Search Results (103)

Blackwater rivers are enriched in humic acids and impoverished in nutrients, sometimes discharging into oceans. Brazil has a coastal zone of about 8700 km, with several blackwater rivers discharging into the Atlantic Ocean, in addition to the Rio Negro of the northern Amazon basin, which is the largest (about 1700 km long) and best-known tropical backwater river. On the other hand, only a few attempts have been made to deal with their hydrochemical composition and how it is related to the hydrochemistry of different water bodies nearby. This paper focuses on a sector of the Atlantic Ocean shore occurring in São Paulo State, enclosing two important Ecological Reserves, i.e., the Restinga State Park of Bertioga and the State Park of Serra do Mar–São Sebastião Nucleus, located at Bertioga and São Sebastião cities, respectively. Physicochemical parameters such as pH and electrical conductivity, as well as the composition of major constituents like sodium, potassium, calcium, magnesium, bicarbonate, chloride, sulfate, nitrate, etc., have been evaluated in two blackwater rivers and one blackwater stream to compare their relative inputs into the Atlantic Ocean. Traditional hydrogeochemical diagrams such as the Piper, Schoeller, Gibbs, van Wirdum, and Wilcox graphs were utilized for investigating the major features of the blackwater’s composition, revealing in some cases that they suffer an accentuated influence of the constituents occurring in the Atlantic Ocean waters, due to backward currents (coastal upwelling or tidal currents). Another highlight of this paper is the measurement of an enhanced concentration of dissolved iron in one blackwater sample analyzed, reaching a value of 1.9 mg/L. Such a finding has also been often reported in the literature for blackwater rivers and streams, as humic and fulvic acids are used to bind Fe³⁺, keeping it in solution. Nowadays, iron in solution has been considered a very important element acting as a natural fertilizer of the coastal ocean because it is an essential nutrient to marine phytoplankton. Full article

Oral delivery of hydrophobic compounds remains challenging due to their poor aqueous solubility and the potential toxicity associated with conventional surfactant-based emulsions. To address these issues, we present a surfactant-free encapsulation strategy using electrosprayed alginate hydrogel beads for the stable and controlled delivery of hydrophobic oils. Hydrophobic compounds were dispersed in high-viscosity alginate solutions without surfactants via ultrasonication, forming kinetically stable oil-in-water dispersions. These mixtures were electrosprayed into calcium chloride baths, yielding monodisperse hydrogel beads. Higher alginate concentrations improved droplet sphericity and suppressed phase separation by enhancing matrix viscosity. The resulting beads exhibited stimuli-responsive degradation and controlled release behavior in response to physiological ionic strength. Dense alginate networks delayed ion exchange and prolonged structural integrity, while elevated external ionic conditions triggered rapid disintegration and immediate payload release. This simple and scalable system offers a biocompatible platform for the oral delivery of lipophilic active compounds without the need for surfactants or complex fabrication steps. Full article

Hydrogel films receive significant attention among researchers because they combine increased stimuli responsiveness and faster responses to the already excellent properties of their component materials. However, their preparation is complex and requires that many difficulties are overcome. The present work presents a new study regarding the preparation of pure and nanoparticle-loaded alginate-based films by spin-coating. Two-microliter solutions of sodium alginate and calcium chloride with different concentrations were deposited on a glass substrate and subjected to rapid rotations of between 100 and 1000 RPM. Film formation can be achieved by optimizing the ratio between the viscosity of the solutions, depending on their concentrations and the rotation speed. When these conditions are in the right range, a homogeneous film is obtained, showing good adherence to the substrate and uniform thickness. Films containing silver nanoparticles were prepared, exploiting the reaction between sodium borohydride and silver nitrate. The two reagents were added to the sodium alginate and calcium nitrate solution, respectively. Their concentration is the driving force for the formation of a uniform film: particles of about 50 nm that are well-dispersed throughout the film are obtained using AgNO₃ at 4 mM and NaBH₄ at 2 or 0.2 mM; meanwhile, at higher concentrations, one can also obtain the precipitation of inorganic crystals. Full article

Recycling plastics waste into concrete represents one of the possible approaches for its valorization, offering both economic and environmental benefits. Although numerous studies have explored the mechanical properties of concrete with plastics waste, its durability performance remains largely unexplored. In this context, this study aims to assess the electrochemical behavior of rebars embedded in reinforced concrete modified by partially replacing natural aggregates with recycled plastics, comparing their behavior to that of conventional concrete. The corrosion of reinforcing steel bars was evaluated by wet and dry cycles (w/d) in calcium chloride solutions, monitoring corrosion potential and potentiostatic polarization resistance, and recording electrochemical impedance spectroscopy (EIS) and polarization curves. In addition, the chloride diffusion tendency and the mechanical performances were assessed in unreinforced samples. The findings indicate that in environments with lower chloride concentrations, concrete with plastic granules provides good protection against rebar corrosion. Although the mechanical results of the studied mixes confirmed that incorporating plastic granules as aggregates in the concrete matrix causes a reduction in compressive strength, as known in the literature, the modified concrete also exhibits improved post-cracking behavior, resulting in enhanced ductility and fracture toughness. Full article

Leveraging the sensitivity of long-period fiber grating (LPFG) to changes in the environmental refractive index, an LPFG-based seawater concentration monitoring sensor is proposed. Considering the highly saltine and alkali characteristics of the sensor’s operating environment, the proposed sensor is packaged by basalt fiber-reinforced polymer (BFRP), and the sensor’s sensitivities were studied by sodium chloride and calcium chloride solution concentration experiments and one real-time sodium chloride solution concentration monitoring experiment. The test results show the wavelength of LPFG, a 3 dB bandwidth and a peak loss of LPFG’s spectrogram change with changes in the concentration of sodium chloride or calcium chloride solutions, but only the wavelength has a good linear relationship with the change in solution concentration, and the sensing coefficient is −0.160 nm/% in the sodium chloride solution and −0.225 nm/% in the calcium chloride solution. The real-time monitoring test further verified the sensor’s sensing performance, with an absolute measurement error of less than 1.8%. The BFRP packaged sensor has good corrosion resistance and a simple structure, and it has a certain application value in the monitoring of salinity in the marine environment and coastal soil. Full article

Water injection is widely recognized as one of the most important operational approaches for enhanced oil recovery in oilfields. However, this process faces significant challenges due to the formation of sulfate and carbonate mineral scales caused by high salinity in both injected water and formation water. To address this issue, the use of mineral scale inhibitors has emerged as a valuable solution. In this study, we evaluated the performance of seven machine learning algorithms (Gradient Boosting Machine; k-Nearest Neighbors; Decision Tree; Random Forest; Linear Regression; Neural Network; and Gaussian Process Regression) to predict inhibitor efficiency. The models were trained on a comprehensive dataset of 661 samples (432 for training; 229 for testing) with 66 features including temperature; concentrations of various ions (sodium; calcium, magnesium; barium; strontium; chloride; sulfate; bicarbonate; carbonate, etc.), and inhibitor dosage levels (DTPMP, PPCA, PBTC, EDTMP, BTCA, etc.). The results showed that GPR achieved the highest prediction accuracy with R² = 0.9608, followed by Neural Network (R² = 0.9230) and Random Forest (R² = 0.8822). These findings demonstrate the potential of machine learning approaches for optimizing scale inhibitor performance in oilfield operations Full article

Extreme precipitation events are one of the common hazards in eastern Texas, generating a large amount of storm water. Water running off urban areas may carry non-point source (NPS) pollution to natural resources such as rivers and lakes. Urbanization exacerbates this issue by increasing impervious surfaces that prevent natural infiltration. This study evaluated the efficacy of rain gardens, a nature-based best management practice (BMP), in mitigating NPS pollution from urban stormwater runoff. Stormwater samples were collected at inflow and outflow points of three rain gardens and analyzed for various water quality parameters, including pH, electrical conductivity, fluoride, chloride, nitrate, nitrite, phosphate, sulfate, salts, carbonates, bicarbonates, sodium, potassium, aluminum, boron, calcium, mercury, arsenic, copper iron lead magnesium, manganese and zinc. Removal efficiencies for nitrate, phosphate, and zinc exceeded 70%, while heavy metals such as lead achieved reductions up to 80%. However, certain parameters, such as calcium, magnesium and conductivity, showed increased outflow concentrations, attributed to substrate leaching. These increases resulted in a higher outflow pH. Overall, the pollutants were removed with an efficiency exceeding 50%. These findings demonstrate that rain gardens are an effective and sustainable solution for managing urban stormwater runoff and mitigating NPS pollution in eastern Texas, particularly in regions vulnerable to extreme precipitation events. Full article

The microencapsulation of bioactive compounds from rapeseed oil using sodium alginate, in the presence and absence of an ultrasonic (US) field, is reported. A Box–Behnken experimental design is used to investigate the influence of process parameters on the microencapsulation yield; then, the response surface methodology is applied, to find their values ensuring its optimum yield. The operating parameters investigated are the ratio of sodium alginate to rapeseed oil, the microencapsulation time and the concentration of the calcium chloride solution. The US bath was used at its nominal power, and the microencapsulation temperature was kept at 20 °C, with a thermostat, for all experiments. A detailed study on the comparison of the two microencapsulation techniques (in the presence and absence of the US field) was carried out. Good results were obtained in the presence of the US field for optimal conditions, when the microencapsulation yield was 90.25 ± 0.02%, higher than the microencapsulation process performed in the absence of the US field, 87.11 ± 0.02%. The results also showed that the use of the US field (optimal conditions) led to an increase in encapsulation efficiency, total phenolic content and antioxidant capacity (76.56 ± 0.02%, 324.85 ± 0.01 mg GAE/g and 57.05 ± 0.12 mg/mL). The physicochemical description of microcapsules was performed using modern characterization methods. These results indicate that by increasing the microencapsulation yield of bioactive compounds through sonication, the process aims to achieve a uniform size distribution of microcapsules. Full article

Brain injury and cerebral inflammation are frequent complications following cardiopulmonary bypass (CPB) resulting in neurocognitive dysfunction, encephalopathy, or stroke. We compared cerebral inflammation induced by del Nido and histidine-tryptophan-α-ketoglutarate (HTK) cardioplegia in a porcine model. Pigs underwent 90 min cardiac arrest using HTK (n = 9) or Jonosteril^®-based del Nido cardioplegia (n = 9), followed by a 120 min reperfusion. Brain biopsies were collected and analyzed for the mRNA and protein expression of hypoxia-inducible factor-1α (HIF-1α) and cytokines. HTK induced a decrease in blood sodium, chloride, and calcium concentration (cross-clamp aorta: p_sodium < 0.01, p_chloride < 0.01, p_calcium < 0.01; 90 min ischemia: p_sodium < 0.01, p_chloride < 0.01, p_calcium = 0.03) compared to the more stable physiological electrolyte concentrations during del Nido cardioplegia. Hyponatremia and hypochloremia persisted after a 120 min reperfusion in the HTK group (p_sodium < 0.01, p_chloride = 0.04). Compared to del Nido, a higher mRNA expression of the proinflammatory cytokine IL-1β was detected in the frontal cortex (HTK: ∆Ct 6.5 ± 1.7; del Nido: ∆Ct 8.8 ± 1.5, p = 0.01) and the brain stem (HTK: ∆Ct 5.7 ± 1.5; del Nido: ∆Ct 7.5 ± 1.6, p = 0.02) of the HTK group. In conclusion, we showed comparability of HTK and del Nido for cerebral inflammation except for IL-1β expression. Based on our study results, we conclude that del Nido cardioplegia is a suitable and safe alternative to the conventional HTK solution. Full article

In this preliminary study, the long-term effects of calcium chloride crosslinking concentration on viability of 16HBE14o- human bronchial epithelial cells embedded in alginate-extracellular matrix (ECM) or alginate–methylcellulose–ECM hydrogels have been investigated. There is currently a limited understanding regarding the effects of crosslinking solution concentration on lung epithelial cells embedded in hydrogel. Furthermore, the effects of calcium chloride concentration in crosslinking solutions on other cell types have not been reported regarding whether the addition of viscosity and stiffness tuning agents such as methylcellulose will alter the responses of cells to changes in calcium chloride concentration in crosslinking solutions. While there were no significant effects of calcium chloride concentration on cell viability in alginate–ECM hydrogels, there is a decrease in cell viability in alginate–methylcellulose–ECM hydrogels crosslinked with 300 mM calcium chloride crosslinking solution. These findings have implications in the maintenance of 16HBE14o- 3D cultures with respect to the gelation of alginate with high concentrations of ionic crosslinking solution. Full article

Municipal solid waste incineration (MSWI) fly ash, containing substantial amounts of calcium (Ca), chloride (Cl), and other valuable elements, offers promising potential as a raw material for carbon capture, utilization (CCU), and alkali production. Despite numerous approaches being explored to enhance calcium ion leaching from fly ash, the combined effects of salt and leaching conditions on ion extraction have not been thoroughly investigated. This study provides a comprehensive examination of various leaching conditions, including primary leaching—optimal for efficiency—secondary leaching, which achieved the highest leaching rate, and reverse secondary leaching, focusing on their impact on calcium extraction efficiency. Considering optimal leaching efficiency and resource utilization, this study identifies the most favorable industrial conditions as a 15 min leaching time, a stirring speed of 200 rpm, a temperature of 25 °C, and a 1:10 liquid-to-solid ratio (L/S ratio). The application of a 6% NaCl solution in salt-assisted leaching elevated the calcium ion concentration from 4101.5 mg/L to 4662.6 mg/L, indicating a substantial improvement in leaching performance. Additionally, in carbonate-assisted and ultrasound-assisted leaching, the introduction of CO₂ further increased calcium extraction amounts, but it did not enhance efficiency, while ultrasonic intervention had minimal impact. This research investigates enhanced efficiencies through multiple optimized and assisted leaching conditions, advancing MSWI fly ash utilization in carbon capture applications while paving new pathways for sustainable industrial practices that could revolutionize waste management and support global environmental objectives. Full article

The tanning industry is among the most environmentally harmful activities globally due to the pollution of lakes and rivers from its effluents. Hexavalent chromium, a metal in tannery effluents, has adverse effects on human health and ecosystems, requiring the development of removal techniques. This study assessed the efficacy of organobentonite/alginate hydrogel beads in removing Cr(VI) from a fixed-bed adsorption column system. The synthesized organobentonite (OBent) was encapsulated in alginate, utilizing calcium chloride as a crosslinking agent to generate hydrogel beads. The effects of the volumetric flow rate, bed height, and initial Cr(VI) concentration on a synthetic sample were analyzed in the experiments in fixed-bed columns. The fractal-like modified Thomas model showed a good fit to the experimental data for the asymmetric breakthrough curves, confirmed by the high R² correlation coefficients and low χ² values. The application of organoclay/alginate hydrogel beads was confirmed with a wastewater sample from an artisanal tannery industry in Belén (Nariño, Colombia), in which a Cr(VI) removal greater than 99.81% was achieved. Organobentonite/alginate hydrogels offer the additional advantage of being composed of a biodegradable polymer (sodium alginate) and a natural material (bentonite-type clay), resulting in promising adsorbents for the removal of Cr(VI) from aqueous solutions in both synthetic and real water samples. Full article

The corrosion of steel rebar embedded in concrete under marine conditions is a major global concern. Therefore, it needs a proper corrosion mitigation method. Various types of corrosion inhibitors are used to mitigate the corrosion of steel rebar in chloride-contaminated concrete; however, selecting the appropriate inhibitor and determining its optimal concentration remains a concern. Therefore, in the present study, three types of inhibitors—calcium nitrite (CN: Ca(NO₂)₂), N,N′-dimethyl ethanol amine (DMEA: (CH₃)₂NCH₂CH₂OH), and L-arginine (LA: C₆H₁₄N₄O₂) in three different concentrations, i.e., 0.3, 0.6 and 1.2 M—were compared with a control (without inhibitor, i.e., blank) sample to determine the optimum concentration of the inhibitor for corrosion resistance performance evaluation of reinforcement bars immersed in 0.3 M NaCl-contaminated concrete pore (NCCP) solution for various durations. The corrosion resistance properties were assessed using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) with immersion duration, and potentiodynamic polarization (PDP) after 168 h of exposure. The results showed that the CN inhibitor performed exceptionally well (corrosion inhibition efficiency greater than 97%) in terms of corrosion resistance. However, due to its hazardous nature and its ban in the U.S. and European Union, CN cannot be used in construction. In comparison, while DMEA showed some effectiveness, LA performed better and is also eco-friendly. The corrosion resistance efficiency of samples containing 0.6 M LA remains above 97% even after 168 h of immersion in the NCCP solution. This efficiency is consistent throughout the entire immersion period, from 1 h to 168 h. Therefore, it is recommended that LA be used as a corrosion inhibitor for steel reinforcement bars instead of CN, particularly in chloride-contaminated concrete, as it is both effective and safer than CN. Full article

In response to rising CO₂ emissions in the cement industry and the growing demand for durable offshore engineering materials, calcium sulphoaluminate (CSA) cement concrete, known for its lower carbon footprint and enhanced corrosion resistance compared to Ordinary Portland Cement (OPC), is increasingly important. However, the chloride transport behavior of CSA concrete in both laboratory and marine environments remains underexplored and controversial. Accordingly, the chloride ion transport behaviors and mechanisms of CSA concrete in laboratory-accelerated drying-wetting cyclic environments using NaCl solution and seawater, as well as in marine tidal environments, were characterized using the rapid chloride test (RCT), X-ray diffraction (XRD), mercury infiltration porosimetry (MIP), and thermogravimetric analysis (TGA). The results reveal that CSA concrete accumulates more chloride ions in NaCl solution than in seawater, with concentrations 2–3.5 times higher at the same water–cement ratio. Microscopic analysis indicates that calcium and sulfate ions present in seawater facilitate the regeneration of ettringite, thereby increasing the density of the surface pore structure. The hydration and repair mechanisms of CSA concrete under laboratory conditions closely resemble those in marine tidal conditions when exposed to seawater. Additionally, this study found that lower chloride ion concentrations and pH levels inhibit the formation of Friedel’s salt. Therefore, laboratory experiments with seawater can effectively simulate CSA concrete’s chloride transport properties in marine tidal environments, whereas NaCl solution does not accurately reflect actual marine conditions. Full article

The aim of this research was to synthesize and characterize alginate–calcium composites using a freeze-drying method, with a focus on their potential applications in biomedicine. This study specifically explored the biochemical properties of these composites, emphasizing their role in blood coagulation and their capacity to interact with DNA. Additionally, the research aimed to assess how the cross-linking process influences the structural and chemical characteristics of the composites. Detailed analyses, including microscopic examination, surface area assessment, and atomic absorption spectrometry, yielded significant results. The objective of this study was to examine the impact of calcium chloride concentration on the calcium content in alginate composites. Specifically, the study assessed how varying concentrations of the cross-linking solution (ranging from 0.5% to 2%) influence the calcium ion saturation within the composites. This investigation is essential for understanding the physicochemical properties of the materials, including calcium content, porosity, and specific surface area. The results are intended to identify the optimal cross-linking conditions that maximize calcium enrichment efficiency while preserving the material’s structural integrity. The study found that higher calcium chloride concentrations in alginate cross-linking improve the formation of a porous structure, enhanced by two-stage freeze-drying. Increased calcium levels led to a larger surface area and pore volume, and significantly higher calcium content. Furthermore, assays of activated partial thromboplastin time (aPTT) showed a reduction in clotting time for alginate composites containing calcium ions, indicating their potential as hemostatic agents. The aPTT test showed shorter clotting times with higher calcium ion concentrations, without enhanced activation of the extrinsic clotting pathway. The developed alginate material with calcium effectively supports hemostasis and reduces the risk of infection. The study also explored the capacity of these composites to interact with and modify the structure of plasmid DNA, underscoring their potential for future biomedical applications. Full article