Scielo RSS <![CDATA[Brazilian Journal of Chemical Engineering]]> vol. 33 num. 3 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[THIRD GENERATION BIODIESEL PRODUCTION FROM MICROALGAE <em>Phormidium autumnale</em>]]> Abstract The aim of this work was to evaluate third generation biodiesel production by the microalgae Phormidium autumnale using sucrose as exogenous carbon source. The study focused on optimization of the different C/N ratios and on the analysis of biofuel quality. The results indicate that a C/N ratio of 40 improved the performance of the system, reaching single-cell oil productivities of 18.9 mg/L in steady-state conditions. This oil has a composition predominantly saturated (45.2%) and monounsaturated (34.7%) suitable for biodiesel synthesis (ester content of 99.8%, cetane number of 58.5%, iodine value of 67.2 gI2/100 g, unsaturation degree of 71.3% and a cold filter plugging point of 6.7 ºC). <![CDATA[DEVELOPMENT OF A NEW PROCESS FOR PURIFICATION OF CAPSULAR POLYSACCHARIDE FROM <em>Streptococcus pneumoniae</em> SEROTYPE 14]]> Abstract The main virulence factor of Streptococcus pneumoniae is the capsular polysaccharide (PS), which is the antigen of all current vaccines that are prepared with PS purified from serotypes prevalent in the population. In this work, three purification strategies were evaluated and a new process was developed for purification of serotype 14 PS (PS14), responsible for 39.8% of diseases in children of 0-6 years old in Brazil. The developed method consists of cell separation by tangential microfiltration, concentration of the microfiltrate by tangential ultrafiltration (50 kDa), diafiltration in the presence of sodium dodecyl sulfate using a 30 kDa ultrafiltration membrane, precipitation with 5% trichloroacetic acid, precipitation with 20% and 60% ethanol, and anion exchange chromatography. The required purity regarding nucleic acids (≤ 2%) and proteins (≤ 3%) was achieved, resulting in a relative purity of 439 mg PS14/mg nucleic acids and 146 mg PS14/mg proteins. The final polysaccharide recovery was 65%, which is higher than the recovery of the majority of processes described in the literature. <![CDATA[EVALUATION OF AEROBIC AND ANAEROBIC BIODEGRADABILITY AND TOXICITY ASSESSMENT OF REAL PHARMACEUTICAL WASTEWATER FROM INDUSTRIAL PRODUCTION OF ANTIBIOTICS]]> Abstract This study evaluates aerobic and anaerobic biodegradability and toxicity of a real pharmaceutical wastewater, which focuses on antibiotics production. Zahn-Wellens and Organization for Economic Cooperation and Development (OECD) methodologies were applied in order to verify the wastewater's biodegradability and Microtox® analysis was performed for toxicity tests. Tests achieved more than 89% and 63% of Total Organic Carbon reduction, showing 80% and 50% of antibiotic removal, for aerobic and anaerobic processes, respectively. Moreover, acute ecotoxicological tests revealed that both techniques decreased the toxic character of real pharmaceutical wastewater. Desorption tests showed that the antibiotic was not degraded, but, in fact, adsorbed onto the sludge. Since biological treatment is the most widely used method for industrial wastewater treatment, this study indicates that this kind of treatment is probably unable to mineralize antibiotics present in pharmaceutical wastewaters, which may induce the development of resistant pathogens. Therefore, efforts must be taken to elucidate the main mechanisms of biological antibiotic removal from wastewaters since the presence of antibiotics in the environment is considered to be an emerging environmental issue. <![CDATA[INCORPORATION AND RELEASE KINETICS OF ALPHA-BISABOLOL FROM PCL AND CHITOSAN/GUAR GUM MEMBRANES]]> Abstract Alpha-bisabolol, an anti-inflammatory and antioxidant compound extracted from candeia trees (Eremanthus erythropappus), was incorporated into hydrophobic polycaprolactone (PCL) and hydrophilic chitosan/guar gum (Ch-G) membranes aiming at the production of bioactive wound dressings. The incorporation efficiency achieved a maximum of ca. 18% (1 gram of alpha-bisabolol per gram of membrane) for Ch-G membranes. For PCL membranes, all of the active compound added was retained (0.2 gram of alpha-bisabolol per gram of membrane). Alpha-bisabolol release in phosphate-buffered saline was relatively slow in both cases, reaching around 6% and 24% after 120 hours respectively for PCL and Ch-G membranes presenting equivalent initial alpha-bisabolol/membrane mass ratios. Both formulations were capable of releasing alpha-bisabolol in the typically recommended topical dose range (from 1 to 10 grams of alpha-bisabolol per gram of vehicle). The extended release periods observed are advantageous, allowing less frequent dressing changes and contributing to turn the treatment more comfortable for the patient. <![CDATA[MODELING PARTICLE SIZE DISTRIBUTION IN HETEROGENEOUS POLYMERIZATION SYSTEMS USING MULTIMODAL LOGNORMAL FUNCTION]]> Abstract This work evaluates the usage of the multimodal lognormal function to describe Particle Size Distributions (PSD) of emulsion and suspension polymerization processes, including continuous reactions with particle re-nucleation leading to complex multimodal PSDs. A global optimization algorithm, namely Particle Swarm Optimization (PSO), was used for parameter estimation of the proposed model, minimizing the objective function defined by the mean squared errors. Statistical evaluation of the results indicated that the multimodal lognormal function could describe distinctive features of different types of PSDs with accuracy and consistency. <![CDATA[MODELING AND SIMULATION OF THE PROCESS OF DEHYDRATION OF BIOETHANOL TO ETHYLENE]]> Abstract The use of carbon-based waste biomass in the production of plastics can partially meet the growing demand for plastics in the near future. An interest in the production of ethylene from bioethanol has been renewing, motivated mainly by environmental appeal and economics. The main objective of this work is the development of a mathematical model for simulation and optimization of the production of ethylene by the dehydration of ethanol, improving the performance of the process. The phenomenological model proposed is based on mass, momentum and energy balances for the process. The results obtained are satisfactory in comparison with theoretical results and experimental data found in the literature. <![CDATA[TRANSITION PHENOMENON INVESTIGATION BETWEEN DIFFERENT FLOW REGIMES IN A ROTARY DRUM]]> Abstract Rotary drums can show different granular flow regimes each one with its own specific flow behavior, which increase the complexity in their study. The way particles move inside the rotary drum is directly related to the mass and energy transfer rates, and consequently to the process performance. Thus, an experimental investigation regarding the transition between different flow regimes inside a rotary drum was carried out in the present work. To the best of our knowledge, the hysteresis phenomenon was observed for the first time in the transition between cataracting-centrifuging regimes, which was shown to be dependent on the physical properties of the particles such as sphericity, density and particle-wall friction coefficient. A new expression for the centrifuging critical rotation speed was proposed in this work. <![CDATA[SYNTHESIS OF PROPYLENE FROM ETHANOL USING PHOSPHORUS-MODIFIED HZSM-5]]> Abstract Effects of phosphorus addition to HZSM-5 on ethanol conversion to propylene were evaluated. Catalysts were characterized by XRF, XRD, nitrogen adsorption, 27Al and 31P MAS NMR, n-propylamine and ammonia TPD. Increasing P content decreased the strength and density of acid total sites. Ethanol dehydration was carried out in a fixed bed reactor operating at atmospheric pressure. Conversion was around 100% for all catalysts. 1.2 wt% of P catalyst showed the highest propylene yield, and was used to evaluate temperature and ethanol partial pressure effects on the product distribution. The highest propylene accumulated productivity was obtained for an ethanol partial pressure of 0.4 atm. Propylene formation was favored in the temperature range 475-500 °C. Significant changes in the product distribution as a function of time on stream were observed at higher temperatures, suggesting stronger catalyst deactivation. The ethylene yield decreased up to 500 °C, rising significantly at 550 °C, possibly due to heavier product cracking reactions. <![CDATA[MOLECULAR THERMODYNAMICS OF MICELLIZATION: MICELLE SIZE DISTRIBUTIONS AND GEOMETRY TRANSITIONS]]> Abstract Surfactants are amphiphilic molecules that can spontaneously self-assemble in solution, forming structures known as micelles. Variations in temperature, pH, and electrolyte concentration imply changes in the interactions between surfactants and micelle stability conditions, including micelle size distribution and micelle shape. Here, molecular thermodynamics is used to describe and predict conditions of micelle formation in surfactant solutions by directly calculating the minimum Gibbs free energy of the system, corresponding to the most stable condition of the surfactant solution. In order to find it, the proposed methodology takes into account the micelle size distribution and two possible geometries (spherical and spherocylindrical). We propose a numerical optimization methodology where the minimum free energy can be reached faster and in a more reliable way. The proposed models predict the critical micelle concentration well when compared to experimental data, and also predict the effect of salt on micelle geometry transitions. <![CDATA[LARGE EDDY SIMULATION COMBINED WITH EQUIVALENT DIAMETER FOR TURBULENT JET MODELLING AND GAS DISPERSION]]> Abstract CFD modelling combines transport phenomena and numerical approaches to solve physical problems. Although numerical modelling of flow scenarios is the cutting edge of flow modelling, there seems to be room for improvement. This paper proposes an approach for jet modelling in a low Mach number computational code. The methodology is based on the equivalent diameter and velocity profile calculated downstream from the jet leak orifice. The novel model DESQr (Diameter of Equivalent Simulation for Quicker Run) is combined with LES (Large Eddy Simulation) to calculate the gas jet profile due to accidental releases. The model is implemented in the framework of FDS (Fire Dynamics Simulator) and the open source code is modified to handle gas dispersion scenarios. Numerical findings for jet modelling and gas dispersion are compared with experimental data. The results are also compared with a commercial CFD tool. Good agreement is observed. Significant computational time reduction is achieved. A free open source CFD tool emerges and the results presented in this work are promising. <![CDATA[CERIUM INCORPORATED INTO A MESOPOROUS MOLECULAR SIEVE (MCM-41)]]> Abstract The synthesis and characterization of a mesoporous molecular sieve (MCM-41) was studied due to its high surface area and large pore volume and to target potential applications in adsorption and catalysis. Rare earth elements have special chemical properties and are efficient promoters for supports. In this study, a mesoporous molecular sieve that incorporates the transition metal cerium (Ce-MCM-41) was synthesized using the hydrothermal method with the goal of improving the structural properties for adsorption. The molar composition of the obtained gel was 1CTMABr: 4SiO2: 1Na2O: 0.2Ce2O3: 200H2O. The pure mesoporous molecular sieve MCM-41 was also synthesized using the same method. The materials were characterized by the following techniques: XRD, BET/BJH, SEM/EDS, TG and FT-IR. A preliminary test to evaluate the materials as adsorbents to remove naphthenic acids present in jet fuel was performed. The results of the characterization showed that the incorporation of the metal cerium did not affect the MCM-41 structure and that mesporous materials were formed. Ce-MCM-41 exhibited good thermal stability, high specific surface area and large pore volume, which are characteristics of a good adsorbent. From the preliminary test, the adsorptive capacity increased by 60% with the incorporation of cerium in the MCM-41 structure. <![CDATA[A CFD STUDY OF DEPOSITION OF PHARMACEUTICAL AEROSOLS UNDER DIFFERENT RESPIRATORY CONDITIONS]]> Abstract Respiratory diseases have received increasing attention in recent decades. Airway bifurcations are difficult regions to study, and computational fluid dynamics (CFD) offers an alternative way of evaluating the behavior of pharmaceutical aerosols used in the treatment of respiratory disorders. In this work, particle deposition was analyzed using a three-dimensional model with four ramifications (three bifurcations), under different respiratory conditions: inhalation, exhalation, and breath holding. The main aim of the work was to verify the medical recommendation to hold one's breath during a few seconds after inhaling pharmaceutical aerosols, rather than exhaling immediately after the inhalation. The deposition of particles with 5 µm diameter was considered. The results showed that the number of aerosols collected on the airway walls was higher for the situation of breath holding, which supported the medical recommendation. <![CDATA[STUDY OF FEEDSTOCK INJECTION TO IMPROVE CATALYST HOMOGENIZATION IN THE RISER OF A FCC]]> Abstract A three dimensional gas-solid reactive flow model based on the Eulerian-Eulerian approach was used to study the effects of different nozzle designs with internal parts inside the FCC riser. The simulations were solved using Computational Fluid Dynamics (CFD) with CFX version 14.0 as tool. The results showed that the nozzle designs have a significant influence on the gas-solid behavior, resulting in an important role in the hydrodynamics and thermal behavior of the riser. Furthermore, the simulations show it is possible to improve the catalyst-gas distribution with an appropriate nozzle design. <![CDATA[CHARACTERISATION OF ASYMMETRIC ALUMINA HOLLOW FIBRES: APPLICATION FOR HYDROGEN PERMEATION IN COMPOSITE MEMBRANES]]> Abstract Asymmetric alumina hollow fibres produced by the phase inversion/sintering method present advantages in that high area/volume ratios and low mass transfer resistances are achieved due to the geometric configuration and the pore size distribution, respectively. Here we characterise hollow fibres that were prepared with different internal coagulants and at different sintering temperatures. Additionally, a palladium membrane was deposited on these different hollow fibres and hydrogen permeabilities through them were compared. More fingers were obtained when a mixture of solvent with water was used as internal coagulant, instead of pure water. At the same sintering temperature, nitrogen permeance through the fibre was increased 5-fold when a mixture of solvent and water was used as internal coagulant instead of pure solvent, and the water flux was increased 7-fold. The decrease in the sintering temperature increased the water permeance through the fibre from 21.4 to 63.9 L h-1 m-2 kPa-1, but decreased its mechanical strength from 74 to 41 MPa. The hydrogen permeance at 450 °C was increased from 5.54x10-5 to 3.06 x10-3 mol m-2 s-1 kPa-1 when using a more permeable hollow fibre as substrate. These results elucidate better conditions to fabricate hollow fibres that present low mass transfer resistances. <![CDATA[ON THE SYNTHESIS OF MOLYBDENUM CARBIDE WITH COBALT ADDITION VIA GAS-SOLID REACTIONS IN A CH<sub>4</sub>/H<sub>2</sub> ATMOSPHERE]]> Abstract Due to ever more severe environmental regulations regarding SOx, NOx and other pollutants' emissions, there has been an interest in developing new and improved catalysts for hydroprocessing reactions. Mo2C has been reported to display good selectivity and activity for those reactions, especially for HDS. Addition of another metal to the carbide structure may improve catalytic properties. Mo2C with low cobalt addition (2.5 and 5%) was obtained via gas-solid reaction in a fixed bed reactor with CH4 (5%)/H2 atmosphere. XRD and TG/DTA analysis of the precursors were carried out in order to understand its mass loss profile, doping metal presence and phase distributions. CoMoO4 as well as MoO3 were identified after calcining doped precursors at 600 °C/180min. SEM, XRD, XRF, TOC, BET and laser granulometric analysis of the reaction products were also performed. Compositions verified by XRF and theoretical values were compatible. At 700 °C both carbide (Mo2C) and oxide (MoO2) phases are present, as identified in XRD analysis and observed by SEM. At 750 °C only single phase Mo2C was verified by XRD, indicating Co dispersion on the carbide matrix. Morphology at this temperature is compatible with pure Mo2C, though XRF indicates Co presence on the material. <![CDATA[ENCAPSULATION OF EXTRACT FROM WINERY INDUSTRY RESIDUE USING THE SUPERCRITICAL ANTI-SOLVENT TECHNIQUE]]> Abstract Grape pomace (seed, skin and stem) is a winery byproduct with high levels of biologically active compounds, such as antioxidants and antimicrobials, that could be converted into high added-value products. Since these components are easily degraded by oxygen, light and high temperature exposure, stabilization is important, for instance, by a microencapsulation process. Therefore, the objective of this study was to investigate the influence on the particle characteristics of the operational conditions applied in the Supercritical Anti-Solvent (SAS) process for the co-precipitation of grape pomace extract and poly(-lactic-co-glycolic acid) (PLGA). The morphology and size of the particles formed, their stability and thermal profile were evaluated, and also the co-precipitation efficiency. The conditions studied allowed the production of microparticles with spherical shape for all operational conditions, with estimated particle size between 4 ± 2 and 11 ± 5 µm, and very good co-precipitation efficiencies (up to 94.4 ± 0.6%). The co-precipitated extract presented higher stability compared to the crude extract, indicating the effectiveness of the co-precipitation process and coating material against degradation processes. <![CDATA[THE USE OF A HIGH LIMESTONE CONTENT MINING WASTE AS A SORBENT FOR CO<sub>2</sub> CAPTURE]]> Abstract In this work, a high limestone content waste was evaluated as a potential material for CO2 capture. The influence of calcination conditions on the CO2 capture capacity was evaluated using 5 cycles of calcination-hydration-carbonation reactions. A Central Composite Design of Experiments was set using calcination temperatures and time as variables. The response evaluated was the CO2 capture measured by thermogravimetric analysis. The results indicate that both calcination temperature and time influence the CO2 capture capacities in the initial cycles but, after a large number of cycles, the effect becomes less relevant. The optimum calcination temperature did not change significantly between cycles - about 893 °C in the first and 850 °C in the fourth cycle. However, the optimum calcination time decreased from 40.1 min in the first to 22.5 min in the fourth cycle. The maximum CO2 capture capacity declines over the reaction cycles due to the sorbent sintering, which becomes more noticeable. Moreover, the waste used in this work is suitable for separating CO2 from flue gas, achieving more than 0.2 g/g of capture capacity after five cycles. <![CDATA[LINEAR STABILITY ANALYSIS AND CFD SIMULATION OF DOUBLE-LAYER RAYLEIGH-BÉNARD CONVECTION]]> Abstract Natural convection in superimposed layers of fluids heated from below is commonly observed in many industrial and natural situations, such as crystal growth, co-extrusion processes and atmospheric flow. The stability analysis of this system reveals a complex dynamic behavior, including the potential multiplicity of stationary states and occurrence of periodic regimes. In this study, a linear stability analysis (LSA) was performed to determine the onset of natural convection as a function of imposed boundary conditions, geometrical configuration and specific perturbations. To investigate the effects of the non-linear terms neglected in LSA, a direct simulation of the full nonlinear problem was performed using computational fluid dynamics (CFD) techniques. The numerical simulation results show an excellent agreement with the LSA results near the onset of convection and an increase in the deviation as the Rayleigh number increases above the critical value. <![CDATA[THE IMPACT OF RADIATION IN THE GAS COMBUSTION MODEL FOR SUGARCANE BAGASSE GRATE BOILER]]> Abstract This work evaluates the impact of different radiation models on the results of Computational Fluid Dynamics (CFD) simulation of a sugarcane bagasse grate boiler. CFD has been applied extensively in the development of comprehensive models for biomass heterogeneous combustion. The model presented in this paper considers the turbulent flow represented by the standard k-ε model and the homogeneous combustion of the volatiles CH4 and CO by the Eddy Dissipation Model (EDM). Thermal profiles have been evaluated by comparing the results obtained without radiation with the results obtained with radiation represented by the P1 Approximation Method and by the Discrete Transfer Method (DTM). The discussion of the flue gas temperature and chemical composition profiles provides useful information regarding the characteristics of the internal flow and of the equipment operating conditions. <![CDATA[OXIDATIVE-REFORMING OF METHANE AND PARTIAL OXIDATION OF METHANE REACTIONS OVER NiO/PrO<sub>2</sub>/ZrO<sub>2</sub> CATALYSTS: EFFECT OF NICKEL CONTENT]]> Abstract In this work the behavior of NiO-PrO2-ZrO2 catalysts containing various nickel loadings was evaluated in the partial oxidation of methane and oxidative-reforming reactions of methane. The catalysts were characterized by X-Ray Diffraction Analysis (in situ-XRD), Temperature Programmed Reduction (H2-TPR), Scanning Electron Microscopy (SEM/EDX) and Adsorption-Desorption of nitrogen (BET area). The reactions were carried out at 750 °C and 1 atm for 5 hours. The catalysts were studied with different nickel content: 0, 5, 10 and 15% (related to total weight of catalyst, wt%). In both reactions, the catalyst containing the mixture of the three oxides (NiO/PrO2/ZrO2) with 15% nickel (15NiPrZr catalyst) showed the best activity for the conversion of the reactants into Syngas and showed high selectivity for H2 and CO. The results suggest that the promoter PrO2 and the Niº centers are in a good proportion in the catalyst with 15% Ni. Our results showed that low nickel concentrations in the catalyst led to high metallic dispersion; however, very low nickel concentrations did not favor the methane transformation into Syngas. The catalyst containing only NiO/ZrO2 in the mixture was not sufficient for the catalysis. The presence of the promoter PrO2 was very important for the catalysis of the POM. <![CDATA[MODELING STYRENE HYDROGENATION KINETICS USING PALLADIUM CATALYSTS]]> Abstract The high octane number of pyrolysis gasoline (PYGAS) explains its insertion in the gasoline pool. However, its use is troublesome due to the presence of gum-forming chemicals which, in turn, can be removed via hydrogenation. The use of Langmuir-Hinshelwood kinetic models was evaluated for hydrogenation of styrene, a typical gum monomer, using Pd/9%Nb2O5-Al2O3 as catalyst. Kinetic models accounting for hydrogen dissociative and non-dissociative adsorption were considered. The availability of one or two kinds of catalytic sites was analyzed. Experiments were carried out in a semi-batch reactor at constant temperature and pressure in the absence of transport limitations. The conditions used in each experiment varied between 16 - 56 bar and 60 - 100 ºC for pressure and temperature, respectively. The kinetic models were evaluated using MATLAB and EMSO software. Models using adsorption of hydrogen and organic molecules on the same type of site fitted the data best. <![CDATA[STUDY OF BINARY AND SINGLE BIOSORPTION BY THE FLOATING AQUATIC MACROPHYTE <em>Salvinia natans</em>]]> Abstract The performance of Salvinia natans macrophyte to recover lead and chromium from single and bicomponent solutions in batch and fixed bed systems was investigated. Equilibrium data were obtained through isotherms and fitted to Langmuir, Freundlich and D-R models for a single component system. In the fixed bed study the breakthrough curves were carried out at three different ratios of concentrations for the bicomponent study and at the concentration of 1 mmol.L-1 for the single system. In order to know the biosorption mechanism, FT-IR analyses were performed for S. natans before and after the uptake of metal ions. The results showed different functional groups in the biomass and the ability of these groups to bind Cr+3 and Pb2+. Studies of the binary system of Cr3+/Pb2+ are not common in the literature, which makes the experimental data obtained in this work very important for providing information that could be used in adsorption processes. <![CDATA[NANOBIOCATALYTIC SYSTEMS BASED ON LIPASE-Fe<sub>3</sub>O<sub>4</sub> AND CONVENTIONAL SYSTEMS FOR ISONIAZID SYNTHESIS: A COMPARATIVE STUDY]]> Abstract Superparamagnetic nanomaterials have attracted interest in many areas due to the high saturation magnetization and surface area. For enzyme immobilization, these properties favor the enzyme-support contact during the immobilization reaction and easy separation from the reaction mixture by use of low-cost magnetic processes. Iron oxide magnetic nanoparticles (Fe3O4, MNPs), produced by the co-precipitation method, functionalized with 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde (GLU), were evaluated as a solid support for Candida antarctica lipase B (CALB) immobilization. The nanomagnetic derivative (11nm) obtained after CALB immobilization (MNPs/APTES/GLU/CALB) was evaluated as biocatalyst in isoniazide (INH) synthesis using ethyl isonicotinate (INE) and hydrazine hydrate (HID) as substrates, in 1,4-dioxane. The results showed that MNPs/APTES/CALB had a similar performance when compared to a commercial enzyme Novozym 435, showing significant advantages over other biocatalysts, such as Rhizhomucor miehei lipase (RML) and CALB immobilized on non-conventional, low-cost, chitosan-based supports. <![CDATA[EVALUATION OF SODIUM CHLORIDE CRYSTALLIZATION IN MEMBRANE DISTILLATION CRYSTALLIZATION APPLIED TO WATER DESALINATION]]> Abstract Crystallization in a Direct Contact Membrane Distillation (DCMD) process was studied both theoretically and experimentally. A mathematical model was proposed in order to predict the transmembrane flux in DCMD. The model fitted well experimental data for the system NaCl-H2O from undersaturated to supersaturated conditions in a specially designed crystallization setup at a bench scale. It was found that higher transmembrane fluxes induce higher temperature and concentration polarizations, as well as higher supersaturation in the vicinity of the solution-vapor interface. In this region, the supersaturation ratio largely exceeded the metastable limit for NaCl crystallization for the whole range of transmembrane fluxes of 0.37 to 1.54 kg/ (m2 h), implying that heterogeneous primary nucleation occurred close to such interface either in solution or on the membrane surface. Solids formed in solution accounted for 14 to 36% of the total solids, whereas solid formed on the membrane surface (fouling) was responsible for 6 to 19%. The remaining solids deposited on other surfaces such as in pumps and pipe fittings. It was also discovered that, by increasing the supersaturation ratio, heterogeneous nucleation in solution increased and on the membrane surface decreased. Heterogeneous nuclei in solution grew in size both by a molecular mechanism and by agglomeration. Single crystals were cubic shaped with well-formed edges and dominant size of about 40 µm whereas agglomerates were about 240 µm in size. The approach developed here may be applied to understanding crystallization phenomena in Membrane Distillation Crystallization (MDC) processes of any scale. <![CDATA[UTILIZATION OF CO<sub>2</sub> IN SEMI-CONTINUOUS CULTIVATION OF <em>Spirulina</em> sp. AND <em>Chlorella fusca</em> AND EVALUATION OF BIOMASS COMPOSITION]]> Abstract Cultivation conditions and the process considerably influence the composition of microalgae. The objective of this study was to use CO2 as a carbon source in semi-continuous cultivation of Spirulina sp. LEB 18 and Chlorella fusca LEB 111 and to evaluate the influence of the renewal rate on the biomass composition and production of these microalgae. Spirulina sp. LEB 18 and Chlorella fusca LEB 111 were cultivated with 10% (v/v) CO2. The blend concentration was 1.6 g L-1, and 20 and 40% (v/v) renewal rates were studied. Spirulina sp. LEB 18 presented the best kinetic results and the maximum biomass concentration and biopolymer yield when grown with CO2 as the carbon source. Under the same conditions (10% (v/v) CO2), the microalgae Spirulina sp. LEB 18 and Chlorella fusca LEB 111 exhibited maximum levels of protein, carbohydrates and lipids.