Drying Behavior of Carrots Dried in a Spout–Fluidized Bed Dryer

The effect of water blanching treatment and the inlet air temperature on drying kinetics as well as the quality attributes of carrot cubes dried in a spout–fluidized bed dryer at 60, 70, 80, and 90°C were analyzed. The material shrinkage and the rehydration potential were calculated to assess the changes in quality of dried carrots. It was found that the value of the air velocity during the drying of carrot cubes in a spout–fluidized bed dryer should be related to the moisture content of the carrot particles. A high value of air velocity at the beginning of the drying cycle and a lower value for the later stages were also required. The linear equation was correlated to the data of shrinkage of raw and blanched carrots. Blanching significantly influenced the coefficients in the shrinkage model derived for drying of carrot cubes in a spout–fluidized bed dryer, while drying temperature did not influence the shrinkage of carrot particles. The intensity of heat and mass transfer during spout–fluidized drying of carrot cubes was dependent on the drying temperature. A correlation was developed to calculate the values of effective moisture diffusivity of dried carrot cubes as a function of the moisture content and temperature of the material. It was observed that for any given time of rehydration, both the moisture content and the rehydration ratio calculated for samples dried at 60°C were higher than for samples dried at temperatures of 60, 70, 80, and 90°C.     

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).     

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.     

A compact process for the treatment of olive mill wastewater by combining OF and UV/H2O2 techniques

Olive oil production results in important quantities of wastewater containing large amounts of total solids and organic carbon as well as low oil concentrations. This paper describes the treatment of olive mill wastewater (OMW) by combining an ultrafiltration (UF) technique and an advanced oxidation process (AOP) using UV/H₂O₂. It further demonstrates the technical feasibility of this compact and stable process to remove a large part of total solids and organic carbon. Indeed, OF reduces the pollutants contained in the OMW with an apparent rejection coefficient R_COD in the range of 94%. The UV/H₂O₂ oxidation process may be easily used, in combination with UF, to finish the treatment of the permeate. The results obtained in batch and continuous mode showed that this technique offered a treated solution which complies with legal requirements. A final concentration of 17 mg_TOC dm⁻³ was obtained, which corresponds to a final COD of 52 mg dm⁻³, while the legal requirement is 125. Furthermore, the final effluent is fully decolorized.     

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.     

Hydrothermal gasification of olive mill wastewater as a biomass source in supercritical water

In this study, the hydrothermal gasification of biomass in supercritical water is investigated. The work is of peculiar value since a real biomass, olive mill wastewater (OMW), is used instead of model biomass compounds. OMW is a by-product obtained during olive oil production, which has a complex nature characterized by a high content of organic compounds and polyphenols. The high content of organics makes OMW a desirable biomass candidate as an energy source. The hydrothermal gasification experiments for OMW were conducted with five different reaction temperatures (400, 450, 500, 550 and 600 °C) and five different reaction times (30, 60, 90, 120 and 150 s), under a pressure of 25 MPa. The gaseous products are mainly composed of hydrogen, carbon dioxide, carbon monoxide and C₁-C₄ hydrocarbons, such as methane, ethane, propane and propylene. Maximum amount of the gas product obtained is 7.71 mL per mL OMW at a reaction temperature of 550 °C, with a reaction time of 30 s. The gas product composition is 9.23% for hydrogen, 34.84% for methane, 4.04% for ethane, 0.84% for propane, 0.83% for propylene, 49.34% for carbon dioxide, and 0.88% for minor components such as n-butane, i-butane, 1-butene, i-butene, t-2-butene, 1,3-butadiene and nitrogen at this reaction conditions.     

Threshold flux measurement of an ultrafiltration membrane module in the treatment of two-phase olive mill wastewater

The critical and threshold flux theories represent an important advance in membrane knowledge. Comprehension of the flux behavior of ultrafiltration (UF) membranes is key to control the fouling issues during the steady operation of the plant. In this regard, differing between critical or threshold flux patterns in the treatment of wastewater effluents by UF is relevant to confirm the level of fouling expected and to verify if no fouling is predictable or if certain amount of fouling cannot be avoided. In the present study, the hydrodynamic behavior of a polymeric UF membrane was analyzed by means of both critical and threshold flux theories and diverse patterns were found depending on the feedstock pollutants concentration and particle size distribution. Results obtained from the pressure-cycling experiments point for a threshold flux pattern in the case of UF of the effluent derived from the extraction process (OMW) disregarding the applied pretreatment, whereas for 1:1 (v/v) mixture of the latter with the wastewater from the fruit washing (OWW) the membrane fits a critical flux trend, indistinctly of the performed pretreatment too, with negligible fouling below the critical conditions. These conclusions are supported by the experimental permeate flux profiles during batch-run operation experiments.     

Removal of organic load and phenolic compounds from olive mill wastewater by Fenton oxidation with zero-valent iron

Pre-treatment of olive mill wastewater (OMW) by Fenton Oxidation with zero-valent iron and hydrogen peroxide was investigated to improve phenolic compounds degradation and the chemical oxygen demand (COD) removal. Experimental procedure is performed with diluted OMW with COD 19 g/L and pH 5.2. The application of zero-valent Fe/H₂O₂ procedure allows high removal efficiency of pollutants from OMW. The optimal experimental conditions were found to be continuous presence of iron metal, acidic pH (2–4) and 1 M hydrogen peroxide solution. The experimental results show that the removal of 1 g of COD need 0.06 M of H₂O₂. At pH 1, the maximum COD removal (78%) is achieved after 1 h. Therefore, with a pH value within 2 and 4 the maximum COD removal reached 92%. Phenolic compounds are identified in treated and untreated OMW by gas chromatography coupled to mass spectrometry (GC–MS). The result shows a total degradation of phenolic compounds and an increasing biodegradability of treated OMW.     

Critical flux analyses on differently pretreated olive vegetation waste water streams: Some case studies

One of the main disadvantages of batch membrane processes is the increase of the pollutant concentration in the feedstock throughout the operation. Operating the plant at constant process conditions leads in many cases to weaker performances and, moreover, to heavy fouling on the membranes. Critical flux-based methods are one of the most used approaches to overcome fouling problems. Within critical flux conditions, only reversible fouling can occur, which can be periodically soft-cleaned.This work studies the relationship between particle size distributions in the feed stream and critical flux values when different pretreatment processes are applied to an olive vegetation waste water stream. The considered pretreatment processes were: coagulation (with aluminum hydroxide and aluminum sulphate), aerobic biodigestion (by means of fungi) and photocatalytic organic matter reduction (by means of nanometric titanium dioxide anatase powders irradiated by UV light). The study was carried out at pilot plant scale (100 L batch capacity).These results were compared with performances and effects on the critical flux value for MF, UF and NF membranes. The different pretreatment on the same waste water stream shifts differently the particle size distribution mainly by organic matter degradation, and this influences heavily the critical flux value and thus the filtration outcome.Finally, the purification of the olive vegetation waste water stream can be performed with a MF, UF, NF and RO membrane system in series, being very careful in choosing the correct operating conditions to avoid the quick formation of an unsustainable fouling.     

Drying of Turnip Seeds with Microwaves in Fixed and Pulsed Fluidized Beds

This article presents experimental and modeled drying kinetics of turnip seeds as a function of the type of air-particle contact (fixed bed, pulsed fluidized bed), humidity of the air, and three levels of microwave irradiation. The effects of those factors on the drying time required to reach a moisture content of 0.1 kg/kg d.b. were determined with an experimental design of 12 experiments by using the software Statgraphics. It was found that in drying, a significant factor was the application of microwaves to a pulsed fluidized bed. The effect of the humidity of the air only became noticed when the moisture contents of the seeds was below 0.2 kg/kg d.b. The simplified variable diffusivity model (SVDM) gave the least deviations for the experimental data. The effective diffusivity values determined in this work are similar to those informed in the literature for experiments without microwave application. The application of microwaves in combination with pulsed fluidization of the turnip seeds resulted in a fourfold increase of the effective diffusivity.     

Modeling of Diffusion in Ellipsoidal Solids: A Simplified Approach

A three-dimensional model was applied to rigorously interpret the diffusion phenomena in ellipsoidal solids. The numerical solution of the diffusion equation was obtained by the finite difference method for ellipsoids of various shape factors. Due to its complexity for practical use, the spheroidal model (two-dimensional model) was utilized as a better alternative. In comparison with the numerical results generated by the three-dimensional model, the spheroidal model still fails to give good predictions in some cases, although it was assumed to have the same volume and surface area (i.e., same shape factor) as that of the ellipsoidal model. Consequently, a simplified approach was developed with satisfactory predictions, that is to apply a one-dimensional model to solve the diffusion problem with equivalent diameter as well as equivalent liquid diffusivity, which is a function of the intrinsic diffusivity and geometry factor.     

Changes in the size of pores during shrinkage (or expansion) of cement paste and concrete

The often-argued and seldom-resolved issue of relating the bulk shrinkage of concrete to changes in the size of pores is analyzed using a simple model. It is shown that the pores in a composite containing both shrinking and nonshrinking solid phases can themselves either shrink or expand when the matrix shrinks, depending on the amount of restraint in the system. The analysis also applies to expansive deformations, which occur with some types of chemical attack of cement paste. A mathematical relationship between the degree of restraint in a composite and the relationship between bulk volume changes and pore volume changes is given. These observations provide guidelines for interpreting the meaning of gaps that often form between aggregate and paste in concrete.     

Investigation of two ultrafiltration membranes for treatment of olive oil mill wastewater

In this study, a promising treatment method is given for the olive oil mill wastewater (OMWW). Although the same steps of this method have been used in different studies before, flow scheme is novel. The membrane filtration of pretreated OMWW was investigated by using two ultrafiltration membranes in this study. Pretreatment steps were pH adjustment (pH = 2) and cartridge filter filtration, and pH adjustment (pH = 6) and cartridge filter filtration. Each step of cartridge filter filtration was batch process and effluent from the filter was recycled back to OMWW tank. Pretreated OMWW was sent to feed vessel of experimental set-up. Recovery of olive oil in the OMWW was realized collecting it from the top of pretreated OMWW. Ultrafiltration membranes used were JW and MW membranes supplied by Osmonics. The effects of main operating parameters (transmembrane pressure, feed flow rate, pH and membrane type) on the permeate flux and membrane fouling were examined. The effectiveness of the different membranes and operating conditions was evaluated using retention coefficients calculated from COD and TOC of experimental studies. The highest permeate flux (25.9 l/m² h) was obtained using MW membrane under operational conditions of Qf = 200 l/h flow rate and TMP = 4 bar, while the highest removals were obtained at Qf = 100 l/h flow rate and TMP = 1 bar. COD, TOC, SS, oil and grease concentrations of MW membrane effluent were 6400 mg/l, 2592 mg/l, 320 mg/l, and 270 mg/l, respectively.     

Treatment of olive mill wastewater by the combination of ultrafiltration and bipolar electrochemical reactor processes

The main purpose of this study was to investigate the removal of the chemical oxygen demand (COD) from olive mill wastewater (OMW) by the combination of ultrafiltration with electrocoagulation process. Ultrafiltration process equipped with CERAVER membrane was used as pre-treatment for electrochemical process. The obtained permeate from the ultrafiltration process allowed COD removal efficiency of about 96% from OMW. Obtained permeate with an average COD of about 1.1 g dm⁻³ was treated by electrochemical reactor equipped with a reactor with bipolar iron plate electrodes. The effect of the experimental parameters such as current density, pH, surface electrode/reactor volume ratio and NaCl concentration on COD removal was assessed. The results showed that the optimum COD removal rate was obtained at a current density of 93.3 A m⁻² and pH ranging from 4.5 to 6.5. At the optimum operational parameters for the experiments, electrocoagulation process could reduce COD from 1.1 g dm⁻³ to 78 mg dm⁻³, allowing direct discharge of the treated OMW as that meets the Algerian wastewater discharge standards (<125 mg dm⁻³).