Diffusion in biological media: a comprehensive numerical-analytical study via surface analysis and diffusivities calculation.

The study of diffusion in biological materials is crucial for fields like food science, engineering, and pharmaceuticals. Research that combines numerical and analytical methods is needed to better understand diffusive phenomena across various dimensions and under variable boundary conditions within food matrices. This study aims to bridge this gap by examining the diffusion of substances through biological materials analytically and numerically, calculating diffusivity and conducting surface analysis. The research proposes a process for sweetening Bing-type cherries (Prunus avium) using sucrose/xylitol solutions and a staining technique utilising erythrosine and red gardenia at varying concentrations (119, 238 and 357 ppm) and temperatures (40, 50 and 60 °C). Given the fruit's epidermis resistance, the effective diffusivities of skin were inferior to those in flesh. Temperature and concentration synergise in enhancing diffusion coefficients and dye penetration within the food matrix (357 ppm and 60 °C). Red gardenia displayed significant temperature-dependent variation (p = 0.001), whereas erythrosine dye remained stable by temperature changes (p > 0.05). Gardenia's effective diffusivities in cherry flesh and skin, at 357 ppm and 60 °C, 3.89E-08 and 6.61E-09 m2/s, respectively, significantly differed from those obtained at lower temperatures and concentrations. The results highlight the temperature-concentration impacts on mass transfer calculations for food colouring processes and preservation methodologies.

Comprehensive assessment for hygrothermal comfort with heat and mass fluxes through a clothing layer during cooling seasons.

A comprehensive analysis is carried out for achieving hygrothermal comfort by using bidirectional heat and mass fluxes between the human skin and its surroundings during cooling seasons, considering the main characteristics of climate, metabolic rate, and clothing fabrics. As hygrothermal comfort is mainly seen as one-direction heat and mass flux from the close surroundings to the human body, without the emitted heat and mass by the human skin, the purpose of the analysis is to find out proper features of the respective clothing fabric according to the inlet boundary conditions, i.e. heat and mass flux from the human body, and the outlet boundary features, i.e. heat and mass flux due to the climate conditions. Thereby, a novel mathematical modelling is developed for heat and mass transfer, respectively. Then, the software Wolfram Mathematica is applied for the numerical solutions of the model. After the model is validated, a sensitivity analysis is carried out. Thereby, it is found that the sensible heat removal by convection, dependent on both airflow and humidity rates, has a great influence on the hygrothermal comfort. Furthermore, solar reflectivity for shortwave radiation, along with longwave radiation from the skin, have influence on the hygrothermal comfort when both ventilation and sweating are set as minimum. Therefore, if the conditions of temperature and relative humidity are proper, both high conductivity and air permeability clothes are recommended. Nevertheless, regarding the reflectivity, it depends on the presence of shortwave radiation, sweating, ventilation, and longwave radiation to consider light-toned or dark colors.

Estimation of diffusion coefficients during carrots cooking in arsenious solution at different temperatures.

This study is based on an investigation of the transport phenomenon, specifically the quantification of arsenic diffusion in carrots within a temperature range of 89 °C-99 °C using a thin plate model. Studying the diffusion of arsenic in carrots is important due to its toxicity, as it can concentrate during cooking. The World Health Organization considers arsenic as one of the ten chemical substances of public health concern. In this study, biennial hybrid carrots of the Nantesa variety were cooked whole with their epidermis in an aqueous solution containing diarsenic trioxide with an As concentration of 5 mgL-1 at 89 °C, 94 °C, and 99 °C. The cooking times of the carrots at different temperatures were based on a specific degree of tenderness, with a value of ≤3 kg m-2. The evaluated data showed consistency with increasing temperature. The calculated effective diffusion coefficients at temperatures of 89 °C, 94 °C, and 99 °C were 5.84E-09 m2s-1, 1.08E-08 m2s-1, and 2.51E-08 m2s-1 for the flesh (DL), and 1.601E-11 m2s-1, 2.15E-11 m2s-1, and 4.39E-11 m2s-1 for the epidermis (DE), respectively. The activation energy for diffusion was determined to be 159.54 kJmol-1 for the and 110.68 kJmol-1 for the epidermis. Similar behaviours were observed in different radial positions of the carrot, where the arsenic content decreased from the periphery to the centre, consistent with studies on diffusion phenomena with other solutes in food. The novelty was the detailed quantification of arsenic diffusion in the Nantes-type hybrid carrot matrix. This study is limited to a specific concentration of 5 mgL-1 of arsenic solution. The findings of this study may have significant implications for public health and food safety.

New trends in modelling of breakthrough curves to remove pollutants using adsorption on advanced monoliths geometries.

This work proposes a rigorous mathematical model capable of reproducing the adsorption process in dynamic regime on advanced monoliths geometries. For this, four bed geometries with axisymmetric distribution of channels and similar solid mass were proposed. In each geometry a different distribution of channels was suggested, maintaining constant the bed dimensions of 15 cm high and 5 cm radius. The mathematical modeling includes mass and momentum transfer phenomena, and it was solved with the COMSOL Multiphysics software using mass transfer parameters published in the literature. The overall performance of the column was evaluated in terms of breakthrough (CA/CA0 = 0.1) and saturation times (CA/CA0 = 0.9). The mass and velocity distributions obtained from the proposed model show good physical consistency with what is expected in real systems. In addition, the model proved to be easy to solve given the short convergence times required (2-4 h). Modifications were made to the bed geometry to achieve a better use of the adsorbent material which reached up to 80%. The proposed bed geometries allow obtaining different mixing distributions, in such a way that inside the bed a thinning of the boundary layer is caused, thus reducing diffusive effects at the adsorbent solid-fluid interface, given dissipation rates of about 323 × 10-11 m2/s3. The bed geometry composed of intersecting rings deployed the best performance in terms of usage of the material adsorbent, and acceptable hydrodynamical behavior inside the channels (maximum fluid velocity = 35.4 × 10-5 m/s and drop pressure = 0.19 Pa). Based on these results, it was found that it is possible to reduce diffusional effects and delimit the mass transfer zone inside the monoliths, thus increasing the efficiency of adsorbent fixed beds.

Fixed-bed column adsorption modeling using Zr biocomposites for fluoride removal.

This research involved conducting continuous adsorption experiments to assess fluoride elimination from drinking water achieved by utilizing biocomposites created from the peels of oranges and apples, which were impregnated with zirconium (Zr), to form BOP-Zr and BAP-Zr, respectively. The findings from the experimental data indicate that BOP-Zr and BAP-Zr are effective biosorbents with a solid ability to remove fluoride selectively. Additionally, these biosorbents were found to be stable, as they do not release Zr into the treated water. Notably, these environmentally friendly biosorbents are derived from renewable sources and enhance the value of waste materials. The study employed various empirical models, including Bohart-Adamas, Thomas, Yoon-Nelson, BDST, Clark, Yan, and Woolborska, to elucidate the mechanisms and crucial parameters involved in fluoride adsorption within packed bed columns. The Yan model demonstrated the highest correlation among these models, indicating a chemical adsorption process with kinetics following a pseudo-second-order pattern. BOP-Zr and BAP-Zr exhibited a maximum adsorption capacity of 59.3 and 47.5 mg/g, respectively, under a flow rate of 4 mL/min and an inlet fluoride concentration of 25 mg/L. The analysis of mass transfer coefficients revealed that the primary step governing the adsorption procedure was diffusion through pores. Consequently, the study conclusively establishes that BOP-Zr and BAP-Zr biocomposites, originating from lignocellulosic biomass remains, present a practical and competitive choice for eliminating fluoride from water. These materials surpass waste materials in performance and rival more expensive options in efficiency and performance.

Use of coconut sugar as an alternative agent in osmotic dehydration of strawberries.

This study aimed to evaluate coconut sugar (CS) as an alternative osmotic agent to sucrose for the osmotic dehydration (OD) of strawberries. OD was performed by immersing strawberries cut into 13.6 ± 0.4 mm edge cubes in osmotic solutions of CS or sucrose, at two different concentrations (40% and 60%, w/w), with and without application of vacuum (AV) in the first 20 min of the process. The total OD time was 300 min. Evaluations of the kinetics of solid gain (SG), water loss (WL), and weight reduction (WR) were performed at 30, 60, 120, 180, 240, and 300 min. SG, WL, and WR increased over the OD time and showed values of up to 7.94%, 63.40%, and 55.94%, respectively. AV increased WL, WR, shrinkage, pH, and total color difference and decreased anthocyanin, ascorbic acid (AA), phenolic, and antioxidant contents. The higher concentration led to higher SG, WL, WR, shrinkage, hardness, and lower moisture content, water activity, anthocyanin, AA, phenolic, and antioxidant contents. The use of CS instead of sucrose had little influence on strawberry properties, except pH and color responses. The optimal treatment was using a 60% CS solution without AV, showing a very distinct color change, hardness increased by approximately 4.5 times and maintenance of acidity, anthocyanins, AA, total phenolics, and antioxidants of 38.0%, 39.6%, 11.8%, 30.0%, 31.1%, and 30.3%, respectively, compared to fresh strawberries. PRACTICAL APPLICATION: Osmotic dehydration of fruit is a process traditionally carried out using sucrose. However, increasing health concerns have made consumers seek alternative sugars to sucrose. The use of coconut sugar made it possible to produce osmo-dehydrated strawberries different from the traditional one, maintaining product quality and process efficiency.

Scaling-up of the adsorption process of ammonia nitrogen onto expanded vermiculite using fixed-bed columns.

Expanded vermiculite was used as an adsorbent to remove ammonia nitrogen from landfill leachate. Bench and pilot-scale adsorption experiments were performed with leachate collected from a closed sanitary landfill located in Curitiba, southern Brazil. At the bench-scale, two different heights of vermiculite and three different flow rates were tested using a fixed-bed column. These tests produced an average uptake capacity of 33.4 mg g-1 for the ammonia nitrogen concentration of 2,560 mg L-1. The Yan model was used to determine the breakthrough and the exhaustion times due to the best fit of the data to this model. At the pilot-scale, the flow rate was determined from the shortest length of the mass transfer zone obtained from bench-scale experiments. Tests were performed using one stainless-steel column filled with 26.2 kg of expanded vermiculite, which resulted in a bed height of 1.6 m. A leachate flow rate of approximately 350 L d-1 was applied to achieve the required contact time of 8.3 h. At this scale, an average uptake capacity of 18.1 mg g-1 was obtained for the ammonia nitrogen concentration of 1,193 mg L-1. It is worth mentioning that the flow rate and the concentration of the adsorbate in the feeding solution are fundamental to improve the operational time of the fixed-bed column. The main goal of this research was the determination of operating conditions to scale-up the adsorption process of ammonia nitrogen onto expanded vermiculite. The contact time was a key parameter to reach this goal.

Novel technologies combined with osmotic dehydration for application in the conservation of fruits: an overview / Novas tecnologias combinadas com desidratação osmótica para aplicação na conservação de frutas: uma revisão

ABSTRACT: Osmotic dehydration (OD) is a technique used for the partial removal of water from foodstuff, including fruit and vegetables, with the aim of producing a desiccated product. The process involves placing the material in a hypertonic solution for several hours and allowing water to move from the cell compartment into the solution by osmosis. OD is influenced by various factors such as the concentration and composition of the osmotic solution, the solution temperature, the type of agitation and the time of exposure, as well as the size, shape and compactness of the food material. The main advantages of OD over conventional drying processes are the superior quality of the dried products and the minimization of shrinkage. In recent years, research effort has focused on the combination of OD with other technologies, such as ultrasound, cryogenic freezing with liquid nitrogen, pulsed electric field, gamma radiation and high hydrostatic pressure. The application of these methods prior to or concomitant with OD accelerates mass transfer and reduces the drying rate of fruit and vegetables by increasing the permeability of cell membranes. In this manner, combined processes tend to be more efficient and economical in comparison with conventional OD because they reduce operating times and; consequently, energy consumption. In addition, the dried products generated by such coupled processes typically exhibit improved nutritional and physicochemical characteristics. This review summarizes the basic principles and applications of OD in combination with other methods, with particular emphasis on the production of dried fruits.

RESUMO: A desidratação osmótica (DO) é uma técnica utilizada para remover parcialmente a água dos alimentos, incluindo frutas e vegetais, com vistas a produção de alimentos secos. O processo consiste em colocar o material em uma solução hipertônica por várias horas e deixar a água passar do compartimento celular para a solução por osmose. A DO é influenciada por vários fatores como a concentração e composição da solução osmótica, a temperatura da solução, o tipo de agitação e o tempo de exposição, assim como o tamanho, forma e compactação do material alimentar. As principais vantagens da DO em relação aos processos de secagem convencionais são que ela dá origem a produtos secos de qualidade superior e minimiza o encolhimento. Nos últimos anos, tem-se investigado a combinação da DO com outras tecnologias, tais como ultrassom, congelamento criogênico com nitrogênio líquido, campo elétrico pulsado, radiação gama e alta pressão hidrostática. A aplicação desses métodos antes ou simultaneamente com a DO acelera a transferência de massa e reduz a taxa de secagem de frutas e vegetais através do aumento da permeabilidade das membranas celulares. Assim, os processos combinados tendem a ser mais eficientes e econômicos do que a DO convencional, pois reduzem o tempo de operação e, consequentemente, o consumo de energia. Adicionalmente, os produtos desidratados gerados através de processos associados geralmente apresentam melhores características nutricionais e físico-químicas. Esta revisão sumariza os princípios básicos e aplicações da DO em combinação com outros métodos, com ênfase especial dada à produção de frutas secas.

Towards the Configuration of a Photoelectrocatalytic Reactor: Part 2-Selecting Photoreactor Flow Configuration and Operating Variables by a Numerical Approach.

This work aims to select a photoreactor flow configuration and operational conditions that maximize the Photocatalytic Space-time Yield in a photoelectrocatalytic reactor to degrade Reactive Red 239 textile dye. A numerical study by Computational Fluid Dynamics (CFD) was carried out to model the phenomena of momentum and species transport and surface reaction kinetics. The photoreactor flow configuration was selected between axial (AF) and tangential (TF) inlet and outlet flow, and it was found that the TF configuration generated a higher Space-time Yield (STY) than the AF geometry in both laminar and turbulent regimes due to the formation of a helical movement of the fluid, which generates velocity in the circumferential and axial directions. In contrast, the AF geometry generates a purely axial flow. In addition, to maximize the Photocatalytic Space-time Yield (PSTY), it is necessary to use solar radiation as an external radiation source when the flow is turbulent. In conclusion, the PSTY can be maximized up to a value of 45 g/day-kW at an inlet velocity of 0.2 m/s (inlet Reynolds of 2830), solar radiation for external illumination, and internal illumination by UV-LEDs of 14 W/m2, using a photoreactor based on tangent inlet and outlet flow.

Towards the Configuration of a Photoelectrocatalytic Reactor: Part 1-Determination of Photoelectrode Geometry and Optical Thickness by a Numerical Approach.

Photoelectrocatalysis has been highlighted as a tertiary wastewater treatment in the textile industry due to its high dye mineralisation capacity. However, design improvements are necessary to overcome photo-reactors limitations. The present work proposes a preliminary configuration of a photoelectrocatalytic reactor to degrade Reactive Red 239 (RR239) textile dye, using computational fluid dynamics (CFD) to analyse the mass transfer rate, radiation intensity loss (RIL), and its effect on kinetics degradation, over a photoelectrode based on a TiO2 nanotube. A study to increase the space-time yield (STY) was carried out through mass transfer rate and kinetic analysis, varying the optical thickness (δ) between the radiation entrance and the photocatalytic surface, photoelectrode geometry, inlet flow rate, and the surface radiation intensity. The RIL was determined using a 1D Beer-Lambert-based model, and an extinction coefficient experimentally determined by UV-Vis spectroscopy. The results show that in RR239 solutions below concentrations of 6 mg/L, a woven mesh photoelectrode and an optimal optical thickness δ of 1 cm is enough to keep the RIL below 15% and maximise the mass transfer and the STY in around 110 g/m3-day.

Alternative activated/KOH adsorbent for phenol adsorption: experimental, industrial case study and mass transfer interpretation.

Removal of phenol from wastewater is essential to achieve permitted concentrations according to the recommendations of USEPA. The adsorption capacity of phenol in activated adsorbent with KOH of Enterolobium contortisiliquum (TAC) was evaluated at different temperatures. The Langmuir isotherm represented the equilibrium data of this study. Thermodynamic process was endothermic, spontaneous, and reversible. The mass transfer parameters ranged from KE 0.68 to 0.96 × 10-3 (cm s-1), Ds 8.95 to 14.35 × 10-9 (cm2 s-1), and Dp 5.023 × 10-8 (cm2 s-1). The PVSDM model represented the adsorption kinetics. Intraparticle diffusion limits the mass transfer process Biot > 100. The two-stage process minimized the total amount of TAC required to achieve the permitted specification of phenol concentration in wastewater from different industrial sectors. TAC showed significant performance in the removal of phenol from wastewater.

A comprehensive comparison of mixing and mass transfer in shake flasks and their relationship with MAb productivity of CHO cells.

The selection of highly recombinant protein (RP)-productive Chinese hamster ovary (CHO) cell lines is widely carried out in shake flasks. It is assumed that increases in the operating parameters in shake flasks lead to impairments in cell growth and RP production. These effects in cells metabolism are widely associated with high mass transfers and hydrodynamic stress. This study examined the impact of commonly used operational parameters on growth and specific productivity (qP) of two CHO cell lines differentially secreting a humanized anti-hIL8 monoclonal antibody (mAb) and cultured in 250 ml flasks. The evaluated parameters are filling volume (10, 15, and 20%), shaking frequency (60 and 120 revolutions per minute -rpm-), and orbital diameter (25.4 and 19 mm). The analysis of the oxygen transfer was done in terms of the measured volumetric mass transfer coefficient (kLa) and of the hydrodynamics in terms of power input per unit volume of liquid (P/V), the turbulent eddy length scale measured by the Kolmogorov's microscale of turbulence, the energy dissipation rate, the average shear stress, and the shear rate. Though almost all measured kinetic and stoichiometric parameters remained unchanged, mAb titer included, significant differences were found in maximum cell concentration, 10-45% higher in conditions with lower values of kLa and P/V. Changes in glucose metabolism contributing to qP were only shown in the higher producer cell line. Non-lethal responses to elevated oxygen transfer and shear stress might be present and must be considered when evaluating CHO cell cultures in shake flasks.

Water Flux Prediction in Direct Contact Membrane Distillation Subject to Inorganic Fouling.

Freshwater is a limited resource, which has driven the development of new purification and water-reuse technologies. One promising technology for water treatment is membrane distillation (MD). One of the main problems of MD, and of many desalination technologies, is membrane fouling, which reduces the performance of the membrane. This work presents a mathematical model that aims to predict distillate fluxes in direct-contact MD when fouling occurs as salts are deposited onto the membrane surface, forming an inorganic fouling layer. The mathematical model uses a heat- and mass-transfer formulation for prediction of the distillate flux under steady state conditions, and it is combined with the cake-filtration theory to represent the distillate fluxes after the onset of membrane fouling. Model results agree well with experimental observation of distillate fluxes, both before (~12-14 kg m-2 h-1) and after the onset of membrane fouling, with root-mean-square errors smaller than 1.4 kg m-2 h-1 in all the experiments. These results suggest that the cake-filtration theory can be used to represent water flux decline in MD membranes prone to inorganic fouling. From our experiments and from the modelling exercise, we found that the onset of membrane failure was relatively constant; the precipitation reaction constant is conditioned by the physicochemical interaction between the feed solution and the membrane; and the rate of flux decline after membrane fouling depends on flow conditions as well as on the precipitation compound. However, the proposed model has limitations that must be addressed in future investigations to validate it under a wider range of operating conditions, for membranes composed by other materials and with different feed solutions to address organic, biological, and/or colloidal fouling, which typically occur under real conditions.

Mathematical modelling of mass transfer phenomena for sucrose and lactitol molecules during osmotic dehydration of cherries.

The diffusion phenomena of sucrose and lactitol in cherries using different proportions during osmotic dehydration was quantified by means of a mathematical model based on Fick's second law. The average effective diffusion coefficient for soluble solids in skin and flesh are 5.37 10-11 m2∕s and 1.24 10-10 m2∕s. Whereas, for water in skin and flesh are 9.27 10-09 m2∕s and 5.48 10-08 m2∕s. A significant difference for water diffusion coefficients (p < 0.05) was observed between the treatments. This could indicate that the diffusion between species and treatments is differential. Effective diffusion coefficients for water in skin and flesh are 2 orders of magnitude greater than effective diffusion coefficients for soluble solids. This is probably due to its lesser molecular weight. Furthermore, the effective diffusion coefficients for water and soluble solids in cherry skin are between 1 and 2 orders of magnitude lower than effective diffusion coefficients for both in cherry flesh, possibly due to the barrier effect exerted by the cherry skin.

Analysis of commonly used batch adsorption kinetic models derived from mass transfer-based modelling.

Modelling of liquid-solid batch adsorption based on mass transfer and conservation equations results in differential equations that may have or not an analytical solution. Even when analytical solutions are available, several simplified models can be considered for evaluating kinetic data of batch adsorption experiments. However, these simplified models are commonly used regardless of the premises considered in its development, and the analysis of the kinetic experiments based on these simplified models may be severely compromised. For this reason, this work presents a detailed development of the phenomenological models, and the hypotheses considered in its development are clearly stated. Typical simplified models derived from the phenomenological ones are obtained, and the conditions considered in the simplification are critically assessed. It was observed that the simplified models fail mainly for considering the concentration of the bulk phase constant over time or considering a linear adsorption isotherm. It must be emphasised that even when phenomenological models must be solved through numerical procedures, its use must be preferred, since the agreement with model premises and experimental conditions are closer, ensuring the quality of the kinetic data analysis.

CFD modeling of different mass transfer coefficients on hydrogen sulfide emission in a flux chamber.

Hydrogen sulfide (H2S) is commonly used as an indicator for odorous gas emission monitoring in wastewater treatment plants. The H2S emission estimations can be performed using algebraic mathematical models or carrying out measurements at the source, with the dynamic flux chamber, for example. This work brings together these two methodologies in a computational fluid dynamics analysis. Fifteen liquid-phase mass transfer coefficient ([Formula: see text]) models were initially evaluated in establishing, at the liquid-gas interface in a flux chamber, an H2S emission flux based on the friction velocity field from three different inlet flows (2, 5, and 10 L min-1). Ten [Formula: see text] models were fully simulated, and the numerical results were compared with available experimental data. The higher the inlet flow, the higher the friction velocity at the interface, and the higher the H2S emission. The H2S emission was also strongly dependent on the constant coefficients of the existing [Formula: see text] models. Small variability on those coefficients generates considerable changes in emissions at the interface. Few and different models performed well in describing the available concentration data at the outlet sampling probe for different inlet flows, which shows there is still no single model capable of representing all simulated friction velocity ranges (0.005 to 0.017 m s-1).

3,5-Dinitrosalicylic Acid Adsorption Using Granulated and Powdered Activated Carbons.

Some nitroaromatic compounds are found in wastewater from industries such as the weapons industry or the wine industry. One of these compounds is 3,5-dinitrosalicylic acid (DNS), widely used in various tests and frequently found as an emerging pollutant in wastewater and to which the required attention has not been given, even though it may cause serious diseases due to its high toxicity. This study investigated the adsorption of DNS using granulated activated carbon (GAC) and powdered activated carbon (PAC) at different temperatures. The results show that in equilibrium, the adsorption takes place in more than one layer and is favorable for the removal of DNS in both GAC and PAC; The maximum adsorption capacity was obtained at 45 °C, with values of 6.97 mg/g and 11.57 mg/g, respectively. The process is spontaneous and exothermic. In addition, there was a greater disorder in the solid-liquid interface during the desorption process. The predominant kinetics using GAC (7.14 mg/g) as an adsorbent is Elovich, indicating that there are heterogeneous active sites, and when PAC (10.72 mg/g) is used, Pseudo-second order kinetics predominate, requiring two active sites for DNS removal. External mass transfer limitations are only significant in GAC, and ATR-FTIR studies in PAC demonstrated the participation of functional groups present on the adsorbent surface for DNS adsorption.

Implementation of kLa-Based Strategy for Scaling Up Porphyridium purpureum (Red Marine Microalga) to Produce High-Value Phycoerythrin, Fatty Acids, and Proteins.

Porphyridium purpureum is a well-known Rhodophyta that recently has attracted enormous attention because of its capacity to produce many high-value metabolites such as the pigment phycoerythrin and several high-value fatty acids. Phycoerythrin is a fluorescent red protein-pigment commercially relevant with antioxidant, antimicrobial activity, and fluorescent properties. The volumetric mass transfer coefficient (kLa) was kept constant within the different scaling-up stages in the present study. This scaling-up strategy was sought to maintain phycoerythrin production and other high-value metabolites by Porphyridium purpureum, using hanging-bag photobioreactors. The kLa was monitored to ensure the appropriate mixing and CO2 diffusion in the entire culture during the scaling process (16, 80, and 400 L). Then, biomass concentration, proteins, fatty acids, carbohydrates, and phycoerythrin were determined in each step of the scaling-up process. The kLa at 16 L reached a level of 0.0052 s-1, while at 80 L, a value of 0.0024 s-1 was achieved. This work result indicated that at 400 L, 1.22 g L-1 of biomass was obtained, and total carbohydrates (117.24 mg L-1), proteins (240.63 mg L-1), and lipids (17.75% DW) were accumulated. Regarding fatty acids production, 46.03% palmitic, 8.03% linoleic, 22.67% arachidonic, and 2.55% eicosapentaenoic acid were identified, principally. The phycoerythrin production was 20.88 mg L-1 with a purity of 2.75, making it viable for food-related applications. The results of these experiments provide insight into the high-scale production of phycoerythrin via the cultivation of P. purpureum in an inexpensive and straightforward culture system.

Adsorption and mass transfer studies of methylene blue onto comminuted seedpods from Luehea divaricata and Inga laurina.

In this work, comminuted seedpods of the forest species Luehea divaricata (LDPR) and Inga laurina (ILPR) were used as alternative and environmental-friendly adsorbents for the methylene blue (MB) removal from aqueous solutions. Batch adsorption experiments were carried out at the native pH of the solution (pH = 8.7), with curves of removal and adsorption capacity crossed at 0.75 g L-1, having 125 mg g-1 for LDPR and 115 mg g-1 for ILPR. The kinetic models of pseudo-first-order (PFO) and HSDM-Crank were the most adequate to represent MB dye concentration decay data for both biosorbents. The equilibrium curves were better adjusted by the Langmuir model for both adsorbents, with maximum adsorption capacity increased from 279 to 325 mg g-1 for LDPR, and 199 to 233 mg g-1 for ILPR, as a function of an increase in temperature from 298 to 328 K. The thermodynamic parameters showed that both systems are spontaneous with a dominance of physisorption. Mass transfer analysis indicates that the external mass transfer is the limiting step, with Bi < 0.5. Surface diffusion increased with the adsorption capacity, presenting linear and exponential behavior for the ILPR and PLPR adsorbents, respectively. Both materials proved to be efficient in treating a simulated effluent with similar industrial wastewater characteristics, reaching superior values at 70% of color removal.

Using hypothesis testing on the mass-transfer effect with sulfate removal as an application.

Sulfate and chemical oxygen demand removal by an anaerobic batch reactor treating of acid mine drainage is modelled. Available models are abundant but excessively complex, with large numbers of free parameters. Here, maximum likelihood and chi-squared hypothesis tests are applied to three simple models, with Malthus-Monod and Fick description, in increasing order of complexity: (i) planktonic single population (of sulfate-reducing bacteria); (ii) planktonic double-competing populations (adding fermentative bacteria); (iii) granule bound double-competing populations. The data set consists of 6 time profiles, sampled from 120 days of operation after stabilization of the reactor in pH 4. Single population is refuted by all profiles, in which the sulfate reduction is 72% larger than fermentatives. The planktonic double-competing population description is refuted at 119 days, with inner granule diffusion rate as low as 10% of the previous period. The results showed that, after an operation time, the influence of mass transfer became more evident and the incorporation of Fick's law in the model was fundamental to the description of this trend. All tests and inferences are performed at the 90% confidence interval due to large systematic uncertainties in the data.