Increase In Solution Conductivity Research Articles

A gas–liquid discharge reactor for water disinfection: Electrical properties and microbicidal effects on viruses and bacteria

As an eco-friendly oxidation technique, gas–liquid underwater discharge is considered a promising water disinfection method. In this study, we constructed a gas–liquid discharge reactor, in which the electrical properties, optimized discharging parameters, and microbicidal effects on coliphage virus and two bacteria (E. coli and S. aureus) were investigated. It is shown that, compared to direct underwater discharge without ventilation, gas–liquid discharges can release higher energy and generate more active species, thus resulting in better inactivation performance. A microbicidal reduction of over 99.9% can be achieved in 5 min of treatment for three types of microbes in 600 ml tap water (σ ∼ 590 μS/cm); specifically, 3.34, 3.95, and 3.65 log reductions were achieved for coliphages, E. coli, and S. aureus, respectively. The observations of microbial morphologies indicate that underwater discharges and their products can severely damage the external structures and internal substances of micro-organisms, which is responsible for the working mechanism of microbial inactivation. The reactor can decrease E. coli from 6.2 × 103–6.4 × 106 CFU/ml to ∼1000 CFU/ml in 5 min, suggesting that this gas–liquid discharge reactor has a low sensitivity to the initial density of suspension. In addition, the reactor can also achieve a satisfactory disinfection effect even in water with high conductivity, although the microbicidal performance of E. coli will be attenuated with an increase in solution conductivity (from 3.82 log reduction at 2 mS/cm to 2.22 log at 15 mS/cm). These advantages indicate the broad applicability of the reactor in water disinfection.

Evaporation of Electrolyte during SVET Measurements: The Scale of the Problem and the Solutions

AbstractThe objective of this work is to investigate the scale of the effect of spontaneous solution evaporation during SVET (Scanning Vibrating Electrode Technique) measurements and demonstrate how it biases the final results. When SVET maps are continuously acquired for more than several hours, the measured currents are smaller than expected. This is attributed to solvent (typically water) evaporation which leads to an increase in solution conductivity over time. If this is not considered when converting the measured potential differences into the local current densities, the SVET results display currents smaller than the true ones. Here, this effect is studied with a platinum disk electrode as source of a constant current and a model corroding system consisting of the AA2024/CFRP galvanic couple. Corrective actions are proposed to mitigate the problem, either in the experimental set‐up or as numerical correction.

An Investigation of the Role of Rapid Chlorine Hydrolysis on the Performance of Electrochemically-Mediated Desalination

A recent United Nations report estimates that more than two billion people presently lack access to clean drinking water and more than four billion people lack access to proper sanitation. Furthermore, steadily rising populations, a changing climate, and growth in the agriculture, energy, and manufacturing sectors jeopardize future water security in many parts of the world. Accordingly, energy-efficient separations of salts and trace contaminates from water represent one of the most significant (and difficult) challenges facing humankind. To address this problem, we have previously reported the development of a promising approach to the separation of salts from seawater which we refer to as electrochemically-mediated desalination (EMD). EMD is an electrokinetic technique which utilizes the electric field gradient formed local to an anode during chloride oxidation to separate charged species from pure water. Despite experimental and computational study of EMD, a deep understanding of phenomena fundamental to the technique has yet to be attained. To this end, we performed time-resolved high resolution electric field gradient measurements and direct conductivity measurements during electrochemical chloride oxidation within a simple system composed of microelectrodes embedded in a straight microchannel. We were surprised by the findings of these measurements. Specifically, a large electric field gradient was measured upstream of the anode during chloride oxidation, however, a local increase in solution conductivity was measured at the same axial position along the channel length during chloride oxidation. To address these seemingly contradictory findings, the experimental system was simulated by finite element modeling. Simulation results showed that electrochemically generated chlorine undergoes rapid hydrolysis and produces substantial quantities of HOCl, H+, and Cl- near the anode. This finding corroborates the experimentally observed increase in solution conductivity near the anode during chloride oxidation. Consequently, we hypothesize that the observed electric field gradient is not indicative of local solution conductivity, but rather is related to a surface interaction between a product of chloride oxidation and the Pt microband electrode used to probe the electric field gradient. Ongoing research seeks to confirm this claim. Ultimately, we conclude that complex aqueous chlorine chemistry significantly limits the utility of chlorine generation for the formation of a local electric field gradient and seawater desalination.

Ceramic Microbial Fuel Cells Stack: power generation in standard and supercapacitive mode

In this work, a microbial fuel cell (MFC) stack containing 28 ceramic MFCs was tested in both standard and supercapacitive modes. The MFCs consisted of carbon veil anodes wrapped around the ceramic separator and air-breathing cathodes based on activated carbon catalyst pressed on a stainless steel mesh. The anodes and cathodes were connected in parallel. The electrolytes utilized had different solution conductivities ranging from 2.0 mScm−1 to 40.1 mScm−1, simulating diverse wastewaters. Polarization curves of MFCs showed a general enhancement in performance with the increase of the electrolyte solution conductivity. The maximum stationary power density was 3.2 mW (3.2 Wm−3) at 2.0 mScm−1 that increased to 10.6 mW (10.6 Wm−3) at the highest solution conductivity (40.1 mScm−1). For the first time, MFCs stack with 1 L operating volume was also tested in supercapacitive mode, where full galvanostatic discharges are presented. Also in the latter case, performance once again improved with the increase in solution conductivity. Particularly, the increase in solution conductivity decreased dramatically the ohmic resistance and therefore the time for complete discharge was elongated, with a resultant increase in power. Maximum power achieved varied between 7.6 mW (7.6 Wm−3) at 2.0 mScm−1 and 27.4 mW (27.4 Wm−3) at 40.1 mScm−1.

Activation of peroxydisulfate by gas–liquid pulsed discharge plasma to enhance the degradation of p-nitrophenol

Pulsed discharge in water and over water surfaces generates ultraviolet radiation, local high temperature, shock waves, and chemical reactive species, including hydroxyl radicals, hydrogen peroxide, and ozone. Pulsed discharge plasma (PDP) can oxidize and mineralize pollutants very efficiently, but high energy consumption restricts its application for industrial wastewater treatment. A novel method for improving the energy efficiency of wastewater treatment by PDP was proposed, in which peroxydisulfate (PDS) was added to wastewater and PDS was activated by PDP to produce more strong oxidizing radicals, including sulfate radicals and hydroxyl radicals, leading to a higher oxidation capacity for the PDP system. The experimental results show that the increase in solution conductivity slightly decreased the discharge power of the pulse discharge over the water surface. An increase in the discharge intensity improved the activation of PDS and therefore the degradation efficiency and energy efficiency of p-nitrophenol (PNP). An increase in the addition dosage of PDS greatly facilitated the degradation of PNP at a molar ratio of PDS to PNP of lower than 80:1, but the performance enhancement was no longer obvious at a dosage of more than 80:1. Under an applied voltage of 20 kV and a gas discharge gap of 2 mm, the degradation efficiency and energy efficiency of the PNP reached 90.7% and 45.0 mg kWh−1 for the plasma/PDS system, respectively, which was 34% and 18.0 mg kWh−1 higher than for the discharge plasma treatment alone. Analysis of the physical and chemical effects indicated that ozone and hydrogen peroxide were important for PNP degradation and UV irradiation and heat from the discharge plasma might be the main physical effects for the activation of PDS.

Efficient removal of Indigo Carmine dye by a separation process.

This study is aimed at developing an innovative approach for Indigo Carmine dye removal from synthetic solutions by electrodialysis, carried out using ion exchange membranes. The batch electrodialysis system was operated at various current intensities: 0.05, 0.1 and 0.15 A. The pH and conductivity of solutions were measured before and after using electrodialysis process. The colour removal efficiency (CR %) was determined by spectrographic analysis and the energy consumption (EC) was calculated. The obtained results show that the pH of treated solution increases due to the increase in solution conductivity. Moreover, the values of CR % and EC increase when increasing current intensity. The optimal value was obtained at 0.15 A (CR > 97%). The membranes were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy.

IMPROVEMENT OF POLY(METHYL METHACRYLATE) ELECTROSPUN FIBER UNIFORMITY BY ADDITION OF POLY(ESTER AMINE)

Linear and hyperbranched poly(ester amine)s (PEAs) were used as additives in electrospinning of low concentration poly( methyl methacrylate) solutions to eliminate beads and improve the fiber uniformity. With only 1 wt% PEA,no matter linear or hyperbranched,the electrospinnability was all improved,and uniform fibers without beads were obtained. Compared to linear PEA,hyperbrchched PEA has better ability in improving the fiber uniformity. The average fiber diameter decreases significantly ( from 1. 9 μm to 1. 0 μm) compared to those obtained at high concentration without PEA. The principle of the improvement in electrospinnability was investigated by measuring the solution properties ( viscosity,conductivity and surface tension),and it was attributed to the significant increase in solution conductivity. The solution viscosity and surface tension only change slightly,while solution conductivity increases greatly with the addition of 1 wt% PEA (including linear and hyperbranched). The hyperbranched PEAs have higher conductivity than the linear PEA because they have more polar end-groups resulted from the multiple branches,and therefore the hyperbranched PEAs have better performance than the linear PEA in improving the electrospinnability of low concentration PMMA solutions. The method reported in this paper could be generalized and provides a good alternative to the existing methods.

Effect of hyperbranched poly(ester amine) additive on electrospinning of low concentration poly(methyl methacrylate) solutions

AbstractElectrospinning of low concentration polymer solutions has the advantage of producing fibers with small diameters, but unfortunately beaded fibers are often observed. This article reports the use of hyperbranched poly(ester amine) (PEA) as an additive for low concentration polymer solutions to eliminate beads and improve the fiber uniformity. Electrospinning of low concentration poly(methyl methacrylate) solutions was investigated. With only 1 wt % hyperbranched PEA, the fiber uniformity was significantly improved. The principle of improvement was investigated by measuring the solution properties, and it is inferred that the improvement is attributed to the significant increase in solution conductivity. The solution viscosity and surface tension only change slightly. The versatility of this approach was demonstrated by electrospinning low concentration solutions of two other polymers: polystyrene and polyoxymethylene. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of a low-molecular-weight cross-linkable macromer on electrospinning of poly(lactide-co-glycolide) fibers

A mixture of low-molecular-weight poly(L-lactide-co-glycolide ethylene oxide fumarate) (PLGEOF) macromer and high-molecular-weight poly(lactide-co-glycolide) (PLGA) was used to produce fibers by electrospinning. PLGEOF is a biodegradable and in situ cross-linkable terpolymer made from building blocks with excellent biocompatibility. PLGA provides the required elongational viscosity to the spinning jet while the unsaturated PLGEOF macromers contribute to in situ crosslinking of fibers and attachment of bioactive functional groups. Mechanical rheometry demonstrated that PLGEOF macromers cross-link in situ by ultraviolet radiation. The addition of PLGEOF macromer to PLGA solutions had a significant effect on size and morphology of the electrospun fibers. The morphology of the electrospun fibers changed from bead- to fiber-like with increasing PLGEOF concentration. As PLGEOF was added to 12 wt% PLGA solutions, the fiber diameter first decreased with 2% PLGEOF and then increased with the addition of 5% and 10% PLGEOF. Our results demonstrate that the fiber size initially is decreased with the addition of PLGEOF due to an increase in solution conductivity and then is increased with further PLGEOF addition due to higher viscosity of the polymerizing mixture.

Determination of instantaneous corrosion rates and runoff rates of copper from naturally patinated copper during continuous rain events

Instantaneous corrosion rates of naturally patinated copper of varying age (16 months, 138 and 145 years) have been determined during continuous rain events in the laboratory with electrochemical impedance spectroscopy using a two-electrode cell. The two-electrode cell was found to yield the same information in bulk rainwater as a conventional three-electrode cell. Relatively constant corrosion rates, between 0.2 and 0.6 μm/y, were determined for samples having a two-layer structure with an inner brownish layer of cuprous oxide and an outer greenish layer of basic copper salts (138, 145 years). Samples with cuprous oxide as the dominating phase of the patina (16 months) showed higher and somewhat increasing corrosion rates during a rain event (from 0.6 to 1.2 μm/y). During a continuous rain event, corrosion rates were found to be approximately 10 (brownish patina) and 25 times (greenish patina) lower than corresponding instantaneous runoff rates. The first flush phenomena of the runoff process, with an increased concentration during first flush and a relatively constant concentration during steady state, was indirectly seen as an increase in solution conductivity during the first rain volume followed by relative constant value. The contribution of the concentration in the first flush to the total annual runoff rate was significant for panels having a greenish layer (138, 145 years) whereas it was negligible for panels having a brownish layer (16 months).

A study on cathodic protection against crevice corrosion in dilute NaCl solutions

Potential and current distributions in a cathodically protected crevice between a simulated coating and segmented mild steel electrodes were measured in dilute NaCl solutions. The distributions became more uniform with time due to an increase in solution conductivity and depletion of dissolved oxygen in the crevice. Generally, a negative shift of control potential and an increase in initial solution conductivity and crevice thickness resulted in a higher polarization level on the steel. However, if the control potential is too negative, the polarization level may be lower than that under a suitable control potential because of hydrogen evolution. On the basis of these results, a mechanism of cathodic protection against crevice corrosion in high-resistivity environments was proposed.

Photooxidation of water and isobutane in aqueous uranyl solutions

The photochemistry and photophysics of uranyl perchlorate in acidified aqueous solutions has been studied using time-resolved absorption and conductivity detection techniques in conjunction with 347 nm laser excitation. The decay in the visible absorption of the lowest electronically excited state of [UO 2(aq)] 2+ with a lifetime of 1.1 μs correlates within an increase in solution conductivity. The latter represents the photooxidation of water to yield hydronium ion and [UO 2(aq)] + along with hydroxyl radical. Quenching of the excited state by added isobutane also occurs and this leads to enhanced conductivity due to hydrogen-abstraction from the alkane by excited uranyl ion. As determined from the conductivity changes, the quantum yield for oxidation of water is 0.06 (±15%).

The role of metal cations on the corrosion behaviour of 8090-T851 alloy in a pH 2.0 solution

The influence of cations such as Cu 2+, Al 3+ and Li + on the corrosion behaviour of 8090-T851(Al-Li) alloy in a pH 2.0 HCl solution was investigated by weight loss and polarisation techniques. Weight loss experiments showed that the effect of cation is a strong function of its nature and concentration and the effect became significant only above a critical concentration. Of the cations studied, Cu 2+ ions were found to be the most aggressive corrosion activators followed by Al 3+ ions while Li + ions showed little effect. Polarisation experiments inferred that Cu 2+ ions influence the corrosion process mainly by accelerating the cathodic reaction. While a decrease in both cathodic and anodic reactions was evident in the presence of Al 3+ ions at higher concentration, Li + ions showed no remarkable affect either on cathodic or anodic reactions. Critical analyses of results of the two experiments indicated that the corrosion activation by Al 3+ ions is due to their chemical reactivity with the corroding substrate. Little enhancement in corrosion by Li + ions is attributed to the increase in solution conductivity in their presence.

Generation by electrospray of monodisperse water droplets for targeted drug delivery by inhalation

An experimental investigation was performed on the feasibility of using an electrospray to produce monodisperse droplets of water in the diameter range 2–10 μm, with the ultimate objective of employing the droplets for targeted delivery of inhaled drugs. Because of the high surface tension of water, the establishment of stable sprays required the use of a sheath flow of CO 2 to prevent breakdown in the gas surrounding the spray and its destabilizing consequences on the electrospray performance. With this expedience, stable sprays of water could be operated at flow rates ranging from 5.8 to 42.4 μl min −1, which resulted in the generation of droplets in the diameter range 5–12 μm. Droplet size was controlled primarily by varying the liquid flow rate. An increase in solution conductivity by the addition of a small amount of NaCl showed that this physical variable can also be used to control droplet size and to produce droplets with diameter smaller than 5 μm. Solutions of too large conductivity ( > 1.2 × 10 −4 Ω −1 cm −1 ) may, however, produce droplets too small for targeted drug delivery. Since the typical ratio of droplet standard deviation over mean diameter was less than 0.10, the droplets can be considered monodisperse. A prototype delivery system was also developed in which provisions were made for complete or partial neutralization of the droplet charge by corona discharge. A co-flow of air was provided to carry the discharged droplets through a delivery line and to evaluate its effects on the droplet monodispersity. It was found that the droplet size distribution broadens because of size-dependent evaporation effects. However, at typical conditions of inhalation, the effect should not compromise the system efficiency for targeted deposition.

Physiology of Melon Leaf Membrane Thermostability During Heat Conditioning

Abstract Seedling leaf segments of 2 Cucumis melo L. cultivars were heated for 15 min at 50°C to observe the influence of duration of temperature conditioning on the acclimation and deacclimation of membrane thermostability. The percentage of injury was measured by the increase in solution conductivity due to electrolyte leakage from leaf segments. Leaves from seedlings held for 5 days at 15° had a higher percentage of injury following heat stress then those held 5 days at 35°. Acclimation for 2 to 4 hr at 35° was enough to reduce the percentage of injury to leaves from 15°-grown plants. Deacclimation for 8 hr at 15° increased the percentage of injury to leaves from plants grown at 35°. Heat injury regressed as a function of mean relative leaf-blade growth rate with temperature and leaf age with temperature yielded predictive regression equations suggesting leaf age is better as a predictor of membrane thermostability than is leaf growth rate.

Leaf Cell Membrane Thermostabilities of Cucumis melo

Abstract Seedling leaf segments of 4 Cucumis melo L. cultivars were heated for 15 min at 50°C to observe the interaction of leaf age, temperature, and acclimation on membrane thermostability. Membrane injury was measured by the increase in solution conductivity due to electrolyte leakage from leaf segments. The threshold temperature for C. melo leaf membrane leakage was about 40°, and 50° was the approximate inflection temperature for 50% injury. Leaf age, growing temperature, and acclimation influenced membrane thermostabilities. Within 5-day-old leaves, heat tolerance was influenced significantly by the growing temperature during 24 hr prior to heat injury.