Using CFD simulations to investigate the shear stress in hydrodynamic cavitation reactors coupled with experimental validation using colony count measurements.

The current work investigates the shear stress distribution in hydrodynamic cavitation reactors with two different geometries using CFD simulations. Venturi type (positive geometry) and bore (negative geometry) were used to induce cavitation. Experimental validation of the predictions from simulations was also conducted by calculating the reduction rate in the colony count of Legionella pneumophila, a pathogenic bacterial strain. Both the numerical and experimental studies revealed the significant influence of the shape of the cavitation-inducing geometry on the flow characteristics and the distribution of shear stress. The simulation data indicated high shear stress formation in the positive geometry as a venturi, with the cavitation ranges for the two reactors being far apart from each other. The experimental study also confirmed that the flow conditions in the venturi-type reactor were more favourable compared to the bore geometry, resulting in a bacterial reduction efficiency as high as 99.98%. It was clearly demonstrated that the geometry of the cavitating device plays a crucial role in deciding the shear stress and its efficacy for the desired applications as per the predictions of the simulation model validated by the experimental results.

Reversed double-beam photoacoustic spectroscopic analysis of photoinduced change in absorption of cellulose fibres.

Photoabsorption properties of cellulose fibres under continuous and modulated irradiation were investigated in situ by the use of reversed double-beam photoacoustic spectroscopy (RDB-PAS). This photoacoustic (PA) measurement enabled observation of ultraviolet- and visible light-induced, electron trap filling, and reductive change on the surface of the fibres. Energy-resolved measurements and analysis of the kinetics of photoinduced de-excitation suggested that electrons that accumulated in the different cellulose crystalline phases had moderate reactivity toward molecular oxygen. Saturation limits of the intensities of the PA and RDB-PAS signals under de-aerated conditions in the presence of surface-adsorbed methanol were estimated for softwood and hardwood cellulose samples. The results suggest that the RDB-PAS technique is a feasible method for the estimation of the electron trap distribution, which is a potential measure of the density of crystalline cellulose defects.

Effect of hydrodynamic cavitation water treatment on Pseudomonas aeruginosa quorum-sensing molecules.

Hydrodynamic cavitation treatment was used for the functional inactivation of quorum-sensing lactone molecules of Pseudomonas aeruginosa. Hydroxyl radicals formed as well as the shear effects during the cavitation process induced the inactivation of the signal molecules through hydrolysis reaction coupled with bacterial destruction. Concentration of two different types of homoserine lactones (HSL) molecules was tested after the treatment at various rotational speeds. It was found that the strongest effects can be achieved at speeds > 2000 rpm. This value is considered as an onset speed of dominant cavitation, and it is in agreement with literature data. The experimental trends were in agreement with the calculations based on the finite element modelling, which show a significant increase in average shear stress at higher rotational speeds. Overall, the work has demonstrated the possible effects of hydrodynamic cavitation on the quorum-sensing molecules of Pseudomonas aeruginosa for the first time.

Assessment of the papermaking potential of processed Miscanthus × giganteus stalks using alkaline pre-treatment and hydrodynamic cavitation for delignification.

One way of satisfying increased market demand and simultaneously achieving a reduced environmental load in the industrial paper production is the use of fibrous agricultural residues. The aims of this study were i) to investigate the effect of alkaline - hydrodynamic cavitation (HC) pre-treatments on the delignification of Miscanthus × giganteus stalks (MGS) and ii) establishing the suitability of MGS as feedstock and their exploitation in pulp and paper manufacturing. It was demonstrated that the proposed treatment is an efficient delignification method for the non-wood fiber sources, such as miscanthus. A significant outcome of this work was the observation that HC treatment preserved the fibres lengths and surface quality of raw MGS, but at the same time increased the amount of kinked and curled fibers present in cavitated miscanthus fibers. The average miscanthus fiber length was found to be relatively short at 0.45 (±0.28) mm, while the slenderness ratio, the flexibility coefficient and Runkel ratio values were calculated to be 28.13, 38.16 and 1.62, respectively. The estimated physical properties of MGS pulp hand-sheets were 24.88 (±3.09) N m g-1 as the tensile index, 0.92 (±0.06) kPa m2 g-1 as the burst index and 4.0 (±0.37) mN m2 g-1 as the tear index. Overall the current work demonstrated effective use of hydrodynamic cavitation for improving the processing in pulp and paper manufacturing.

Ultrasound-Assisted Extraction of Cannabinoids from Cannabis Sativa L. Optimized by Response Surface Methodology.

Ultrasonication was used to extract bioactive compounds from Cannabis sativa L. such as polyphenols, flavonoids, and cannabinoids. The influence of 3 independent factors (time, input power, and methanol concentration) was evaluated on the extraction of total phenols (TPC), flavonoids (TF), ferric reducing ability of plasma (FRAP) and the overall yield. A face-centered central composite design was used for statistical modelling of the response data, followed by regression and analysis of variance in order to determine the significance of the model and factors. Both the solvent composition and the time significantly affected the extraction while the sonication power had no significant impact on the responses. The response predictions obtained at optimum extraction conditions of 15 min time, 130 W power, and 80% methanol were 314.822 mg GAE/g DW of TPC, 28.173 mg QE/g DW of TF, 18.79 mM AAE/g DW of FRAP, and 10.86% of yield. A good correlation was observed between the predicted and experimental values of the responses, which validated the mathematical model. On comparing the ultrasonic process with the control extraction, noticeably higher values were obtained for each of the responses. Additionally, ultrasound considerably improved the extraction of cannabinoids present in Cannabis. PRACTICAL APPLICATION: Low frequency ultrasound was employed to extract bioactive compounds from the inflorescence part of Cannabis. The responses evaluated were-total phenols, flavonoids, ferric reducing assay and yield. The solvent composition and time significantly influenced the extraction process. Appreciably higher extraction of cannabinoids was achieved on sonication against control.

Intensification of biogas production using pretreatment based on hydrodynamic cavitation.

The present work investigates the application of hydrodynamic cavitation (HC) for the pretreatment of wheat straw with an objective of enhancing the biogas production. The hydrodynamic cavitation reactor is based on a stator and rotor assembly. The effect of three different speeds of rotor (2300, 2500, 2700 rpm), wheat straw to water ratios (0.5%, 1% and 1.5% wt/wt) and also treatment times as 2, 4 and 6 min have been investigated in the work using the design of experiments (DOE) approach. It was observed that the methane yield of 31.8 ml was obtained with untreated wheat straw whereas 77.9 ml was obtained with HC pre-treated wheat straw confirming the favourable changes during the pre-treatment. The combined pre-treatment using KOH and HC gave maximum yield of biogas as 172.3 ml. Overall, it has been established that significant enhancement in the biogas production can be obtained due to the pretreatment using HC which can also be further intensified by combination with chemical treatment.

Fabrication of bacterial cellulose thin films self-assembled from sonochemically prepared nanofibrils and its characterization.

Bacterial cellulose (BC) film formation could be a critical issue in nanotechnology applications such as biomedical or smart materials products. In this research, purified pretreated BC was subjected to high intensity ultrasound (HIUS) and was investigated for the development of BC films. The morphological, structural and thermal properties of the obtained films were studied by using FE-SEM, AFM, FT-IR, XRD, TGA and DSC characterizations. Results showed that the most favorable purification treatment was the 0.01 M NaOH at 70°C for 2h under continuous stirring. The most suitable ultrasound operating conditions were found to be, 1cm distance of ultrasonic probe from the bottom of the beaker, submerged in cold water bath cooling around 12 ± 2°C. The power (25 W/cm(2)), time (30 min), BC concentration (0.1%w/w), amplitude (20 µm) and frequency (20 kHz) were maintained constant.

Properties of ultrasound extracted bicomponent lignocellulose thin films.

Agricultural and forest residues obtained after harvesting are promising renewable sources, suitable as a source of pulp for cellulose nanocrystal manufacturing. Cavitation-assisted softening of the lignin-carbohydrate matrix offers sample opportunity for cellulose fibril liberation and degradation of amorphous cellulose. The present work addresses cavitation assisted cellulose fibril and crystal liberation and film forming properties of the supernatant phase of treated agricultural and forest residues. The effectiveness of this method has been evaluated according to crystallinity indices and hydrogen bond energies, as measured by FT-IR analysis. It has been observed that the use of cavitation increased the crystallinity and caused partial removal and degradation of the lignin matrix. Overall, it appears that considerable improvement of crystallinity can be obtained from agricultural and forest residues through the use of cavitation.

Modeling the shear rate and pressure drop in a hydrodynamic cavitation reactor with experimental validation based on KI decomposition studies.

A mathematical model describing the shear rate and pressure variation in a complex flow field created in a hydrodynamic cavitation reactor (stator and rotor assembly) has been depicted in the present study. The design of the reactor is such that the rotor is provided with surface indentations and cavitational events are expected to occur on the surface of the rotor as well as within the indentations. The flow characteristics of the fluid have been investigated on the basis of high accuracy compact difference schemes and Navier-Stokes method. The evolution of streamlining structures during rotation, pressure field and shear rate of a Newtonian fluid flow have been numerically established. The simulation results suggest that the characteristics of shear rate and pressure area are quite different based on the magnitude of the rotation velocity of the rotor. It was observed that area of the high shear zone at the indentation leading edge shrinks with an increase in the rotational speed of the rotor, although the magnitude of the shear rate increases linearly. It is therefore concluded that higher rotational speeds of the rotor, tends to stabilize the flow, which in turn results into less cavitational activity compared to that observed around 2200-2500RPM. Experiments were carried out with initial concentration of KI as 2000ppm. Maximum of 50ppm of iodine liberation was observed at 2200RPM. Experimental as well as simulation results indicate that the maximum cavitational activity can be seen when rotation speed is around 2200-2500RPM.

ZnO-modified cellulose fiber sheets for antibody immobilization.

Cellulose fiber sheets impregnated with saccharide capped-ZnO nanoparticles were used as bioactive materials for antibody immobilization. First, ZnO nanoparticles were synthesized in the presence of glucose (monosaccharide), sucrose (disaccharide) as well as alginic acid and starch (polysaccharides). The pine cellulose fibers were then modified by the obtained saccharide capped nanoparticles and further incorporated into the sheets. The presence of ZnO significantly improved the immobilization of the antibodies on the surface of the sheets. After rewetting the alginic acid-ZnO modified sheets with saline solution, the retention of antibodies was about 95%. A high degree of the immobilization of biomolecules is an important feature for possible fabrications of bioactive- or biosensing-papers and we successfully tested the sheets on the detection of blood types using (A, B, and D blood antibodies). The ZnO nanoparticles affected also the other properties of the sheets. The ZnO-modified fiber sheets showed higher values of tensile index (strength), smoothness and opacity, while the value of porosity was substantially lower than that of the unmodified sheet. The presence of ZnO nanoparticles provided also the antimicrobial activity to the sheets. They showed a strong activity against bacteria (Escherichia coli and Staphylococcus aureus) and strong resistance to the attack of cellulase producing fungus Gloeophyllum trabeum.

Hydrodynamic cavitation as a novel approach for delignification of wheat straw for paper manufacturing.

The present work deals with application of hydrodynamic cavitation for intensification of delignification of wheat straw as an essential step in the paper manufacturing process. Wheat straw was first treated with potassium hydroxide (KOH) for 48 h and subsequently alkali treated wheat straw was subjected to hydrodynamic cavitation. Hydrodynamic cavitation reactor used in the work is basically a stator and rotor assembly, where the rotor is provided with indentations and cavitational events are expected to occur on the surface of rotor as well as within the indentations. It has been observed that treatment of alkali treated wheat straw in hydrodynamic cavitation reactor for 10-15 min increases the tensile index of the synthesized paper sheets to about 50-55%, which is sufficient for paper board manufacture. The final mechanical properties of the paper can be effectively managed by controlling the processing parameters as well as the cavitational parameters. It has also been established that hydrodynamic cavitation proves to be an effective method over other standard digestion techniques of delignification in terms of electrical energy requirements as well as the required time for processing. Overall, the work is first of its kind application of hydrodynamic cavitation for enhancing the effectiveness of delignification and presents novel results of significant interest to the paper and pulp industry opening an entirely new area of application of cavitational reactors.

Polarization optical-histochemical characterization and supramolecular structure of carbohydrate fibrils.

Topo-optical staining reactions were used to investigate the structures of bacterial cellulose, insect chitosan and alginic acid from brown algae. Polysaccharide complexes, glycosaminoglycans and sulfate groups were presented and demonstrated selectively. Chitosan and alginic acid are structurally similar to glycosaminoglycans (GAGs), which are constituents of human amyloid fibrils. The staining sequences shown can be used as reliable methods for histochemistry with light and polarization microscopy. They will help to clarify the complex protein-polysaccharide structure of amyloid fibrils.

Xylanase and ultrasound assisted pulping of wheat straw.

In the present work, a novel approach to pretreat wheat straw pulping was investigated with ultrasound and xylanase to achieve maximum reduction in lignin content. Sequential xylanase pretreatment and alkaline pulping was found to reduce kappa number by 0.31 to 4.84 % compared with only alkaline pulping alone at different pulping conditions. Although Klason lignin of ultrasound-treated straw was found to be 7.37 % less compared with untreated straw, sequential ultrasound pretreatment and alkaline pulping could not show any significant reduction in kappa number compared with alkaline pulping alone. Also, sequential xylanase and ultrasound pretreatment could not show any significant reduction in kappa number. Total yield of the pulp was found to be less in ultrasound-assisted processing compared with both alkaline pulping alone and sequential xylanase pretreatment and alkaline pulping.

Viscoelastic properties and antimicrobial activity of cellulose fiber sheets impregnated with Ag nanoparticles.

A silver nanoparticle colloid was prepared by a modified Tollens method using d-glucose as the reduction agent. The obtained nanoparticles were used for the modification of pine, linter and recycled cellulose fibers. Although the silver contents were relatively low (0.05-0.13 wt.%), the cellulose-sheets prepared from the modified fibers show improved mechanical and viscoelastic properties. The tensile index (strength) increased with up to 30% in comparison to the index of the sheets obtained from the untreated fibers. The influence of the nanoparticles on the viscoelastic properties of the cellulose sheets was investigated by dynamic mechanical analysis (DMA) in the temperature range from -120 to 20 °C and with a force frequency of 100 Hz. A broad relaxation transition positioned at -80 °C was observed in the loss modulus spectrum of all the cellulose sheets, while the Ag-modified sheets exhibited higher storage moduli values in the whole temperature range. The antimicrobial activity tests show that the pine, silver and recycled cellulose fiber sheets with silver nanoparticles can be successfully employed to prevent the viability and growth of the common pathogens Staphylococcus aureus, Escherichia coli and Candida albicans.

Cavitation assisted delignification of wheat straw: a review.

Wheat is grown in most of the Indian and Chinese regions and after harvesting, the remaining straw offers considerable promise as a renewable source most suitable for papermaking and as a pulping resource. Delignification of wheat straw offers ample scope for energy conservation by way of the application of the process intensification principles. The present work reviews the pretreatment techniques available for improving the effectiveness of the conventional approach for polysaccharide component separation, softening and delignification. A detailed overview of the cavitation assisted delignification process has been presented based on the earlier literature illustrations and important operational guidelines have been presented for overall low-cost and amenable energy utilization in the processes. The effectiveness of the methods has been evaluated according to yield and properties of the isolated fibers in comparison to the conventional treatment. Also the experimental results of one such non-conventional treatment scheme based on the use of hydrodynamic cavitation have been presented for the pulping of wheat straw. The effect of hydrodynamically induced cavitation on cell wall matrix and its components have been characterized using FT-IR analysis with an objective of understanding the cavitation assisted digestion mechanism on straws. It has been observed that the use of hydrodynamic cavitation does not degrade the fibrillar structure of cellulose but causes relocalisation and partial removal of lignin. Overall it appears that considerable improvement can be obtained due to the use of pretreatment or alternate techniques for delignification, which is an energy intensive step in the paper making industries.

Piezoelectric Effect of Cellulose Nanocrystals Thin Films.

Ultrathin films of aligned cellulose nanocrystals (CNCs) were assembled on mica supports by using electric field-assisted shear. The relationship between polarization gradients and strain mechanics of the obtained films was examined by monitoring their deflection with an atomic force microscope operated in contact mode. The piezoelectric response of the films was ascribed to the collective contribution of the asymmetric crystalline structure of the cellulose crystals. The magnitude of the effective shear piezoelectric constant (d25) of highly ordered CNC films was determined to be 2.1 Å/V, which is comparable to that of a reference film of a piezoelectric metal oxide.

Dielectrophoresis of cellulose nanocrystals and alignment in ultrathin films by electric field-assisted shear assembly.

Ultrathin films of cellulose nanocrystals (CNCs) are obtained by using a convective assembly setup coupled with a low-strength external AC electric field. The orientation and degree of alignment of the rod-like nanoparticles are controlled by the applied field strength and frequency used during film formation. Calculated dipole moments and Clausius-Mossotti factors allowed the determination of the critical frequencies, the peak dielectrophoresis as well as the principal orientation of the CNCs in the ultrathin films. As a result of the combination of shear forces and low electric field highly ultrathin films with controlled, unprecedented CNC alignment are achieved.