreaders’. Since the early ‘90s these extraordinary surfactants have become an irreplaceable component in various products and processes. However, the true nature of their specific wetting behaviour has not been fully revealed and their underlying wetting mechanisms are still poorly understood despite substantial scientific interest during the last decades. In this thesis is an attempt to shed light on specific wetting and spreading behaviour of trisiloxane solutions. Commercial superspreader products were tested in various environments in order to get further insight into their performance in specific practical applications. Experimental investigation of wetting of superspreader solutions on surfaces of different hydrophobicity and comparison to that of a conventional surfactant revealed superiority of trisiloxanes. Exceptional interfacial activity was explained in terms of the specific chemical structure and ‘T’-shape of the molecule. However, sensitivity of the trisiloxane head to low pH and long-time ageing in aqueous environment was revealed. Performance of binary mixtures of commercial superspreaders and conventional surfactant was also assessed. Behaviour of trisiloxanes in the capillary action was studied. Finally, a comprehensive mathematical model for trisiloxane wetting, which incorporates diffusion as the governing factor of the wetting process, was developed.

No description available.

Rapid isolation and identification of spores from various environmental samples is necessitated because anthrax spores can be used as biological weapons. The hydrophobic nature of spores may allow for their rapid concentration and partial purification from contaminating materials. In this study, spores from four taxonomic groups of Bacillaceae were isolated, purified and characterized for hydrophobicity by hexadecane partitioning, surface morphology by scanning electron microscopy, and steady-state fluorescence by spectroscopy. The morphology of spores was similar within taxonomic groups and dissimilar between groups. Spore hydrophobicity ranged from 0.3% to 65% and all spores had fluorescence emission peaks at 335 nm and 450 nm. The excitation maxima for the peak at 450 nm were shifted to higher wavelengths for the least hydrophobic spores. Regression analysis demonstrated a correlation between the taxonomic identity, as established by fatty acid analyses, and hydrophobicity. Hydrophobicity can be used to help isolate spores from complex environmental samples and intrinsic fluorescence is helpful in discriminating the taxonomic groups.

Biodegradation of poorly water soluble hydrocarbons, such as n-alkanes and polycyclic aromatic hydrocarbons (PAHs) is often limited by the low availability of the pollutant to microbes. Adhesion of microorganisms to the oil-water interface can influence this availability. Our approach was to study a range of compounds and mechanisms to promote the adhesion of a hydrophilic PAH degrading bacterium, Pseudomonas fluorescens LP6a, to an oil-water interface and examine the effect on biodegradation of phenanthrene by the bacteria. The cationic surfactants cetylpyridinium chloride (CPC), poly-L-lysine and chlorhexidine gluconate (CHX) and the long chain alcohols 1-dodecanol, 2-dodecanol and farnesol increased the adhesion of P. fluorescens LP6a to n-hexadecane from ca. 30% to ca. 90% of suspended cells adhering. The alcohols also caused a dramatic change in the oil-water contact angle of the cell surface, increasing it from 24° to 104°, whereas the cationic compounds had little effect. In contrast, cationic compounds changed the electrophoretic mobility of the bacteria, reducing the mean zeta potential from –23 to –7 mV in 0.01M potassium phosphate buffer, but the alcohols had no effect on zeta potential. This results illustrate that alcohols acted through altering the cell surface hydrophobicity, whereas cationic surfactants changed the surface charge density. Phenanthrene was dissolved in heptamethylnonane and introduced to the aqueous growth medium, hence forming a two phase system. Introducing 1-dodecanol at concentrations of 217, 820 or 4100 mg/L resulted in comparable increases in phenanthrene biodegradation of about 30% after 120 h incubation with non-induced cultures. After 100 h of incubation with LP6a cultures induced with 2-aminobenzoate, 4.5% of the phenanthrene was mineralized by cultures versus more than 10% by the cultures containing initial 1-dodecanol or 2-dodecanol concentrations of 120 or 160 mg/L. The production and accumulation of metabolites in the aqueous phase responded similarly to the addition of 1-dodecanol. Further experiments showed that the positive influence of the alcohols could not be attributed to the changes in surface and interfacial tension or increase in biomass concentration. The results suggest that enhanced adhesion of bacterial cells to the oil-water interface was the main factor responsible for the observed increase in phenanthrene biodegradation by P. fluorescens LP6a. / Chemical Engineering

Three residues, Phe190, Leu193 and Val302, which have been proposed to define the S₁ site of prolidase of <i>Lactococcus lactis</i> NRRL B-1821 (<i>L. lactis</i> prolidase), may limit the size and polarity of specific substrates accepted by this enzyme (Yang, S. I., and Tanaka, T. 2008. Characterization of recombinant prolidase from <i>L. lactis</i> changes in substrate specificity by metal cations, and allosteric behavior of the peptidase. FEBS J. 275, 271-280). These residues form a hydrophobic pocket to determine the substrate specificity of <i>L. lactis</i> prolidase towards hydrophobic peptides, such as Leu-Pro and Phe-Pro, while little activity was observed for anionic Asp-Pro and Glu-Pro. It is hypothesized that the substrate specificity of <i>L. lactis</i> prolidase would be changed if these residues are substituted with hydrophilic amino acid residues individually or in combinations by site-directed mutagenesis (SDM). In addition to the changes in substrate specificity, other characteristics of wild type prolidase, such as allosteric behaviour and substrate inhibition may receive influences by the mutations (Yang & Tanaka, 2008). To test this hypothesis, mutations were conducted on these three residues at the S₁ site. Mutated <i>L. lactis</i> prolidases were subsequently analyzed in order to examine the roles of these residues in the substrate specificity, allosteric behaviour, pH dependency, thermal dependency and metal dependency of prolidase. The results showed the significant changes in these kinetic characteristics of single mutants, such as L193E, L193R, V302D and V302K and double mutants, L193E/V302D and L193R/V302D. Leu193 was suggested to be a key residue for substrate binding. The mutants L193R, V302D, L193R/V302D and L193E/V302D lost their allosteric behaviour, and the substrate inhibition of the wild type was no longer observed in V302D and L193E/V302D. The results indicated Val302 to be more important for these properties than other S₁ site residues. Moreover, together with the observations in molecular modelling of the mutants, it was proposed that interactions of Asp302 with Arg293 and His296 caused the loss of allosteric behaviour and substrate inhibition in the V302D mutant. The investigations on the pH dependency suggested that His296 acted as proton acceptor in <i>L. lactis</i> prolidase's catalysis. It was expected that the electrostatic microenvironment surrounding His296 was influenced by the charged mutated residues and side chains of dipeptide substrates, thus the protonation of His296 was affected. It was suggested that the introduced positive charge would stabilize the deprotonated form of His296 thus to maintain the activities of the mutants in more acidic condition compared to wild type prolidase. The study of thermal dependency revealed that all non-allosteric prolidases had higher optimum temperatures, suggesting that the loss of allosteric behaviour resulted in more rigid structures in these prolidases.

Ecosystems are disturbed to extract synthetic crude oil from the Athabasca Oil Sands Region (AOSR) in northern Alberta, Canada. Successful reclamation of mined oil sands sites depends on maximizing water storage and minimizing the potential for erosion. Soil water repellency in the AOSR affects undisturbed sites and consequently reclamation materials. Extreme water repellency may lead to low infiltration rates and hinder reclamation. There is a lack of information about the naturally occurring and pre-existing levels of soil water repellency in the AOSR. Thus, questions arise about the degree of naturally occurring water repellency and the potential for severe water repellency in reclamation soils. Studies were conducted on nine sites in the AOSR in the summers of 2008 and 2009. A range of undisturbed and reclaimed sites, as well as mineral and organic reclamation materials were examined. Five undisturbed Jack Pine stands (classified as A ecosites), four reclaimed sites and reclamation materials including mineral soil, peat and leaf and lichen covering the forest floor (LFH) were studied. For a comparison of methods, one grasslands site in central Saskatchewan was included. Mini and standard tension infiltrometers were compared as a means of measuring soil water repellency index (RI). There was strong variability in RI values between the infiltrometer methods. The mean RI values from the mini infiltrometers were higher than from the standard infiltrometer (9.61 and 3.46, respectively). The variability within sites dominated the variability in RI for the two methods. Despite these obvious trends, RI values between infiltrometer sizes were statistically different for only two individual sites. Increasing the number of sampling points in the second field season did not reduce the variability. The simpler, less expensive mini infiltrometer is as effective as the standard infiltrometer in measuring soil water repellency. This will enable more efficient and extensive monitoring of soil water repellency in reclaimed and undisturbed sites in the AOSR. Soil water repellency of reclaimed and undisturbed sites was investigated in situ using RI, the water droplet penetration time (WDPT) test, and the molarity of ethanol droplet (MED) test. These measures showed similar trends. Variability in soil water repellency was high at both reclaimed and undisturbed sites. The average RI value for the surface of reclaimed sites was higher than that of the subsurface at reclaimed sites; however, there were no statistical differences between RI values of surface reclaimed and undisturbed sites (P =0.213) due to high spatial variability. The critical water content (CWC) of reclamation materials was determined by measuring the contact angle (CA) and WDPT. Generally, CA and WDPT were inversely related to water content, though variability was high and the relationship between water content was weak. The clearest relationship between water repellency and water content was present for the mineral soil samples. Reclaimed mineral soil was generally wettable above gravimetric water contents of 5-10 %, while the coarse textured tarball affected materials were only subcritically water repellent. There was no relationship between water repellency and water content for peat and LFH. The degree of water repellency was statistically higher for peat materials with increasing decomposition levels. The average WDPT was 44, 128 and 217 s for fibric, mesic, and humic peat, respectively. With careful management and monitoring, water repellency may not be a major limitation to reclamation success. The mini tension infiltrometer is an effective method for monitoring soil water repellency in the AOSR.