Intense Stirring Research Articles

Enhancing microstructural integrity and mechanical performance of thick wire-arc directed energy deposited eutectic aluminum-silicon solid structure through continuous multi-pass friction stir processing

In wire-arc directed energy deposition (waDED), fabricating larger 3D components with single-layer tracks is challenging due to limitations in track thickness, requiring the development of bead overlapping strategies. However, fusion-based 3D-printed aluminum structures often show porosity and coarse-grained microstructures, limiting their industrial applications. To address these limitations, this study employs continuous multi-pass friction stir processing (FSP) on a waDED-produced aluminum block (140 mm × 150 mm × 28 mm). The severe plastic deformation induced by FSP triggers dynamic recrystallization (DRX), promoting the formation of equiaxed grains with an average grain size 8.75 times smaller than the as-fabricated waDED sample (67.03 μm vs 7.66 μm). Transmission Electron Microscopy (TEM) revealed decreased dislocation loops post-FSP, indicating DRX and dislocation annihilation. X-ray micro-computed tomography (X-CT) examination showed complete elimination of porosity in the waDED sample, owing to the intense mechanical stirring induced during FSP. Scanning electron microscopy (SEM) images of the waDED samples showed fibrous eutectic networks disrupted by FSP, leading to a uniform distribution of broken Si particles within the α-Al matrix. Hardness decreased by approximately 38 % (86 HV0.1 vs 53 HV0.1), while the average ultimate tensile strength decreased by about 4 % in the FSP-treated samples (159.19 MPa vs 153.02 MPa). Additionally, the formation of alpha fiber and weak cube texture components during FSP enhances ductility, as evidenced by a sixfold improvement in elongation (1.93 % vs 11.59 %). This textural transformation contributes to the characteristic deeper and more uniform dimples in the FSP-treated samples, indicative of ductile fracture, compared to the premature failure patterns in as-deposited samples.

Marine microalgae Schizochytrium demonstrates strong production of essential fatty acids in various cultivation conditions, advancing dietary self-sufficiency

IntroductionPolyunsaturated fatty acids (PUFAs) are essential nutrients that humans obtain from their diet, primarily through fish oil consumption. However, fish oil production is no longer sustainable. An alternative approach is to produce PUFAs through marine microalgae. Despite the potential of algae strains to accumulate high concentrations of PUFAs, including essential fatty acids (EFAs), many aspects of PUFA production by microalgae remain unexplored and their current production outputs are frequently suboptimal.MethodsIn this study, we optimized biomass and selected ω-3 PUFAs production in two strains of algae, Schizochytrium marinum AN-4 and Schizochytrium limacinum CO3H. We examined a broad range of cultivation conditions, including pH, temperature, stirring intensity, nutrient concentrations, and their combinations.ResultsWe found that both strains grew well at low pH levels (4.5), which could reduce bacterial contamination and facilitate the use of industrial waste products as substrate supplements. Intensive stirring was necessary for rapid biomass accumulation but caused cell disruption during lipid accumulation. Docosahexaenoic acid (DHA) yield was independent of cultivation temperature within a range of 28–34°C. We also achieved high cell densities (up to 9 g/L) and stable DHA production (average around 0.1 g/L/d) under diverse conditions and nutrient concentrations, with minimal nutrients required for stable production including standard sea salt, glucose or glycerol, and yeast extract.DiscussionOur findings demonstrate the potential of Schizochytrium strains to boost industrial-scale PUFA production and make it more economically viable. Additionally, these results may pave the way for smaller-scale production of essential fatty acids in a domestic setting. The development of a new minimal culturing medium with reduced ionic strength and antibacterial pH could further enhance the feasibility of this approach.

Enhanced metal-free photocatalyst performance by synergistic Coupling of internal magnetic field and piezoelectric field

Graphitic carbon nitride (g-C3N4) is a promising metal-free photocatalyst; however, its high carrier recombination rate and insufficient redox capacity limit its degradation effect on antibiotics. In order to overcome these shortcomings, the photocatalytic activity is improved by regulating the spin polarization state, constructing the internal electric field, and applying the external piezoelectric field. In this paper, the chlorine-doped and nitrogen-deficient porous carbon nitride composite carbon quantum dots (Nv-Cl/UPCN@CQD) has been synthesized successfully. The doping position of chlorine and spin polarization properties are verified by DFT calculation. The key intermediates *O2− and *OOH for the synthesis of reactive oxygen species were detected by in-situ infrared testing, which promotes the production of •O2− and H2O2. The degradation rate constant of Nv-Cl/UPCN@CQD for removal of tetracycline is 8.45 times higher than that of g-C3N4. The active oxygen production and degradation efficiency of piezoelectric photocatalysis under the synergistic effect of intense stirring and vis-light irradiation are much higher than those of photocatalysis and piezoelectric catalysis, and the conversion of H2O2 to •OH is promoted by piezoelectric field. This paper provides a reliable way to improve the performance of piezoelectric photocatalysts by adjusting their energy band, electronic structure and piezoelectric force.

Effect of High-Frequency Electric Pulse on the Solidification Microstructure and Properties of Hypoeutectic Al-Si Alloy.

The effects of different pulse frequencies on the microstructure grain size and solid solubility of Al-9Si alloy were systematically investigated using OM, SEM, and EDS. The impact on the mechanical properties of the alloy was analyzed using a micro-Vickers hardness tester and multifunctional friction tester. During solidification, the Al-9Si alloy is exposed to high-frequency electric current pulses with a current density of 300 A/cm2 and frequencies of 0 Hz, 500 Hz, 1000 Hz, and 2000 Hz. The experimental results show that the Lorentz force also increases as the high-frequency pulse frequency increases. Intense electromagnetic stirring leads to grain refinement. However, as the pulse frequency continues to grow, the combined effect of Joule heating and Lorentz force results in an enlargement of the melt zone and an increase in grain size. At a pulse frequency of 1000 Hz, the eutectic structure size of the Al-9Si alloy is optimal, with the average size being reduced to 13.87 μm and a dense distribution, effectively eliminating primary Si. The EDS results revealed that the high-frequency pulse led to a more uniform distribution of Si elements within the matrix, and the solid solubility of Si in the α-Al matrix increased to a maximum value of 1.99%, representing a 39.2% increase. At a pulse frequency of 1000 Hz, the sample demonstrates the most favorable mechanical properties, with the friction coefficient reaching a minimum value of 0.302, representing a 37.7% decrease in the average friction coefficient. The results demonstrate that high-frequency pulsing is an effective method for enhancing the mechanical properties of Al-9Si alloy.

DEVELOPMENT OF SODIUM CHLORIDE BRINES TECHNOLOGY FROM HALITE WASTE

The results of a study of the composition of solid halite waste (halite dump and quarry salt) from potash production were presented in the work. The form of calcium sulfate and its localization in solid halite waste have been determined. It was established that in the quarry salt calcium sulfate was presented in the form of anhydrite and dihydrate, and in the halite dump the impurity was only in the form of anhydrite. Photomicroscopic photography of the surface of large halite crystals showed that calcium sulfate in the halite dump was localized mainly on the surface of halite, and on particles of quarry salt. Calcium sulfate crystals were pressed into the crystalline surface of halite due to the processes of dissolution - crystallization occurring under the influence of atmospheric precipitation and changes temperatures. An assessment of the influence of ultrasonic and hydromechanical effects on the treated aqueous suspension of halite waste for purification of calcium sulfate impurities was presented. The possibility of removing most of the CaSO4 without additional reagent treatment of the halite suspension has been proven. The optimal technological parameters for the duration and intensity of ultrasonic and hydromechanical effects on the treated environment have been found. It was found that ultrasonic treatment of halite in a saturated salt brine of sodium chloride at a ratio of L:S = 5:1 for 6 min with a frequency of 22 kHz, intensity of 9.4 W/cm2, amplitude of ultrasonic vibrations of 80 μm and intensive stirring allows to achieve 80% extraction of calcium sulfate from both quarry salt and halite dump. Based on the results obtained, the feasibility of using ultrasonic treatment was demonstrated and an effective technology was proposed for the preparation of sodium chloride and (or) technical salt brines with a residual calcium sulfate impurity content of less than 0.5 wt.%, which can subsequently be used in various industries.

Mass Transfer in the Processes of Native Lignin Oxidation into Vanillin via Oxygen

The influence of mass transfer intensity on the kinetics of the catalytic oxidation of flax shives with oxygen in alkaline media to aromatic aldehydes and pulp was studied. The process was carried out in two autoclaves, with moderate stirring (stirrer engine of 8 W) and intense stirring (stirrer engine of 200 W). The oxidation of flax shives into vanillin, syringaldehyde, and pulp was shown to proceed as a completely diffusion-controlled process under the studied conditions, both moderate and intense stirring. Depending on the process conditions, it can be limited by stages of oxygen transfer through the diffusion boundary layer near the gas–liquid interface (low intensity of mass transfer) as well as by reagents’ inner diffusion in the porous and solid matter of the flax shive particle (high intensity of mass transfer). The results on the influence of the stirring speed and volume of the reaction mass on the rates of oxygen consumption and vanillin accumulation were obtained. They were described using a known simple model connecting the intensity of mass transfer and the stirring power density in the bulk of the liquid phase in terms of algebra equations.

Chitosan Hydroxyapatite: Physic-chemical Properties and its Effect on the Growth and Development of Broiler Chickens

The current study aimed to obtain a calcium-containing, biocompatible drug based on chitosan Bombyx mori. Composites of Chitosan (CS) Bombyx mori with hydroxyapatite (HA) in the ratio of CS/HA = 50:50 mass percentage were synthesized in situ conditions at Ca/P = 1.67 mol% with intensive stirring for one hour at a speed of 1400 rpm and a temperature of 40 ± 2ºС. It was revealed that the components form an intermediate complex through –N-Ca, O-Ca, O (glycosidic bond)–Ca, H–O-bonds interacted by electrostatic forces. Atomic force microscopy studies indicated particles in the 100-50 nm size range on the polymer matrix surface. The polymer matrix prevented the growth of HA crystals and particle agglomeration. It was also determined that the CS/HA composite was non-toxic, and the LD50 was more than 5000 mg/kg. The composites were introduced into the chickens’ diet in groups for 30 days at 25 to 40 mg/kg doses. The findings indicated an increased survival rate of chickens by 100%, improved the morphological parameters of the blood, and enhanced the contents of calcium, phosphorus, and hemoglobin. The addition of CS/HA=50:50 mass percentage contributed to an increase in the number of erythrocytes in the blood of broilers and hemoglobin by 11-12%. It should be noted that CS/HA did not adversely affect other morphological parameters of chicken blood. Therefore, CS/HA is recommended for the prevention of osteoporosis and osteomalacia in broiler chickens.

STIRRING OF METAL MELTS FOR IMPROVING THE EFFICIENCY OF THE “LADLE – FURNACE” UNITS Message 2. NEW METHOD FOR ELECTROMAGNETIC STIRRING OF METALLIC MELT IN “LADLE – FURNACE” UNIT

The features of refractory lining’s wear of “ladle – furnace” unit at work on metallurgical mini-plant with intensive stirring of liquid metal by gas and electromagnetic field is studied. It was established that the most affected areas are slag zone, ladle’s bottom, as well as side wall, near which the electromagnetic stirrer is located. The stability of these areas determines the duration of the ladle working between repairs. Recommendations for recovery of the lining’s working layer have been developed. Also, there are formulated the requirements for rationalization of melt stirring modes. Theoretical studying of influence of electromagnetic stirring on heat & mass transfer processes in liquid metal bath of metallurgical aggregates (in particular, during homogenization of alloy in free turbulence mode at input of additives) was investigated. New electromagnetic stirrer was designed in the PTIMA NASU, and it is proposed for technologies of melting and finishing of alloys. The stirrer creates the pulsating magnetic field, and its force lines spread equally intensively both in the horizontal and vertical planes. It is shown that design of developed stirrer, its power supply by industrial frequency 50 Hz, and physical nature of the generated field’s action provide the simplicity of its making and operation. So, new stirrer has essential technical, economic and technological advantages in comparison with known stirrers of travelling magnetic field at the same parameters of electromagnetic systems. Joint research performed by specialists of the PTIMA NASU and IED NASU with using mathematical modeling and experiments on aluminum melt showed the following. It is possible to realize a wide range of stirring modes, both intensity and melt movement directions. Thus, the application of developed electromagnetic stirrer in the “ladle – furnace” units will allow to significantly expand the possibilities for finishing liquid alloys on chemical composition and temperature, especially at small metallurgical plants.

Mixing and Overturning Across the Brazil‐Malvinas Confluence

AbstractThe rates of isopycnal stirring and water mass transport by mesoscale eddies, and of diapycnal mixing by small‐scale turbulence, across the Brazil‐Malvinas Confluence (BMC) are assessed from a set of microstructure and hydrographic measurements in the Argentine Basin. This assessment is founded on a theoretical framework that applies a triple decomposition to the temperature variance equation and assumes eddies to transfer potential vorticity downgradient. The BMC is found to host widespread intense isopycnal stirring at rates of O(103–104 m2 s−1), and generally weak diapycnal mixing at rates of O(10−6–10−5 m2 s−1). Despite such disparity, both diapycnal mixing and isopycnal stirring play roles of comparable importance in determining regional water mass properties within surface and mode waters. In deeper layers, isopycnal stirring prevails. Eddies are further diagnosed to effect an important cross‐BMC transport, at rates of O(1 m2 s−1). When scaled by the along‐stream extent of the BMC, these rates integrate to volume transports that may be as large as O(10 Sverdrups). This suggests that cross‐BMC transfers of waters are substantially effected by eddy‐induced flows.

Changes in the structure of polysaccharides under different extraction methods

Changes in the structure of polysaccharides under different extraction methods

Fe-SiC-Sn-Mn reinforced surface composite via FSP: A comprehensive analysis

This investigation reports a maiden work on the fabrication of surface composite through hybrid reinforcement powders by adding Fe, Mn, and Sn metallic powders to ceramics (SiC) in aluminum AA5083 alloy matrix via friction stir processing. Stitched micrographs were employed to demonstrate the variation in grain size distribution from the stir zone (10 µm) to the base metal (52.68 µm) during the processing. With the aid of scanning electron microscopy, energy dispersive spectroscopy, area mapping and X-ray diffraction analysis, it has been determined how reinforcement was distributed and what phases evolved in the stir zone. Tensile test was performed to evaluate the strength of the fabricated composite and micro-hardness maps indicated a 54.4 % increase in hardness after processing.The observed enhancement is attributed to the Hall-Petch and pinning effect. A potentiodynamic polarization test was carried out to study the corrosion behavior and it was ascertained that corrosion resistance of the processed sample got enhanced because of grain refinement, formation of galvanic couple and breakdown of second phase particles owing to intense stirring.

Modeling of Organic Fouling in an Ultrafiltration Cell Using Different Three-Dimensional Printed Turbulence Promoters.

Designing turbulence promoters with optimal geometry and using them for ultrafiltration systems has been a key challenge in mitigating membrane fouling. In this study, six different turbulence promoters were created using three-dimensional printing technology and applied in dead-end ultrafiltration. Three-dimensional-printed (3DP) turbulence promoter configurations were integrated into a classical batch ultrafiltration cell. The effects of these configurations and the stirring speeds on the permeate filtration flux, organic rejections, and membrane resistances were investigated. The fouling control efficiency of the 3DP promoters was evaluated using two polyethersulfone membranes in a stirred ultrafiltration cell with model dairy wastewater. The Hermia and resistance-in-series models were studied to further investigate the membrane fouling mechanism. Of the Hermia models, the cake layer model best described the fouling in this membrane filtration system. It can be concluded that the 3DP turbulence promoters, combined with intense mechanical stirring, show great promise in terms of permeate flux enhancement and membrane fouling mitigation. Using a well-designed 3DP turbulence promoter improves the hydrodynamic flow conditions on the surface of the stirred membrane separation cells based on computational fluid dynamics modeling. Therefore, the factors effecting the fabrication of 3DP turbulence promoters are important, and further research should be devoted to revealing them.

A novel membrane stirrer system enables foam-free biosurfactant production.

Bioreactors are the operative backbone, for example, for the production of biopharmaceuticals, biomaterials in tissue engineering, and sustainable substitutes for chemicals. Still, the Achilles' heel of bioreactors nowadays is the aeration which is based on intense stirring and gas sparging, yielding inherent drawbacks such as shear stress, foaming, and sterility concerns. We present the synergistic combination of simulations and experiments toward a membrane stirrer for the efficient bubble-free aeration of bioreactors. A digital twin of the bioreactor with an integrated membrane-module stirrer (MemStir) was developed with computational fluid dynamics (CFD) studies addressing the determination of fluid mixing, shear rates, and local oxygen concentration. Usability of the MemStir is shown in a foam-free recombinant production process of biosurfactants (rhamnolipids) from glucose with different strains of Pseudomonas putida KT2440 in a 3-L vessel and benchmarked against a regular aerated process. The MemStir delivered a maximal oxygen transfer rate (OTRmax ) of 175 mmol L-1 h-1 in completely foam-free cultivations. With a high space-time yield (STY) of 118 mgRL L-1 h-1 during a fed-batch fermentation, the effectiveness of the novel MemStir is demonstrated. Simulations show the generic value of the MemStir beyond biosurfactant production, for example, for animal cell cultivation.

Нуклеация гидрата метана в присутствии нанофибриллярной целлюлозы

Is it possible to slow down gas hydrate nucleation by introducing additional surfaces into the system? This process usually occurs at phase boundaries, i.e., the appearance of new surfaces (solid particles) in the system should rather increase the probabilityof hydrate formation. In this work, the effect of carboxylated cellulose nanofibrils (CNF) dispersed in water on the formationof methane hydrate under intensive stirring was investigated. It was found that, under identical conditions, 0.5 mass% CNF allowed reducing the hydrate nucleation rate and suppressing the "memory" effect characteristic for hydrate formation from distilled water (DW). The analysis of the "survival" functions revealed that the mechanism of the CNF inhibitory action is to reduce the number of hydrate nucleation centers. This can be explained by the participation of CNF in the disturbance of the hydrogen bond network:for example, mechanical "destruction" of pre-critical nuclei by inhibitor particles under intensive stirring. The data obtained suggest the development of a new class of kinetic hydrate inhibitors based on dispersions.

Understanding the distribution of platinum group metals and gold in the process of copper-nickel slag depletion with gas mixtures

This paper describes the results of a study that looked at the distribution of platinum group metals (PGMs) (Pt, Pd, Rh, Ru, Ir) and Au between Cu – Ni – Fe bottom phase and dump slag as a result of pyrometallurgical depletion of slag, a by-product of oxidizing smelting of sulphide copper-nickel concentrate. The pyrometallurgical process was performed in a bubbling mode using reducing gas mixtures of various compositions. The consumption of reducing agent was found to be the key factor governing the output of the bottom phase and hence the chemical composition of the products. For the first time ever, the authors used the results of the chemical analysis of the products to calculate the distribution coefficients for PGMs and gold between the bottom phase versus the slag when the depletion process involved an intensive stirring of the melt. Thus, a variation range was established for the distribution coefficients of noble metals, as well as the threshold concentration of Fe in the melt. Once the latter has been reached, the distribution coefficients remain almost unchanged and the extraction of PGMs into dump slag is minimal. Using scanning electron microscopy and electron probe microanalysis, the authors established how many noble metals get carried away with dump slag. Proneness of Au to get dissolved in silicate melts was revealed, which is also typical of Cu. The conducted study helped establish that only 5% of Pt, Pd and Rh gets carried away with dump slag, which is the least loss. At the same time, about 10% of Ru and Ir goes into dump slag. The data reflecting the behavior of Au during slag depletion with reducing gas mixtures confirm that the maximum recovery of this metal from the slag would only be possible under a high reduction potential of the system. This corresponds to the minimum concentration of Fe in the bottom phase of 50% wt.

Comparative studies of the discharge of hydronium ions on zinc, copper and aluminum cathodes

Electrochemical reduction of hydrogen (hydronium ion) was carried out on zinc, aluminum and copper cathodes from acidic aqueous solutions containing sulfuric acid (0.09, 0.18 and 0.36 mol/l) to study the effect of electrolyte acidity, the type of cathodes used and potential values on electrolysis indicators. The studies were carried out on the potentiostat using a three-electrode cell under conditions of intensive electrolyte stirring with a magnetic stirrer. At the initial stage, electrolysis was performed in the following modes: potentiodynamic measurements at a sweep rate of 1 mV/s in the potential range Е = –(700÷850) mV on a copper and aluminum electrode and Е = –(1000÷1150) mV on a zinc electrode. In the indicated potential range, hydronium discharge parameters at each cathode were calculated: Tafel slope, apparent transfer coefficients and exchange currents. Dependences of these parameters on electrolyte acidity were considered. Average values of steady state potentials were obtained, which, similar to the apparent exchange current, significantly depended on the cathode material: –923.1 mV (zinc cathode); +36.1 mV (copper cathode), and –603.7 mV (aluminum cathode) (AgCl/Ag). The effect of surfactants on all the kinetic parameters considered was shown. The order of the reaction with and without surfactant additives was determined. At the next stage, the electrochemical parameters of hydronium discharge on the copper electrode only were compared. It was shown that the electrochemical parameters significantly depend on the cathodic potential range where they are determined, and on the methods used for their calculation. It was noted that the process proceeds in the region of mixed kinetics. As the electrode polarization decreases, the hydrogen discharge mechanism changes, while the proportion of electrochemical kinetics will increase in the region of mixed kinetics. We suppose that the data obtained can also be of practical importance for the zinc electrolysis technology. The data obtained in this research on the electrochemical parameters of hydrogen discharge in a wide range of potentials on cathodes made of different metals as well as on the effect of electrolyte acidity on the behavior of surfactants during electrolysis will expand knowledge about the zinc electrolysis technology.

Green materials for construction industry from Italian volcanic quarry scraps

Italian volcanic quarry scraps, with fine particle size and of little market interest, have been considered for the manufacturing of lightweight geopolymers and highly porous foams. Both powders have been alkali activated with NaOH solution at 8 M and 3 M, respectively.Geopolymers were characterized in terms of density, porosity, humidity absorption/desorption, mechanical strength and microstructure. All samples (with a bulk density of 1.5–1.6 g/cm3) exhibited a porosity of approximatively 35 vol% but featured a quite variable compressive strength (3–7 MPa), depending on the use of pumice or lapillus. The same quarry scraps were easily converted into highly porous foams (porosity of 75 vol%), by intensive mechanical stirring of alkali-activated suspensions, with the help of a surfactant.

COMBINED METHOD OF WASTEWATER TREATMENT OF A SMALL-CAPACITY BREWERY

With the help of the proposed circuit of EMT, the method of simultaneous measurements of the static characteristics of the magnetic fluid: specific electrical conductivity χt, magnetic susceptibility kt and temperature t of the magnetic fluid, which is recommended to be used for wastewater treatment of breweries, was investigated. A combined method of cleaning has been developed and the appropriate technological scheme has been improved, which provides, together with the use of mechanical cleaning devices, the use of an additional filter for magnetizing wastewater samples, which includes a special zone for the introduction of a pre-calculated magnetic liquid. Thus, in the process of wastewater treatment, mini-breweries using the proposed combined method, after applying methods of pre mechanical cleaning, use the wastewater interaction and the magnetic fluid: after intensive stirring of the mixture, the droplets of magnetic fluid dissolve in impurities and a weakly magnetic fluid is formed, which enters the magnetic separator for further cleaning. A rational ratio of wastewater: magnetic fluid (WW:MF), WW:MF = 8,7‧10-3: 1 was found. A comparison of the data obtained using informative methods with the data given in the regulatory documents witness the effectiveness of the proposed combined method of beer wastewater treatment in relation to the norms of water discharge into the city sewer, namely, the hydrogen pH indicator decreases as a result of the treatment by 34.6%, COD by 7.14 times, BOD5 by 1.52 times, suspended substances by 1.52 times, calcium cations Ca2+ by 1.53 times, magnesium cations Mg2+ by 1.51 times, total hardness dH by 1.64 times, carbonate hardness KH by 1, 86 times.

Continuous long-term glucose biosensor in agitation condition for bioconversion processes

The use of a glucose biosensor in the bioconversion processes is challenging due to a long period of intensive stirring that is required to mix the heterogenous substants together. In this work, a glucose biosensor was developed to be accurate and robust for an extended period of measuring time in agitated conditions. The sensor probe was fabricated by electro-polymerization of polyaniline (PANI) nanostructures on a gold wire before putting in gold nanoparticles (AuNPs) and carrageenan (carr) solution to make an PANI-carr-AuNPs layer. Then the probe was soaked in PQQ-Glucose dehydrogenase (GDH) solution before coating with polyurethane (PU) to prevent the enzymes from leaching away from the sensor. The sensor probe showed a sensitivity of 0.85 μA/mg/ml of glucose with R2 of 0.9973. The storage stability of the probe was up to 4 days with stable signal. In agitated condition of 150 rpm, steady signals from the sensor were continuously obtained for 72 h. In sugarcane bagasse hydrolysis with speed at 150 rpm for 72 h, the biosensor continuously displayed signals which were not significantly different in glucose concentration to the results from the HPLC method. This biosensor displayed promising applications in bioconversion processes.

The impact of river sand mining on remobilization of lead and cadmium in sediments – A case study of the Jialing River

Due to the fast pace of urbanization worldwide, industrial sand mining activities have imposed great pressure on the environment, and consequently, these activities have led to serious environmental problems in aquatic ecosystems. However, the current understanding of the effect of sand mining on heavy metal remobilization in river sediments remains incomplete. The present study employed sediment quality guidelines (SQGs) and the sequential extraction (SE) and diffusive gradients in thin films (DGT) techniques to comprehensively investigate the effect of sand mining on the remobilization process of heavy metals in the aquatic system of the Jialing River. The SQGs results indicated that stations (S1 to S4) with sand mining disturbance exhibited Pb and Cd accumulation in surface sediments. Both Ctotal-Pb (61.78–122.04 mg·kg−1) and Ctotal-Cd (0.85–3.96 mg·kg−1) were higher than CSQGI (60 mg·kg−1 for Pb and 0.5 mg·kg−1 for Cd) and TEC (35.8 mg·kg−1 for Pb and 0.99 mg·kg−1 for Cd) limitation in most of sand mining stations. Pb and Cd were mainly bounded in the acid-soluble/exchangeable fraction (F1) and oxidizable fraction (F3) of the surface sediments. At the four stations with sand mining disturbance, about 5–10 folds of DGT-labile Pb and Cd were released in deep sediments (−9 to −12 cm), and Pb and Cd exhibited a transport trend from the sediments into the overlying water, while the above phenomenon was not observed at the two stations without sand mining activities. Correlation analysis revealed that DGT-labile Pb and Cd were suitably correlated with the F1 and F3 fractions, indicating that the acid-soluble/exchangeable and oxidizable fractions were the main sources leading to Pb and Cd remobilization in the sediments. A potential mechanism explanation may be that (1) intense sediment stirring could result in remobilization of the weakly bound fraction, which is related to the contribution of the F1 fraction, and (2) Cd/Pb experienced a corelease process with sulfur due to O2 introduction (elevation of the dissolved oxygen level) attributed to sediment evacuation, which is related to the contribution of the F3 fraction. The above results suggested that sand mining in the Jialing River should be paid high attention to prevent heavy metal pollution in aquatic ecosystem.