Activity coefficient of hydrochloric acid in HCl/MgCl2 mixtures and HCl/NaCl/MgCl2 mixtures from 5 to 45°C

Magnesium, the dominant bivalent cation in natural seawater, exerts a substantial influence on the patterns of ion interactions in this saline medium. Mean activity coefficients of hydrochloric acid in mixtures of this acid with magnesium chloride at four ionic strengths, namelyI=0.1, 0.3809, 0.6729, and 0.8720 mole-kg^–1, were obtained from emf measurements of cells without liquid junction at nine temperatures from 5 to 45°C. The three highest ionic strengths correspond to seawater of salinities 20, 35, and 45, respectively. In addition, mixtures of HCl, NaCl, and MgCl₂ were studied atI=0.6729, the molal ratio of NaCl to MgCl₂ being maintained at 7.202 as in natural seawater. The Harned coefficients _{1 2} were found to decrease slowly with increase in temperature. The trace activity coefficient of HCl in solutions of MgCl₂ as well as in NaCl MgCl₂ mixtures was found to be nearly identical with that measured earlier in synthetic seawater of the same ionic strength but containing NaCl, MgCl₂, KCl, and CaCl₂.     

The Alternating-Direction Schemes and Numerical Analysis for the Three-dimensional Seawater Intrusion Simulation

Both numerical simulation and theoretical analysis of seawater intrusion in coastal regions are of great theoretical importance in environmental sciences. The mathematical model can be described as a coupled system of three dimensional nonlinear partial differential equations with initial-boundary value problems. In this paper, according to the actual conditions of molecular and three-dimensional characteristic of the problem, we construct the characteristic finite element alternating-direction schemes which can be divided into three continuous one-dimensional problems. By making use of tensor product algorithm, and priori estimation theory and techniques, the optimal order estimates in H1 norm are derived for the error in the approximate solution.     

Liquid–solid extraction of butyltin compounds from marine samples

Environmental damage due to organotins (TBT, DBT, MBT) released from antifouling paints is well documented. The concentrations of these compounds in seawater are usually at ppt (parts per 10¹²) levels. Many analytical techniques, including chromatographic and spectrophotometric ones, have been presented in the literature to detect organotins at these low levels. Liquid-liquid extraction is commonly employed as a concentration method. However, it presents some disadvantages during sampling campaigns and requires large volumes of toxic and expensive solvents. In this paper we propose an analytical method based on a liquid-solid extraction procedure that can be easily performed in the field and is characterized by good recoveries and high enrichment factors. Three different solid phases (Carbopack, LC 8 and LC 18) and five different eluting agents (methanol/tropolone, methanol, dichloromethane, hexane and diethyl ether) were evaluated. Carbopack and LC 18 were the most suitable solid phases. Inorganic tin was not retained on these solid phases and a separation of TBT from DBT and MBT was achieved, performing the elution in two steps with methanol and methanol/tropolone. In this way GF AA was suitably employed to obtain butyltin speciation data.     

Numerical analysis of a finite volume scheme for a seawater intrusion model with cross‐diffusion in an unconfined aquifer

We consider a degenerate parabolic system modeling the flow of fresh and saltwater in a porous medium in the context of seawater intrusion. We propose and analyze a finite volume scheme based on two‐point flux approximation with upwind mobilities. The scheme preserves at the discrete level the main features of the continuous problem, namely the nonnegativity of the solutions, the decay of the energy and the control of the entropy and its dissipation. Based on these nonlinear stability results, we show that the scheme converges toward a weak solution to the problem. Numerical results are provided to illustrate the behavior of the model and of the scheme.     

Identification of New Photodegradation Byproducts of the Antifouling Agent Irgarol in Seawater Samples

Abstract

A photodegradation study for Irgarol was carried out in order to investigate several products of degradation formed in different environmental matrices and under different conditions. Deionized water, groundwater and seawater samples, spiked at 30–100 μg/L with Irgarol, were irradiated using a xenon are lamp and/or sunlight. Aliquots of the spiked water samples were taken at different times of irradiation and compounds were isolated from the water samples by means of solid-phase extraction (SPE) using either C₁₈ or PLRP-s cartridges. Separation and detection of the compounds was accomplished by several analytical methodologies such as liquid chromatography-diode array detection (LC-DAD), liquid chromatography-electrospray ionization/mass spectrometry (LC-ESI/MS) and gas chromatography-mass spectrometry (GC-MS). Four new byproducts, with molecular weights of 167, 197, 207 and 213, were identified in this photodegradation study. When the photolysis was carried out with xenon lamp, half-lives of Irgarol were 103.8, 125.4 and 107.5 minutes in deionized water, groundwater and seawater, respectively. In seawater samples, a 98% of degradation was observed for Irgarol, after 217 hours of solar irradiation, being the main byproduct formed that corresponding to M_w = 213. On the other hand, the use of two different sensitizers -(TiO₂/H₂O₂), (FeCI₃/H₂O₂)- was also evaluated in deionized water samples containing Irgarol. These experiments were carried out in order to evaluate the use of these two sensitizers for decontamination of polluted waters.     

Improvement of the analysis of the biochemical oxygen demand (BOD) of Mediterranean seawater by seeding control

Biochemical oxygen demand (BOD) is a useful parameter for assessing the biodegradability of dissolved organic matter in water. At the same time, this parameter is used to evaluate the efficiency with which certain processes remove biodegradable natural organic matter (NOM). However, the values of BOD in seawater are very low (around 2 mg O₂ L⁻¹) and the methods used for its analysis are poorly developed. The increasing attention given to seawater desalination in the Mediterranean environment, and related phenomena such as reverse osmosis membrane biofouling, have stimulated interest in seawater BOD close to the Spanish coast. In this study the BOD analysis protocol was refined by introduction of a new step in which a critical quantity of autochthonous microorganisms, measured as adenosine triphosphate, is added. For the samples analyzed, this improvement allowed us to obtain reliable and replicable BOD measurements, standardized with solutions of glucose-glutamic acid and acetate. After 7 days of analysis duration, more than 80% of ultimate BOD is achieved, which in the case of easily biodegradable compounds represents nearly a 60% of the theoretical oxygen demand. BOD₇ obtained from the Mediterranean Sea found to be 2.0 ± 0.3 mg O₂ L⁻¹ but this value decreased with seawater storage time due to the rapid consumption of labile compounds. No significant differences were found between two samples points located on the Spanish coast, since their organic matter content was similar. Finally, the determination of seawater BOD without the use of inoculum may lead to an underestimation of BOD.     

The ammonia-ammonium equilibrium in seawater at temperatures between 5 and 25°C

The stability constantK ₁of the equilibrium NH ₃ +H⁺NH ₄ ⁺ was determined by potentiometric titration in synthetic seawaters of 5 to 40 (per mille) salinity and sodium chloride solutions between 0.2 and 0.7M ionic strength at temperatures of 5, 15 and 25°C. Moreover,K ₁was determined in sulfate-free seawater of 35 salinity and 25°C. The dependence of logK ₁on salinity (or ionic strength) and temperature can be reasonably well described by linear relations. TheK ₁obtained for sulfate-free seawater agrees very well with earlier experimental results and theoretical predictions. From the measuredK ₁and literature data on the equilibrium NH ₃ (atm)NH ₃ (aq., NaCl), the atmospheric concentration of ammonia at equilibrium with seawater was estimated.     

New Process for the Sulfonation of Algal/PEI Biosorbent for Enhancing Sr(II) Removal from Aqueous Solutions—Application to Seawater

Sulfonic resins are highly efficient cation exchangers widely used for metal removal from aqueous solutions. Herein, a new sulfonation process is designed for the sulfonation of algal/PEI composite (A*PEI, by reaction with 2-propylene-1-sulfonic acid and hydroxylamine-O-sulfonic acid). The new sulfonated functionalized sorbent (SA*PEI) is successfully tested in batch systems for strontium recovery first in synthetic solutions before investigating with multi-component solutions and final validation with seawater samples. The chemical modification of A*PEI triples the sorption capacity for Sr(II) at pH 4 with a removal rate of up to 7% and 58% for A*PEI and SA*PEI, respectively (with SD: 0.67 g L⁻¹). FTIR shows the strong contribution of sulfonate groups for the functionalized sorbent (in addition to amine and carboxylic groups from the support). The sorption is endothermic (increase in sorption with temperature). The sulfonation improves thermal stability and slightly enhances textural properties. This may explain the fast kinetics (which are controlled by the pseudo-first-order rate equation). The sulfonated sorbent shows a remarkable preference for Sr(II) over competitor mono-, di-, and tri-valent metal cations. Sorption properties are weakly influenced by the excess of NaCl; this can explain the outstanding sorption properties in the treatment of seawater samples. In addition, the sulfonated sorbent shows excellent stability at recycling (for at least 5 cycles), with a loss in capacity of around 2.2%. These preliminary results show the remarkable efficiency of the sorbent for Sr(II) removal from complex solutions (this could open perspectives for the treatment of contaminated seawater samples).     

反渗透淡化水调质稳定性及健康性实验研究

反渗透淡化水因矿物质含量低、稳定性差,需进行调质以改善水质。通过研究调质后水体碳酸钙沉淀势CCPP、Ryznar稳定指数R.S.I.、拉森指数LR、氧化还原电位ORP等指标与调质剂(NaHCO₃、CaCl₂)投加量间的关系,为反渗透淡化水调质剂投加剂量提供依据。研究表明：NaHCO₃为50 ~90 mg·L^-1时,随着投加量的增加,R.S.I.降低（趋近于6.0~7.0）,水质稳定性改善,NaHCO₃为90~110 mg·L^-1时,随着投加量的增加,R.S.I.升高（偏离了6.0~7.0）,水质稳定性变差;随着NaHCO₃投加量的增加,CCPP降低,水质由沉淀倾向变为腐蚀倾向,当NaHCO₃投加量达到70 mg·L^-1时,CCPP趋于稳定,水质稳定;随着NaHCO₃投加量的继续增加,LR降低,水质稳定性改善,而ORP降低,当NaHCO₃投加量达到90 mg·L^-1时,ORP趋于平缓。建议NaHCO₃投加量为90 mg·L^-1。随着Ca²⁺投加量的增加,R.S.I.、CCPP降低,水体稳定性变差;CaCl₂投加量增加,LR增加,水质稳定性变差,ORP增大,水质健康性变差。建议CaCl₂投加量为20 mg·L^-1。