Dissolution Of Solids Research Articles

Mechanisms of dissolution and crystallization of amorphous glibenclamide

Amorphous solid dispersions enhance the dissolution and oral bioavailability of poorly water-soluble drugs. However, the link between polymer properties and formulation performance has not been fully clarified yet. We studied the effect of hydroxypropyl cellulose (HPC) polymers molecular weight (Mw) on the storage stability, dissolution kinetics and supersaturation stability of spray-dried amorphous glibenclamide (GLB) formulations. The solid-state stability of amorphous GLB during storage was significantly enhanced by both the 40 kDa (HPC-SSL) and 84 kDa (HPC-L) polymers, regardless of Mw differences. In contrast, HPC-SSL maintained significantly higher aqueous drug concentrations during dissolution, compared to HPC-L (its higher Mw analogue). Dedicated dissolution experiments, in situ optical microscopy and solid-state characterization revealed that aqueous drug concentrations were determined by the interplay between crystallization inhibition, drug ionization, wetting and solubilization effects: (1) HPC prevents surface nucleation, hence inhibiting crystallization, (2) intestinal colloids (bile salts and phospholipids) increase supersaturated drug concentrations via wetting and solubilization effects and (3) pH and drug ionization severely impact the degree of supersaturation. The better performance of the lower Mw HPC-SSL was due to its superior inhibition of surface crystallization. These insights into the molecular mechanisms of dissolution and crystallization of amorphous solids provide foundation for rational formulation development.

Femtosecond laser-produced heterogeneous wettability surfaces for turning Leidenfrost drop spinning

Liquid droplets on superheated surfaces produce the Leidenfrost effect. This phenomenon might lead to droplet manipulation and control strategies in microfluidics and thermal management. However, Leidenfrost droplets move randomly and irregularly on superheated surfaces and the manufacturing of special surfaces to control Leidenfrost droplet movement poses great challenges. Here, we propose a simple and environment-friendly method to create heterogeneously wetting surface structures to control the spin motion of droplets on superheated brass using femtosecond laser patterning. The water contact angle of the superhydrophobic area on the surface was ∼160°, and the superhydrophilic area showed ∼7°. A z-shaped pattern was fabricated, which segmented the vapor film and influenced gas flow, and it resulted in the spinning of oval-shaped droplets analogous to a spinning egg. We used simulation to explain this phenomenon and also expanded the application of this droplet control in accelerating dissolution of solids and mechanical driving. This study provides the basis for a creative control method using the Leidenfrost droplet phenomenon, which has broad implications in steam-driven droplet motion and future fluid manipulation.

Dissolution behavior of mixed calcium‑cobalt carbonates at 25 °C in contact with different gas phases

The potential immobilization of cobalt in various environments can be achieved through the incorporation of Co into carbonate minerals, forming solid solutions of (Ca1-xCox)CO3. However, the thermodynamic properties of these minerals are not well-understood due to conflicting data from natural observations and experiments. In this work, a series of mixed calcium‑cobalt carbonates were prepared and their interaction with aqueous solution was investigated. Depending on the Co/(Ca + Co) mol ratio (XCo) of the mixed solution, ranging from 0.00 to 1.00, pure calcite, Co-bearing calcite, Co-bearing aragonite, Ca-bearing spherocobaltite and pure spherocobaltite were successively synthesized using a precipitation method. Upon dissolution of the Co-bearing solids (XCo = 0.10–1.00) in N2-degassed water (NW) and air-saturated water (AW), the Co concentration of the aqueous solutions increased gradually to a stable state of 0.017–0.191 and 0.018–0.186 mmol/L after 240–360 d dissolution, respectively. When the dissolution occurred in CO2-saturated water (CW), the Co concentration initially spiked to 0.372–2.258 mmol/L within 6 h ∼ 15 d and then decreased to a stable range of 0.030–0.559 mmol/L after 240–360 d. The Co/(Ca + Co) mol ratio in the aqueous solution (XCo2+,AS) was significantly lower than the Co/(Ca + Co) atomic ratio in the solids (XCo,SS), particularly when dissolved in NW and AW. During these dissolution processes in NW, AW and CW at 25 °C, the average log IAP values at the final stable state were determined as follows: for calcite (CaCO3), the values were −8.25 ± 0.03 in NW, −8.34 ± 0.11 in AW, and −8.10 ± 0.08 in CW; for spherocobaltite (CoCO3), they were −9.24 ± 0.26 in NW, −9.39 ± 0.23 in AW, and −9.38 ± 0.09 in CW. Furthermore, the log IAP values increased from those typical for calcite to −7.89 ± 0.01 ∼ −7.84 ± 0.10 for the solid with XCo,SS = 0.187 as XCo,SS increased, eventually aligning with those typical of spherocobaltite. Lippmann diagrams, constructed using the Guggenheim parameters a0 = 2.30 and a1 = 0.265 for the “subregular” calcite-spherocobaltite solid solutions [(Ca1-xCox)CO3] with a miscibility gap ranging from XCo,SS = 0.251 to 0.858, highlighted the “peritectic” point at XCo2+,AS = 0.0538 on the solutus. This analysis revealed that the solids dissolved non-stoichiometrically in water. Consequently, the Co-poor aqueous solution would reach equilibrium with the Co-rich calcite-structure phase at the solid surface.

Influence of inorganic solid particles on the stability of water-in-crude oil emulsions: Evaluating the role of surface charge

This study examines the effect of inorganic solid particles on the stability of water-in-oil (W/O) emulsions formed during the transportation, refining, and storage of crude oil. The surface properties of inorganic particles, such as kaolinite and calcite, can influence the interface between crude oil and water, affecting the stability of the emulsion. The study evaluates the quantitative effect of these particles on emulsion stability and investigates how surface properties affect the emulsions. Emulsions were prepared using crude oil and synthetic brine, with calcite and kaolinite added as inorganic solid particles. Adding inorganic solids increased the volume of released water and altered the emulsion stability, with high concentrations decreasing the formation of stable emulsions. The dissolution of inorganic solids increased the pH of the solution and promoted demulsification due to the high surface potential of crude oil. The solid particles enhanced the formation of oil-in-water-in-oil (O/W/O) emulsions, generating unstable emulsions. The study also found that increasing temperature and adding inorganic solids decreased the emulsion height over time, which was predicted by the emulsion layer growth model. The coagulation rate constant was a tuning parameter, with a higher value implying higher internal repulsion and stronger coagulation between water droplets, facilitating emulsion instability. It has been observed that elevating the storage temperature and introducing kaolinite accelerates the coagulation rate constant, whereas the addition of calcite decreases this value, ultimately contributing to the stabilisation of the emulsions.

Surface Energy in the Processes of Disintegration of Solids

Objective. The purpose of the study is to experimentally measure the surface energy of solids during their grinding.Method. The study is based on the use of methods for determining the surface tension of solids. At least 20-25% of all electricity produced in the world is spent on grinding materials in industry. When the resulting particles are reduced to tens of nanometers, the contribution of surface energy (st) to the grinding work becomes so large that it is difficult not to take it into account. Measuring the surface tension of liquids has long been proven. But measuring (st) of solids causes great difficulties. Currently, more than twenty methods for determining (st) are known.Result. Based on the phenomenon of spontaneous bending of thin thread-like structures, a method for determining (st) has been developed. Examples are given in which (st) at the phase interface plays an important role in obtaining samples with a microstructure using the method of severe plastic deformation (SPD). To obtain fine metal powders, one of the variants of the SPD method has been proposed. A method has been found for the physical activation of aluminum granules, which increases the reaction rate of the metal in an aqueous environment by about a thousand times. This is necessary for the development of an anaerobic power plant capable of operating at great depths.Conclusion. The new technology makes it possible to obtain high-purity, non-oxidized metal powders without toxic waste and emissions and with energy costs lower than in all known methods.

The dissolution of total suspended solids and treatment strategy of tailwater in a Litopenaeus vannamei recirculating aquaculture system

The dissolution of total suspended solids and treatment strategy of tailwater in a Litopenaeus vannamei recirculating aquaculture system

Dissolution and Growth Kinetics and the Rate-Controlling Step in Transformation of Amorphous to Crystalline Phase Using Antisolvent Crystallization

The kinetics of the formation of amorphous disodium guanosine 5′-monophosphate and its transformation to the heptahydrate phase were studied under various operating conditions using in situ Raman and focused beam reflectance measurement (FBRM). Supersaturation, solvent composition, feed concentration, addition rate, and viscosity were shown to affect the rate-determining steps of the transformation. The rate-controlling mechanisms in the overall kinetics have been confirmed. The observation of the slurry viscosity of the suspension of the amorphous phase shows the option to observe the phase transformation. The transformation process was affected by the dissolution, growth, and supersaturation in which the rate-controlling step was divided into two sections, such as the initial and later sections of the transformation. The overall rate constants were determined by combining the constants of the dissolution rate and the growth rates of each section. In situ Raman spectroscopy examination of the concentration of solution and solids can determine the rate-limiting processes during the transformation. The zero-order, first-order, and surface reaction equations as kinetic equations are highlighted and compared for the dissolution of the amorphous solids and the growth of the heptahydrate crystals. The dissolution of the amorphous (metastable form) and the growth of the heptahydrate (stable form) were found to be best fitted to the zero-order kinetic model. In particular, the variation of particle size distribution over time can give the rate-determining steps. These results suggest that the data measured by Raman spectroscopy and FBRM can be successfully coupled into a dissolution and growth model to further grasp and interpret the phase transformation. A dissolution rate-controlling step was dominated by a pattern in which both supersaturation and amorphous dissolution decreased simultaneously, and the growth rate-controlling step was shown in a pattern in which either supersaturation or amorphous dissolution was constant. Furthermore, the growth of heptahydrate crystals at a viscosity of the suspension with the amorphous solids below 70 cp and the dissolution of the amorphous solids above it can be used as the key determinant. Using the method developed and the kinetic constants obtained in this work, it is possible to create an appropriate control strategy to produce the desired form in the final product.

Maximizing well productivity by using filter cake breaker for synthetic-based mud drill-in fluid (SBMDIF) system

• Formation damage has a significant impact on the overall performance. • An effective filter cake breaker selection is critical to minimize formation damage. • The straightforward reaction of meso‑surfactant and nano-surfactant filter cake breakers with barite. • Surfactant-based filter cake breaker was more efficient in removing synthetic-based drilling mud. Formation damage has a significant impact on the overall performance of the well productivity. Removal of filter cake which is deemed to be the main strategy of formation damage remediation is crucial in open hole completion with pre-slotted liner or stand-alone screen (SAS) as a mean of sand control. Without proper planning, inefficient filter cake removal can lead to tremendous consequences since filter cake can plug the sand control component. Making the condition worse, sand control component is susceptible to plugging. This highlights the importance of selecting an effective filter cake breaker that can successfully remove the filter cake through dissolution of the main solids that constitute the major portions of the filter cake which could be the weighting material, barite, or calcium carbonate. Besides that, a proper understanding of the mechanism of the filter cake breaker chemical would be very beneficial to comprehend the filter cake breaker efficiency. The laboratory study attempted to emulate the reservoir condition. Regained permeability testing using High Pressure High Temperature (HPHT) Filter Press aimed to test the ability of several commercial filter cake breakers in removing synthetic-based-mud drill-in-fluids (SBMDIF). Chelating-based filter cake breaker, meso‑surfactant-based filter cake breaker and nano-surfactant-based filter cake breaker were the samples to be tested in the laboratory work. The condition of the filter cake after being soaked statically was visually interpreted and the regain permeability was recorded. The mechanism of each filter cake breaker to remove the SBMDIF filter cake was also examined. Based on the experimental study, meso‑surfactant-based filter cake breaker was found to be more effective to remove SBMDIF filter cake compared to chelating-based filter cake breaker and nano-surfactant-based filter cake breaker.

Development of semi-moist formulated feed for female orange mud crabs, Scylla olivacea (Herbst, 1796) broodstocks with graded lipid levels

The present study examined the physical characteristics of semi-moist formulated feeds to the reproductive maturation of female orange mud crab, Scylla olivacea. In this study, two experiments were conducted. The first experiment compared four types of natural diets; fish offal (discarded organ), mangrove clams (Polymesoda erosa), black devil snail (Faunus ater), and commercial shrimp feeds (control), to select the basal diet for the formulation of feeds. Proximate compositions of the different diets revealed that the mangrove clam, P. erosa (protein = 81.63 % and lipid = 13.54 %) is the most suitable ingredients for the mud crabs’ diet. Fatty acid analysis also showed that mangrove clams had the highest concentration of ARA, EPA, and DHA at 0.56 %, 1.62 %, and 2.68 % respectively. In the second experiment, four isonitrogenous feed (~42 %) with different lipid percentages; T1: 6 %, T2: 8 %, T3: 10 %, and T4: 12 % were formulated to investigate the effects of the lipid inclusion on maturation of mud crabs. The effects of different levels of lipid on palatability, feed water stability, nutrient leaching, buoyancy, and total solids were studied prior to feeding experimentation. The palatability tests showed high attractability of the crabs towards the feeds. Meanwhile, high water stability (dry matter retention) were recorded in all experimental feeds after long immersion hours, with low nutrient leaching, and low solids disintegration. Later, feeding trial on 120 matured female mud crabs (carapace width: 10.24 ± 0.66 cm and body weight: 186.42 ± 37.90 g) revealed that the semi-moist formulated feeds are readily accepted by the crabs. The crabs from all treatments recorded positive body weight gain (BWG) and specific growth rate (SGR) with crabs fed T4 dominating (BWG = 11.43 g, 14.65 g, and 12.13 g; SGR = 0.35 %day-1, 0.13 %day-1, and 0.08 %day-1 during 30-, 60-, and 90-day of feeding trials respectively) (p < 0.05). Similarly, morphological results showed that high GSI was noted in S. olivacea fed with T4, increasing at subsequent feeding trials (10.44 %, 11.03 %, and 14.51 %) (p < 0.05), which were inversely proportional with the HSI (8.92 %, 5.11 %, and 4.76 %) (p < 0.05) compared to other treatments, probably contributed by the high percentage of lipid inclusion. These findings demonstrate that diets contained 12 % lipid and 42 % protein (T4) is ideal for somatic and reproductive growth of S. olivacea. Yet, a nutrient dose-response study is expected to be carried out in the future to estimate the optimum lipid level required for reproductive and growth performance in S. olivacea.

A New Model of Chemical Dissolution of Solids: an Analysis of the Mechanism of Dissolution of Monodispersed Materials

On the basis of a new model of chemical dissolution, an analysis of the kinetic parameters obtained using the modified V.V. Dolivo-Dobrovolsky equation was carried out. It shows that the change in parameters during the transition from one mineral to another is subject to a compensation effect. Additionally, calculations based on the new dissolution model made it possible to distinguish between the systemic and individual properties of minerals of the same nature in the process of dissolution. These minerals differ from each other by the concentration of ac tive surface complexes, and are combined into a system by a single transmission coefficient and the same value of the lifetime of the active complex.

Sonochemistry of actinides: from ions to nanoparticles and beyond

AbstractSonochemistry studies chemical and physical effects in liquids submitted to power ultrasound. These effects arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species. In principle, each cavitation bubble can be considered as a microreactor initiating chemical reactions at mild conditions. In addition, microjets and shock waves accompanied bubble collapse produce fragmentation, dispersion and erosion of solid surfaces or particles. Microbubbles oscillating in liquids also enable nucleation and precipitation of nanosized actinide compounds with specific morphology. This review focuses on the versatile sonochemical processes with actinide ions and particles in homogenous solutions and heterogenous systems. The redox reactions in aqueous solutions, dissolution or precipitation of refractory solids, synthesis of actinide nanoparticles, and ultrasonically driving decontamination are considered. The guideline for further research is also discussed.

Evaluation of impact of sludge types and solids content on sludge treatment using microwave enhanced advanced oxidation process

ABSTRACT The microwave enhanced advanced oxidation process (MW-AOP) has been applied to pre-treat different sludge types and high solids content. Secondary sludge not only had the highest solids and nutrient content but also yielded higher treatment efficiency than primary or mixed sludge. In the case of secondary sludge with 4% total solids (TS), the total suspended solids (TSS) concentration was reduced by 32% while soluble chemical oxygen demand concentration increased from 1% to 40% after treatment at 110°C. A high level of nutrient release was also achieved; about 65% total phosphate (TP) solubilized at 110°C. The degree of secondary sludge disintegration was dictated by temperature and hydrogen peroxide dosage. The optimal operating temperature for the system was 110°C, and sludge containing TS up to 8% was treated effectively. Secondary sludge with 8% TS had a TSS reduction of 41% after treatment at 110°C while COD solubilization was about 45%; about 55% TP was solubilized at 10 min holding time. Treatment of sludge with higher solids content would allow for handling larger amounts of sludge at a given period and reduce heating cost per unit of treated sludge. The inter-relationship between the degree of sludge disintegration and changes in chemical and physical properties was also clearly demonstrated here. The treated sludge would be an ideal substrate for anaerobic digestion or phosphorous recovery processes. High levels of nutrients (phosphorus and nitrogen) and metal release, and solids disintegration from sludge containing high solids content would make subsequent resource recovery processes more effective and economical.

Improving rehydration properties of spray-dried milk protein isolates by supplementing soluble caseins

Spray-dried milk protein isolates (MPIs) are important dairy ingredients but may not have desirable rehydration properties for industrial applications. In the present study, rehydration properties of MPIs were improved by spray-drying MPI dispersions containing different amounts of soluble caseins in the form of derivatized MPI (dMPI). dMPI was prepared by alkalizing MPI dispersions to pH 11.0 and subsequently acidifying to pH 6.8 (the pH-cycle). All the spray-dried MPIs had the similar bulk density (around 0.33 g/cm−3), composition, size distribution (1–100 µm), and SEM morphology. However, the decrease of hydrodynamic diameter, dissolution of total solids and proteins, and disruption of particles during the dynamic rehydration were accelerated as the dMPI content increased, indicating the improved rehydration properties. The improvement in rehydration properties was not due to the wettability that decreased as the dMPI:MPI mass ratio changed from 0:8 to 8:0, but resulted from the reduced cross-linking of casein micelles on powder surface and the increased surface porosity during the hydration as observed for partially hydrated samples. The present work may assist industrial applications of spray-dried MPIs.

Chitin as a Sorbent Superior to Other Biopolymers: Features and Applications in Environmental Research, Energy Conversion, and Understanding Evolution of Animals

Chitin is an effective sorbent which can be used in environmental monitoring, beyond obvious applications in withholding metal-containing pollutants from wastewater- or nuclear fuel reprocessing flows, since background levels in (purified) chitin are very low except for a few metals (Fe, Cu, Al, Ti, and Zn). Since retention of Mx+ and their complexes on chitin depend on an oxidation state, and to a lesser extent the presence of possible ligands or co-ligands, partition between chitin samples exposed to sediment and those exposed to water can be changed by environmental factors such as local biota producing or absorbing/metabolizing effective ligands such as citrate or oxalate and by changes of redox potential. Thermodynamics are studied via log P, using calibration functions log P vs. 1/r or log P vs. Σσ (sum of Hammett parameters of ligand donor groups) for di- and trivalent elements not involved in biochemical activity (not even indirectly) and thus measuring “deviations” from expected values. These “deviations” can be due to input as a pollutant, biochemical use of certain elements, precipitation or (bio-induced reduction of SO42− or CO2) dissolution of solids in sediment. Biochemical processes which occur deep in sediment can be detected due to this effect. Data from grafted chitin (saturation within ≤ 10 min) and from outer surfaces of arthropods caught at the same site do agree well. Log P is more telling than total amounts retrieved. Future applications of these features of chitin are outlined.

Numerical modeling of the diffusional transport of nitrogen in multi-phase solid titanium and its application to determine diffusion coefficients

As part of a program to understand the dissolution of nitrogen-rich titanium solids in liquid titanium, this manuscript presents a numerical study of nitrogen transport in titanium at elevated temperatures. A Landau transformation was applied to the equations governing mass transport which were used as the basis for the numerical model. The numerical model was used initially to simulate nitrogen transport in a planar geometry and the predicted nitrogen concentration profiles and displacement of Ti–N phase boundaries showed good agreement with analytically derived solutions. The numerical model was then used to simulate nitrogen transport in commercially pure titanium cylinders. The model results were shown to be sensitive to the diffusion coefficients of Ti–N phases present in the system. Based on the sensitivity analysis, diffusion coefficients at 1650 °C of 4.3 × 10 − 11 m 2 s − 1 , 1.6 × 10 − 11 m 2 s − 1 and 1.7 × 10 − 12 m 2 s − 1 for β-Ti, α-Ti and TiN phases, respectively, were back calculated using the model. The model predictions, using the new diffusion coefficients, showed good agreement with previously published data in terms of both the nitrogen concentration profiles and displacements of Ti–N phase boundaries under the conditions examined in the study. The comparison indicates the presented model is capable of accurately approximating the transport of nitrogen in titanium at elevated temperatures.

Jupiter’s “cold” formation in the protosolar disk shadow

Context.Atmospheric compositions offer valuable clues to planetary formation and evolution. Jupiter has been the most well-studied giant planet in terms of its atmosphere; however, the origin of the Jovian atmospheric composition remains a puzzle as the abundances of nitrogen and noble gases as high as those of other elements could only originate from extremely cold environments.Aims.We propose a novel idea for explaining the Jovian atmospheric composition: dust pileup at the H2O snow line casts a shadow and cools the Jupiter orbit so that N2and noble gases can freeze. Planetesimals or a core formed in the shadowed region can enrich nitrogen and noble gases as much as other elements through their dissolution in the envelope.Methods.We compute the temperature structure of a shadowed protosolar disk with radiative transfer calculations. Then, we investigate the radial volatile distributions and predict the atmospheric composition of Jupiter with condensation calculations.Results.We find that the vicinity of the current Jupiter orbit, approximately 3 − 7 AU, could be as cold as ≲30 K if the small-dust surface density varies by a factor of ≳30 across the H2O snow line. According to previous grain growth simulations, this condition could be achieved by weak disk turbulence if silicate grains are more fragile than icy grains. The shadow can cause the condensation of most volatile substances, namely N2and Ar. We demonstrate that the dissolution of shadowed solids can explain the elemental abundance patterns of the Jovian atmosphere even if proto-Jupiter was formed near Jupiter’s current orbit.Conclusions.The disk shadow may play a vital role in controlling atmospheric compositions. The effect of the shadow also impacts the interpretation of upcoming observations of exoplanetary atmospheres by JWST.

Integrating column leaching experiments and geochemical modelling to predict the long-term alkaline stability during erosion process for gypsum amended bauxite residue

Gypsum amendment is widely used to resolve alkalinity issues and implement sustainable management for bauxite residue disposal areas (BRDAs). Amended BRDAs under natural conditions suffer from long-term erosion processes. Nevertheless, the effect of erosion on amendment efficacy is rarely assessed. In this study, by integrating the geochemical modelling of PHREEQC and column leaching experiments, the dissolution of alkaline solids in bauxite residue (BR) and gypsum amendment, as well as their environmental behaviors, were determined through a 1-year simulated rainfall leaching experiment. The PHREEQC simulation results demonstrated that Na+ ion strength, CO2 partial pressure and rainfall, all affected the saturation index (SI) of calcite significantly and accelerated its corrosion, leading to the dissolution of gypsum and calcite in a relatively stable state. However, Na+ ion strength and rainfall significantly acted on the SI of gypsum, which lead to loss of Ca2+ and reduction of alkaline stability. In addition to the effects of Na+ and Ca2+ on the saturation concentration of gypsum and calcite solution, Na+ and Ca2+ also exhibited significant effects on the equilibrium of chemical species reactions. The column results confirmed that stability of gypsum and calcite was consistent with the simulation results of PHREEQC in the BRDAs environment. Furthermore, multiple linear regressions revealed differences in combined contributions of rainwater and atmospheric CO2 on the stability of calcite and gypsum. The PHREEQC simulation provides a new approach to predict long-term alkaline stability of BR as well as to establish sustainable remediation on BRDAs during erosion process.

A stable and accurate scheme for solving the Stefan problem coupled with natural convection using the Immersed Boundary Smooth Extension method

The dissolution of solids has created spectacular geomorphologies ranging from centimeter-scale cave scallops to the kilometer-scale “stone forests” of China and Madagascar. Mathematically, dissolution processes are modeled by a Stefan problem, which describes how the motion of a phase-separating interface depends on local concentration gradients, coupled to a fluid flow. Simulating these problems is challenging, requiring the evolution of a free interface whose motion depends on the normal derivatives of an external field in an ever-changing domain. Moreover, density differences created in the fluid domain induce self-generated convecting flows that further complicate the numerical study of dissolution processes. In this contribution, we present a numerical method for the simulation of the Stefan problem coupled to a fluid flow. The scheme uses the Immersed Boundary Smooth Extension method to solve the bulk advection-diffusion and fluid equations in the complex, evolving geometry, coupled to a θ-L scheme that provides stable evolution of the boundary. We demonstrate 3rd-order temporal and pointwise spatial convergence of the scheme for the classical Stefan problem, and 2nd-order temporal and pointwise spatial convergence when coupled to flow. Examples of dissolution of solids that result in high-Rayleigh number convection are numerically studied, and qualitatively reproduce the complex morphologies observed in recent experiments.

How to evaluate the mass transfer resistances in dense solid–liquid suspensions

The dissolution of solids in slurry stirred tanks is affected from the solid concentration distribution to different extend, depending on the agitation conditions. In this work, the relationship between solid–liquid mixing and mass transfer is investigated by estimating the characteristic times of different phenomena: liquid mixing, solid dissolution, diffusion of the dissolved species in the vessel volume. The analysis is based on Electrical Resistance Tomography data collected during the simultaneous operations of dissolution and mixing. For dilute solid–liquid systems, the relative importance of the solid dissolution and the liquid mixing depends on the particle size and the impeller speed, while the diffusion in stagnant zones is often negligible. Instead, the diffusion mechanism has an important effect on mass transfer for dense systems, where strong axial gradients of solid concentration are established and the stirred tank volume can be divided into a lower zone containing a cloud of dense mixture and an almost stagnant clear liquid layer on top. Based on original and literature experimental data, a method for the main mass transfer resistance identification depending on the agitation condition, the solid volume fraction distribution and the soluble particle size is suggested.

Effect of SRT and digester staging on the anaerobic digestion of municipal sludge

The effect of solids retention time (SRT) on the mesophilic anaerobic digestion of a mixture of primary and waste activate sludge (WAS) was investigated. Twelve laboratory-scale (8 L) digesters were operated in triplicate at four different SRTs (5, 10, 20 and 40 days). The performance of the digesters was evaluated through measuring gas production and composition, total and volatile suspended solids (TSS & VSS) and other effluent quality parameters. VSS removal ranged between 37.6 and 53.6%. The rate of solids disintegration was modeled as a first-order decay reaction taking place in a plug-flow reactor with recycle. The calculated biodegradable fraction of the VSS and the first-order reaction rate constant were 55.3% and 0.38 d−1, respectively. During the second phase of the study, a comparison between multistage digesters in series versus a single-stage digester of equivalent total SRT was performed. Staging was found to always affect greater VSS destruction than single-stage operation. A mathematical model describing VSS destruction in a multistage reactor was developed.