Granule Radius Research Articles

Rapid formation of granules coupling n-DAMO and anammox microorganisms to remove nitrogen

Granular sludge exhibits unique features, including rapid settling velocity, high loading rate and relative insensitivity against inhibitors, thus being a favorable platform for the cultivation of slow-growing and vulnerable microorganisms, such as anaerobic ammonium oxidation (anammox) bacteria and nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) microorganisms. While anammox granules have been widely applied, little is known about how to speed up the granulation process of n-DAMO microorganisms, which grow even slower than anammox bacteria. In this study, we used mature anammox granules as biotic carriers to embed n-DAMO microorganisms, which obtained combined anammox + n-DAMO granules within 6 months. The results of whole-granule 16S rRNA gene amplicon sequencing showed the coexistence of anammox bacteria, n-DAMO bacteria and n-DAMO archaea. The microbial stratification along granule radius was further elucidated by cryosection-16S rRNA gene amplicon sequencing, showing the dominance of n-DAMO archaea and anammox bacteria at inner and outer layers, respectively. Moreover, the images of cryosection-fluorescence in situ hybridization (FISH) verified this stratification and also indicated a shift in microbial stratification. Specifically, n-DAMO bacteria and n-DAMO archaea attached to the anammox granule surface initially, which moved to the inner layer after 4-months operation. On the basis of combined anammox + n-DAMO granules, a practically useful nitrogen removal rate (1.0 kg N/m3/d) was obtained from sidestream wastewater, which provides new avenue to remove nitrogen from wastewater using methane as carbon source.

Diffusion Deposition of Nanoparticles in a Layer of Granules

The deposition of aerosol nanoparticles has been studied in a model granular filter composed of parallel monolayers of contacting spherical granules with a square packing, where each even monolayer is shifted in its plane relative to an odd layer by the granule radius in two directions normal to one another. The monolayers of the granules are oriented normal to an incident flow. The efficiencies of diffusion collection of point particles by the granules have been calculated as depending on the distance between the layers in the regime of a three-dimensional gas flow at small Reynolds numbers $$\operatorname{Re} $$ $$ \ll $$ 1 within a Peclet number range of $${\text{Pe}}$$ = 102−104. The calculation results have agreed with the published data and the results of measuring the deposition of monodisperse nanoparticles from nitrogen and helium upon filtration through layers of monodisperse metal spheres. The possibility of using a layer of granules as a diffusion battery for measuring the sizes of aerosol particles has been discussed.

Theoretical understanding of the optimum conditions for a mainstream granular nitritation-anammox reactor coupled with anaerobic pretreatment

Mainstream nitritation-anammox processes with anaerobic pretreatment may provide a paradigm-shifting strategy for achieving more energy-efficient and cost-saving wastewater treatment, and most efforts in this area were through bench studies. To better understand the performance of bench systems and make possible predication of key parameters beyond experiments, a mathematical model was developed in this study. The model inputs include hydraulic retention time (HRT), influent chemical oxygen demand (COD), sulfate, ammonium, and nitrate, as well as the bulk dissolved oxygen, while the outputs include the COD degradation, nitrogen removal pathways, and biomass partitioning in the reactor and along the granule radius. The simulated results suggest that the COD/N ratio of anaerobic effluent is highly related to the HRT of the anaerobic pretreatment, and it can significantly impact the fractions of AOB, NOB, anammox bacteria and denitrifiers, as well as their contribution to nitrogen conversion in the subsequent nitritation-anammox reactor. The optimal conditions for achieving a reliable and robust anaerobic pretreatment system is predicted to have an HRTHAR of 11 h that can provide an effluent COD/N ratio of 2 for the subsequent nitritation-anammox reactor to achieve ~93% total nitrogen removal (~76% by anammox) at HRTAMX of 8 h. The proposed model can be valuable to the optimization of the anaerobic pretreatment - mainstream anammox system.

Numerical modelling of flow field within a packed bed of granular material

Computational domain discretization is the pre-processing stage in CFD analysis and it highly contributes to reducing the level of solution error as well as increasing the numerical stability of a model. The discretization of domain representing a packed bed of granular material is a demanding task due to the topology of the model consisting of spherical granules contacting tangentially and narrow regions in the direct vicinity of the contact point. Therefore the aim of the carried out research is to define guidelines to effectively discretize the computational domain representing the packed bed of granular material and validate it using Particle Image Velocimetry (PIV). Two methods of contact point representation between granules (contact point extension, granule radius reduction) and two mesh types (tetrahedral, polyhedral) are examined within the paper. Differences between the analyzed cases are discussed and compared to experimental research results. The obtained results prove that the applied method significantly affects the calculated porosity but does not affect the flow field considerably. Polyhedral mesh turned out to be preferable as the numerical model converges within substantially lower number of iterations and the obtained results are not as affected by the numerical diffusion as in the case of tetrahedral mesh.

Analytical solution of diffusion model for nutrient release from controlled release fertilizer

An analytical method has been developed to solve the initial value problem which arises from Fick’s diffusion equation encountered in the modelling of the Controlled Release Fertilizers. The proposed analytical solution is developed using the modified Adomian decomposition method. This method does not require the discretization method, reliability and efficiency of this method is more and it also reduces the calculation time. The model has predicted the effect of granule radius and diffusion coefficient on the nutrient release and total release time of Controlled Release Fertilizer. Model has predicted that increase in the radius of granule reduces the release and vice versa in case of diffusion coefficient. Detailed understanding of these parameters helps in improved designing of Controlled Release Fertilizer.

Development of control release urea fertilizer model for water and nitrogen movement in flooded rice

Application of control release fertilizer in rice cultivation is a smart way to reduce the environmental nitrogen contamination and enhance the nitrogen use efficiency. The effect of coating thickness and radius of urea granule on nitrogen release rate was modelled, but their effect on nitrogen transformation in soil was not modelled for any crop. In this study, a simple rice water and nitrogen balance model was integrated with a nitrogen release rate model and the effect of coated urea on nitrogen transformations was studied in the CRF-applied flooded rice. The simulated nitrogen release during urea hydrolysis was verified with literature data for uncoated, polymer-coated and mix urea (polymer-coated + uncoated) cases. The integrated model successfully predicted the lag, linear and decay periods of nitrogen release, and peak nitrogen concentration during urea hydrolysis and declining trend during nitrogen transformations. The integrated model could be used as a management tool for determining optimum coating thickness and urea radius for which the nitrogen loss to environment is minimum.

Evaluation of mainstream nitrogen removal by simultaneous partial nitrification, anammox and denitrification (SNAD) process in a granule-based reactor

The mainstream anaerobic ammonium oxidation (anammox) has attracted extensive attention recently, particularly due to its potential of transforming current wastewater treatment plants from energy consuming to energy neutral or positive. However, the presence of biodegradable chemical oxygen demanding (COD, 20–80mgCODL−1) in the mainstream anammox reactor stimulates the growth of heterotrophic bacteria, which would compete for oxygen with ammonia-oxidizing bacteria (AOB) and for nitrite with anammox bacteria, thus interfering with the autotrophic nitrogen removal process. In the present work, with consideration of granule size distribution, a one-dimensional model describing the mainstream simultaneous partial nitrification, anammox and denitrification (SNAD) in a granule-based reactor was established, calibrated and validated, based on the long-term experimental results. Through applying the verified model, simulation studies were conducted and the results showed that the effluent total nitrogen concentration of <5mgNL−1 could be achieved at C/N ratio of 0.2–0.6, DO concentration of 0.2–0.4mgL−1 and granule radius of 300–600μm. The combined effects indicated that the SNAD process with TN removal efficiency >90% was obtained at C/N ratio and DO concentration of 0.2–1.0 and 0.2–0.4mgO2L−1 respectively. Finally, the various granule size distribution patterns were simulated, which confirmed that the size distribution needed to be incorporated in the model to accurately describe the granular anammox system, considering a model based on a uniform granule size does not reflect the real situations. These results provide guides to optimize the operation of mainstream granular autotrophic nitrogen removal process.

Modeling Nutrient Release fromSwelling Polymer-Coated Urea

Abstract. A new model of controlled nutrient release from coated urea (CRCU) has been developed that considers swelling in the presence of an aqueous coating. The water uptake was described using irreversible thermodynamics theory in this model. According to the model, the radius of the swollen pellet was found to be linearly related to time, and the nutrient release was found to be a function of the swollen granule radius. Importantly, the model showed high prediction accuracy for the granule radius with a R2 = 0.99 and a root mean square error (RMSE) of 0.06 mm. The model was validated by comparison with the release profile of a single granule with a R2 = 0.86 and a RMSE of 2.28%. However, a large prediction deviation within populations of granules in static water was noted, which was caused by the reduction in the driving force of release. Therefore, a mathematics model that considers the reduction in the driving force of release requires further research.

Global sensitivity analysis applied to drying models for one or a population of granules

The development of mechanistic models for pharmaceutical processes is of increasing importance due to a noticeable shift toward continuous production in the industry. Sensitivity analysis is a powerful tool during the model building process. A global sensitivity analysis (GSA), exploring sensitivity in a broad parameter space, is performed to detect the most sensitive factors in two models, that is, one for drying of a single granule and one for the drying of a population of granules [using population balance model (PBM)], which was extended by including the gas velocity as extra input compared to our earlier work. β2 was found to be the most important factor for the single particle model which is useful information when performing model calibration. For the PBM‐model, the granule radius and gas temperature were found to be most sensitive. The former indicates that granulator performance impacts drying behavior, the latter is informative with respect to the variables that primarily need to be controlled during continuous operation. In addition, several GSA techniques are analyzed and compared with respect to the correct conclusion and computational load. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1700–1717, 2014

Nonstationary Combustion of Methane with Gas Hydrate Dissociation

Kinetics of methane hydrate dissociation at combustion in the air atmosphere at the outer pressure of 1 bar was studied experimentally. Dissociation is divided into several characteristic time stages with different rates of gas hydrate decomposition. There is a very high temperature gradient along the granule radius. At combustion the movement velocities of dissociation front and pores are high. Thermal imaging of the powder surface demonstrates significant temperature maldistribution. Spatially nonuniform escape of methane from a sample leads to local temperature and concentration maldistributions in the flame, which cause thermal instability of the flame front and the loss of hydrodynamic stability. Instability of combustion generates two equivalent mechanisms of convective transfer: the shear laminar flow and large-scale vortices, which intensify fuel and oxidizer mixing. Experimental data have revealed not only the local spatial-time nonuniformities but also significantly nonstationary character of the averaged flow. The measured instantaneous and average velocities of methane on the powder surface allowed an estimate of the stoichiometric ratio. The maximal velocity of methane propagation corresponded to 1 mm/s in experiments without combustion and to 15 mm/s with combustion.

ENCAPSULATION OF NPK MINERAL FERTILIZER GRANULES BY DIFFERENT TYPES OF ALKYD RESINS

Three different kinds of alkyd resins were used for encapsulation a commercial granules fertilizers NPK (N 12%, P2O5 8% and K2O 18%) with particle diameter ranges from 3 to 5 mm. The total concentration of the alkyd coated film was less than 10 % of the total weight of the fertilizer composition. The release rate was measured by conductivity test. The area of the coating film was determined by mathematical calculations. Controlled release parameters including membrane thickness, granule radius and type of resin were taken into consideration.

Modeling NPK release from spherically coated fertilizer granules

Controlled release of nutrients from fertilizers is desired for its optimal uptake by plants and crops. In our previous study [22], we considered saturation of a non-electrolytic nutrient and its release from a spherically coated fertilizer granule, assuming only molecular diffusion. In the present study, release of three types of nutrients (NPK) from their commonly used commercial fertilizer sources, stuffed in a coated spherical fertilizer granule is investigated using both molecular and ionic diffusions. One of the nutrients is potassium chloride (KCl), a strong electrolyte, the other is diammonium phosphate ((NH 4) 2HPO 4), a weak electrolyte, and the third is urea ((NH 2) 2CO), a non-electrolyte. The release takes place from the granule’s surface area in contact with the soil. The contact area is varied from almost a point to the lower hemisphere with the help of a parameter. The latter case helps to evaluate the release time for basal form of fertilizer application. The effects of granule radius, nutrients release rate, contact area, association constant, pH, and temperature on the release time of nutrients are studied. Variations in release time are much more pronounced from a spherical granule of larger radius having almost point contact with alkaline soil at higher temperatures and for a weak electrolyte of lower association constant. The release time is computed using the techniques of deterministic mathematical modeling and computer simulation. Sensitivity analysis has also been done by giving small variations in the parameters of pH modulator, in the ionic diffusion coefficients of strong- and weak-electrolytes and evaluating root mean squared deviations (RMSD) in release time. Values of RMSDs are negligible, establishing the stability and accuracy of the technique used. Such studies are useful in manufacturing coated spherical granules according to the varying soil conditions, educating the farmers about optimal use of the granules, and also deciding the basal or dispersal form of application of nutrients according to the crop.

Application of 3D X-ray tomography to investigation of structure of sinter mixture granules

X-ray tomography was applied to the investigation of the structure of sinter mixture granules. Different components such as ore, concentrate, coke breeze and limestone were identified and their sizes and spatial distribution estimated. Classification of the granule structure by the thickness of the adhering fines layer in a proportion to the whole granule radius has been estimated. Excessive amount of fines (concentrate) in a mixture leads to the increasing presence of granules with an adhering fines layer thicker than a half of the granule radius. Abnormal structures of granules have been observed in some cases such as microgranules embedded in the adhering layer of bigger granules, granules formed as the result of two or more granules coalescence or granules formed without a nucleus particle with a structure similar to pellets.

The ultrasonic-enhanced factor of mass-transfer coefficient in the supercritical carbon dioxide extraction

Based on several hypotheses about the process of supercritical carbon dioxide extraction, the onflow around the solute granule is figured out by the Navier-Stocks equation. In combination with the Higbie’s solute infiltration model, the link between the mass-transfer coefficient and the velocity of flow is found. The mass-transfer coefficient with the ultrasonical effect is compared with that without the ultrasonical effect, and then a new parameter named the ultrasonic-enhanced factor of mass-transfer coefficient is brought forward, which describes the mathematical model of the supercritical carbon dioxide extraction process enhanced by ultrasonic. The model gives out the relationships among the ultrasonical power, the ultrasonical frequency, the radius of solute granule and the ultrasonic-enhanced factor of mass-transfer coefficient. The results calculated by this model fit well with the experimental data, including the extraction of Coix Lacryma-jobi Seed Oil (CLSO) and Coix Lacryma-jobi Seed Ester (CLSE) from coix seeds and the extraction of Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA) from the alga by means of the ultrasonic-enhanced supercritical carbon dioxide extraction (USFE) and the supercritical carbon dioxide extraction (SFE) respectively. This proves the rationality of the ultrasonic-enhanced factor model. The model provides a theoretical basis for the application of ultrasonic-enhanced supercritical fluid extraction technique.

Mathematical model and computer simulation for release of nutrients from coated fertilizer granules

Controlled release of nutrients from coated fertilizer granules is desired for optimal uptake by plants and crops. We study the saturation and release of nutrients from a coated spherical fertilizer granule having varying contact areas with the soil using the techniques of mathematical modeling and computer simulation. The effects of granule radius, diffusion coefficient and contact area on saturation time as well as on the release time of nutrients are studied. The effect of evaporation loss on the saturation time is also investigated. Understanding these effects quantitatively is very useful in determining the radius and coating width while manufacturing such granules and also educating the farmers about selection of the granules.

Prediction of nitrate release from polymer-coated fertilizers using an artificial neural network model

Polymer-coated fertilizers (PCF) are currently the most popular controlled-release fertilizers, and offer great advantages over conventional fertilizers. To understand the release of PCF, a generalized regression neural network (GRNN) was used to predict nitrate release profiles. A total of 30 PCFs were used for the experiment, and nitrate release profiles in water were obtained to train the GRNN model. Input vectors of the model were controlled-release parameters, including membrane thickness, temperature, granule radius and saturated concentration of the nutrient, and output vectors of the model were nitrate release profiles. The results showed that the predicted values were in fairly good agreement with the observed ones, and the performance of the GRNN model was superior to a theoretical model. The GRNN model revealed that the thickness of coating membrane was the most important parameter in controlling nitrate release, followed by temperature, granule radius and saturated concentration of nitrate. The GRNN model was a useful tool in solving non-linear prediction problems in the development of PCF, and the nitrate release profile of PCF could be optimized with GRNN by adjusting controlled-release parameters, which provides an alternative method to achieve a PCF product with the desired nutrient release characteristics.

Coloring of silica glass with silver nanoparticles

The possibility of doping of surface layers of optical fused silica with silver nanogranules upon heating of a thin Ag film on the silica surface by a CO2 laser beam (P ≈ 30 W, λ = 10.6 μm) is established. The effect of exposure time on the doped layer structure has been investigated. The absorption band of the colloidal solution of Ag in silica has been studied. It is shown that this band is homogeneously broadened and its peak (at 420 nm) corresponds to the small volume filling factor (q < 0.1) at an average granule radius of about 3 nm. Based on the measurements of the radial distributions of the reflectance and refractive index over the doped region at λ = 633 nm, it is revealed that the doped layer is an area-irregular asymmetric step waveguide.

Relationship between size and mass transfer resistance in aerobic granules

To investigate the size effect of aerobic granules on mass transfer efficiency by introducing the effective factor and the modified Thiele modulus. Batch experiments of aerobic granules with different sizes were conducted to study the size effect of granules on mass transfer resistance. Results showed that both specific substrate removal and biomass growth rates were size dependent, i.e. reduced rates were observed at big sizes. It was found that the diffusion resistance described by the effective factor and the Thiele modulus increased with the increase of the size of aerobic granules. The effective factor should be controlled at values higher than 0.44 and the Thiele modulus lower than 1.05 for efficient mass transfer in aerobic granules. Based on the coupled effective factor and Thiele modulus, an operation guidance including granule radius, kinetics of biomass and environmental conditions could be proposed for stable aerobic granulation.

Mathematical Model for Potassium Release from Polymer-coated Fertiliser

An exact mathematical model based on Fick's Second Diffusion Law was developed to predict the release rate of polymer-coated fertiliser using a numerical solution and Fourier series expansion. From the explicit mathematical model, an approximate solution for the nutrient release was obtained. The model showed that the nutrients release was mainly controlled by the diffusion coefficient, membrane thickness and granule radius. This model was simpler compared with the original numerical solution, and different radii of polymer-coated controlled-release fertiliser was used to verify the approximate release model. The nutrient was mainly released in the linear stage, and the cumulative percentage of nutrient release decreased when the granule radius increased. The cumulative release profile of potassium from the polymer-coated fertiliser into water agreed with the prediction of the model on the whole.

Theoretical model to determine the effects of geometrical factors on the resorption of calcium phosphate bone substitutes

A theoretical approach was used to determine the effect of geometrical factors on the resorption rate of calcium phosphate bone substitutes that are either dense, microporous, and/or contain spherical macropores. Two cases were considered: (a) macroporous blocks that can be invaded by resorbing cells either directly because the structure is fully open-porous, or indirectly after some resorption of the macropores walls and/or interconnections. (b) Microporous or dense blocks/granules that cannot be invaded by resorbing cells, i.e. can only be resorbed from the outside to the inside, layer by layer. The theoretical approach was based on five assumptions: (i) the pores are spherical; (ii) the pores are ordered according to a face-centered cubic packing; (iii) the resorption is surface-controlled; (iv) the resorption is only possible if the surface can be accessed by blood vessels of 50 μm in diameter; and (v) the resorption time of a given amount of calcium phosphate is proportional to the net amount of material. Based on these assumptions, the calculations showed that the resorption time of a macroporous block could be minimized at a specific pore radius. This pore radius depended (i) on the size of the bone substitute and (ii) on the interpore distance. Typical radii were in the range of 100–400 μm. These values are similar to the numerous pore size optima mentioned in the scientific literature. For microporous or dense blocks/granules, the model suggested that a relatively small radius should be preferred. Such a radius leads to an optimum combination of a high surface area favorizing resorption and the presence of large intergranular gaps favorizing blood vessel ingrowth. In that case, the optimum of granule radius is around 100–200 μm. Finally, a very good agreement was found between the predictions of the model and experimental data, i.e. the model explained in all but two cases the results with an accuracy superior to 80%. In conclusion, the model appears to be a useful tool to better understand in vivo results, and possibly better define the geometry and distribution of the pores as well as the size of a bone substitute.