Béatrice Biscans

Biologically induced phosphorus precipitation in aerobic granular sludge process.

Aerobic granular sludge is a promising process for nutrient removal in wastewater treatment. In this work, for the first time, biologically induced precipitation of phosphorus as hydroxyl-apatite (Ca(5)(PO(4))(3)(OH)) in the core of granules is demonstrated by direct spectral and optical analysis: Raman spectroscopy, Energy dispersive X-ray (EDX) coupled with Scanning Electron Microscopy (SEM), and X-ray diffraction analysis are performed simultaneously on aerobic granules cultivated in a batch airlift reactor for 500 days. Results reveal the presence of mineral clusters in the core of granules, concentrating all the calcium and considerable amounts of phosphorus. Hydroxyapatite appears as the major mineral, whereas other minor minerals could be transiently produced but not appreciably accumulated. Biologically induced precipitation was responsible for 45% of the overall P removal in the operating conditions tested, with pH varying from 7.8 to 8.8. Major factors influencing this phenomenon (pH, anaerobic phosphate release, nitrification denitrification) need to be investigated as it is an interesting way to immobilize phosphorus in a stable and valuable product.

A thermochemical approach for calcium phosphate precipitation modeling in a pellet reactor

Calcium phosphate precipitation is studied in this article. The P-recovery process is carried out in a fluidized sand bed, the so-called pellet reactor which presents major advantages from the hydrodynamical viewpoint. The associated chemistry is yet relatively complex, due to pH gradient along the column and to the residence time of the various precipitates. The experimental observations showed three different phenomena: first, an agglomeration of fines around the sand grains is observed, second, a stagnation of fines in the bed occurs while a significant amount of fines also leaves the bed with the liquid effluent. The purpose of this work is to validate the thermodynamical model developed in our previous works on a semi-industrial sized pilot. Additional experimental runs carried out for various operating conditions showed the robustness of the model. These results open some interesting perspectives for the determination of optimized operating conditions at industrial scale.

Optimization of struvite precipitation in synthetic biologically treated swine wastewater - Determination of the optimal process parameters

A sustainable way to recover phosphorus (P) in swine wastewater involves a preliminary step of P dissolution followed by the separation of particulate organic matter. The next two steps are firstly the precipitation of struvite crystals done by adding a crystallization reagent (magnesia) and secondly the filtration of the crystals. A design of experiments with five process parameters was set up to optimize the size of the struvite crystals in a synthetic swine wastewater. More than 90% of P was recovered as large crystals of struvite in optimal conditions which were: low Mg:Ca ratio (2.25:1), the leading parameter, high N:P ratio (3:1), moderate stirring rate (between 45 and 90 rpm) and low temperature (below 20 °C).These results were obtained despite the presence of a large amount of calcium and using a cheap reactant (MgO). The composition of the precipitates was identified by Raman analysis and solid dissolution. Results showed that amorphous calcium phosphate (ACP) co-precipitated with struvite and that carbonates were incorporated with solid fractions.

Preparation of microspheres of ketoprofen with acrylic polymers by a quasi-emulsion solvent diffusion method

A quasi-emulsion solvent diffusion method to prepare microspheres of ketoprofen with an acrylic polymer was studied. The solvent and drug concentration profiles in the continuous emulsion phase were determined experimentally under different processing conditions, in order to investigate the mechanism of microsphere formation. It was found that the solvent removal rate from the emulsion droplets as well as the microsphere size distribution, were affected by factors such as the drug-to-polymer ratio, the initial difference of temperature between the emulsion phases, and the solvent/non-solvent ratio. The results of the investigations concerning the morphology and the ketoprofen dissolution profiles, obtained from in vitro dissolution studies, are also presented. The difference in the hardening of the periphery of the emulsion droplets resulted in different drug release rates, as clearly shown by the experimental data. It was concluded that solidification and water uptake are compromising processes during microsphere formation. Depending on the cases considered, it may be the solidification or the water uptake which dominates the process.

Preparation of hydroxyapatite by neutralization at low temperature—influence of purity of the raw material

Abstract A method to prepare hydroxyapatite—Ca10(PO4)6(OH)2—at low temperature is studied. This simple and non-polluting method consists in neutralizing a suspension of lime (Ca(OH)2) with a solution of orthophosphoric acid. The chemical and physical properties of the initial lime particles have a great influence on the quality of the hydroxyapatite produced. Several kinds of lime were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, size analysis, specific surface area and chemical analysis and tested in this work. Among the impurities contained in the lime, magnesium ion shows a strong influence on the formation of hydroxyapatite. The stoichiometry of the hydroxyapatite precipitate and its purity once calcinated depend on the quality of the raw materials.

Modeling of the dissolution of calcium hydroxyde in the preparation of hydroxyapatite by neutralization

Abstract In order to control the properties of hydroxyapatite particles, the method based on neutralization of a suspension of lime with orthophosphoric acid is studied. The dissolution of lime is the first step in the process and is described here. After a preliminary study of the hydrodynamics of the reactor, a kinetic model, based on diffusion theory, was developed. It describes the increase of calcium concentration in a dynamic system. The effects of stirring rate, temperature and acid flow rate on the dissolution of lime were determined experimentally. The acid flow rate influenced the reaction rate the most.

Modelling of the Mechanism of Formation of Spherical Grains Obtained by the Quasi-Emulsion Crystallization Process

In order to improve particle properties, new processes combining granulation and crystallization are being developed. This present work deals with the spherical crystallization process by the quasi-emulsion mechanism applied to a pharmaceutical drug, ketoprofen. The dierent steps occurring in the process are ®rst the formation of an O/W emulsion, then the creation of the supersaturation of drug into the droplets by mass transfer and heat transfer, and ®nally the nucleation, growth and agglomeration of drug crystals inside the droplets. The mechanism of formation has been modelled in order to aid control of the size, shape and internal structure of grains as a function of the droplet size.

Particle design Part B: batch quasi-emulsion process and mechanism of grain formation of ketoprofen

This study deals with the spherical crystallization process by the quasi-emulsion mechanism, applied to a pharmaceutical. The objective is to produce spherical agglomerates made of a number of small crystals of the drug, having properties adequate for direct compression when manufacturing tablets. The aim of this work is to make the link between the process and these properties. The different steps occurring in the process are the fortnation of an emulsion whose droplets are made of the drug dissolved in a solvent, the creation of the supersaturation of the drug in the droplets by mass and heat transfer and the nucleation, growth and agglomeration of drug crystals inside the droplets. The process has been carried out in a batch laboratory scale device. The variation of the operating parameters on the one hand and of the relative proportions of the various components on the other have enabled us to determine the influence on the internal and external structures of the produced agglomerates which influence the ability to be compressed. The identitication of the phenomena occurring has led to a proposed mechanism for the formation of the agglomerates.

Modelling of a continuous fluidized-bed crystallizer effects of mixing and segregation on crystal size distribution during the crystallization of tetrahydrate sodium perborate

Abstract A modelling of a continuous fluidized-bed crystallizer is developed. The model is based on the description of the fluidized bed as a multistage crystallizer, in order to take into account the segregation and particles mixing within the bed. This model is compared to experimental data obtained during the laboratory-scale crystallization of tetrahydrate sodium perborate. It gives a better prediction of the mean size of the product than a usual model of suspended bed based on the assumption of perfect size classification. It can also predict the size distribution of the crystals along the column.

Coupling High Throughput Microfluidics and Small-Angle X-ray Scattering to Study Protein Crystallization from Solution

In this work, we propose the combination of small-angle X-ray scattering (SAXS) and high throughput, droplet based microfluidics as a powerful tool to investigate macromolecular interactions, directly related to protein solubility. For this purpose, a robust and low cost microfluidic platform was fabricated for achieving the mixing of proteins, crystallization reagents, and buffer in nanoliter volumes and the subsequent generation of nanodroplets by means of a two phase flow. The protein samples are compartmentalized inside droplets, each one acting as an isolated microreactor. Hence their physicochemical conditions (concentration, pH, etc.) can be finely tuned without cross-contamination, allowing the screening of a huge number of saturation conditions with a small amount of biological material. The droplet flow is synchronized with synchrotron radiation SAXS measurements to probe protein interactions while minimizing radiation damage. To this end, the experimental setup was tested with rasburicase (known to be very sensitive to denaturation), proving the structural stability of the protein in the droplets and the absence of radiation damage. Subsequently weak interaction variations as a function of protein saturation was studied for the model protein lysozime. The second virial coefficients (A2) were determined from the X-ray structure factors extrapolated to the origin. A2 obtained values were found to be in good agreement with data previously reported in literature but using only a few milligrams of protein. The experimental results presented here highlight the interest and convenience of using this methodology as a promising and potential candidate for studying protein interactions for the construction of phase diagrams.