Shrinkage Kinetics during Convective Drying of Selected Berries

Drying and shrinkage kinetics of gooseberry, black and red currants, cherry, and blackberry were studied using a fully automated experimental apparatus, designed for continuous monitoring of the material moisture content, its temperature, and surface area. Experimental drying curves were approximated with a modified exponential model. The volume and surface area of berries were determined from the pictures taken during drying and transformed into digital images. The procedure for calculation of the object-related pixels in a two-dimensional plane to the temporal three-dimensional volume and surface area of the berries was developed. The modified exponential model was proposed to correlate the volumetric and surface area shrinkage with moisture content. Volumetric shrinkage at the end of drying was maximal (0.3) for black currant and minimal (0.45) for gooseberry.     

Constant and Intermittent Drying Characteristics of Olive Cake

The drying kinetics of olive cake, the solid by-product of the olive oil extraction process, has been experimentally investigated in a small-scale tray dryer using both constant and intermittent (on/off) heating schemes. The parameters investigated include inlet air temperature and intermittency of heat input. The drying kinetics was interpreted through two mathematical models, the Page equation and the Lewis equation. The Page equation was most appropriate in describing the drying behavior of olive cake. A diffusion model was used to describe the moisture transfer and the effective diffusion coefficient at each temperature was determined. The dependence of the effective diffusion coefficient on drying temperature can be adequately explained based on an Arrhenius-type relation. The effective diffusion coefficient varied between 7.6 × 10^?8 and 2.5 × 10^?7 m²/min with an activation energy of 38.55 kJ/mol. Comparison of time evolution of material moisture content due to intermittent and constant drying is also made.     

Constant and Intermittent Drying Characteristics of Olive Cake

The drying kinetics of olive cake, the solid by-product of the olive oil extraction process, has been experimentally investigated in a small-scale tray dryer using both constant and intermittent (on/off) heating schemes. The parameters investigated include inlet air temperature and intermittency of heat input. The drying kinetics was interpreted through two mathematical models, the Page equation and the Lewis equation. The Page equation was most appropriate in describing the drying behavior of olive cake. A diffusion model was used to describe the moisture transfer and the effective diffusion coefficient at each temperature was determined. The dependence of the effective diffusion coefficient on drying temperature can be adequately explained based on an Arrhenius-type relation. The effective diffusion coefficient varied between 7.6 × 10^-8 and 2.5 × 10^-7 m²/min with an activation energy of 38.55 kJ/mol. Comparison of time evolution of material moisture content due to intermittent and constant drying is also made.     

Drying of Lentil Including Shrinkage: A Numerical Simulation

This article presents a theoretical study about drying of lentil including shrinkage. The two-dimensional unsteady-state diffusion modeling written in the oblate spheroidal coordinates system considers the volume variation effect, convective boundary condition at the surface of the solid, and variable thermo-physical properties. The governing equation was discretized using the finite-volume method and the linear equations system was solved by Gauss-Siedel iterative method. To validate the model, numerical results of the average moisture content were compared with experimental data from eight experiments and a good agreement was obtained. The diffusion coefficients for all drying experiments are determined using the least square error technique.     

Drying of Lentil Including Shrinkage: A Numerical Simulation

Abstract

This article presents a theoretical study about drying of lentil including shrinkage. The two-dimensional unsteady-state diffusion modeling written in the oblate spheroidal coordinates system considers the volume variation effect, convective boundary condition at the surface of the solid, and variable thermo-physical properties. The governing equation was discretized using the finite-volume method and the linear equations system was solved by Gauss-Siedel iterative method. To validate the model, numerical results of the average moisture content were compared with experimental data from eight experiments and a good agreement was obtained. The diffusion coefficients for all drying experiments are determined using the least square error technique.     

A Simple Data Processing Approach for Drying Kinetics Experiments

A simple mathematical approach is proposed to be applied to drying kinetics raw data processing. The data collected in a drying experiment of powder cork under constant air drying conditions served as case study to present the methodology. Two functions (linear and third-degree polynomial) were used to fit solid moisture content in the constant drying rate and the falling rate periods. The drying rate curve was obtained by differentiation and the time at which the drying rate period's transition occurs was determined iteratively until virtually continuous functions were achieved. The critical moisture content was easily identified and two falling drying rate periods were detected.

The powder cork moisture decrease was also used to test several semiempirical models available in the literature. The Logarithmic, Midilli, and Page Modified I models were the ones that revealed the best correlations performance. When the methodology proposed was applied using these models, the critical moisture content was underpredicted.

The effective moisture diffusivity and the activation energy were also obtained for powder cork after the proposed mathematical approach has been applied on the raw data obtained in experiments performed at different air drying temperatures.     

Olive mills effluent (OME) wastewater post-treatment using activated clay

Olive mill effluent (OME) wastewater embodies a challenge for environmental scientists and engineers. It is characterized by high values of COD, BOD, and phenolic content. A series of treatment steps composed of settling, centrifugation, and filtration was consecutively used to condition OME wastewater. The filtrate was then subjected to a post-treatment process, namely adsorption on activated clay. The dynamic response of phenols concentration, pH, and COD, using different concentrations of activated clay, showed a peak at which maximum adsorption capacity was achieved. The maximum adsorption capacity for the tested concentrations of activated clay was reached in less than 4 h. It is thought that adsorption of phenols and organics is reversible and mainly due to hydrophobic interactions. The maximum removal of phenols was about 81%, while it reached about 71% for organic matter.     

Shrinkage and Deformation of Agave atrovirens Karw Tissue during Convective Drying: Influence of Structural Arrangements

The influence of structural arrangements of Agave discs cut transversally (ADCT) and longitudinally (ADCL) on moisture loss, shrinkage, and shape was evaluated during convective drying by physical and image parameters.

ADCT showed lower drying and shrinkage rates than ADCL. The fractal exponent (d) relating volume and thickness of samples rose from 1.552 ± 0.126 to 2.394 ± 0.128 and from 1.662 ± 0.111 to 1.848 ± 0.070 for ADCT and ADCL, respectively, which indicates that shrinkage was nonisotropic for both cases.

Parameters considered for evaluating the changes of size and shape of Agave discs at macro- and microscopic levels during drying were projected area (PA), major length (ML), shape factor (SF), and fractal dimension of contour (FD_C). The values obtained for these parameters demonstrated that changes in shrinkage and shape of both samples were dependent on structural arrangements of the samples. During the drying of ADCT samples, which have short and rigid structures, pronounced creasing was observed compared to ADCL materials, which are mainly formed by long and rigid structures. Also, it was observed that orientation of fibers influenced shrinkage and deformation.     

Transfer of Phenolic Compounds from Olive Mill Wastewater to Olive Cake Oil

The transfer of the phenolic compounds from olive mill wastewater (OMW) to oil extracted under microwave from olive cake (OC) was carried out by using the following operations: mixing of the olive mill wastewater with the olive cake, drying of the mixture and recovery by solvent of the olive cake oil enriched by phenolic compounds. In the first part of this work, we made a screening design using a Hadamard matrix to quickly locate the factors influencing the process. Among five potentially influential parameters, we found that only three were actually active (OMW/OC ratio noted R, mixing velocity of mixture Vm and mixing time Tm). In the second part, fractional factorial design (2^5?1) was performed to evaluate the effects of five variables (three of them being selected by screening with exposition time Te and radiation power P) and their eventual interactions. The p value (p < 0.05) indicated that R, P,Te, Vm and Tm had significant effects on the response followed by the interaction effects between R‐P, P‐Te, R‐Vm, Te‐Vm, Te‐Tm, and Vm‐Tm. Under optimal conditions, the addition of OMW to OC increased the phenolic compounds content in the oil from 0.04 ± 0.01 to 0.13 ± 0.02 g/L.     

Recovery and Removal of Phenolic Compounds from Olive Mill Wastewater

Food wastes are today considered as a cheap source of valuable components since the existent technologies allow the recovery of target compounds and their recycling inside the food chain as functional additives in different products. Olive mill wastewater (OMW) is generated from olive oil extraction systems. It has high added-value compounds namely phenolics, recalcitrants, pectin, and some important enzymes. It causes a certain amount of toxicity/phytotoxicity because of its phenolic compounds. OMW also has significant impacts when discharged directly into surface waters. Therefore, the treatment of olive mill wastewater is very much needed. Several types of techniques have been investigated for OMW treatment along with recovery and removal of its phenolic compounds. Among these techniques, physical ones are utilized for extraction purposes, while chemical and biological methods are applied in order to diminish organic load. In this review, current status and recent developments in the recovery and removal of phenolic compounds from OMW have been critically examined.     

Drying Behavior of Meat Samples at Various Fiber Directions and Air Conditions

The aim of this study was to investigate the effects of meat fiber directions and air conditions on moisture and temperature developments, shrinkage, and effective diffusivity constants compared to homogenous minced meat samples. The lean meat with three fiber directions and minced meat samples were dried at temperatures of 48 and 70°C and air flow rates of 0.5, 1.0, and 1.7 m/s. The minced meat samples showed 1.0 ± 0.19 to 4.4 ± 0.03°C higher temperature values and 2.3 ± 0.004 to 6.2 ± 0.003% lower moisture losses than the lean meat samples in all fiber directions. The lowest temperatures were observed in lean meat with h ₁ (normal flow, normal drying) fiber direction. The highest moisture loss and diffusion coefficient were observed in lean meat with h ₂ (parallel flow, normal drying) and v (normal flow, parallel drying) fiber directions, which also possessed the shortest drying times (10.4 and 13.4 h, respectively). The estimated diffusion coefficient values ranged between 1.11 × 10^?9 and 5.54 × 10^?9. The results indicated that lean and minced meat samples differed in their drying behaviors in a tray dryer under the tested conditions with >90% reproducibility (or ≤10% coefficient of variation).     

Water Diffusivity and Drying Kinetics of Air Drying of Figs

The aim of this study is to evaluate experimentally the effective diffusion coefficient and the drying kinetics of whole unpeeled figs (Ficus carica L. var. tsapela) in terms of drying conditions. Estimation of the effective diffusion coefficient was carried out employing Fick's law for unsteady diffusion, which was solved analytically and numerically. In both methods, shrinkage effect was considered. The results from the two methods were compared and presented together with the limited results from the literature. The estimated effective diffusion coefficient values by both methods were fitted to a modified Arrhenius equation. Finally, a model predicting drying kinetics was developed. The model's coefficients were associated to the experimental conditions.     

Changes in Olive and Olive Oil Characteristics During Maturation

Changes in olive properties and oil quality, oxidative stability, phenolic and chemical composition of two common Turkish varieties (Memecik and Edremit) during maturation were investigated. Olive samples were collected in their own growing region for five different harvest dates and processed to oil with a laboratory scale mill. Metabolic behaviors of these two varieties along with the maturation were different in terms of some compositional parameters. Oleic acid, triolein, β-sitosterol, oleuropein, hydroxytyrosol, and tyrosol contents of olive or olive oils fluctuated with maturation. However, changes in average weight, flesh/pit ratio, water and oil contents of the olives were observed. Phenolics such as trans cinnamic acid contents of both olive fruits decreased whereas cyanidin 3-O-glucoside and cyanidin 3-O-rutinoside anthocyanins increased. Free fatty acids of virgin olive oils were found independent of maturity although some slight changes were determined in peroxide value, dien and trien conjugations. Some compositional parameters such as pigment concentration, tocopherols, stearic acid, linolenic acid, palmitodiolein and monounsaturated/polyunsaturated fatty acid ratio decreased while linoleic acid, dioleolinolein, palmitooleolinolein and Δ-5-avenasterol percentages increased with the maturation. A clear discrimination was observed with principal component analysis. The data obtained can also be considered useful for providing information to determine the ideal maturity stage.     

An Effective Moisture Diffusivity Model Deduced from Experiment and Numerical Solution of Mass Transfer Equations for a Shrinkable Drying Slab of Microalgae Spirulina

From experimental data, Spirulina effective moisture diffusivity was analytically estimated by considering two diffusion regions and the product shrinkage. Then, the moisture diffusivity was deduced from the numerical solutions of mass transfer equations by minimizing the difference between experimental and simulated drying curves and by taking into account the slab thickness variation. The range of moisture diffusivity used for simulations was estimated from minimal and maximal values of experimental effective diffusivities and calculation started with the mean value of experimental effective diffusivities. Identified effective diffusivities ranged from 1.79 × 10^?10 to 6.73 × 10^?10 m²/s. These diffusivities increased strongly with drying temperature and decreased slightly with moisture content. A suitable model correlating effective diffusivity, temperature, and moisture content was then established. Effective diffusivities given by this model were very close to experimental ones with a relative difference ranging from 0.5 to 24%.     

Drying Kinetics Prediction of Solid Waste Using Semi‐Empirical and Artificial Neural Network Models

The drying process of organic solid waste is investigated, based on an experimental study involving its drying kinetics. The experiments were conducted in a thin‐layer fixed‐bed dryer under various operational conditions. The problem of selecting the best fit for solid waste moisture content as a function of time is addressed as well, using artificial neural network (ANN) models and four well‐known drying kinetics correlations commonly applied to biological materials. According to the statistical analysis employed, the simulations showed good results for the ANN, and the Overhults model provided optimum agreement with experimental data among all other models evaluated. Empirical correlations between the Overhults model parameters and the drying operational conditions using nonlinear regression techniques were determined.     

A Novel Alternative Method for Modeling the Effects of Air Temperature and Slice Thickness on Quality and Drying Kinetics of Tomato Slices: Superposition Technique

The effect of air temperature (AT) and slice thickness (ST) on the quality and drying kinetics of tomato slices were studied. The drying period of tomato slices to reach the moisture content of 15% (wb) ranged from 2.6 to 18.7 h. The water diffusivity, activation energy, and resistance to diffusion ranged from 1.4 × 10^?10 to 2.8 × 10^?9 m²/s, 21.25 to 23.4 kJ/mol, and from 939 to 4590 m² s/kg, respectively. Drying had a significant effect on ascorbic acid, soluble solid, acidity, and pH (P = 0.01). The ascorbic acid degradation was greatly influenced by ST. The results show that time-temperature superposition technique (TTST) was very efficient in the modeling of the drying process. The proposed TTST provides a novel alternative in curve-fitting exercise of drying data. Neural networks also showed favorable performance in estimating the drying functions.     

An Integrated Process of Olive Mill Wastewater Treatment

Abstract

Olive mill wastewater (OMWW) is considered as a challenge for environmental scientists. It is characterized by high values of total organics expressed by chemical oxygen demand (COD), biological oxygen demand (BOD₅), and phenols. In this paper, an integrated process of OMWW treatment, which includes lime precipitation, filtration using a novel technology of a membrane filter press (a pilot scale) and a post‐treatment using activated carbon adsorption for the filtrate, was studied. Lime precipitation has removed ～71% of phenols, ～39% of COD, and ～88% of BOD₅ with a rise in the total suspended solids (TSS) from 31 kg/m³ (before precipitation) to 69 kg/m³ (after precipitation).

The filtration and dewatering operation cycle is approximately 125–150 min. Filtration was examined at different feed pressure (3–5 bar), different slurry concentrations (23–69 kg/m³, dry weight), and filter aid pre‐coat with different additions of diatomite body feed. Specific cake resistance, α, was found to increase with the increase in feed pressure and to decrease with diatomite pre‐coating and slurry concentration increase. However, a further decrease in α values was obtained using diatomite body feed. Cake dewatering, via membrane squeezing, was applied using hot water (65°C) and cake moisture was dropped from ～64% before squeezing to 35% after squeezing. Twenty minutes were found enough for that stage to be accomplished. With vacuum application, for 30 min, over the hot cakes, cake moisture decreased to ～20% for cakes with an average thickness of 1 cm. The produced cakes lose more moisture by storing in open air (on the shelf), reaching an equilibrium value of 9% in 2–3 days. Calorific value of produced cake is 15.71 MJ/kg, suggesting strongly its use as an energy source. Activated carbon was used as an efficient sorbent for removing the remaining phenols and total organics from the filtrate as a post‐treatment showing promising results. Maximum removal of phenols and total organics, by lime precipitation and filtrate post‐treatment using activated carbon adsorption, reached ～99.7% and ～80%, respectively.

A process flowsheet and preliminary cost estimates are presented and compared with other processes. The thermal energy produced by the burning of the produced cakes would be enough for the thermal needs of both the olive mill plant and the proposed treatment process.     

Drying Kinetics in a Vertical Gas‐Solid System

A one‐dimensional steady‐state two‐fluid model has been developed to demonstrate the drying kinetics in the vertical up‐flow gas‐solid system. The model takes into account mass, momentum, and heat transfer between the continuous and dispersed phases. A set of non‐linear differential equations have been solved numerically for the velocity, moisture content, and temperature of both the continuous and dispersed phases along the dryer length. The effect of operating parameters on drying kinetics has been critically examined and the model simulations are compared with the data reported in the literature.