Decreasing Salt Concentration Research Articles

Impact of dilution on stochastically driven methanogenic microbial communities of hypersaline anoxic sediments.

Sediments underlying the solar salterns of S'Avall are anoxic hypersaline ecosystems dominated by anaerobic prokaryotes, and with the especial relevance of putative methanogenic archaea. Slurries from salt-saturated sediments, diluted in a gradient of salinity and incubated for > 4 years revealed that salt concentration was the major selection force that deterministically structured microbial communities. The dominant archaea in the original communities showed a decrease in alpha diversity with dilution accompanied by the increase of bacterial alpha diversity, being highest at 5% salts. Correspondingly, methanogens decreased and in turn sulfate reducers increased with decreasing salt concentrations. Methanogens especially dominated at 25%. Different concentrations of litter of Posidonia oceanica seagrass added as a carbon substrate, did not promote any clear relevant effect. However, the addition of ampicillin as selection pressure exerted important effects on the assemblage probably due to the removal of competitors or enhancers. The amended antibiotic enhanced methanogenesis in the concentrations ≤ 15% of salts, whereas it was depleted at salinities ≥ 20% revealing key roles of ampicillin-sensitive bacteria.

Modeling the combined resistance to microwave treatments and salt conditions of Escherichia coli and Staphylococcus aureus.

In the present study, the efficiency of the combined effect of microwave irradiation treatments together with salt concentration was assessed against Escherichia coli and Staphylococcus aureus. Microbial survival has been modeled through a one-step Weibull equation considering the non-isothermal profiles during the heating treatments. Three sodium chloride concentrations 0.5%, 3.5%, and 8.5% (w/v) treated under three microwave power levels (450, 600, and 800 W) were studied. Predictive models were validated using the determination coefficient (R2), root mean squared error and the acceptable prediction zone with external data obtained from ultra high temperature milk. The results obtained suggested that increasing microwave power levels and decreasing salt concentrations led to a higher microbial inactivation, being the δ values (time for achieving a first decimal reduction) for E coli of 19.57 s at 800 W and 0.5% NaCl. In contrast, experimental data of S aureus showed a higher variability since it presented more resistance to the microwave treatments. The results obtained and generated models can be used as decision-making tools to set specific guidelines on microwave treatments for assuring food safety.

Comparing Theoretical Salt Concentration Profiles in a Polymer Electrolyte with Experimental Measurements using Operando Raman Spectroscopy

Concentrated solution theory has furthered our understanding of ion transport in electrolytes. This theory can be used to predict salt concentration profiles under an applied current if the transport properties of the electrolyte (conductivity (κ), restricted diffusion coefficient (D), and the cation transference number with respect to the solvent velocity ()), and the thermodynamic factor (T f ) are known. In this work, we provide the first study comparing the predicted salt concentration profiles with measurements based on operando Raman spectroscopy. Concentration polarization is asymmetrical; the increase in salt concentration near the positive electrode is a factor of two greater than the decrease in salt concentration near the negative electrode. We find qualitative agreement between theory and experiment. Further work is needed to resolve the quantitative differences.

Marangoni flow induced in a waterbody by the impact of a raindrop

In this study, the Particle Image Velocimetry (PIV) technique is employed to investigate the transient flow that arises when a freshwater drop impinges onto the surface of a water body. Our measurements show that in addition to the impact of the drop itself, surfactant and salt concentration play a crucial role in determining the resulting flow on and near the surface. The latter contributions arise from surface tension gradients that arise from merging the drop’s water with the water on the surface, which reduces the concentrations of salt and surfactant. As the surface tension of water falls with decreasing salt concentration, the decrease in salt concentration leads to a Marangoni flow, which moves radially outward from the impact area. On the other hand, the reduction in surfactant concentration causes a reverse Marangoni flow, which flows towards the impact point as the surface tension of water increases with decreasing surfactant concentration. The overall direction and strength of the flow depend on the Weber number and the surfactant and salt Marangoni numbers. Experiments indicate that when the surfactant Marangoni number dominates, the radial flow due to the drop’s impact quickly reverses direction giving rise to a jet-like flow from the impact point in the downward direction. In contrast, when the salt Marangoni flow dominates, the radial flow persists for a longer duration, and the diameter of the region free of PIV particles on the surface is larger than for the freshwater case. The height of the water column increases with increasing Weber and surfactant Marangoni numbers but decreases with salt Marangoni number. The strength and direction of the surface flow are crucial for enhancing the mixing of dissolved gases in the near-surface layer into the water body.

A Universal Descriptor in Determining H2 Evolution Activity for Dilute Aqueous Zn Batteries

AbstractLarge‐scale energy storage with aqueous Zn batteries (AZBs) have bright future, but their practical application is impeded by H2 evolution reaction (HER), which results in poor stability of Zn–metal anodes. Here, using linear sweep voltammetry in dilute salt aqueous electrolytes, it is discovered that as the salt concentration decreases, HER is gradually suppressed, which is contrary to prior beliefs. Combining calculations and experiments, it is demonstrated that HER derives predominantly from the sum of Zn2+‐solvated water rather than the average amount of water in the Zn2+‐solvation structural unit or free water without interaction with Zn2+, which answers the puzzle from above. This result, which differs fundamentally from the previous understandings, sheds new light on the mysterious role of water chemistry in controlling HER and contributes to a more rational design of advanced electrolytes for AZBs.

Promoting ion and heat transfer of solid polymer electrolytes by tuning polymer chain length and salt concentration

ABSTRACT The heat and mass performance of solid polymer electrolytes (SPEs) directly affects their application in solid-state batteries (SSBs). However, high crystallinity and charged clusters hinder the transport of Li+ in SPEs, resulting in low ion diffusivities and thermal conductivities. Therefore, understanding the effects of SPE structure on ion transport and heat conduction is critical for SPE designing. In this work, the ion diffusivities and thermal conductivities of SPEs containing polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt with different PEO chain lengths and salt concentrations are studied and the structural properties are analyzed to determine the mechanisms of ion transport and heat conduction. The results show that the crystallinity and charged clusters decrease in SPEs with short-chain PEO and low salt concentration, thereby improving ion transfer and heat conduction. Moreover, phonon spectra shift to a higher-frequency domain when salt concentration increases, which induces a decrease in thermal conductivity. Decreased salt concentration and chain length increased conductivity by 350% and 176%, respectively, and thermal conductivity by 122% and 140%, respectively. These findings, which indicate that SPEs with short-chain PEO and low salt concentration have better ion and heat transfer, provide valuable insight into the design of PEO-LiTFSI electrolytes.

Effects of instantaneous changes in temperature, light, and salinity on the dynamics of dissolved organic carbon release by Sargassum thunbergii

Although macroalgae are regarded as the emerging fourth category of “blue carbon”, few studies are available on the dynamics of dissolved organic carbon (DOC) release. Sargassum thunbergii is a typical intertidal macroalgae; and tidal action usually triggers instantaneous changes in temperature, light and salinity. Therefore, we investigated the mechanism of short-term changes in temperature, light and salinity on DOC release by S. thunbergii. As well as these factors coupled with desiccation, the combined effect of DOC release was revealed. The results showed the DOC release rate of S. thunbergii was from 0.028 to 0.037 mg C g −1(FW) h−1 under different photosynthetically active radiation (PAR, 0–1500 μmol photons m−2 s−1). The DOC release rate of S. thunbergii was from 0.008 to 0.208 mg C g −1(FW) h−1 under different salinity (5–40). The DOC release rate of S. thunbergii was from 0.031 to 0.034 mg C g −1(FW) h−1 under different temperature (10–30 °C). Either the increase in intracellular organic matter concentration due to increased photosynthesis (change in PAR and temperature, active), cell dehydration due to dry-out process (passive) or the decrease in extracellular salt concentration (passive) would lead to an increase in the difference in osmotic pressure and promote DOC release.

Mechanism of Chromium Separation and Concentration from Tannery Wastewater by Membrane Methods

The article specifies conditions for a nanofiltration process employing a diafiltration method with a constant volume diafiltration (NF-CVD) for exhausted chromium tannery wastewater treatment and describes a mechanism of the examined process carried out for model wastewater. The authors prove that a decrease in salt concentration in the NF-CVD process is an important factor that enables effective concentration of chromium. Based on the proposed chromium separation and concentration mechanisms, it was found that this effect may be achieved by (1) limiting the formation of an ionic adsorption-polarization layer and (2) reducing the increase in the osmotic pressure caused by a change in the separation properties of the membrane. The article shows that in the analyzed system a higher amount of the solvent introduced at the diafiltration stage and a lower process pressure that ensures a reduction in salt retention translate to a high level of salt removal. In regenerates, after the NF-CVD processes in which at least the same volume of a washing diluent as the volume of the retentate after the pre-concentration step was used, salt concentration below 10 g L-1 and chromium concentration about three times higher than in the case of the feed solution were obtained. Therefore, the proposed solution implements the circular economy strategy in the tannery.

Electrokinetic energy conversion of high pressure-driven flow with pressure-viscosity effect at high zeta potential

In this study, the electrokinetic energy conversion efficiency is investigated theoretically in high pressure-driven flow with the pressure-viscosity effect. Calculations of the electrokinetic flow in a straight nanochannel are based on the Poisson-Boltzmann equation and modified fluid momentum equation. Once the viscosity of fluid is dependent on the pressure, the strongly non-linear governing equation should be solved simultaneously due to the unknown fluid viscosity. Thus, the domain perturbation method is used to solve the distributions of flow velocity and pressure. Based on obtained velocity and pressure, the maximum conversion efficiency is calculated by thermodynamic analysis. Results show the maximum efficiency increases with the decrease of salt concentration and the peak efficiency can be obtained at sufficiently low salt concentration. For a given salt concentration, the maximum efficiency decreases monotonously with the increase of pressure-viscosity coefficient. Besides, the maximum energy conversion efficiency of ignoring the pressure-viscosity effect is larger than that of considering the pressure-viscosity effect.

Multiscale characterization reveals oligomerization dependent phase separation of primer-independent RNA polymerase nsp8 from SARS-CoV-2

RNA replication and transcription machinery is an important drug target for fighting against coronavirus. Non-structure protein nsp8 was proposed harboring primase activity. However, the RNA primer synthesis mechanism of nsp8 is still largely unknown. Here, we purified dimer and tetramer forms of SARS-CoV-2 nsp8. Combined with dynamic light scattering, small-angle neutron scattering and thermo-stability analysis, we found that both dimer and tetramer become loosened and destabilized with decreasing salt concentration, and the dimer form is more stable than the tetramer form. Further investigation showed that nsp8 dimer and tetramer can undergo phase separation but exhibit different phase separation behaviors. Nsp8 dimer can form liquid-like droplets in the buffer with a low concentration of NaCl; phase separation of nsp8 tetramer depends on the assistance of RNA. Our findings on different phase separation behaviors of nsp8 dimer and tetramer may provide insight into the functional studies of nsp8 in coronavirus.

Salt transport in a large agro-urban river basin: Modeling, controlling factors, and management strategies

Salinity poses a severe threat to urban and agricultural areas. Excess salt can accumulate in soils and groundwater, thereby impacting crop growth and productivity. In this study we quantify the influence of driving forces on salt transport in Colorado's South Platte River (drainage area of 62,937 km2) and investigate possible mediation strategies to reduce salinity levels in both urban and agricultural river reaches. A river salt transport model was developed that utilizes a water allocation model and accounts for multiple inputs and outputs of salt within the river network, including tributaries, wastewater treatment plants, road salt, return flows from rainfall and irrigation, and groundwater discharge. The flow and salt models are run on a monthly basis between 2002 and 2006 and tested against stream discharge and in-stream salinity concentration at multiple gage sites. A sensitivity analysis was implemented to determine the controlling factors behind salt transport in the river system by river reach and by season (spring, summer, fall, winter). SA results were used to guide selection of management practices (n = 256) that can control salinity in both urban and agricultural areas. For urban areas, during spring/summer and fall/winter, the most efficient management practice is to decrease WWTP effluent salinity concentration by 35% and to decrease applied road salt by 35%, respectively, resulting in decreases of 10–30% decrease in river salt concentration. For agricultural areas, the only management practices that achieve an in-river salinity concentration (1,000 mg/L) that prevents crop yield decrease during irrigation are aggressive practices that focus on WWTP effluent concentration, return flow salinity, and urban road salt. Results points to the extreme challenge of managing salinity in the South Platte River Basin and other similar basins and the aggressive urban approaches that must be implemented to sustain irrigation practices in the downstream regions of the basin.

Specific ion effects on soil aggregate stability and rainfall splash erosion

Soil interparticle forces can pose important effects on soil aggregate stability and rainfall splash erosion. Meanwhile, these interparticle forces are strongly influenced by specific ion effects. In this study, we applied three monovalent cations (Li+, Na+, and K+) with various concentrations to investigate the influence of specific ion effects on aggregate stability and splash erosion via pipette and rainfall simulation methods. The specific ion effects on soil interparticle forces were quantitatively evaluated by introducing cationic non-classical polarization. The results showed that aggregate stability and splash erosion had strong ion specificity. Aggregate breaking strength and splash erosion rate at the same salt concentration followed the sequence as Li+ > Na+ > K+. With decreasing salt concentration, the difference in aggregate breaking strength or splash erosion rate between different cation systems increased initially (1–10–2 mol L–1) and later was nearly invariable (10–2–10–4 mol L–1). The experimental results were well quantitatively explained by soil interparticle forces considering cationic non-classical polarization. Furthermore, both aggregate breaking strength and splash erosion rate of three cations revealed a strong positive linear relation with net force subjected to cationic non-classical polarization (R2 = 0.81, R2 = 0.81). These results demonstrated that different non-classical polarization of cations resulted in different soil interparticle forces, and thus led to differences in aggregate stability and splash erosion. Our study provides valuable information to deeply understand the mechanisms of rainfall splash erosion.

Practical evaluation of four classification levels of Soil Taxonomy, Hungarian classification and WRB in terms of biomass production in a salt-affected alluvial plot

In a salt-affected alluvial plot, increased biomass is associated with increasing elevation and decreasing salt concentration. All four levels of three classification systems, the Soil Taxonomy (ST), the Hungarian classification (HU) and the WRB were evaluated in a 100 m regular grid of 85 profiles for their applicability for biomass estimation (using 10-year average NDVI as proxy) and their correlation with ground elevation. NDVI values reflecting soil formation chronology (from the least to the most developed soils) were found on the first (least detailed) level of the classification systems. By analyzing the aspects of practical applicability, mainly at the detailed levels 3 and 4, HU performed the best in terms of class separability, WRB showed the most homogeneous classes, HU provided the closest correlation with elevation; while ST operated with the lowest number of classes, and, consequently, had a lower level of homogeneity and weaker correlation with elevation. Both HU and WRB performed well in most aspects, but the latter showed greater homogeneity. WRB had twice as many classes as HU and four times as many compared to ST; thus, their homogeneity increased accordingly.The implementation of a soil classification without profound tests might result in counterproductive classes in terms of class separability, homogeneity of classes, correlation with environmental parameters, and parsimony of classes.

Concentration and pH effect on the electronic circular dichroism and anisotropy spectra of aqueous solutions of glyceric acid calcium salt.

Electronic circular dichroism (ECD) and anisotropy spectra carry information on differential absorption of left- and right-circularly polarized light (LCPL and RCPL) by optically active compounds. This makes them powerful tools for the rapid determination of enantiomeric excesses (ee) in asymmetric synthetic and pharmaceutical chemistry, as well as for predicting the ee inducible by ultraviolet (UV) CPL. The ECD response of a chiral molecule is, however, critically dependent on the properties of the surrounding medium. Here, we report on the first ECD/anisotropy spectra of aqueous solutions of the calcium salt dihydrate of glyceric acid. A systematic study of the effect of the salt concentration and pH on the chiroptical response revealed significant changes and the appearance of a new ECD band of opposite sign. Based on the literature, this can be rationalized by the increase in the relative proportion of free glyceric acid/glycerate to Ca2+ complexes with glycerate with decreasing salt concentration or pH. Glyceric acid can be readily produced under astrophysical conditions. The anisotropy spectra of the solution containing prevalently the free form of this dihydroxy carboxylic acid resemble the ones of previously investigated aliphatic chain hydroxycarboxylic acids and proteinogenic amino acids. This indicates possible common handedness of stellar CPL-induced asymmetry in the potential comonomers of primitive proto-peptides.

Investigation on stress corrosion cracking of API 5L X65 steel in CO2 corrosion medium

This investigation studied the simultaneous effect of temperature (in the range of 30–70 °C) and NaCl concentration (in the range of 1–20 wt%) on stress corrosion cracking behavior of API 5L X65 steel in CO2 corrosion medium. The results of slow strain rate tensile test and surface characterization revealed that SCC susceptibility increased by an increase in temperature and a decrease in NaCl salt concentration. Furthermore, potentiodynamic polarization technique was employed in case of condition with the highest SCC susceptibility and illustrated that contribution of anodic dissolution and hydrogen involvement was the main SCC mechanism.

Changes in Salinity and Toxicity of Soil Contaminated with De-icing Agents during Growing Season

De-icing agents (ice and snow control materials) are applied to prevent ice and snow deposits on the roads in winter period. The extensive use of de-icing agents in countries with cold climate creates problems for the environment. In this study, the dynamics of de-icing salt concentrations in sod-podzolic soil was revealed in laboratory and field experiments. Twelve de-icing agents of different chemical groups (chlorides, acetates and formates) were studied. Under laboratory conditions, application of high doses of chloride reagents led to an increase of salt concentration in soil up to a level of slightly saline soils. Contaminated soils had salt levels high enough to be toxic to plants and soil microorganisms. However, under field conditions, soil salinity eventually decreased due to salt washout by atmospheric precipitation. By the end of the growing season, salt concentration corresponded to a background level. The decrease in salt concentration was accompanied by a decrease in soil toxicity. Acetate and formate de-icing agents demonstrated the least environmental effect. Our results suggest that magnesium chloride was the least harmful among the de-icers of chloride group while the most commonly used road de-icing salt sodium chloride was the most persistent and toxic to terrestrial plants and soil microbiota.

Glutamate signaling from a single sensory neuron mediates experience-dependent bidirectional behavior in Caenorhabditis elegans.

Orientation and navigation behaviors of animals are modulated by past experiences. However, little is known about the mechanisms by which sensory inputs are translated into multi-directional orientation behaviors in an experience-dependent manner. Here, we report a neural mechanism for bidirectional salt-concentration chemotaxis of Caenorhabditis elegans. The salt-sensing neuron ASE right (ASER) is always activated by a decrease of salt concentration, while the directionality of reorientation behaviors is inverted depending on previous salt experiences. AIB, the interneuron postsynaptic to ASER, and neurons farther downstream of AIB show experience-dependent bidirectional responses, which are correlated with reorientation behaviors. These bidirectional behavioral and neural responses are mediated by glutamate released from ASER. Glutamate acts through the excitatory glutamate receptor GLR-1 and inhibitory glutamate receptor AVR-14, both acting in AIB. These findings suggest that experience-dependent reorientation behaviors are generated by altering the magnitude of excitatory and inhibitory postsynaptic signals from a sensory neuron to interneurons.

Analysis of purification of charged giant vesicles in a buffer using their size distribution.

We have analyzed the purification of charged giant unilamellar vesicles (GUVs) prepared in a buffer containing various concentrations of salt using their size distribution. The membranes of GUVs were synthesized by a mixture of dioleoylphosphocholine (DOPC) and dioleoylphosphatidylglycerol (DOPG) lipids. The DOPG mole fractions (X) in the membranes of GUVs were 0.10, 0.25, 0.40, 0.55, 0.70, 0.90 in a physiological buffer containing 162 mM salt. In addition, for a fixed value of X the concentrations of salt (C) in the buffer were 12, 62, 112, 162, 212, 312, 362 mM. The size distribution histograms of experimentally investigated unpurified and purified GUVs were fitted with the lognormal distribution and obtained the multiplication factor [Formula: see text] for mean ([Formula: see text]) and [Formula: see text] for standard deviation ([Formula: see text]) of the lognormal distribution. The key parameters [Formula: see text] and [Formula: see text] were responsible for changing the average size and size distribution of unpurified GUVs to purified ones. The theoretically fitting equation of experimentally obtained X- and C-dependent values of [Formula: see text] and [Formula: see text] provided the calibration equation for estimating the average size of purified GUVs theoretically for any values of X and C. The estimated size of purified GUVs increased with the increase in electrostatic effect (i.e., increase in vesicle surface charge density or decrease in salt concentration in buffer). The estimated size of purified GUVs varied with X and C, which supported the previous report qualitatively. These investigations might be helpful in the field of cell/chemical biology for understanding the process of purification of vesicles/cells investigated by any other techniques.

Concentrated brines in aqueous methanolic solutions in supercritical conditions: Effect of concentration and composition from molecular dynamics simulations

We have performed constant pressure constant temperature classical molecular dynamics simulations to study the effects of salt concentration and solvent composition of sodium chloride solutions at supercritical conditions. Structural properties of sodium chloride in water-methanol binary mixtures in supercritical conditions were determined in terms of potentials of mean force, radial distribution functions and hydrogen bonding. Potentials of mean force of Na+-Cl− ion-pairs in the binary mixtures showed the presence of contact ion pairs and solvent shared ion pairs and the depth of both the configurations increased with methanol content in the mixture and decreasing salt concentration. In a solution of low salt concentration, all the ions were found to be present as one single cluster whereas in higher salt concentration, smaller clusters of variable sizes were formed. The cluster size distribution shows strong dependence on salt concentration and less pronounced effect on the solvent composition.

Physicochemical Characteristics and Microbial Communities in Gochujang, a Traditional Korean Fermented Hot Pepper Paste.

Gochujang is a Korean fermented hot pepper paste beneficial to human health by providing various nutrients. In this study, its physicochemical characteristics were identified, and its microbial communities were analyzed by high-throughput sequencing. The interrelationship between physicochemical characteristics and microbial composition was investigated to reveal the properties of gochujang before and after fermentation. After fermentation, all samples showed decreased salt concentration, pH, and reducing sugar content, while the acidity and amino-type nitrogen increased. The water content, salt concentration, amino-type nitrogen, and reducing sugar differed according to the batches of samples. Bacillus, Aerosakkonema, and Enterococcus were identified as the predominant bacterial genera. Furthermore, Aerosakkonema was the most abundant genus before fermentation; however, it was replaced by Bacillus as it decreased after fermentation. For the fungi, Aspergillus dominated before fermentation, whereas Zygosaccharomyces and Millerozyma dominated after fermentation. The high level of amino-type nitrogen in gochujang was related to the relative abundance of B. haynesii/B. licheniformis before fermentation. Additionally, the high abundance of Z. rouxii after fermentation was related to the flavor of gochujang. This comprehensive analysis of the microbial community associated with the physicochemical properties of gochujang could help in understanding the factors affecting the quality of the product.