Removal Of Divalent Cations Research Articles

Innovative cation exchange-driven carbon migration and recovery patterns in anaerobic fermentation of waste activated sludge

Despite numerous treatments have been developed to enhance anaerobic fermentation of waste activated sludge, the innovative cation exchange (CE) approach has been rarely reported, little attempt was conducted to revealcarbon source fate. The interphase carbon balance was illustrated to clarify endogenous carbon dissolution, biotransformation,and recovery patterns. By CE-mediated divalent cation removal, almost 34.72 % of particulate carbon sources were dissolved in 2-day treatment, corresponding to soluble carbon content of 1165.58 mg C/L. Most of the originally dissolved carbon sources (58.01–66.81 %) were bio-transformed to volatile fatty acids with high bioavailability, while the further transformation to biogas was inhibited, contributing to recoverable carbon source accumulation. Overall, 21.38 % of total solid carbon sources were recovered through 8-day fermentation, the carbon extraction was implemented by solid–liquid separation with carbon loss of 14.21–22.91 %, manifesting the valid carbon recovery of 85.05–87.96 mg C/g VSS. Such CE-driven carbon recovery provided negentropy benefits in sustainable cycle economy.

Extractable latex yield from Taraxacum kok-saghyz roots is enhanced by increasing rubber particle buoyancy

Taraxacum kok-saghyz (TK) is a leading alternative rubber-producing plant that produces natural rubber (NR) latex in laticifers within its roots. Unlike the tropical rubber tree, Hevea brasiliensis, TK can be grown in temperate regions, such as the northern United States, as the basis of a domestic rubber production industry. To support such an industry, efficient, scalable rubber extraction techniques are needed. In this study, aqueous extraction was used to recover TK natural rubber latex (TNRL) from four harvests of greenhouse-produced TK roots with a new technique that improves rubber particle buoyancy in root homogenate by chelation. The new method includes harvest, cleaning, and homogenization of freshly harvested roots, followed by centrifugation, vacuum collection of latex, and purification. Treatment of homogenate with ethylenediaminetetraacetic acid (EDTA), a divalent cation chelator, allowed more than twice as much latex to be extracted from fresh homogenate. EDTA-treated rubber particles contained lower concentrations of divalent cations than untreated ones in fresh homogenate and homogenate stored for two weeks. Long term (three months) storage of root homogenate similarly yielded more latex than fresh homogenate and had low divalent cation rubber particle concentrations, indicating that heavy cations had slowly leached from the particles into the aqueous medium during storage. Rubber particle size was larger in this treatment suggestive of rubber particle agglomeration but this was prevented and reversed by EDTA. Removal of divalent cations via chelation increased particle packing density of particles in concentrated latex and appeared to increase the gel content of dried latex samples. Molecular characterization of dried samples of purified TNRL established that the rubber was of the high molecular weight needed for product manufacturing.

A two-step green liquid-liquid extraction strategy for selective lithium recovery and application to seawater

Efficiently harvesting lithium from seawater remains a challenge due to the extremely dilute concentration of lithium ions (Li+) and the existence of many foreign metal ions that are far more abundant. Here, a hydrophobic deep eutectic solvent (HDES)-based two-step liquid-liquid extraction (LLE) strategy is developed for the first time that realizes the separation of dilute Li+ (<1 mg/L) from solutions with a high concentration of sodium, potassium, magnesium and calcium ions. This strategy contains the removal of divalent cations and selective recovery of Li+, which minimizes the influence of coexisting metal ions. In the first LLE step, the unwanted divalent cations are removed with a negligible loss of Li+ by the bis(2-ethylhexyl)phosphate/kerosene (DEHPA/KERO) system. Then, the DEHPA/HDES system can selectively extract Li+ from monovalent cations. All solvents used are readily available and low cost with methyltrioctylammonium chloride and decanoic acid at a 1:2 mol ratio (N8881Cl/2DecA) as the main extractant. Extraction equilibrium is reached within 10 s. The single extraction efficiency of Li+ is 66.4%, and the separation coefficient of lithium and sodium (βLi/Na) reaches 11.6 at the optimized extraction conditions. Finally, the proposed two-step LLE strategy is applied to the simulated seawater. The extraction performance of N8881Cl/2DecA-DEHPA was not significantly weakened after being reused ten times.

Removal of divalent cations and oxyanions by keratin-derived sorbents: Influence of process parameters and mechanistic studies

Keratin has become a promising adsorbing material for the removal of heavy metals from polluted water due to its environmentally benign nature, unique chemical structure, and binding ability. We developed keratin biopolymers (KBP-I, KBP-IV, KBP-V) using chicken feathers, and assessed their adsorption performance against metal-containing synthetic wastewater at varying temperatures, contact times, and pH. Initially, a multi-metal synthetic wastewater (MMSW) containing cations (Cd2+, Co2+, Ni2+) and oxyanions (CrVI, AsIII, VV) was incubated with each KBP under different sets of conditions. Temperature results exhibited that KBP-I, KBP-IV and KBP-V showed higher metals adsorption at 30 °C and 45 °C, respectively. However, the adsorption equilibrium was achieved for selective metals within 1 h of incubation time for all KBPs. For pH, no significant difference was observed in adsorption in MMSW due to buffering of pH by KBPs. To minimize buffering, KBP-IV and KBP-V were tested further for single-metal synthetic wastewater at two different pHs i.e. 5.5 and 8.5. KBP-IV and KBP-V were selected due to their buffering capacities and high adsorption abilities for oxyanions (pH 5.5) and divalent cations (pH 8.5), respectively indicating that chemical modifications changed and enhanced the functional groups of the keratin. X-ray Photoelectron Spectroscopy analysis was performed to demonstrate the adsorption mechanism (complexation/chelation, electrostatic attraction, or chemical reduction) for the removal of divalent cations and oxyanions by KBPs from MMSW. Furthermore, KBPs exhibited adsorption behavior for Ni2+ (qm = 2.2 mg g−1), Cd2+ (qm = 2.4 mg g−1), and CrVI (qm = 2.8 mg g−1) best described by Langmuir model with the coefficient of determination (R2) values >0.95 while AsIII (KF = 6.4 L/g) was fitted well to the Freundlich model with R2 value >0.98. Based on these findings, we anticipate that keratin adsorbents have the potential to employ at a large scale for water remediation.

Positively Charged Poly(Piperazinamide) Nanofiltration Membranes for the Fast Removal of Metal Ions

AbstractPositively charged nanofiltration (NF) membranes with high perm‐selectivity are highly desired to remove divalent cations such as Ca2+ and Mg2+ ions to ensure the safety of domestic and industrial water supply. In this work, a poly(piperazinamide) NF membrane with a positively charged surface is fabricated via the surfactant‐assembly regulated interfacial polymerization (SARIP) of piperazine (PIP) and 1,3,5‐trimesoyl chloride (TMC). The surfactant assembly can accelerate PIP monomer into the hexane to react with TMC monomer, thus reducing the difference in the trans‐interface diffusion of PIP and the diffusion of TMC in hexane, forming an interfacial polymerization with a stoichiometric characteristic. By tuning the concentration ratio of PIP and TMC, a positively charged poly(piperazinamide) NF membrane will be achieved. At the same time, utilizing the superior hydrophilicity of bacterial cellulose nanofibers nanofilm, a crumpled poly(piperazinamide) active layer is successfully constructed, resulting in a permeating flux up to 22 L m−2 h−1 bar−1 and simultaneously with a MgCl2 rejection &gt;96%. The performance of this positively charged poly(piperazinamide) NF membrane is superior to most other positive NF membranes for the removal of divalent cations so far.

Comparison of ion removal from waste fermentation effluent by nanofiltration, electrodialysis and ion exchange for a subsequent sulfuric acid recovery

Nutrient recovery from wastewater in the form of acids/bases by electrodialysis with bipolar membranes or diffusion dialysis facilitates the current demand for a green economy and circular production. However, bipolar membranes are sensitive to scaling, mainly by calcium and magnesium salts, as well as to biofouling caused by microbial growth and linked aspects. This work aimed to reduce divalent cations to a value below 10 ppm and DOC content of a residual liquid waste stream after microbial fermentation and before a bipolar electrodialysis/diffusion dialysis step for nutrient and acid/base recovery. In this context, three pretreatment technologies were analyzed: nanofiltration, electrodialysis with monovalent cation-exchange membranes, and ion-exchange resins. Nanofiltration and electrodialysis with monovalent cation-exchange membrane were demonstrated to be suitable pretreatments with 92–96 % Mg2+ and Ca2+ removal and 86–94 % DOC removal. Ion-exchange resins had excellent divalent cation removal but no DOC removal, therefore requiring additional treatment to remove organic substances and prevent membranes’ biofouling. Electrodialysis with monovalent cation-exchange membranes was preferable over nanofiltration due to the 1.6-fold concentration factor for sulfate ions. In contrast, nanofiltration had lower energy consumption and higher stability in divalent cation rejection. Results obtained in this study are valuable for selecting an appropriate treatment for resource recovery and water reclamation from industrial wastewater and for biotechnological downstream processes.

Phospholipid recovery from sweet whey by combination of electrodialytic processes and understanding of specific mechanisms involved

Electrodialysis with bipolar membrane (EDBM) combined with a subsequent 4–6 fold dilution was demonstrated to allow high phospholipid (PL) recovery and defatting rate. However, the economic and environmental drawbacks of such dilution limit the process application in the food industry. To overcome them, original combinations of treatment with EDBM, applicable in the food industry (demineralization by conventional electrodialysis (ED) and diafiltration), were tested for the first time and compared with the EDBM + dilution process. The most promising combination was the EDBM + ED process. Indeed, demineralization by ED after EDBM allowed to reach the highest divalent cation removal (70.2 % versus 2.3 and 39.7 % respectively for dilution and diafiltration) and defatting rate (76.6 % versus 54.2 and 23.0 % respectively for dilution and diafiltration). Furthermore, this combination allowed to concentrate phosphatidylethanolamine by 15 X compared to its content in initial sweet whey and to reach the highest PL yield (25.9 g/100 L of sweet whey versus 13.3 and 8.99 g/100 L respectively for dilution and diafiltration). These high performances were associated with different phenomena occurring during the treatments performed after EDBM and leading to specific impacts on ionic strength, mineral content and composition. From those phenomena, it was possible to understand the key role of the removal of divalent cations in the formation of lipoprotein complexes, highlighting that it was not only due to the reduction in pH and ionic strength. Consequently, EDBM combined with ED appears to be an attractive industrial process, as it combined the ecofriendly advantages of electrodialytic technics, while limiting water consumption, avoiding the production of large volumes of effluents and the use of chemical agents.

Electrochemically activated layered manganese oxide for selective removal of calcium and magnesium ions in hybrid capacitive deionization

Selective removal of ions is a promising new venture with tremendous upsides for resource recovery and sustainability. Traditional methods such as membrane filtration, electrodialysis or ion-exchange resins are either non-selective or too expensive. To fulfil the gap in technology, a hybrid capacitive deionization (HCDI) device utilizing an electrochemically activated layered MnO2 cathode was proposed. The cathode was infused with structural water and can effectively screen strong electrostatic repulsions from Mn atoms within the MnO2 layers, enabling preferential intercalation of divalent cations Ca2+ and Mg2+. Comparative ion removal experiments showed a high selectivity of Ca2+ over K+ (SD/M = 18.0) and Mg2+ over K+ (SD/M = 17.5) at a discharge current of 10 mA g−1 in equimolar binary salt solutions. Preferential divalent cation removal was even maintained in solutions where the ionic strength of monovalent cations was equivalent to divalent cations. In-situ Raman spectroscopy furthered showed that the intercalation of cations resulted in the replacement of water molecules which consequently altered the intensities of v1 and v2 bands of MnO2. The extent of water replacement was characterized by a change in the ratio of v2to v1 intensity and higher divalent cation selectivities were observed to follow smaller changes in intensity ratio.

Performance of a Hybrid ED–NF Membrane System for Water Recovery Improvement via NOM Fouling Control

Natural organic matter (NOM) complicates water treatment and causes formation of disinfection byproducts (DBPs). NOM is removed well by nanofiltration (NF) but causes extensive membrane fouling, especially in the presence of divalent cations. This research investigated a hybrid electrodialysis-nanofiltration (ED–NF) system to treat freshwaters containing hardness and NOM. ED removes most ions but little to no NOM, and the ED diluate is, then, treated with NF to remove NOM with reduced fouling. Subsequently, some or all of the ED concentrate can be mixed with the NF permeate to increase water recovery, limit NOM concentration (and thereby reduce DBPs), and control the ion content. Compared to NF alone, ED–NF increases product water yield. NF fouling was reduced by the removal of divalent cations in ED. Spectroscopic and resonant scattering measurements of fouled membranes near the calcium K-edge reveal a significant contribution to NF fouling by calcium bridging between carboxyl groups in NOM and on the membrane surface. This novel ED–NF system allows several control “knobs” to increase water recovery and reduce DBP formation potential by adjusting ED water recovery, ED diluate (and concentrate) ionic composition, and the fraction of concentrate remixed with NF permeate to form the product water.

Concurrent removal of hardness and fluoride in water by monopolar electrocoagulation

Water treatment based on electrocoagulation (EC) is attractive since required chemicals and colloids are produced in-situ. However, optimisation of EC operation parameters is necessary to enhance its efficiency. We optimised EC cell parameters by the response surface method (RSM). The optimal removal efficiencies of hardness (63%) and fluoride (97%) were achieved at 1.98 kW h/m3. With the removal of divalent cations, some anionic species concurrently remove via an energetically feasible route to adjust the charge balance. When simulated water is used (450 mg/L TDS, 580 mg/L CaCO3, 10 mg/L fluorides and pH 6.50), 83% hardness and 99% fluoride are removed with 0.69 kW h/m2 energy consumption. The chemical species in the solution matrix, particularly SO42, significantly affect the hardness and fluoride removal efficiencies. The contaminated EC sludge resulted from feed water is characterised by spectroscopic methods to probe hardness and fluoride removal mechanisms. In the presence of Mg2+, F- interacts with Al-sludge sites forming≡MgF−OH. When Ca2+ and F- are present, both ≡CaF−OH and ≡CaF are formed. In Ca2+, Mg2+ and F- treated Al-sludge dominates CaF−OH and ≡CaF over ≡MgF−OH.

Molecular mechanisms of heavy metals resistance of Stenotrophomonas rhizophila JC1 by whole genome sequencing.

In this study, a higher metal ions-resistant bacterium, Stenotrophomonas rhizophila JC1 was isolated from contaminated soil in Jinchang city, Gansu Province, China. The Pb2+ (120mg/L) and Cu2+ (80mg/L) removal rate of the strain reached at 76.9% and 83.4%, respectively. The genome comprises 4268161bp in a circular chromosome with 67.52% G + C content and encodes 3719 proteins. The genome function analysis showed czc operon, mer operon, cop operon, arsenic detoxification system in strain JC1 were contributed to the removal of heavy metals. Three efflux systems (i.e., RND, CDF, and P-ATPase) on strain JC1 genome could trigger the removal of divalent cations from cells. cAMP pathway and ABC transporter pathway might be involved in the transport and metabolism of heavy metals. The homology analysis exhibited multi-gene families such as ABC transporters, heavy metal-associated domain, copper resistance protein, carbohydrate-binding domain were distributed across 410 orthologous groups. In addition, heavy metal-responsive transcription regulator, thioredoxin, heavy metal transport/detoxification protein, divalent-cation resistance protein CutA, arsenate reductase also played important roles in the heavy metals adsorption and detoxification process. The complete genome data provides insight into the exploration of the interaction mechanism between microorganisms and heavy metals.

Six fruit and vegetable peel beads for the simultaneous removal of heavy metals by biosorption

ABSTRACT In this study, a comparison between the biosorption performance of six fruit and vegetable peels, namely kiwifruit (KP), apple, banana, cucumber, orange and potato immobilized on sodium alginate beads has been made. Inductively coupled plasma coupled with mass spectroscopy was used for measuring the concentration of metal ions in solution before and after biosorption. A range of kinetic models were also applied to the biosorption batch data. The results showed that biosorption percentage of the ions were different on the various beads. For example, the decreasing order of biosorption by one KP bead at equilibrium was Cd > Cu > Hg > Ni > Pb > Cr > As, with approximately 92%, 84%, 80%, 75%, 67%, 34%, and 17% simultaneous removal of ions, respectively. The fastest biosorption was seen with Cd and Pb, as both reached equilibrium by 24 h. Equilibrium time of all other ions occurred by 48 h. While all beads in their unmodified form were suitable for the removal of divalent cations, KP bead showed significantly higher removal of the anion hexavalent Cr. Biosorption of Cd, Hg and Ni was limited by both pseudo-first order and pseudo-second order reaction rates. For Cr and Cu, the reaction was controlled by film diffusion and pseudo-first order rates. At a higher solution concentration, the preference of ions biosorbed as well as their percentage removed changed. Overall, the results indicated that KP beads show promise as a cost-effective method for removing toxic ions by biosorption, especially hexavalent chromium from drinking water.

A Porous Material Made from Curdlan by EDTAD Functionalization Shows High Adsorption Capacity on Removal of Cu2+ and Zn2+ from Water

A linear bacterial β-1,3-glucan, curdlan, was functionalized by ethylenediamine tetraacetic dianhydride (EDTAD) to form a porous insoluble material (Curd-E) in this study. Various technics, including FTIR, solid state 13C NMR, XRD, TGA, and SEM, were combined to determine the chemical and microscopic structure of the resultant. It's suggested that EDTAD esterified and cross-linked C6-hydroxyl groups of curdlan molecules to form the porous Curd-E. Moreover, Curd-E showed high adsorption capacity on Cu2+ (224.97 mg/g, pH 6.0) and Zn2+ (255.64 mg/g, pH 4.5) in comparison with the biomaterial and mineral based adsorbents. Data also indicated that the site affinity of Curd-E for cations was in the order of chelation > coordination/complexation > ion exchange. Besides, 2-site Langmuir and 2-step Freundlich isotherms gave the best interpretation for Cu2+ adsorption and Zn2+ adsorption, respectively. Since the adsorption capacity maintained 91.8% ± 0.8% after five cycles of adsorption/desorption, it is believed that Curd-E is suitable for removal of divalent cations in wastewater as a novel candidate.

Capacitive Deionization of Divalent Cations for Water Softening Using Functionalized Carbon Electrodes.

Water softening is a relatively untapped area of research in capacitive deionization (CDI). In this work, we demonstrate how an asymmetric combination of oxidized and aminated carbon can be used for selective removal of divalent cations for water softening. We first show how higher electrosorption performances can be achieved in single-salt experiments involving NaCl, KCl, MgCl2, and CaCl2 before proceeding to multi-salt experiments using different combinations of the four salts. The salt combinations are chosen to investigate one of the three factors: (1) ionic mass, (2) ionic charge, or (3) concentration. We show how divalent selectivity can be achieved due to high local electrostatic attraction between negatively charged oxygen moieties and divalent cations. Additionally, an ion-exchange process between the oxidized carbon surface and cations can result in lower pH values, which prevent the precipitation of scale-forming ions.

Uphill transport in improved reverse electrodialysis by removal of divalent cations in the dilute solution: A Nernst-Planck based study

Reverse electrodialysis is a relatively new technology for non-carbon based and renewable energy harvesting from river and sea water. Because of the existing salinity gradients between those two types of water, selective transport of counter-ions from the sea to the river water through an ion-exchange membrane generates a voltage drop across it, which can drive electricity through an external electric device. The decrease in power density caused by the presence of divalent ions in the solutions because of the uphill transport of these ions against their concentration gradient can be mitigated by treating the river water in order to remove such type of ions. In this work, the effects of the fraction of salt with divalent cation in the dilute solution on the energy harvesting process in a permeable cation-exchange membrane system with well-stirred bathing solutions under reverse electrodialysis conditions, are theoretically investigate on the basis of the Nernst-Planck transport equations. Interesting results, which are related to the uphill transport of the cations against their concentration gradient, emerge from the asymmetric distribution of the cationic concentrations in the inner boundaries of the membrane because of the ionic partitioning in permeable membranes.

Ultrathin Nanofiltration Membrane from Confined Polymerization within the Nanowire Network for High Efficiency Divalent Cation Removal.

Membranes with high permeance and high rejection for di- and multivalent cation removal are highly desired for efficient brackish water and industrial water treatment. In this work, we report a facile strategy for constructing ultrathin nanofiltration (NF) membranes by in situ cross-linking of amine which is confined in a network film. The network made of single-walled carbon nanotubes (SWCNTs) serves as a framework for poly(ethylene imine) (PEI) to attach and stay, facilitating the formation of a polyamine (PA) layer with high quality and controlled thickness. Benefiting from the ultrathin thickness of the SWCNT network (∼31 nm), an active layer (∼34 nm thick) comes with a high permeance of 27 L m-2 h-1 bar-1 along with a high rejection of 97% to MgCl2, 2-5 times higher than the NF membranes with the same high rejection for MgCl2 reported so far. In addition, the SWCNT-interpenetrated PA structure endows the ultrathin NF membrane with good operational stability. This work demonstrates the capability to control the position, thickness, and even quality of the PA layer by using a confined framework and provides a feasible strategy for the fabrication of highly permeable ultrathin NF membranes with a reinforced active layer.

Removal of divalent ions from viscous polymer-flooding produced water and seawater via electrodialysis

The presence of multivalent ions in polymer-flooding produced water (PFPW) hampers its recycling mainly because i) they increase the risk of scaling and reservoir souring (sulfate), ii) they interfere with the viscosifying effect of the fresh polyelectrolyte. It is desirable to achieve the removal of most multivalent ions without completely desalting the stream. With the adequate process conditions, electrodialysis could help to achieve this goal, so this work focused on evaluating the removal of divalent ions from synthetic PFPW through varying operational conditions. The experimental work consisted on batch experiments run in an electrodialysis-stack composed of strong Neosepta ion-exchange membranes. Synthetic PFPW solutions containing a mixture of monovalent and divalent ions were desalted at four different current densities, and three different temperatures. Additionally, the effect of the dissolved polymer on the removal was assessed by performing half of the experiments on polymer-containing solutions and half of them on solutions without it. Our results demonstrate that it is possible to achieve preferential removal of divalent cations (calcium and magnesium) through electrodialysis, especially when employing low current densities (24 A/m2) and high temperature (40 °C). The removal of sulfate, a divalent anion, is also accelerated in these conditions. The presence of polyelectrolyte did not significantly affect the removal rate of divalent ions. Thus, it is concluded that meticulous application of ED to minimize concentrations of divalent ions in PFPW is a potential effective way for water and polymer recycling in enhanced oil recovery situations, as an alternative to the use of other non-selective desalination technologies.

Mechanism of Selective Ion Removal in Membrane Capacitive Deionization for Water Softening.

Capacitive deionization (CDI) is an emerging technology capable of selective removal of ions from water. While many studies have reported chemically tailored electrodes for selective ion removal, the selective removal of divalent cations (i.e., hardness) over monovalent cations can simply be achieved using membrane CDI (MCDI) equipped with ion exchange membranes (IEMs). In this study, we use both experimental and modeling approaches to systematically investigate the selective removal of Ca2+ over Na+. Specifically, the impacts of current density, hydraulic retention time, and feed composition on the selectivity of Ca2+ over Na+ were investigated. The results from our study suggest a universal correlation between the ratio of molar fluxes and the ratio of spacer channel ion concentrations, regardless of operating conditions and feed composition. Our analysis also reveals inherent and universal trade-off relationships between selectivity and the Ca2+ removal rate and between selectivity and the degree of Ca2+ removal. This fundamental understanding of the mechanism of selective ion removal in MCDI can also be applied to flow-electrode CDI processes that employ IEMs.

CatSper channels are regulated by protein kinase A

Mammalian sperm must undergo capacitation as a preparation for entering into hyperactivated motility, undergoing the acrosome reaction, and acquiring fertilizing ability. One of the initial capacitation events occurs when sperm encounter an elevated HCO3- concentration. This anion activates the atypical adenylyl cyclase Adcy10, increases intracellular cAMP, and stimulates protein kinase A (PKA). Moreover, an increase in intracellular Ca2+ concentration ([Ca2+] i ) is essential for sperm capacitation. Although a cross-talk between cAMP-dependent pathways and Ca2+ clearly plays an essential role in sperm capacitation, the connection between these signaling events is incompletely understood. Here, using three different approaches, we found that CatSper, the main sperm Ca2+ channel characterized to date, is up-regulated by a cAMP-dependent activation of PKA in mouse sperm. First, HCO3- and the PKA-activating permeable compound 8-Br-cAMP induced an increase in [Ca2+] i , which was blocked by the PKA peptide inhibitor PKI, and H89, another PKA inhibitor, also abrogated the 8-Br-cAMP response. Second, HCO3- increased the membrane depolarization induced upon divalent cation removal by promoting influx of monovalent cations through CatSper channels, which was inhibited by PKI, H89, and the CatSper blocker HC-056456. Third, electrophysiological patch clamp, whole-cell recordings revealed that CatSper activity is up-regulated by HCO3- and by direct cAMP injection through the patch-clamp pipette. The activation by HCO3- and cAMP was also blocked by PKI, H89, Rp-cAMPS, and HC-056456, and electrophysiological recordings in sperm from CatSper-KO mice confirmed CatSper's role in these activation modes. Our results strongly suggest that PKA-dependent phosphorylation regulates [Ca2+] i homeostasis by activating CatSper channel complexes.

Selective removal of divalent cations by polyelectrolyte multilayer nanofiltration membrane: Role of polyelectrolyte charge, ion size, and ionic strength

We fabricated polyelectrolyte multilayer (PEM) nanofiltration (NF) membranes using a layer-by-layer (LbL) method for effective removal of scale-forming divalent cations (Mg2+, Ca2+, Sr2+, and Ba2+) from feedwaters with different salinities. Two polymers with opposite charges, polycation (poly(diallyldimethylammonium chloride), PDADMAC) and polyanion (poly(sodium 4-styrenesulfonate), PSS), were sequentially deposited on a commercial polyamide NF membrane to form a PEM. Compared to pristine and PSS-terminated membranes, PDADMAC-terminated membranes demonstrated much higher rejection of divalent cations and selectivity for sodium transport over divalent cations (Na+/X2+) due to a combination of both Donnan- and size-exclusion effects. A PDADMAC-terminated membrane with 5.5 bilayers exhibited 97% rejection of Mg2+ with selectivity (Na+/Mg2+) greater than 30. We attribute the order of cation rejection (Mg2+ > Ca2+ > Sr2+ > Ba2+) to the ionic size, which governs both the hydration radius and hydration energy of the cations. The ionic strength (salinity) of the feed solution had a significant influence on both water flux and cation rejection of PEM membranes. In feed solutions with high ionic strength, abundant NaCl salt screened the charge of the polyelectrolytes and led to swelling of the multilayers, resulting in decreased selectivity (Na+/X2+) and increased water permeability. The fabricated PEM membranes can be potentially applied to the pretreatment of mild-salinity brackish waters to reduce membrane scaling in the main desalination stage.