Hydrogen and Oxygen Bubble Attachment to a Bitumen Drop

Air bubble – bitumen attachment is a critical step in the flotation of bitumen from mined oil sand. In this study, single bubble – bitumen drop attachment was observed directly using a novel experimental technique. Induction time is determined and used as an indication of bubble‐bitumen attachment potency for both hydrogen and oxygen bubbles. The attachment tests were conducted in deaerated municipal water (City of Edmonton tap water) at temperatures ranging from 22–50°C. Induction times measured for hydrogen bubble attachment were shorter than those for oxygen bubbles. Coalescence tests were also conducted in the absence of bitumen, and showed that hydrogen bubbles coalesced more rapidly than oxygen bubbles in both deaerated municipal water and clear (solids‐free) process water.     

双流态微泡浮选机气液两相流测试结果分析

介绍了双流态微泡浮选机的特点,采用激光粒子动态分析仪测量了该浮选机矿化器内微泡发生器段和矿化管部分以及浮选槽内的微泡时均速度、脉动速度和粒径分布情况,分析了不同充气量与药剂量对微泡的影响;对比表明,该机在宏观流态、紊动特性以及形成的微气泡尺寸、粒径分布和浓度等方面为微细粒煤泥浮选创造了最佳的流体动力学环境。     

Combination of Ozonation and the Fenton Processes for Landfill Leachate Treatment: Evaluation of Treatment Efficiency

Single processes such as ozonation, ozone/hydrogen peroxide, Fenton and several combined treatment schemes were applied for leachate collected from a waste disposal site. The implementation of combined Fenton and ozonation processes resulted in the highest chemical oxygen demand removal (77% from initial value) among all the treatment methods applied, while biodegradability improvement was observed during the Fenton pre-treatment only. Some decrease of chemical oxygen demand was obtained during the single ozonation or combined schemes including ozone resulting in slight if any biodegradability improvement. The addition of hydrogen peroxide to ozonation did not enhance chemical oxygen demand, dissolved organic carbon or biochemical oxygen demand removal compared to ozone alone. Ferric chloride coagulation used as a pre-treatment stage did not improve subsequent chemical oxygen demand removal by ozonation or the Fenton processes. Taking into account the effective chemical oxygen demand, dissolved organic carbon removal and biodegradability improvement the single Fenton process seems to be a preferable treatment method for the leachate treatment. Some reduction in toxicity to Daphnia magna was observed after the application of the studied treatment methods.     

Successful Removal of Algae through the Control of Zeta Potential

Abstract

Algae can interfere with treatment processes at a water treatment works. Coagulation control is critical to reduce the impact of algae on downstream processes. This paper investigates the coagulation and flotation of four species of algae – Asterionella formosa, Melosira sp., Microcystis aeruginosa, and Chlorella vulgaris. The zeta potential at optimum removal was measured and it was observed that when the zeta potential was reduced to between ?8 mV and +2 mV, removal of algae and associated organic material was optimized, irrespective of the coagulant dose or pH. Process control using zeta potential is therefore a viable tool for algae removal.     

Simultaneous Removal of Algae and Their Secondary Algal Metabolites from Water by Hybrid System of DAF and PAC Adsorption

Abstract

The feasibility of a hybrid system consisting of powdered activated carbon (PAC) adsorption and dissolved air flotation (DAF) processes was examined for the simultaneous removal of algae (anabaena and mycrocystis) and their secondary algal metabolites (2‐methylisoboneol and geosmin). Before studying the hybrid system, adsorption equilibrium and kinetics of organics (2‐methylisoboneol and geosmin) produced from algae on three powdered activated carbons (wood‐based, coal‐based, coconut‐based) were studied. The flotation efficiency of algae and PAC in DAF process was evaluated with zeta potential measurements. Interestingly, we found that the agglomerate of bubble and PAC particle can be successfully floated by DAF. In addition, the simultaneous removal of algae and organics (i.e., secondary algal metabolites) dissolved in water can be achieved by using the hybrid system of adsorption/DAF processes.     

Attachment of solid particles to air bubbles in surfactant-free aqueous solutions

This paper presents a mechanism to explain the attachment of solid particles to air bubbles in surfactant-free aqueous solutions where both solids and air bubbles have the same sign of zeta potential via investigating the mechanical properties of micro air bubbles and the adsorption of hydroxide on air bubble surfaces.Particle-bubble attachment was measured in a Hallimond tube. The results indicate that purified quartz particles attached to air bubbles in surfactant-free deionised water, and the attachment increased with the pH of the aqueous solutions. The mechanical properties of micro air bubbles in aqueous solutions were measured using a novel micromanipulation technique. It was found that the micro air bubbles were pseudo-elastic and spherical in the solutions. The rigidity of the air bubbles decreased with increasing pH of the solutions. When a moving particle with a certain kinetic energy collided with an air bubble in a surfactant-free aqueous solution, the deformation of the air bubble varied with pH of the solution. In an alkaline solution, the micro air bubble was much softer and the deformation was larger than that in an acidic solution. The larger deformation of the softer air bubble resulted in a large contact area between the solid particle and the air bubble, therefore increasing the attachment, and reducing the rebound.The attachment of purified quartz particles to air bubbles in surfactant-free aqueous solutions was possibly due to hydrogen bond formation. The OH⁻ ions on air bubble surfaces formed hydrogen bonds with silicon and oxygen atoms in ≡Si-O-Si≡ or with the adsorbed OH group on quartz surfaces.     

Hydrodynamics and recovered papers deinking in an ozone flotation column

This work was aimed at investigating the potential use of ozone flotation for recovered papers deinking. The mixing characteristics and the bubble size of a Venturi aerated laboratory flotation column were studied in the presence of simplified model systems and of an industrial pulp slurry. Experimental results showed that surfactants dissolved in the pulp slurry stabilized air bubbles while cellulose fibers promoted coalescence. Moreover, bubble buoyancy was sufficient to fluidize the fiber suspension generating perfect mixing. The gas–liquid transfer coefficient of ozone (k_La) estimated from gas hold-up, air bubble size and k_La measured in water was high enough (0.84 1/s) for the complete transfer of ozone in the pulp slurry and the generation of ozone-free gas effluent. With O₃ dosage of 0.8 mg O₃/mg COD, ozone flotation allowed increasing chemical oxygen demand removal from 41 to 63% with no effect on the ink flotation efficiency, which remained close to that obtained with air flotation, i.e. ～92%.     

Study of the production of hydrogen bubbles at low current densities for electroflotation processes

BACKGROUND: Flotation processes are widely used in waste‐water treatment and it is quite important to have a tool to determine and optimize the size distribution of the bubbles produced. In this work, the electrochemical production of bubbles to enhance the performance of electrocoagulation processes by flotation is studied. To do this, a current density range characteristic of electrocoagulation processes is used to produce microbubbles (<5 mA cm^?2), instead of the higher values used in other studies to characterize electroflotation in non‐combined processes. RESULTS: Current density and pH were found to influence the process significantly. In the range used, higher current densities allow a larger number of small size bubbles to be obtained, appropriate for use in electroflotation processes. However, at the boundaries of the range, the size of the bubbles was increased advising against use. Neutral pH values also favour the formation of small bubbles, and the presence of possible competing reactions have to be considered because they diminish the gas flow and affect the number of bubbles and their size. The roughness of the surface of the electrode material also has an important influence. CONCLUSIONS: The image acquisition and analysis system developed allows measurement of the size distribution of hydrogen bubbles in the range of current densities studied. Current density and pH seem to be the main parameters affecting the mean diameter of bubbles and the amount of gas produced, and the electrode material may also influence hydrogen production significantly. Copyright © 2010 Society of Chemical Industry     

Measurement of sliding velocity and induction time of a single micro‐bubble under an inclined collector surface

In this study, interactions between a gas bubble and a flat solid surface were investigated by determining two dynamic parameters, bubble sliding velocity underneath an inclined solid surface and induction time of the gas bubble attaching to the solid surface in aqueous solutions. A single micro‐bubble was allowed to move vertically toward an inclined solid surface. After reaching its terminal velocity, the bubble approaches the inclined solid surface and slides underneath it. Complete trajectory of the bubble movement was monitored and recorded by a high‐speed CCD video imaging system. Various types of gas bubbles (CO₂, air, H₂, and O₂) and solid surfaces such as bitumen‐coated Teflon, hydrophobized and hydrophilic silica were used in sliding velocity and induction time measurements. The effect of water chemistry (industrial process water and de‐ionized water) and surface heterogeneity on bubble sliding velocity and induction time was investigated. The results showed that the sliding velocity of micro‐bubbles under an inclined solid surface is a strong function of water chemistry, gas type, temperature and hydrophobicity of the solid surface. This study provides relevant information on bubble–solid interactions that would assist in the understanding of bubble–solid attachment under diverse conditions.     

Three‐dimensional numerical simulation of coalescence and interactions of multiple horizontal bubbles rising in shear‐thinning fluids

The dynamics of multiple horizontal bubbles rising from different orifice arrangements in shear‐thinning fluids was simulated numerically by three‐dimensional Volume of Fluid method. The effects of bubble size, rheological properties of shear‐thinning fluids, and orifice structure arrangements on multiple bubbles interaction and coalescence were analyzed, and the mechanisms of bubble coalescence and breakup were fully discussed and elucidated. The variation of bubble rising velocity during coalescence process and freely rising processes for different orifice arrangements was also deeply investigated. The critical initial horizontal intervals for coalescence of multiple horizontal bubbles with various orifice arrangements were attained by simulation, which could serve as the critical criterion of bubble coalescence or noncoalescence. Furthermore, the critical bubble interval was predicted based on the film drainage model, the prediction accords well with the simulation result and is quite conducive for the design and optimization of perforated gas–liquid contact equipment. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3528–3546, 2015     

Experimental investigation of interfacial mass transfer mechanisms for a confined high‐reynolds‐number bubble rising in a thin gap

Interfacial mass transfer is known to be enhanced for confined bubbles due to the efficiency of the transfer in the thin liquid films between them and the wall. In the present experimental investigation, the mechanisms of gas–liquid mass transfer are studied for isolated bubbles rising at high Reynolds number in a thin gap. A planar laser induced fluorescence (PLIF) technique is applied with a dye the fluorescence of which is quenched by dissolved oxygen. The aim is to measure the interfacial mass fluxes for pure oxygen bubbles of various shapes and paths rising in water at rest. In the wakes of the bubbles, patterns due to the presence of dissolved oxygen are observed on PLIF images. They reveal the contrasted contributions to mass transfer of two different regions of the interface. The flow around a bubble consists of both two thin liquid films between the bubble and the walls of the cell and an external high‐Reynolds‐number in‐plane flow surrounding the bubble. Mass transfer mechanisms associated to both regions are discussed. Measurement of the concentration of dissolved oxygen is a difficult task due to the nonlinear relation between the fluorescence intensity and the concentration in the gap. It is however possible to accurately measure the global mass flux transferred through the bubble interface. It is determined from the fluorescence intensity recorded in the wakes when the oxygen distribution has been made homogeneous through the gap by diffusion. Assuming a reasonable distribution of oxygen concentration through the gap at short time also allows a measurement of the mass fluxes due to the liquid films. A discussion of the results points out the specific physics of mass transfer for bubbles confined between two plates as compared to bubbles free to move in unconfined flows. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2394–2408, 2017     

Breakup dynamics of slender bubbles in non‐newtonian fluids in microfluidic flow‐focusing devices

This study aims to investigate the breakup of slender bubbles in non‐Newtonian fluids in microfluidic flow‐focusing devices using a high‐speed camera and a microparticle image velocimetry (micro‐PIV) system. Experiments were conducted in 400‐ and 600‐μm square microchannels. The variation of the minimum width of gaseous thread with the remaining time before pinch‐off could be scaled as a power‐law relationship with an exponent less than 1/3, obtained for the pinch‐off of bubbles in Newtonian fluids. The velocity field and spatial viscosity distribution in the liquid phase around the gaseous thread were determined by micro‐PIV to understand the bubble breakup mechanism. A scaling law was proposed to describe the size of bubbles generated in these non‐Newtonian fluids at microscale. The results revealed that the rheological properties of the continuous phase affect significantly the bubble breakup in such microdevices. © 2012 American Institute of Chemical Engineers AIChE J,, 2012     

CFD studies coupling hydrodynamics and solid‐liquid mass transfer in slug flow for matter removal from tube walls

Organic matter deposition on internal surfaces constitutes a drawback that impairs the efficiency of several industrial processes. To overcome this problem, sparging a train of bubbles could be useful since its presence strongly increases the wall shear stress. A detailed numerical mass‐transfer study between a finite soluble wall and the liquid around a rising Taylor bubble was performed, simultaneously solving velocity and concentration fields. The bubble passage throws solute backward and is responsible for radial dispersion. There is also an increase in the transfer rate with enhancements between 10 and 20% (depending on liquid average velocity and bubble length) compared to single‐phase flow. Mass‐transfer coefficients along the different hydrodynamic regions around the bubble nose, liquid film, and wake were characterized and their values compared with those from literature. The results suggest a promising potential of bubble train flow to enhance organic matter removal from walls in biological systems. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2420–2439, 2017     

Research on the Feasibility of Spraying Micro/Nano Bubble Ozonated Water for Airborne Disease Prevention

This research combined micro/nano bubble techniques with ozone disinfection to determine feasibility of applying micro/nano bubble ozonated water in preventing tomato airborne disease. Results indicated that dissolving ozone in micro/nano bubbles is more efficient than using a mixing pump. In our in vitro studies, when dissolved ozone concentration was 1.6 mg/L, a 5.2 to 3.3 log reduction in Alternaria solani Sorauer conidia was observed; with concentration of 1.8 mg/L, there was a 5.0 to 3.7 log reduction in Cladosporium fulvum conidia. Furthermore, spraying ozonated water in a certain concentration range (0.6–1.8 mg/L) had no significant negative effects on tomato growth.     

Multiphase reacting flow studies of bubble column ozonation reactor for water remediation

A multiphase Volume‐of‐fluid (VOF) model was developed to gain further insights into the reactive flow parameters and electrical capacitance tomography (ECT) measurements on the remediation of hazardous organic pollutants. Low ozone bubble frequencies were obtained for high surface tension fluids, and the liquid viscosity affected the ozone bubbling frequency. The VOF model indicated that the increase of inlet gas velocity enriched the ozone bubble detachment and concomitantly generated larger ozone bubbles, decreasing the detoxification rates. VOF mappings and ECT visualizations of gas‐liquid unveiled preferential routes and highlighted the attenuation of the axisymmetric behavior of the ozonation bubble column under high‐interaction regimes.     

协同催化臭氧化工艺对水中微量有机污染物的降解

选用城市二级出水作为试验原水,通过静态试验考察了O3、O3/C、O3/UV、O3/UV/C对水中难以生化降解的微量有机物的处理效果。结果表明：波长为254 nm的紫外线和活性炭对水中微量有机物的臭氧化过程具有协同催化作用,并可大幅度提高对臭氧的利用率;在紫外线和活性炭的协同催化臭氧化作用下,对水在254nm处紫外吸光度（E254）的去除率达到87.40%,水中CODCr的去除率可达到59.79%,臭氧的利用率可提高到91.4%。通过考察叔丁醇和碳酸氢钠两种自由基捕捉剂对O3/UV/C反应器处理效果的影响,表明在紫外线和活性炭的协同催化臭氧化作用下,水中有机污染物的氧化降解是多种自由基反应的结果,其中以羟基氧化反应为主。     

Gas‐Liquid Mass Transfer Approach applied to the Modeling of Flotation in a Bubble Column

A kinetic model developed to describe flotation in a bubble column is presented. This model, developed on the basis of the theory of mass transfer in gas‐liquid flows, makes explicit in its formulation the effect of the superficial saturation of bubbles on the kinetics of flotation. The model is applied to the simulation of flotation column experiments for which the classical first‐order models, commonly used in flotation modeling, are insufficient to represent the flotation kinetics. The results of the simulations obtained under different hypotheses of simplification and compared to experimental data show that the model succeeds in representing the flotation kinetics in these cases.     

Treatment of dyehouse waste‐water by supercritical water oxidation: a case study

BACKGROUND: Supercritical water oxidation (SCWO) of dyehouse waste‐water containing several organic pollutants has been studied. The removal of these organic components with unknown proportions is considered in terms of total organic carbon concentration (TOC), with an initial value of 856.9 mg L^?1. Oxidation reactions were performed using diluted hydrogen peroxide. The reaction conditions ranged between temperatures of 400–600 °C and residence times of 8–16 s under 25 MPa of pressure. RESULTS: TOC removal efficiencies using SCWO and hydrothermal decomposition were between 92.0 and 100% and 6.6 and 93.8%, respectively. An overall reaction rate, which consists of hydrothermal decomposition and the oxidation reaction, was determined for the hydrothermal decomposition of the waste‐water with an activation energy of 104.12 ( ± 2.6) kJ mol^?1 and a pre‐exponential factor of 1.59( ± 0.5) × 10⁵ s^?1. The oxidation reaction rate orders for the TOC and the oxidant were 1.169 ( ± 0.3) and 0.075 ( ± 0.04) with activation energies of 18.194 ( ± 1.09) kJ mol^?1, and pre‐exponential factor of 5.181 ( ± 1.3) L^0.244 mmol^?0.244 s^?1 at the 95% confidence level. CONCLUSION: Results demonstrate that the SCWO process decreased TOC content by up to 100% in residence times between 8 and 16 s under various reaction conditions. The treatment efficiency increased remarkably with increasing temperature and the presence of excess oxygen in the reaction medium. Color of the waste‐water was removed completely at temperatures of 450 °C and above. Copyright © 2010 Society of Chemical Industry     

Effect of Frothers on Bubble Size and Foam Stability in Potash Ore Flotation Systems

The objective of this project was to compare the effect of a selective flotation frother (MIBC) and powerful frothers (DEMPH and DF‐1012) on bubble size and foamability in water and in brine. In water, the bubble size is clearly reduced by flotation frothers which prevent bubbles from coalescing. The present study shows that the bubbles do not coalesce in brine and, therefore, frothers do not affect the size of bubbles in brine. The dynamic foamabality index measured in brine is much lower than that in water for weak frothers (e.g. MIBC); for both tested strong frothers the foamability measurements in brine reveal formation of meta‐stable foams.     

基于高溶气量的新型气浮系统的性能

引言近年来,随着我国水资源短缺和水体污染日趋严重,废水的处理和净化更加受到人们的重视[1]。作为一种重要的水处理技术,气浮净水在我国得到了迅速发展:在用于给水中含藻、低浊和受轻微污染水体的净化,及排水中印染、造纸、皮革、炼油、电镀、化工、化纤、餐饮、浴室等废水的处理中都已经取得了较好的效果[2]。目前,气浮研究及应用主要偏向于电解凝聚气