A facial chemical etching method was developed for fabricating superhydrophobic aluminum surfaces. The resultant surfaces were characterized by scanning electron microscopy, water contact angle (WCA) measurement, and optical methods. The surfaces of the modified aluminum substrates exhibit superhydrophobicity, with a WCA of 154.8• ± 1.6• and a water sliding angle of about 5• . The etched surfaces have binary structure consisting of the irregular microscale plateaus and caves in which there are the nanoscale block-like convexes and hollows. The superhydrophobicity of aluminum substrates occurs only in some structures in which the plateaus and caves are appropriately ordered. The resulted surfaces have good self-cleaning properties. The results demonstrate that it is possible to construct superhydrophobic surface on hydrophilic substrates by tailoring the surface structure to providing more spaces to trap air.
The oil film after water flooding is a very important type of microscopic residual oil for an oil-wet reservoir. In this study, an artificial oil film model was designed to simulate the micro residual oil absorbed on the rock surface. Numerous experiments were carried out to explore the detachment mechanisms of two kinds of crude oil films and oil recovery performances in different fluid media with the flow rate. The results show that the increasing flow rate positively affects the oil film detachment but is still limited in the action area and displacement efficiency. It is also found that surfactants with different interfacial tensions (IFTs) and emulsification behaviors all can promote the dislodging of the oil film. The results show that the most important factor contributing to the detachment of the oil film is the emulsification rather than IFT reduction. Strong emulsification is useful to lessen the thickness of the oil film and disperse the oil droplets into a smaller size without considering the flow rate. This paper also provides evidence that, for the case of a higher proportion on heavy components of crude oil, strong emulsification capability is the chief driver for the oil enhancement mechanism for surfactant flooding.
In chemical flooding processes, in situ emulsification between oil displacing agents and crude oil has a significant effect on enhanced oil recovery. Currently, this in situ emulsification process is still little understood. Aiming at this problem, we devised a novel experimental parameter (emulsification index) for better emulsification characterization (i.e., quantification of emulsification capability) and used this parameter to investigate the effect of crude oil–water interfacial tension (IFT) on the emulsification capability of three typical surfactant types. From comprehensive analysis of 111 experimental test results, we found that there was a critical IFT (σc) in the range of IFT level 10–4 to 101 mN/m in which the emulsification index and IFT went from no correlation to that of inverse log correlation. This critical IFT varies with the composition of crude oil and water. During oil displacement experiments, experimental observation of the emulsification process not only confirmed the aforementioned complex phenomenon between the emulsification capability and IFT but also demonstrated that the emulsification index was an effective parameter characterizing emulsification capability in a crude oil–water system during displacement process.
Effects of thermal hydrolysis temperature on the physical properties of municipal sludge was further studied by a series of experiments. There was a decrease in bound water content with an increase in hydrolysis temperature, while there was an increase in pH at temperatures below 120 °C, and a decrease at temperatures exceeding 120 °C. An analysis of settleability, centrifugation and vacuum filtration of the treated sludge indicated that the threshold temperature was 120 °C, which was the same as the temperature for the bound water content and particle size. In addition, raw sludge with a solids content of 100 g/L, exhibited significant non-Newtonian fluid characteristics. At thermal hydrolysis temperatures exceeding 120 °C, non-Newtonian fluid characteristics including liquid and solid characteristics were significantly weakened. The consistency index (k) decreased from 5.90 Pa·s to 0.068 Pa·s, while the flow index (n) increased from 0.31 to 0.74, suggesting that thermal hydrolysis sludge was much closer to Newtonian fluids compared to raw sludge. Modification of bound water content, particle size and viscosity with hydrolysis temperature, revealed the nature of improved dewaterability by thermal hydrolysis. The fractal dimension of the sludge floc increased from 2.74 to 2.90, meaning that the floc became more compact after thermal hydrolysis.
Rheology measurement, a state-of-the-art technology in a multitude of engineering disciplines, has often been used for computational fluid dynamic simulation of wastewater treatment processes, especially in anaerobic digestion and dewatering. In this work, rheological tests were used to study the semi-solid characteristics of sludge and a good result was obtained. The inorganic coagulants polyaluminum chloride (PAC) and ferric chloride (FC) both increased the floc strength of sludge, leading to higher rheology parameters such as elastic modulus, viscous modulus and specific thixotropy area. Curiously, the shape of all rheological curves exhibited little change with increasing coagulant dosage. The results indicated that various physical and chemical actions among coagulants and sludge flocs relate only to rigid structure, not to the nature of rheology behavior. Frequency sweep tests clearly showed that elastic modulus was a logarithmic function of frequency, suggesting that sludge could not properly be called a soft material due to its inorganic particles. An improved viscoelastic model was successfully developed to predict the experimental data of creep and recovery tests in the linear viscoelastic region. Furthermore, complicated viscoelastic behavior of sludge was also observed, and all the rheology tests could provide the optimum dosage of PAC but not the optimum dosage of FC.
In this paper, flow behavior for activated sludge and thermal treated sludge at different process temperature and various solids content were analyzed. Results show viscosity of activated sludge and thermal treated sludge both decreased with increasing temperature, while temperature dependence of viscosity for both types of sludge were not same at the whole study range. The relationship between viscosity and temperature could be expressed by Arrhenius equation for activated sludge, and it was interesting that this law was only suitable when certain solid content (80 g/L) for thermal treated sludge. Moreover, the logistic model was certified to be accurate in describing the functionality for thermal treated sludge. As solid content was at range of 80-100 g/L, active energy of viscosity for both kinds of sludge were similar, indicating that physicochemical properties' change of sludge after thermal hydrolysis had little effect on viscosity sensibility. Arrhenius law was also suitable for describing the relationship between storage modulus and process temperature for activated sludge. However, for thermal treated sludge, Arrhenius law was invalid. Yield stress for activated sludge was prominent, while it could be ignored for thermal treated sludge.
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