BACKGROUND: The objective of this study was to investigate the feasibility of developing an integ... more BACKGROUND: The objective of this study was to investigate the feasibility of developing an integrated bio-electrochemical system for the removal of ethanolamine from wastewater by combining an Fe(III)-based microbial fuel cell (MFC) with a continuous Fe(II) oxidation system for simultaneous oxidation and reduction of iron in the same compartment. The ethanolamine in the Fe(III)-based MFC can be effectively converted to electrical energy by using the catalytic activity of microorganisms. In this respect, the authors investigated whether the introduction of a system for Fe(III) regeneration could enhance the sustainability of both power generation and the removal of ethanolamine in this integrated system.
h i g h l i g h t s Alcohol group of ETA was effectively degraded in an air-cathode single-chambe... more h i g h l i g h t s Alcohol group of ETA was effectively degraded in an air-cathode single-chamber MFC. Adding goethite in MFC with acetate and ammonium increased the ammonium removal. The maximum power density of the MFC with goethite and ETA was 210 mW m À2. a b s t r a c t A microbial fuel cell (MFC) with biological Fe(III) reduction was implemented for simultaneous ethano-lamine (ETA) degradation and electrical energy generation. In the feasibility experiment using acetate as a substrate in a single-chamber MFC with goethite and ammonium at a ratio of 3.0 (mol/mol), up to 96.1% of the ammonium was removed through the novel process related to Fe(III). In addition, the highest voltage output (0.53 V) and maximum power density (0.49 W m À2) were obtained. However, the ammonium removal and electrical performance decreased as acetate was replaced with ETA. In the long-term experiment , the electrical performance markedly decreased where the voltage loss increased due to Fe deposi-tion on the membranes.
The electrokinetic process with Fenton oxidation is a useful method to remediate soils co-contami... more The electrokinetic process with Fenton oxidation is a useful method to remediate soils co-contaminated with hydrophobic organics and heavy metals. In this study, an enhanced electrokinetic-Fenton process with a soil flushing method was investigated for the homogeneous and simultaneous removal of total petroleum hydrocarbons (TPHs) and zinc from contaminated soil. In addition, we investigated the removal mechanisms of different types of organic contaminants in real co-contaminated soil with TPHs, poly-cyclic aromatic hydrocarbons (PAHs), and zinc. In the artificially spiked soil, TPHs were homogeneously treated , and the removal of TPHs and zinc significantly improved using 10 % hydrogen peroxide (H 2 O 2) with 20 mM sodium dodecyl sulfate (SDS) in the anode and 20 mM SDS and 20 mM NaOH in the cathode. In the real co-contaminated soil, the remediation efficiencies of TPHs and zinc decreased because of the natural soil properties. However, we found satisfactory simultaneous treatability of TPHs and PAHs using 20 % H 2 O 2 with 20 mM SDS in the anode and 20 mM SDS and 20 mM NaOH in the cathode. Furthermore, the removal of individual PAHs was different depending on the individual PAH.
Aqueous two-phase system (ATPS) droplet generation has significant potential in biological and me... more Aqueous two-phase system (ATPS) droplet generation has significant potential in biological and medical applications because of its excellent biocompatibility. However, the ultralow interfacial tension of ATPS makes droplet generation extremely challenging when compared with the conventional water-in-oil (W/O) system. In this paper, we passively produced ATPS droplets with a wide range of droplet size and high production rate without the involvement of an oil phase and external forces. For the first time, we reported important information of the flow rate and capillary (Ca) number for passive, oil-free ATPS droplet generation. It was found that the range of Ca numbers of the continuous phase under the jetting flow regime is 0.3−1.7, as compared to less than 0.1 in the W/O system, indicating the ultralow interfacial tension in ATPS. In addition, we successfully generated ATPS droplets with a radius as small as 7 μm at the maximum frequency up to 300 Hz, which has not been achieved in previous studies. The size and generation frequency of ATPS droplets can be controlled independently by adjusting the inlet pressures and corresponding flow rates. We found that the droplet size is correlated with the pressure and flow rate ratios with the power-law exponents of 0.8 and 0.2, respectively.
This work shows the potential of nickel (Ni) nanoparticles (NPs) stabilized by polymers for accel... more This work shows the potential of nickel (Ni) nanoparticles (NPs) stabilized by polymers for accelerating carbon dioxide (CO 2) dissolution into saline aquifers. The catalytic characteristics of Ni NPs were investigated by monitoring changes in diameter of CO 2 microbubbles. An increase in ionic strength considerably reduces an electrostatic repulsive force in pristine Ni NPs, thereby decreasing their catalytic potential. This study shows how cationic dextran (DEX), nonionic poly(vinyl pyrrolidone) (PVP), and anionic carboxy methylcellulose (CMC) polymers, the dispersive behaviors of Ni NPs can be used to overcome the negative impact of salinity on CO 2 dissolution. The cationic polymer, DEX was less adsorbed onto NPs surfaces, thereby limiting the Ni NPs' catalytic activity. This behavior is due to a competition for Ni NPs' surface sites between the cation and DEX under high salinity. On the other hand, the non/anionic polymers, PVP and CMC could be relatively easily adsorbed onto anchoring sites of Ni NPs by the monovalent cation, Na +. Considerable dispersion of Ni NPs by an optimal concentration of the anionic polymers improved their catalytic capabilities even under unfavorable conditions for CO 2 dissolution. This study has implications for enhancing geologic sequestration into deep saline aquifers for the purposes of mitigating atmospheric CO 2 levels. Greenhouse gas emissions attributed to anthropogenic activities have increased significantly over the past century and continue to escalate. This increase causes measurable impacts on global warming, leading to climate-related concerns such as the unprecedented rising of sea levels along with more frequent and intense wildfires, floods, droughts, and tropical storms. Such adverse effects not only disrupt natural ecosystems, but they also pose serious risks to human populations 1. Carbon dioxide (CO 2) from fossil fuel combustion and industrial processes has accounted for 78% of the total greenhouse gas emissions 2. Although natural systems can absorb CO 2 back as part of the carbon cycle, these natural uptake processes are not enough to offset the escalating amount of anthropo-genic CO 2 released into the atmosphere 3. Mitigation of CO 2 emissions is an imminent global concern and must be urgently addressed by both political and technological implementations. As a result, many strategies have been proposed to mitigate global atmospheric CO 2 levels 4-6. One promising strategy is to inject CO 2 into subsurface rock formations because they provide the largest storage potential 7-10. Among various geological storage options (e.g., saline aquifers, depleted oil or natural gas reservoirs, and coalbed reservoirs), deep saline aquifers provide the highest potential capacity, with approximately 10,000 billion metric tons of carbon in total 11. However, safe storage through a solubility trapping process is controversial since most of the injected CO 2 remains as CO 2 molecules in the absence of a catalyst for enhancing the reaction rate of carbonic acid (H 2 CO 3) formation 12. This reaction rate is further hindered due to a high salinity content in brine, as preferable saline concentrations for CO 2 storage range under 5% weight per volume while some aquifers have salinities ranging up to 25% 13. As a result, the strategy of the accelerated CO 2 dissolution process should be investigated in order to achieve a more feasible means of storing CO 2 into deep saline aquifers.
Chemical enhanced oil recovery (EOR) is a successful method for increasing crude oil recovery. Ho... more Chemical enhanced oil recovery (EOR) is a successful method for increasing crude oil recovery. However, chemicals commonly used for enhanced oil recovery operations possess adverse biological impacts. To meet the legislative requirement and environmental protection demands, the performance of a highly biodegradable nonionic surfactant derived from tannic acid, a possible alternative, was evaluated using a microfluidic technology for the replacement of chemically synthesis surfactant by green chemistry products. Aqueous micro-droplets containing the surfactant in crude oils were used for measurements of interfacial tension (IFT) reduction. The degree of interfacial tension reduction by sodium dodecyl sulfate (SDS), one of the most popular conventional surfactants, was also quantified for performance comparison. The potential of the biosurfactant for IFT reduction of light crude oil was superior to that of SDS. To evaluate the feasibility of the biosurfactant in improvement of recovery efficiency, surfactant-assisted flooding was tested under a random microfluidic network at the optimal concentrations, and the results were in good agreement with IFT reduction tests. The utilization of the polymer in a biosurfactant synthesis process effectively enhanced high sweep efficiency by decreasing a viscous fingering effect. The biosurfactant proved to be adequate and can sufficiently alleviate environmental concerns adopted by chemical flooding EOR.
Aqueous microdroplet generation in gaseous phase is an emerging area of research due to its numer... more Aqueous microdroplet generation in gaseous phase is an emerging area of research due to its numerous advantages compared to conventional liquid-liquid system including high system throughput and fast mixing. In this paper, we numerically studied the aqueous droplet generation in an inertial air flow in a T-junction droplet generator to understand the droplet formation mechanisms. The Volume of Fluid method is employed to track the interface between two immiscible fluids. The two-phase flow behavior of water droplet in air in the T-junction microchannel over a wide range of Capillary number (0.0001-0.1), and Reynolds number (0.1-100) was examined. At various Reynolds and Capillary numbers, unique flow regime mapping was determined including squeezing, dripping, jetting, unstable dripping, and unstable jetting. It was found that stable aqueous droplets are generated in the squeezing and dripping flow regimes. On the other hand, the unstable dripping flow regime is unable to sustain spherical droplets as they travel downstream. In the unstable jetting flow regime, a stream of water moves downstream and then it's tip splits into small or large fragments of water. The results show that the droplet size increases as Capillary and Reynolds numbers increases and decreases, respectively. As both Capillary and Reynolds numbers increase, the droplet generation frequency increases, reaching its maximum at 223 Hz.
Recent advent of Aqueous-Two-Phase-System (ATPS), more biologically friendly compared to conventi... more Recent advent of Aqueous-Two-Phase-System (ATPS), more biologically friendly compared to conventional oil-water systems, has shown great potential to rapidly generate aqueous droplets without tedious post-processing. However, understanding of underlying physics of droplet formation in ATPS is still in its infancy. In this paper, we investigate hydrodynamic behaviors and mechanisms of all-aqueous droplet formation in two flow-focusing droplet generators. Two incompatible polymers namely polyethylene glycol (PEG) and dextran (DEX) are mixed in water to make ATPS. The influence of inlet pressures and flow-focusing configurations on droplet sizes, and thread breakup length is studied. Flow regime mapping for two different configurations of droplet generators possessing junction angles of 30° and 90° is also obtained. The results show that droplet size is very susceptible to the junction angle while inlet pressures of the PEG and DEX flows readily control four main flow regimes including back flow, dripping, jetting and stratified.
The recent advent of aqueous two-phase system (ATPS) has shown great potential to rapidly generat... more The recent advent of aqueous two-phase system (ATPS) has shown great potential to rapidly generate microscale aqueous droplets without tedious post-processing. ATPS provides a more biologically friendly and straightforward method to manufacture aqueous droplets compared with conventional oil-water systems and as such, it has been employed in many biomedical applications. Although the cost-effective manufacturing of aqueous droplets has been feasible by direct generation in ATPS, an understanding of the underlying physics of droplet formation in ATPS is still in its infancy. In this paper, we investigated the hydrodynamic behavior and mechanisms of all-aqueous droplet formation in two flow-focusing droplet generators. This study specifically tests whether ATPS in different geome-tries generates aqueous droplets with different sizes and properties. To achieve these goals, two incompatible polymers, namely polyethylene glycol (PEG) and dextran (DEX), were mixed in water to make ATPS. The influences of inlet pressures and flow-focusing configurations on droplet size, droplet generation frequency, and thread breakup length were quantified. In addition, flow regime mapping for the two different droplet generators at 30° and 90° junction angles was obtained. The results show that droplet size is very susceptible to the junction angle. On the other hand, inlet pressures of the PEG and DEX flows readily control five main flow regimes including PEG Back Flow, DEX Back Flow, Dripping Flow, Jetting Flow and Stratified Flow. It is observed that generated droplets in the Jetting Flow regime are larger in the case of 30°, whereas larger droplets are obtained in the Dripping Flow regime at 90° configuration. The frequency of droplet generation increases and decreases by increasing P PEG and P DEX, respectively. Finally, we characterized flow regimes by the Capillary number (Ca) of the PEG flow.
This work reports a microfluidic study investigating the feasibility of accelerating gaseous carb... more This work reports a microfluidic study investigating the feasibility of accelerating gaseous carbon dioxide (CO 2) dissolution into a continuous aqueous phase with the use of metallic nickel (Ni) nanoparticles (NPs) under conditions specific to carbon sequestration in saline aquifers. The dissolution of CO 2 bubbles at different pH levels and salinities was studied to understand the effects that the intrinsic characteristics of brine in real reservoir conditions would have on CO 2 solubility. Results showed that an increased shrinkage of CO 2 bubbles occurred with higher basicity, while an increased expansion of CO 2 bubbles was observed with a proportional increase in salinity. To achieve acceleration of CO 2 dissolution in acidic brine containing high salinity content, the catalytic effect of Ni NPs was investigated by monitoring change in CO 2 bubble size at various Ni NPs concentrations. The optimal concentration for the Ni NPs suspension was determined to be 30 mg L −1 ; increasing the concentration up to 30 mg L −1 showed a significant increase in the dissolution of CO 2 bubbles, but increasing from 30 to 50 mg L −1 displayed a decrease in catalytic potential, due to the decreased translational diffusion coefficient that occurs at higher concentrations. The optimal additive concentration of Ni NPs was tested with variations of solution at acidic and basic conditions and different levels of salinity to reveal how effectively the Ni NPs behave under real reservoir conditions. At the acidic level, Ni NPs proved to be more effective in catalyzing CO 2 dissolution and can sufficiently alleviate the negative impact of salinity in brine. C arbon capture and sequestration technology for mitigating anthropogenic greenhouse gas emissions has attracted much attention in response to international concerns about global warming and ocean acidification. 1−3 Among the types of reservoirs that could be employed in geologic carbon sequestration, deep saline aquifers are considered to be one of the most appropriate options for large-scale commercial carbon dioxide (CO 2) storage due to their large storage capacities. The potential capacity of saline reservoirs was estimated to be approximately 5-fold higher than that of depleted oil−natural gas reservoirs. 4 A critical characteristic of saline aquifers for CO 2 storage is the amount of metal cations found in the brine, because metals such as magnesium (Mg), calcium (Ca), and iron (Fe) could react with the introduced CO 2 to promote carbon mineralization, thereby increasing permanent storage of CO 2. 5 Another contribution to safe storage potential that brine possesses is the solubility trapping mechanism; mobile free-phase CO 2 can migrate upward and risk leakage, but CO 2 that dissolves into brine and reaches an equilibrium state increases the density of the brine which then carries the dissolved CO 2 downward and reduces risk of leakage. 6 However, the feasibility of carbon sequestration via the solubility trapping and mineralization processes in saline aquifers is controversial mainly due to the slow reaction rate of carbonic acid (H 2 CO 3) formation from CO 2 injected into brine. 7 This reaction rate can further be negatively impacted by site-specific conditions of saline aquifers. The preferable depths for CO 2 storage are usually at 800 to 2000 m from surface level, and these depths can contain salinity concentrations of 5% to more than 25% weight per volume, respectively. 8
Many consumer products containing ZnO have raised concern for safety in regard to environmental i... more Many consumer products containing ZnO have raised concern for safety in regard to environmental impact and the public health. Widely used sunscreens for protecting against UV and avoiding sunburns represent a great exposure to nano-ZnO, one of the ingredients commonly applied in sunscreens. Applying nanoproducts on beaches may release nanoparticles unintentionally into the ocean. Despite the accumulation of such nanoproducts in the ocean harming or being detrimental to critical marine organisms, few studies have investigated the release and potential toxicity of nanoparticles extracted from products and compared them with those from industrial-type nanoparticles. Results show that the cyto-toxicity of both industrial-and sunscreen-derived nano-ZnO to the marine diatom algae, Thalassiosira pseudo-nana, increased as exposure increases over time, as measured by growth inhibition (%) of the algae at a constant concentration of nano-ZnO (10 mg/L). The extent of toxicity appeared to be higher from industrial-type nano-ZnO compared with sunscreen-extracted nano-ZnO, though the extent becomes similar when concentrations increase to 50 mg/L. On the other hand, at a fixed exposure time of 48 h, the cytotoxicity increases as concentrations increase with the higher toxicity shown from the industrial-type compared with sunscreen-induced nano-ZnO. Results indicate that while industrial-type nano-ZnO shows higher toxicity than sunscreen-derived nano-ZnO, the release and extent of toxicity from nano-ZnO extracted from sunscreen are not trivial and should be monitored for the development of safe manufacturing of nanomaterials-induced products.
Increased manufacture of TiO 2 nanoproducts has caused concern about the potential toxicity of th... more Increased manufacture of TiO 2 nanoproducts has caused concern about the potential toxicity of these products to the environment and in public health. Identification and confirmation of the presence of TiO 2 nanoparticles derived from consumer products as opposed to industrial TiO 2 NPs warrant examination in exploring the significance of their release and resultant impacts on the environment. To this end, we examined the significance of the release of these particles and their toxic effect on the marine diatom algae Thalassiosira pseudonana. Our results indicate that nano-TiO 2 sunscreen and toothpaste exhibit more toxicity in comparison to industrial TiO 2 and inhibited the growth of the marine diatom T. pseudonana. This inhibition was proportional to the exposure time and concentrations of nano-TiO 2. Our findings indicate a significant effect, and therefore, further research is warranted in evaluation and assessment of the toxicity of modified nano-TiO 2 derived from consumer products and their physi-cochemical properties.
The production of nanomaterials (NMs) is expected to grow continuously, yet their transformation,... more The production of nanomaterials (NMs) is expected to grow continuously, yet their transformation, transport, release mechanisms, and interactions with contaminants under environmental conditions remain poorly understood. Few studies have investigated the effects of contaminants on fate and transport of NMs, especially siloxanes that are widely found in products. It is hypothesized that the model contaminant, siloxane (e.g., 1,1,3,3-tetramethyldisiloxane (TMDS)) may influence the mechanisms and transport kinetics of NMs under different release pathways. Sand column experiments were carried out under two different scenarios: the release from a mixed TMDS and nano-ZnO suspension (A) and the release of nano-ZnO from sand contaminated with TMDS (B). Results show that interparticle reactions are dominant in (A) and particle-porous interactions are responsible for blocking effects governing in (B). Insights, especially the kinetics of nano-ZnO from co-transport by a contaminant and from porous media preloaded with a contaminant, and environmental factors affecting the release and retention of nano-ZnO in saturated sand are unveiled. These two dominant transport mechanisms (e.g., interparticle reactions and blocking effects) were derived. This study indicates that the release of ZnO NPs is influenced by the presence of TMDS; the extent of mobility and their transport pathways depend on the pre-existence of TMDS in porous media.
Carbon sequestration into deep saline aquifers has been considered a promising technology for mit... more Carbon sequestration into deep saline aquifers has been considered a promising technology for mitigating heavy atmospheric carbon dioxide (CO 2) concentration. When gaseous CO 2 is continuously injected into these aquifers, resident brine near a wellbore area is rapidly evaporated while precipitating significant amounts of salt at pores, thereby damaging the aquifer media unfavorable for subsequent CO 2 injection. In addition, the continuous injection of CO 2 at a large volume significantly hinders dissolution of CO 2 into brine. In this study, we propose a new method of sequential water injection with gaseous CO 2 for in-situ generation of micro-sized CO 2 bubbles that minimizes the brine drying-out and simultaneously accelerates CO 2 dissolution. We observed that, with this method, a partial volume of CO 2 dissolves effectively into the co-injected water during pumping, thereby decreasing the rate of brine drying-out at pores. Another benefit of sequential injection is the significantly increased rate of CO 2 hydration induced by the large surface-to-volume ratio of tiny bubbles at micro to nanoscale. To further accelerate CO 2 hydration, we investigated reactive dynamics of bubble-driven CO 2 hydration at different frequencies of sequential injection and pH levels of the solution. Operation at a higher frequency with higher basicity proved to be the most effective in decreasing the bubble size and therefore accelerating CO 2 hydration into brine, which is a more feasible CO 2 storage plan.
Ethanolamine (ETA) is widely used as a metal corrosion inhibitor and for CO 2 capture. The treatm... more Ethanolamine (ETA) is widely used as a metal corrosion inhibitor and for CO 2 capture. The treatment of ETA in wastewater involves advanced oxidation or electrolysis, which requires excessive energy since it is a not readily biodegradable organic containing amine. In this study, a microbial fuel cell (MFC) for simultaneous ETA degradation and electricity generation was investigated. 80 mL of an air-cathode single-chamber MFC was designed to determine the degradation and by-products formation of ETA and the power density. The reactor was inoculated with return activated sludge taken from a local wastewater treatment plant. This system was able to remove 91% of chemical oxygen demand (COD) and 37% of ammonia when ETA was injected into the MFC. A maximum power density of 240 mW m À2 (7.65 mW m À3) and a Coulombic efficiency of 18.2% were obtained with the ETA-fed MFC. From the results, although further research is required to treat ammonium derived from ETA degradation and to improve the performance of the MFC, it was found that the MFC would be a promising technology for ETA wastewater treatment, as well as electricity production.
BACKGROUND: The objective of this study was to investigate the feasibility of developing an integ... more BACKGROUND: The objective of this study was to investigate the feasibility of developing an integrated bio-electrochemical system for the removal of ethanolamine from wastewater by combining an Fe(III)-based microbial fuel cell (MFC) with a continuous Fe(II) oxidation system for simultaneous oxidation and reduction of iron in the same compartment. The ethanolamine in the Fe(III)-based MFC can be effectively converted to electrical energy by using the catalytic activity of microorganisms. In this respect, the authors investigated whether the introduction of a system for Fe(III) regeneration could enhance the sustainability of both power generation and the removal of ethanolamine in this integrated system.
h i g h l i g h t s Alcohol group of ETA was effectively degraded in an air-cathode single-chambe... more h i g h l i g h t s Alcohol group of ETA was effectively degraded in an air-cathode single-chamber MFC. Adding goethite in MFC with acetate and ammonium increased the ammonium removal. The maximum power density of the MFC with goethite and ETA was 210 mW m À2. a b s t r a c t A microbial fuel cell (MFC) with biological Fe(III) reduction was implemented for simultaneous ethano-lamine (ETA) degradation and electrical energy generation. In the feasibility experiment using acetate as a substrate in a single-chamber MFC with goethite and ammonium at a ratio of 3.0 (mol/mol), up to 96.1% of the ammonium was removed through the novel process related to Fe(III). In addition, the highest voltage output (0.53 V) and maximum power density (0.49 W m À2) were obtained. However, the ammonium removal and electrical performance decreased as acetate was replaced with ETA. In the long-term experiment , the electrical performance markedly decreased where the voltage loss increased due to Fe deposi-tion on the membranes.
The electrokinetic process with Fenton oxidation is a useful method to remediate soils co-contami... more The electrokinetic process with Fenton oxidation is a useful method to remediate soils co-contaminated with hydrophobic organics and heavy metals. In this study, an enhanced electrokinetic-Fenton process with a soil flushing method was investigated for the homogeneous and simultaneous removal of total petroleum hydrocarbons (TPHs) and zinc from contaminated soil. In addition, we investigated the removal mechanisms of different types of organic contaminants in real co-contaminated soil with TPHs, poly-cyclic aromatic hydrocarbons (PAHs), and zinc. In the artificially spiked soil, TPHs were homogeneously treated , and the removal of TPHs and zinc significantly improved using 10 % hydrogen peroxide (H 2 O 2) with 20 mM sodium dodecyl sulfate (SDS) in the anode and 20 mM SDS and 20 mM NaOH in the cathode. In the real co-contaminated soil, the remediation efficiencies of TPHs and zinc decreased because of the natural soil properties. However, we found satisfactory simultaneous treatability of TPHs and PAHs using 20 % H 2 O 2 with 20 mM SDS in the anode and 20 mM SDS and 20 mM NaOH in the cathode. Furthermore, the removal of individual PAHs was different depending on the individual PAH.
Aqueous two-phase system (ATPS) droplet generation has significant potential in biological and me... more Aqueous two-phase system (ATPS) droplet generation has significant potential in biological and medical applications because of its excellent biocompatibility. However, the ultralow interfacial tension of ATPS makes droplet generation extremely challenging when compared with the conventional water-in-oil (W/O) system. In this paper, we passively produced ATPS droplets with a wide range of droplet size and high production rate without the involvement of an oil phase and external forces. For the first time, we reported important information of the flow rate and capillary (Ca) number for passive, oil-free ATPS droplet generation. It was found that the range of Ca numbers of the continuous phase under the jetting flow regime is 0.3−1.7, as compared to less than 0.1 in the W/O system, indicating the ultralow interfacial tension in ATPS. In addition, we successfully generated ATPS droplets with a radius as small as 7 μm at the maximum frequency up to 300 Hz, which has not been achieved in previous studies. The size and generation frequency of ATPS droplets can be controlled independently by adjusting the inlet pressures and corresponding flow rates. We found that the droplet size is correlated with the pressure and flow rate ratios with the power-law exponents of 0.8 and 0.2, respectively.
This work shows the potential of nickel (Ni) nanoparticles (NPs) stabilized by polymers for accel... more This work shows the potential of nickel (Ni) nanoparticles (NPs) stabilized by polymers for accelerating carbon dioxide (CO 2) dissolution into saline aquifers. The catalytic characteristics of Ni NPs were investigated by monitoring changes in diameter of CO 2 microbubbles. An increase in ionic strength considerably reduces an electrostatic repulsive force in pristine Ni NPs, thereby decreasing their catalytic potential. This study shows how cationic dextran (DEX), nonionic poly(vinyl pyrrolidone) (PVP), and anionic carboxy methylcellulose (CMC) polymers, the dispersive behaviors of Ni NPs can be used to overcome the negative impact of salinity on CO 2 dissolution. The cationic polymer, DEX was less adsorbed onto NPs surfaces, thereby limiting the Ni NPs' catalytic activity. This behavior is due to a competition for Ni NPs' surface sites between the cation and DEX under high salinity. On the other hand, the non/anionic polymers, PVP and CMC could be relatively easily adsorbed onto anchoring sites of Ni NPs by the monovalent cation, Na +. Considerable dispersion of Ni NPs by an optimal concentration of the anionic polymers improved their catalytic capabilities even under unfavorable conditions for CO 2 dissolution. This study has implications for enhancing geologic sequestration into deep saline aquifers for the purposes of mitigating atmospheric CO 2 levels. Greenhouse gas emissions attributed to anthropogenic activities have increased significantly over the past century and continue to escalate. This increase causes measurable impacts on global warming, leading to climate-related concerns such as the unprecedented rising of sea levels along with more frequent and intense wildfires, floods, droughts, and tropical storms. Such adverse effects not only disrupt natural ecosystems, but they also pose serious risks to human populations 1. Carbon dioxide (CO 2) from fossil fuel combustion and industrial processes has accounted for 78% of the total greenhouse gas emissions 2. Although natural systems can absorb CO 2 back as part of the carbon cycle, these natural uptake processes are not enough to offset the escalating amount of anthropo-genic CO 2 released into the atmosphere 3. Mitigation of CO 2 emissions is an imminent global concern and must be urgently addressed by both political and technological implementations. As a result, many strategies have been proposed to mitigate global atmospheric CO 2 levels 4-6. One promising strategy is to inject CO 2 into subsurface rock formations because they provide the largest storage potential 7-10. Among various geological storage options (e.g., saline aquifers, depleted oil or natural gas reservoirs, and coalbed reservoirs), deep saline aquifers provide the highest potential capacity, with approximately 10,000 billion metric tons of carbon in total 11. However, safe storage through a solubility trapping process is controversial since most of the injected CO 2 remains as CO 2 molecules in the absence of a catalyst for enhancing the reaction rate of carbonic acid (H 2 CO 3) formation 12. This reaction rate is further hindered due to a high salinity content in brine, as preferable saline concentrations for CO 2 storage range under 5% weight per volume while some aquifers have salinities ranging up to 25% 13. As a result, the strategy of the accelerated CO 2 dissolution process should be investigated in order to achieve a more feasible means of storing CO 2 into deep saline aquifers.
Chemical enhanced oil recovery (EOR) is a successful method for increasing crude oil recovery. Ho... more Chemical enhanced oil recovery (EOR) is a successful method for increasing crude oil recovery. However, chemicals commonly used for enhanced oil recovery operations possess adverse biological impacts. To meet the legislative requirement and environmental protection demands, the performance of a highly biodegradable nonionic surfactant derived from tannic acid, a possible alternative, was evaluated using a microfluidic technology for the replacement of chemically synthesis surfactant by green chemistry products. Aqueous micro-droplets containing the surfactant in crude oils were used for measurements of interfacial tension (IFT) reduction. The degree of interfacial tension reduction by sodium dodecyl sulfate (SDS), one of the most popular conventional surfactants, was also quantified for performance comparison. The potential of the biosurfactant for IFT reduction of light crude oil was superior to that of SDS. To evaluate the feasibility of the biosurfactant in improvement of recovery efficiency, surfactant-assisted flooding was tested under a random microfluidic network at the optimal concentrations, and the results were in good agreement with IFT reduction tests. The utilization of the polymer in a biosurfactant synthesis process effectively enhanced high sweep efficiency by decreasing a viscous fingering effect. The biosurfactant proved to be adequate and can sufficiently alleviate environmental concerns adopted by chemical flooding EOR.
Aqueous microdroplet generation in gaseous phase is an emerging area of research due to its numer... more Aqueous microdroplet generation in gaseous phase is an emerging area of research due to its numerous advantages compared to conventional liquid-liquid system including high system throughput and fast mixing. In this paper, we numerically studied the aqueous droplet generation in an inertial air flow in a T-junction droplet generator to understand the droplet formation mechanisms. The Volume of Fluid method is employed to track the interface between two immiscible fluids. The two-phase flow behavior of water droplet in air in the T-junction microchannel over a wide range of Capillary number (0.0001-0.1), and Reynolds number (0.1-100) was examined. At various Reynolds and Capillary numbers, unique flow regime mapping was determined including squeezing, dripping, jetting, unstable dripping, and unstable jetting. It was found that stable aqueous droplets are generated in the squeezing and dripping flow regimes. On the other hand, the unstable dripping flow regime is unable to sustain spherical droplets as they travel downstream. In the unstable jetting flow regime, a stream of water moves downstream and then it's tip splits into small or large fragments of water. The results show that the droplet size increases as Capillary and Reynolds numbers increases and decreases, respectively. As both Capillary and Reynolds numbers increase, the droplet generation frequency increases, reaching its maximum at 223 Hz.
Recent advent of Aqueous-Two-Phase-System (ATPS), more biologically friendly compared to conventi... more Recent advent of Aqueous-Two-Phase-System (ATPS), more biologically friendly compared to conventional oil-water systems, has shown great potential to rapidly generate aqueous droplets without tedious post-processing. However, understanding of underlying physics of droplet formation in ATPS is still in its infancy. In this paper, we investigate hydrodynamic behaviors and mechanisms of all-aqueous droplet formation in two flow-focusing droplet generators. Two incompatible polymers namely polyethylene glycol (PEG) and dextran (DEX) are mixed in water to make ATPS. The influence of inlet pressures and flow-focusing configurations on droplet sizes, and thread breakup length is studied. Flow regime mapping for two different configurations of droplet generators possessing junction angles of 30° and 90° is also obtained. The results show that droplet size is very susceptible to the junction angle while inlet pressures of the PEG and DEX flows readily control four main flow regimes including back flow, dripping, jetting and stratified.
The recent advent of aqueous two-phase system (ATPS) has shown great potential to rapidly generat... more The recent advent of aqueous two-phase system (ATPS) has shown great potential to rapidly generate microscale aqueous droplets without tedious post-processing. ATPS provides a more biologically friendly and straightforward method to manufacture aqueous droplets compared with conventional oil-water systems and as such, it has been employed in many biomedical applications. Although the cost-effective manufacturing of aqueous droplets has been feasible by direct generation in ATPS, an understanding of the underlying physics of droplet formation in ATPS is still in its infancy. In this paper, we investigated the hydrodynamic behavior and mechanisms of all-aqueous droplet formation in two flow-focusing droplet generators. This study specifically tests whether ATPS in different geome-tries generates aqueous droplets with different sizes and properties. To achieve these goals, two incompatible polymers, namely polyethylene glycol (PEG) and dextran (DEX), were mixed in water to make ATPS. The influences of inlet pressures and flow-focusing configurations on droplet size, droplet generation frequency, and thread breakup length were quantified. In addition, flow regime mapping for the two different droplet generators at 30° and 90° junction angles was obtained. The results show that droplet size is very susceptible to the junction angle. On the other hand, inlet pressures of the PEG and DEX flows readily control five main flow regimes including PEG Back Flow, DEX Back Flow, Dripping Flow, Jetting Flow and Stratified Flow. It is observed that generated droplets in the Jetting Flow regime are larger in the case of 30°, whereas larger droplets are obtained in the Dripping Flow regime at 90° configuration. The frequency of droplet generation increases and decreases by increasing P PEG and P DEX, respectively. Finally, we characterized flow regimes by the Capillary number (Ca) of the PEG flow.
This work reports a microfluidic study investigating the feasibility of accelerating gaseous carb... more This work reports a microfluidic study investigating the feasibility of accelerating gaseous carbon dioxide (CO 2) dissolution into a continuous aqueous phase with the use of metallic nickel (Ni) nanoparticles (NPs) under conditions specific to carbon sequestration in saline aquifers. The dissolution of CO 2 bubbles at different pH levels and salinities was studied to understand the effects that the intrinsic characteristics of brine in real reservoir conditions would have on CO 2 solubility. Results showed that an increased shrinkage of CO 2 bubbles occurred with higher basicity, while an increased expansion of CO 2 bubbles was observed with a proportional increase in salinity. To achieve acceleration of CO 2 dissolution in acidic brine containing high salinity content, the catalytic effect of Ni NPs was investigated by monitoring change in CO 2 bubble size at various Ni NPs concentrations. The optimal concentration for the Ni NPs suspension was determined to be 30 mg L −1 ; increasing the concentration up to 30 mg L −1 showed a significant increase in the dissolution of CO 2 bubbles, but increasing from 30 to 50 mg L −1 displayed a decrease in catalytic potential, due to the decreased translational diffusion coefficient that occurs at higher concentrations. The optimal additive concentration of Ni NPs was tested with variations of solution at acidic and basic conditions and different levels of salinity to reveal how effectively the Ni NPs behave under real reservoir conditions. At the acidic level, Ni NPs proved to be more effective in catalyzing CO 2 dissolution and can sufficiently alleviate the negative impact of salinity in brine. C arbon capture and sequestration technology for mitigating anthropogenic greenhouse gas emissions has attracted much attention in response to international concerns about global warming and ocean acidification. 1−3 Among the types of reservoirs that could be employed in geologic carbon sequestration, deep saline aquifers are considered to be one of the most appropriate options for large-scale commercial carbon dioxide (CO 2) storage due to their large storage capacities. The potential capacity of saline reservoirs was estimated to be approximately 5-fold higher than that of depleted oil−natural gas reservoirs. 4 A critical characteristic of saline aquifers for CO 2 storage is the amount of metal cations found in the brine, because metals such as magnesium (Mg), calcium (Ca), and iron (Fe) could react with the introduced CO 2 to promote carbon mineralization, thereby increasing permanent storage of CO 2. 5 Another contribution to safe storage potential that brine possesses is the solubility trapping mechanism; mobile free-phase CO 2 can migrate upward and risk leakage, but CO 2 that dissolves into brine and reaches an equilibrium state increases the density of the brine which then carries the dissolved CO 2 downward and reduces risk of leakage. 6 However, the feasibility of carbon sequestration via the solubility trapping and mineralization processes in saline aquifers is controversial mainly due to the slow reaction rate of carbonic acid (H 2 CO 3) formation from CO 2 injected into brine. 7 This reaction rate can further be negatively impacted by site-specific conditions of saline aquifers. The preferable depths for CO 2 storage are usually at 800 to 2000 m from surface level, and these depths can contain salinity concentrations of 5% to more than 25% weight per volume, respectively. 8
Many consumer products containing ZnO have raised concern for safety in regard to environmental i... more Many consumer products containing ZnO have raised concern for safety in regard to environmental impact and the public health. Widely used sunscreens for protecting against UV and avoiding sunburns represent a great exposure to nano-ZnO, one of the ingredients commonly applied in sunscreens. Applying nanoproducts on beaches may release nanoparticles unintentionally into the ocean. Despite the accumulation of such nanoproducts in the ocean harming or being detrimental to critical marine organisms, few studies have investigated the release and potential toxicity of nanoparticles extracted from products and compared them with those from industrial-type nanoparticles. Results show that the cyto-toxicity of both industrial-and sunscreen-derived nano-ZnO to the marine diatom algae, Thalassiosira pseudo-nana, increased as exposure increases over time, as measured by growth inhibition (%) of the algae at a constant concentration of nano-ZnO (10 mg/L). The extent of toxicity appeared to be higher from industrial-type nano-ZnO compared with sunscreen-extracted nano-ZnO, though the extent becomes similar when concentrations increase to 50 mg/L. On the other hand, at a fixed exposure time of 48 h, the cytotoxicity increases as concentrations increase with the higher toxicity shown from the industrial-type compared with sunscreen-induced nano-ZnO. Results indicate that while industrial-type nano-ZnO shows higher toxicity than sunscreen-derived nano-ZnO, the release and extent of toxicity from nano-ZnO extracted from sunscreen are not trivial and should be monitored for the development of safe manufacturing of nanomaterials-induced products.
Increased manufacture of TiO 2 nanoproducts has caused concern about the potential toxicity of th... more Increased manufacture of TiO 2 nanoproducts has caused concern about the potential toxicity of these products to the environment and in public health. Identification and confirmation of the presence of TiO 2 nanoparticles derived from consumer products as opposed to industrial TiO 2 NPs warrant examination in exploring the significance of their release and resultant impacts on the environment. To this end, we examined the significance of the release of these particles and their toxic effect on the marine diatom algae Thalassiosira pseudonana. Our results indicate that nano-TiO 2 sunscreen and toothpaste exhibit more toxicity in comparison to industrial TiO 2 and inhibited the growth of the marine diatom T. pseudonana. This inhibition was proportional to the exposure time and concentrations of nano-TiO 2. Our findings indicate a significant effect, and therefore, further research is warranted in evaluation and assessment of the toxicity of modified nano-TiO 2 derived from consumer products and their physi-cochemical properties.
The production of nanomaterials (NMs) is expected to grow continuously, yet their transformation,... more The production of nanomaterials (NMs) is expected to grow continuously, yet their transformation, transport, release mechanisms, and interactions with contaminants under environmental conditions remain poorly understood. Few studies have investigated the effects of contaminants on fate and transport of NMs, especially siloxanes that are widely found in products. It is hypothesized that the model contaminant, siloxane (e.g., 1,1,3,3-tetramethyldisiloxane (TMDS)) may influence the mechanisms and transport kinetics of NMs under different release pathways. Sand column experiments were carried out under two different scenarios: the release from a mixed TMDS and nano-ZnO suspension (A) and the release of nano-ZnO from sand contaminated with TMDS (B). Results show that interparticle reactions are dominant in (A) and particle-porous interactions are responsible for blocking effects governing in (B). Insights, especially the kinetics of nano-ZnO from co-transport by a contaminant and from porous media preloaded with a contaminant, and environmental factors affecting the release and retention of nano-ZnO in saturated sand are unveiled. These two dominant transport mechanisms (e.g., interparticle reactions and blocking effects) were derived. This study indicates that the release of ZnO NPs is influenced by the presence of TMDS; the extent of mobility and their transport pathways depend on the pre-existence of TMDS in porous media.
Carbon sequestration into deep saline aquifers has been considered a promising technology for mit... more Carbon sequestration into deep saline aquifers has been considered a promising technology for mitigating heavy atmospheric carbon dioxide (CO 2) concentration. When gaseous CO 2 is continuously injected into these aquifers, resident brine near a wellbore area is rapidly evaporated while precipitating significant amounts of salt at pores, thereby damaging the aquifer media unfavorable for subsequent CO 2 injection. In addition, the continuous injection of CO 2 at a large volume significantly hinders dissolution of CO 2 into brine. In this study, we propose a new method of sequential water injection with gaseous CO 2 for in-situ generation of micro-sized CO 2 bubbles that minimizes the brine drying-out and simultaneously accelerates CO 2 dissolution. We observed that, with this method, a partial volume of CO 2 dissolves effectively into the co-injected water during pumping, thereby decreasing the rate of brine drying-out at pores. Another benefit of sequential injection is the significantly increased rate of CO 2 hydration induced by the large surface-to-volume ratio of tiny bubbles at micro to nanoscale. To further accelerate CO 2 hydration, we investigated reactive dynamics of bubble-driven CO 2 hydration at different frequencies of sequential injection and pH levels of the solution. Operation at a higher frequency with higher basicity proved to be the most effective in decreasing the bubble size and therefore accelerating CO 2 hydration into brine, which is a more feasible CO 2 storage plan.
Ethanolamine (ETA) is widely used as a metal corrosion inhibitor and for CO 2 capture. The treatm... more Ethanolamine (ETA) is widely used as a metal corrosion inhibitor and for CO 2 capture. The treatment of ETA in wastewater involves advanced oxidation or electrolysis, which requires excessive energy since it is a not readily biodegradable organic containing amine. In this study, a microbial fuel cell (MFC) for simultaneous ETA degradation and electricity generation was investigated. 80 mL of an air-cathode single-chamber MFC was designed to determine the degradation and by-products formation of ETA and the power density. The reactor was inoculated with return activated sludge taken from a local wastewater treatment plant. This system was able to remove 91% of chemical oxygen demand (COD) and 37% of ammonia when ETA was injected into the MFC. A maximum power density of 240 mW m À2 (7.65 mW m À3) and a Coulombic efficiency of 18.2% were obtained with the ETA-fed MFC. From the results, although further research is required to treat ammonium derived from ETA degradation and to improve the performance of the MFC, it was found that the MFC would be a promising technology for ETA wastewater treatment, as well as electricity production.
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