Solutions Of Various Concentrations Research Articles

Insights into surrogate respiratory droplet behaviour on inclined surfaces: Implications for disease transmission

Disease transmission via fluid ejections from infected individuals presents a significant public health challenge. The ejected droplet frequently lands on substrates with varying orientations, including horizontal, vertical, and inclined. However, the behaviour of disease-causing droplets on inclined substrates remains unexplored. Recent research has demonstrated that droplet evaporation, flow, and colloidal deposition are significantly altered when surfaces are inclined. Changes in contact angle impact evaporative flux and induce flow between the top and bottom edges of the droplet. This study examines the behaviour of simulated respiratory droplets containing NaCl, mucin, and micrometer-sized particles as pathogen surrogates, focusing on substrate inclinations of 0°, 45°, and 90° on glass surfaces. As respiratory droplets evaporate, their solute concentration rises, altering both surface tension and viscosity. The study explores the coupled effects of solute concentration variations and asymmetric evaporative flux at varying relative humidity conditions and droplet volumes. The presence of salt and mucin induces Marangoni flow, potentially altering evaporation, flow patterns, and deposition dynamics. Additionally, sedimentation flow influences crystal nucleation sites and precipitation patterns. Results reveal unprecedented crystallization dynamics on inclined substrates, with notable differences in nucleation and growth based on the angle of inclination. Optical profilometry and confocal microscopy further show that surrogate bacterial particles accumulate excessively at the bottom edge of inclined droplets, suggesting an elevated risk of pathogen survival on inclined fomites. These findings highlight the critical importance of considering substrate orientation in understanding the transmission of disease through surface-bound droplets, offering insights that could inform public health strategies.

A Simple Production Process for Prolonging the Microbiological Shelf-Life and Improving the Sensorial Quality of Refrigerated Shucked Mussel (Mytilus galloprovincialis) Products Marketed in Greece

ABSTRACT Commercial production of refrigerated shucked mussels (SM) in Greece presents several challenges that are associated with short shelf-life, lack of taste and development of brown color in the filling medium. To overcome these problems an alternative mussel body recovery process in combination with different filling media, namely brines and white vinegar solutions of various concentrations, was used for the production of SM. A 2-fold to 5-fold increase in the shelf-life of the various SM products was observed when compared against control, while significant improvements were also found in both taste and visual appearance of the products.

Sustainable construction materials from alkali-activated waste fiberglass and waste refractory

In this work, waste fiberglass was up-cycled, alone, or mixed with used alumina-zirconia-silica (AZS) refractory from dismantled glass melting furnaces. Alkali activation was performed by suspending fiberglass and fiberglass/AZS powders in NaOH aqueous solution of various concentrations (8M, 6M, and 3M). The activation of waste fiberglass with 8M NaOH yields a gel with calcium and sodium-containing aluminosilicate hydrates. The addition of AZS refractory enabled the release of aluminates into the solution, which had beneficial effects on the mechanical properties. Low molarity activation yielded weaker materials which could be used as precursors for firing at moderate temperatures (800 °C and 1000 °C) to create cellular glass-ceramics, with a total porosity of up to 92 %. The firing of 8M activated samples resulted in glass ceramics with a 66–75 % porosity range and compressive strength of 10–23Mpa. The compressive strength-to-density ratio before and after firing was comparable to that of established commercial construction materials.

Specific features of reduction of plutonium(VI) ozonation products in solutions of various nature alkalis

The decomposition processes of plutonium hydroxo compounds formed under ozonation conditions in MOH (M = Li, Na, K) solutions of various concentrations were studied by UV–Vis spectroscopy using a modified nonlinear least squares method. The influence of the nature of alkali on the kinetics and mechanisms of spontaneous reduction of alkaline solutions of hydroxo compounds of plutonium(VII) was discovered. This influence and the “anomalies” in the UV–Vis spectra for ozonized plutonium solutions are associated with the presence in the systems of iron compounds in the form of impurities in commercially available LiOH, NaOH and KOH (analytically pure, chemically pure, and ultrapure grade). Even trace amounts of impurities in alkaline solutions of plutonium compounds change the mechanisms of their reduction through the active participation of iron in redox processes. They include the oxidation of iron to ferrate(VI) ions FeO42–, followed by reduction to Fe3+, probably through the stage of formation of an intermediate with a hydroxo derivative of plutonium(VI). As a result of the analysis of large arrays of spectral data, the spectra of individual components corresponding to compounds of plutonium(VI, VII) and iron (VI) were isolated.

Gelatin-Sodium Alginate Hydrogels Cross-Linked by Squaric Acid and Dialdehyde Starch as a Potential Bio-Ink.

Hydrogels as biomaterials possess appropriate physicochemical and mechanical properties that enable the formation of a three-dimensional, stable structure used in tissue engineering and 3D printing. The integrity of the hydrogel composition is due to the presence of covalent or noncovalent cross-linking bonds. Using various cross-linking methods and agents is crucial for adjusting the properties of the hydrogel to specific biomedical applications, e.g., for direct bioprinting. The research subject was mixtures of gel-forming polymers: sodium alginate and gelatin. The polymers were cross-linked ionically with the addition of CaCl2 solutions of various concentrations (10%, 5%, 2.5%, and 1%) and covalently using squaric acid (SQ) and dialdehyde starch (DAS). Initially, the polymer mixture's composition and the hydrogel cross-linking procedure were determined. The obtained materials were characterized by mechanical property tests, swelling degree, FTIR, SEM, thermal analysis, and biological research. It was found that the tensile strength of hydrogels cross-linked with 1% and 2.5% CaCl2 solutions was higher than after using a 10% solution (130 kPa and 80 kPa, respectively), and at the same time, the elongation at break increased (to 75%), and the stiffness decreased (Young Modulus is 169 kPa and 104 kPa, respectively). Moreover, lowering the concentration of the CaCl2 solution from 10% to 1% reduced the final material's toxicity. The hydrogels cross-linked with 1% CaCl2 showed lower degradation temperatures and higher weight losses than those cross-linked with 2.5% CaCl2 and therefore were less thermally stable. Additional cross-linking using SQ and DAS had only a minor effect on the strength of the hydrogels, but especially the use of 1% DAS increased the material's elasticity. All tested hydrogels possess a 3D porous structure, with pores of irregular shape and heterogenic size, and their swelling degree initially increased sharply to the value of approx. 1000% during the first 6 h, and finally, it stabilized at a level of 1200-1600% after 24 h. The viscosity of 6% gelatin and 2% alginate solutions with and without cross-linking agents was similar, and they were only slightly shear-thinning. It was concluded that a mixture containing 2% sodium alginate and 6% gelatin presented optimal properties after gel formation and lowering the concentration of the CaCl2 solution to 1% improved the hydrogel's biocompatibility and positively influenced the cross-linking efficiency. Moreover, chemical cross-linking by DAS or SQ additionally improved the final hydrogel's properties and the mixture's printability. In conclusion, among the tested systems, the cross-linking of 6% gelatin-2% alginate mixtures by 1% DAS addition and 1% CaCl2 solution is optimal for tissue engineering applications and potentially suitable for 3D printing.

Suppression of aerosol dispersion by highly viscoelastic poly(acrylic acid)- and poly(ethylene oxide)-based coolants during bone drilling

Bone drilling in neurosurgical, dental, and orthopedic procedures, combined with the use of coolants, generates a dispersion of bone particles, coolants, and blood aerosols in the air. This poses the threat of airborne transmission of infectious diseases between patients and medical practitioners. Highly viscoelastic polymeric poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) solutions of various concentrations were used as coolants during bone drilling at different mass flow rates to suppress aerosol generation, thereby mitigating the threat of cross-infection. The results revealed that the PAA and PEO solutions provide less advection than water and a comparable cooling performance. However, excessive viscoelasticity of PEO causes the fluid to rise along the cutting burr (the Weissenberg effect), thereby reducing the cooling coverage area. In contrast, slightly lower viscoelasticity of PEO results in a high cooling coverage area. The cooling coverage area is smaller for the PAA at 20 ml/min because the corresponding PAA solution easily swirls or splashes away from the drilling location. However, at 80 ml/min, the supplied PAA solution sufficiently cools the drilling area, despite the loss through splashing. The numbers of atomized droplets of water and the PAA and PEO solutions were quantified and compared to investigate the degree of aerosol formation and dispersion. The solution with the strongest viscoelasticity most significantly suppressed aerosolization and produced the fewest dispersed aerosol droplets during bone drilling.

Extracts of the Canadian goldenrod (Solidago Canadensis L.) – promising agents with antimicrobial, anti-inflammatory and hepatoprotective activity

S. canadensis L. and S. virgaurea L. are the most common species of Solidago L. in Europe and with a long tradition of use in medicine for various therapeutic purposes: diseases of the urinary tract, gastrointestinal tract, diabetes, allergies and antiseptic purposes. Therefore, the research of species of the Solidago genus, which have a rich content of natural BACs, and the development of new effective medicinal products of plant origin are relevant. The aim. The method of work is the phytochemical and pharmacological study of extracts of the Canadian goldenrod herb, obtained by ethanol solutions of various concentrations, for the innovative perspective of creating new medicines based on them with antimicrobial, anti-inflammatory and hepatoprotective activity. Materials and methods. The objects of the study were extracts of herb from Canadian goldenrod, obtained using purified water, 40 %, 70 % and 90 % ethanol. Phytochemical study of the extracts was performed by TLC and spectrophotometry. Study of acute toxicity, antimicrobial, anti-inflammatory and hepatoprotective activity of extracts was carried out according to standard methods. Research results. A study of the phytochemical composition and pharmacological activity of extracts of herb from Canadian goldenrod obtained with different solvents. It was established that extracts of herb from Canadian goldenrod show anti-inflammatory activity. The most pronounced antiexudative activity is shown by the extract of the Canadian goldenrod herb (extractant - 40 % ethanol), reducing the degree of swelling by 24.77 %. Herb extracts from from Canadian goldenrod in acute toxic liver damage show moderate hepatoprotective activity, which is somewhat inferior to the comparative drug "Silibor". A more intense and effective effect on the hepatobiliary system was shown by the extract of the Canadian goldenrod herb (extractant - 40 % ethanol). Conclusions. The perspective of creation based on herb of Canadian goldenrod new drugs with hepatoprotective activity. The most promising substance turned out to be an extract of herb from Canadian goldenrod obtained with a 40 % ethanol solution.

Biomimetic fiber/hydrogel composite scaffolds based on chitosan hydrogel and surface modified PCL chopped-microfibers

Hydrogel/fiber composites have received wide attention as tissue engineering scaffolds due to the outstanding properties of fibers and hydrogels. In the current research, a hydrogel/fiber composite scaffold was made based on chitosan-modified polycaprolactone (PCL) microfibers and chitosan hydrogel as a binder. The presence of chitosan as a modifier on the surface of fibers and as a binder between fibers can create scaffolds with excellent structural and mechanical properties. To this end, the three-dimensional microfibers were first functionalized with amine groups. Then, the chitosan chains were attached to the fibers by an aldehyde coupling agent and Schiff base reaction. FTIR and Raman spectroscopies corroborated that chitosan was successfully immobilized on PCL fibers. Chitosan-modified fibers were molded with chitosan solutions of various concentrations and the prepared composite scaffolds were stabilized using ionic crosslinking. The obtained composites represented a porous 3D structure with highly interconnected pores. The compressive modulus increased by 19 and 2.7 folds and the tensile modulus was augmented by 28 and 4 folds, in respective dry and swollen states with increasing hydrogel concentration from 0.1 to 1 %. Hydrogel/fiber composites were able to preserve cell viability, and increasing the hydrogel proportion increased adhesion, proliferation and penetration of cells into the scaffold.

Galvanic Corrosion Behavior of Zn and Al Couples in NaCl Solution

Multi-materialization is being promoted in automotive structural materials, and fuel economy is being improved by replacing steel with aluminum and other lightweight metallic materials. Automotive steel is often galvanized for corrosion protection, and galvanic corrosion of aluminum and zinc in an atmospheric environment is a very important issue in evaluating automotive durability. Zinc is usually considered to be an anode when combined with aluminum, but its galvanic corrosion behavior can be complicated by environmental conditions because the corrosion potentials of the two are relatively close. Therefore, the objective of this study is to investigate the galvanic corrosion behavior of the couples consisting of zinc and aluminum under corrosive environmental conditions.The galvanic couple used in this study was fabricated from AA1050 Al and zinc plates. The width and length of both plates are 10 mm and 15 mm, respectively. After connecting lead wires to each plate, both plates were embedded in epoxy resin. To fabricate coplanar galvanic couples in this study, both plates were placed separately along the surface from a gap size of 500 um. The surfaces of the galvanic pairs were polished with SiC paper to JIS 2000 grit and cleaned with EtOH. The test solutions used in this study were aqueous NaCl solutions of various concentrations from 0.01 to 2 M, prepared with Milli-Q water and reagent grade chemicals. Galvanic currents and corrosion potentials were measured to investigate the galvanic corrosion behavior of the couples after 72 hours of galvanic corrosion experiments in the test solutions.The results of the galvanic corrosion test showed that the immersion potentials of the galvanic couples were lower at higher NaCl concentrations. The galvanic current decreased with immersion time, finally reaching about 1 uA in all NaCl solutions. The results of the electrochemical impedance measurements for galvanic couples in various NaCl concentrations showed that the impedance gradually increased with immersion time. It was also found that the impedance can be expressed as an electrical equivalent circuit consisting of two time constants, and that the impedance increases at intermediate frequencies between 0.1 and 1 Hz, which is thought to correspond to the dissolution reaction of Zn. This was the same trend as the behavior of the galvanic current. These results suggest that prolonged immersion reduces the galvanic current and the dissolution rate of zinc due to the passivation of the A1050 surface and the suppression of cathodic reactions.

Novel thermally regenerated flexible cellulose-based films

AbstractIn this work, cellulose powder obtained by acid hydrolysis of industrial Eucalyptus kraft pulp was dissolved in NaOH/Urea/H2O system (7/12/81 wt%) in a concentration of 6% (w/v). Cellulose films were prepared by spreading the dissolved cellulose over glass plates, followed by thermal regeneration – a novel approach reported here for the first time. To obtain final flexible films, plasticization was carried out by immersion in aqueous glycerol solutions of various concentrations (10 to 70 wt%) and hot-pressing (at 0.1 MPa and 105 ºC) was used to dry and compress the cellulose films. The resulting films were characterized by Attenuated Total Reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, contact angle measurements, transparency analysis, and gas permeabilities (oxygen and water vapor). Highly flexible films containing up to 50 wt% of glycerol were successfully obtained, exhibiting no glycerol release upon manual handling. Overall, the produced films demonstrated dense and compact structure, good transparency, flexibility and malleability, and very low oxygen permeability.

Strain Hardening in Dilute Binary Al–Cu, Al–Zn, and Al–Mn Alloys: Experiment and Modeling

During thermo-mechanical processing, dissolved alloying elements have a huge impact on the microstructure evolution by influencing the overall dislocation storage rate. Especially, for non-heat treatable Al alloys, the effects of strain-hardening and solid solution strengthening are of significant practical interest. In the present work, a detailed study of the room temperature work-hardening behavior of binary Al–Cu, Al–Zn, and Al–Mn alloys with varying solute concentrations is carried out. Stress–strain curves at different strain rates are recorded and computationally analyzed by an advanced 3-Internal-Variables-Model (3IVM) approach for the dislocation density evolution. The initial strengthening rate is examined as a function of the solute concentration.

Microscopic Raman-based rapid detection of submicron/nano polypropylene plastics in tea and tea beverages

Polypropylene (PP) is suitable for a broad range of applications and represents the most extensively utilized plastic in food packaging. Micro- and nano-PP plastics are prevalent categories of microplastics (MPs). However, the majority of MPs particles currently utilized in laboratory studies are man-made polystyrene (PS) spheres, and there has been limited research on micrometer- and nanoscale PP plastic particles. This study aims to employ a top-down approach in crafting micro/nanoparticle (M/NPs) models of PP particles, ensuring their enhanced relevance to real-world environments. Micro/nano PP particles, featuring a negatively charged particle size ranging from 203 to 2101 nm, were synthesized through variations in solution concentration and volume. Simultaneously, the devised MPs model was employed to develop a Raman-based qualitative and quantitative detection method for micro/nano PP particles, considering diverse sizes and concentrations. This method integrates Raman spectroscopy and microscopy to measure PP particles with varying sizes, utilizing the coffee ring effect. The Limit of detection (LOD) for 203 nm PP reached 31.25 μg/mL, while those for 382–2101 nm PP were approximately 3.9 μg/mL. The method underwent quantitative analysis by introducing 203 nm PP nanospheres into real food media (i.e., tea beverages, tea leaves), revealing a minimum LOD of approximately 31.25 μg/mL.

Development of products with extended shelf life

The goal of the research is to evaluate the flavor and rheological compositions formed in the process of structuring gel-like solutions of various concentrations into individual processes of the technological scheme for the production of semi-finished products and complex interaction in the structure of the finished product, taking into account the use of gelling agents and dietary supplements. The article presents some features of the flow of physicochemical reactions that make it possible to describe the dynamics of the interaction of nutrients in the formed binary compositions of carbohydrate-fat structures of plant systems in the technological process.Methods. To carry out the tests, the potentiometric method was used and the pH of each sample was determined using the Expert-001-3pH device. Determinations of sugars were carried out according to GOST 8756.13-87 using the permanganate method; dry substances according to GOST 31640-2012; organoleptic assessment according to GOST ISO 6658–2015. Samples of semi-finished products containing 25–30% fruit and citrus juices, 0.1–0.5% freeze-dried aromatic plants, 0.3–0.5% berry or vegetable powders, 0.3–0.6% spices were the objects of the research.The results. It has been established that the use of cellulose and glycerin in the formulation of carbohydrate-fat binary compositions based on fruit, citrus juices, berry or vegetable powders and spicy-aromatic raw materials contributes to the formation of an elastic, delicate film structure and a complex of flavoring and aromatic substances, depending on the type of raw materials and VAD used. With an increase in the concentration of cellulose, the films become denser, and in combination with the main raw materials (juice, powders, spices), the amount of dry substances and extract content increase, the films become opaque and less elastic. It has been found that in all samples, with an increase in spicy-aromatic raw materials, the number of inclusions increases and the films acquire a mosaic appearance. For clarity of experiments, graphs of the dependence of the type of main raw material and VAD on the concentration of the recipe composition and the formation of the flavor and aromatic range have been presented.Conclusion. The experimental data and dependencies obtained will be useful when considering more complex processes of mass transfer, sucrose inversion, and destruction of protein-carotenoid complexes. The perception of flavor and density of edible films is complex: the balance between sweetness, extractivity and threshold values of sensory characteristics are the main criteria for the organoleptic quality of the films being developed. It increases with the concentration of VAD and the type of juices or powders used. A richer and more pronounced taste appears.

Enhancing sensitivity of trace copper detection based on coupled optoelectronic oscillator

We propose to employ coupled optoelectronic oscillator (COEO) for trace copper detection to achieve an enhanced sensitivity and stability. By replacing the optical source of the traditional OEO with an optical feedback loop, the oscillation frequency is determined by the cavity loop length in conjunction with the laser output wavelength. The sensing head, which is fabricated by inserting a fusion spliced fiber with large lateral offset fusion splicing in a Sagnac loop, act as a wavelength selection component in the laser loop. Hence, the oscillation frequency changes with the varying solution concentration. Benefitting from the matching of the laser loop and the OEO loop, the final oscillation mode is more stable. By comparing the performance of the COEO-based, single-loop and dual-loop OEO-based sensors, the highest sensitivity of 41.1 Hz/(uMol/L) is obtained by the COEO-based sensor. Since the positive feedback of two loops, the single mode oscillation can be implemented without additional devices.

COMPLEXATION OF IRON(III) WITH TSC AND FTSC IN H2SO4 SOLUTIONS OF VARIABLE COMPOSITION

The process of complex formation of iron (III) with thiosemicarbazide and 1-formyl-3-thiosemicarbazide in H2SO4 solutions of various concentrations was studied using the potentiometric method. The stability constants of the resulting complexes were calculated, and the ionization constants of the ligands were estimated under the same conditions. It was shown that the stepwise nature of complex formation does not depend on the concentration of hydrogen ions. However, the stability of the complexes decreases with increasing pH. A study of the complex formation of iron(III) with thiosemicarbazide and its acyl derivative showed that there are both similarities and differences in the nature of complex formation. Both ligands react with iron(III) in a stepwise manner, forming stable complexes. With increasing temperature, the stability of the complexes increases. Changing the ionic strength of the solution and the concentration of H2SO4 equally affect the stability of the complexes. At the same time, moving from thiosemicarbazide to 1-formyl-3-thiosemicarbazide, the number of particles formed in the solution decreases, and the stability of the complexes decreases.

Identification of lubricant viscosity to minimize the frictional impact of colonoscopy on colonic mucosa

Applying a lubricant to the colonic mucosa and reducing the dynamic friction coefficient (DFC) between the endoscopic shaft and colonic mucosa may reduce colonoscopy invasiveness. However, the ideal lubricant viscosity remains unknown. Here, we developed a DFC measurement model integrating samples of colonic mucosa from forensic autopsy specimens into a simulated bowel bend and determined the low-friction lubricant viscosity that minimizes the DFC. Carboxymethyl cellulose, xanthan gum, hydroxyethyl cellulose, sodium alginate, and sodium polyacrylate aqueous solutions of various concentrations were used as lubricants. Low-friction lubricants minimized the load on the colonic mucosa during colonoscope insertion and reduced the total endoscopy insertion time. The highest correlation was between the DFC and the lubricant viscosity at a shear rate of 100 1/s. The lowest DFC was almost constant at approximately 0.09, irrespective of the chemical composition of the lubricant, and the low-friction lubricant viscosity (100 1/s) was 0.031–0.086 (median: 0.059). The viscosities of conventional colonoscopic lubricants were suitable for lubricating the anorectal skin owing to their low DFC, but too high for lubricating the colonic mucosa because of their high DFC. The utilization of the low-friction lubricants with the optimal viscosity can reduce the stress on colonic mucosa during colonoscopy.

Reinforcement of nanostructured polyacrylamide hydrogels through the generation of secondary physical network using the nanoparticles’ functional groups

The main drawback regarding hydrogels utilization in biomedical engineering is represented by their weak mechanical properties and it is often addressed either by using nanospecies as fillers or by generating secondary networks that strengthen the material. Our study validates a new synthesis route of obtaining double-network nanostructured materials making use of the functional groups of an adsorbed glyco-protein on carbon-based nanospecies. Following a simple procedure, the decorated nanospecies were embedded in a synthetic polymer and subsequently formed a secondary hydrogen-bond based network through incubation in natural polyphenol solutions of various concentrations. The natural macromolecule's adsorption was evaluated through FTIR and DLS measurements. When compared to the single-network nanostructured materials, the double-network hydrogels exhibited lower affinity to aqueous media and improved ability to dissipate energy upon mechanical stress, depending on the amount of the employed natural crosslinker. As a result of generating the second network through incubation in polyphenol aqueous solution, the surface storage and loss moduli exceed the values of the bulk ones, as indicated by rheology and nanoindentation tests. The properties of the double-network hydrogels can also be tailored towards more hydrophilic surfaces with increased roughness through the control of the supplementary crosslinker amount. Considering the studied physical-chemical properties, and especially their mechanical characteristics, the obtained materials hold great promise for biomedical applications, particularly for the fabrication of scaffolds for wound dressing, soft or low load bearing tissue regeneration and repair.

Optical activity of trans-4-hydroxy-L-proline in sodium chloride solutions

The optical activity oftrans-4-hydroxy-L-prolinein deionized water and sodium chloride solutions of various concentrations has been investigated through polarimetry. The specific rotation of thecompounddecreases in the magnitude in solutions with the salt concentration of 0 to 2.000 Mbut does not change significantly in the concentration range of 2.500 to 3.500 M. The specific rotations at the salt concentrations from 4.000 to 5.000 M are smaller in the magnitude and do not vary significantly. Theconcentration dependence is explained basedon thecorrelation between the specific rotation and the square root of the solutiondielectric constant.

Приготовление растворов различной концентрации

When preparing treatment solutions of fertilizers and pesticides for technological processes, one should mix liquids taking into account the precise dosing of components. However, the existing designs of dosing and mixing devices do not provide qualitative dosing. Moreover, a sharp increase of fraction quantity may result in a hydraulic impact. To eliminate these disadvantages, based on analytical research of available designs and patent search results, the authors worked out a mixer for preparing solutions of various concentrations. The device is also capable of changing the ratio of components in the process of operation. The device provides smooth change of preparation concentrations due to the design of dosing valves forming square-shaped ports with a changing configuration. The port plates move relative to each other both horizontally and vertically. The proposed device smoothly changes the concentration of the solution, thereby providing for more accurate dosing. It was experimentally found that a smoother change in the flow rate of treatment liquid according to the solution concentration is observed at a distance from the axes of symmetry of the dosing device disks to the rotation axis of the distribution ports, equal to 0.04 to 0.1 m. The deviation of the actual treatment liquid flow rate from the calculated one does not exceed 5%. The integration of the developed mixer into the systems of fertigation units, sprayers and other specialized machines will ensure better quality of the fine irrigation of plants, seeds, and soil.

Optimization of Chromium (VI) Adsorption using Microalgae Biomass (Spirulina sp.) and its Application in Leather Tannery Waste

<p class="E-JOURNALAbstractBodyEnglish">This study was conducted to examine the adsorption of Cr (VI) metal using Spirulina sp (inactive) biomass and its application in leather tannery wastewater. The treatment was carried out to determine the influence of independent variables on Cr (VI) adsorption with variations in pH, contact time, and metal solution concentration. The values of the solution pH, adsorption time, and concentration of the best metal solution were used to determine the center points of the optimization variables through Response Surface Methodology (RSM). The results showed that based on the FTIR test, macromolecules present in Spirulina sp biomass included amino, carboxylate, and hydroxy groups. The combination of factor variables that produced the optimum response was at pH 3.165, contact time of 66.58 minutes, and Cr (VI) metal ion solution concentration of 22.9 mg/L, resulting in a Cr (VI) adsorption efficiency of 69.66%. The adsorption pattern was included in the Freundlich adsorption isotherm, and the application of Spirulina sp biomass adsorbent to tannery waste reduced the concentration of Cr (VI) from 3.9 g/L to an undetectable level at <1.4 g/L.</p>