Search

Cactus has shown great capabilities as a bio coagulant/flocculent in the treatment of wastewater and as a factor for sustainable development of the environment, due to its abundance and non-toxicity for human health. This has encouraged the present study based on the design of experiments to optimize the two operating factors: the bio coagulant dosage and initial pH. The effect of these considered factors on turbidity and chemical oxygen demand (COD) reduction performances was investigated to treat sewage wastewater from plants by the coagulation/flocculation process using the response surface methodology (RSM) based on a central composite faced design (CCFD). The effect of the pH on the supernatant turbidity removal and the COD reduction was very significant whereas that of the coagulant dosage was insignificant on the COD removal efficiency. Experimental results revealed that the maximum reduction of turbidity and COD could be reached at a coagulant dosage of 28 mg/l and a pH of 12. At these optimal conditions, the removal efficiency of turbidity and COD was 98.33% and 96.55% respectively. By the end of the treatment, final values of 0.84 NTU and 20.8 mg/l were obtained for turbidity and COD, respectively. A notable decrease of orthophosphate (O- PO4−2), nitrite (N-NO3−), ammonium (N-NH4+) and suspended matter (SM) was observed. The study also showed that the quadratic regression model could be used as a theoretical basis for the process based on a high coefficient of determination R2 value > 0.96, obtained from the analysis of variances (ANOVA).

In this work, we present our MCNP6.1 modeling of some critical fast experimental benchmarks, aiming to qualify our cross section libraries derived from ENDF/B-VII.1, ENDF/B-VII, JEFF-3.1, JENDL-3.3, and JENDL-4.0. The analyzed benchmarks are characterized by simple geometries which helps to have taken precise results, and concerning the type: HEU-MET-FAST (highly enriched uranium). Those benchmarks are extracted from the International Handbook of Evaluated Criticality Safety Benchmark Experiments (IHECSBE) published by the Nuclear Energy Agency [1]. A detailed comparison of the results of our simulation was made in order to highlight the influence of these nuclear data types on our calculations, due to its importance for the stability of nuclear reactors. We interpreted the difference between calculation and experiment ($$C{-}E$$) for the principal parameter $$k_{\textrm{eff}}$$ through a comparison of the fission and capture rates of the major fissile elements. The different spectral indices F28/F25, F49/F25, F37/F25, C28/F25, and F23/F25 at the cores center are also calculated. For the majority of the studied HEU (highly enriched uranium) benchmark cases, The ENDF/B-VII and JEFF-3.1 have a good agreement with the experimental ones, concerning the $$k_{\textrm{eff}}$$ results. The average discrepancy from the experimental values for ENDF/B-VII is 0.42$$\%$$, and 0.39$$\%$$ for JEFF-3.1. An overestimation was observed for most evaluations concerning benchmarks with tungsten carbonate reflectors. The best results were obtained by JENDL-3.3, with a maximal discrepancy $$C{-}E$$ estimated 0.47$$\%$$ concerning fission rate, and 4.25$$\%$$ for capture rate. In analyzing the spectral indices, for GODIVA and FLATTOP-25, the best results were obtained by JENDL-4.0 with a maximal discrepancy of 2.66$$\%$$.

International audience; This study focused on electrocoagulation treatment of leachate effluent using aluminum electrodes in a discontinuous system, the modeling and optimization of which were carried out using the response surface methodology (RSM) basing on the central composite design (CCD). Moreover, individual and interaction effects of principal independent factors (current density (X1), initial pH (X2), electrolysis time (X3), and distance between electrodes (X4)), on chemical oxygen demand (COD) removal efficiency response, were investigated. The obtained results were in good agreement with the predicted ones with correlation factors R2 Dec = 0.94 and R2 Ajusted = 0.88. At the optimal conditions, maximal removal efficiency was achieved for values of chemical oxygen demand (COD), total organic carbon, total nitrogen, and turbidity of 79.8%, 78%, 45.4%, and 99.9%, respectively. The quite good agreement between the experimental values and the predicted results confirms the reliability of the RSM approach in the modeling and optimizing of the leachate treatment using an electrocoagulation process. © 2018 Desalination Publications. All rights reserved.

A pretreatment with H2O2 was conducted to improve the performance of the anaerobic digestion (AD) process for a partial treatment of tannery wastewater (TWW). Four different H2O2 dosages (0.5, 1, 2, and 4 g/L) were tested by adding to TWW different volumes of a 30% (m/v) H2O2 solution in order to improve the biodegradability of TWW organic load and decrease the total Cr concentration. Indeed, a less total Cr concentration was detected in pretreated samples that showed a minimum removal efficiency of 11% and a maximum removal efficiency of 41%. Moreover, several Biomethane Potential tests (BMP) were conducted to assess the enhanced biodegradability of pretreated TWW. Methane yields resulted in 594, 1151, 1090, 767, and 525 mL CH4/g TVS for the unpretrated TWW and for those pretreated with 0.5, 1, 2, and 4 g/L of H2O2, respectively. BMP tests proved that the best pretreatment condition for TWW, in terms of methane production and consequently total COD reduction, was achieved with a low dosage of H2O2 (0.5 g H2O2/L), corresponding to 1.0·10−4 g H2O2/g TVS and 3.2·10−5 g H2O2/g COD, whereas the highest dosage (4 g H2O2/L) was not related to the highest methane yield. Such contradictory results highlights the relevance of an appropriate dosage of H2O2, Finally, a kinetic study was also conducted.

Respirometry has been used in this work to assess the effect of S0/X0 ratio, knowing that this ratio is a very important operational parameter in the conduct of wastewater treatment plant. It affects its design and operation; part of the respirometry calculations, dissolved oxygen transfer coefficient KLa is calculate for each respirometric experiment, due to the fact that operational condition change. Under endogenous conditions OURend is calculated using the linear portion of the variation of DO concentration under no aeration conditions. Then the OURend is used in the endogenous phase at a no oxygen concretion variation to calculate the KLa. Samples of wastewater, with different S0/X0 ratios in the range between 0.01 and 0.23, containing sometimes ATU, a nitrification inhibitor, were injected in the respirometer with DO concentration variation recording. Exogenous OURexo were calculated from the DO data and they show that as S0/X0 ratio increased total OURt increased too as well as total oxidation time. However when, COD is present alone the removal kinetics is more rapid than when both substrates (nitrogen and carbonaceous) are present. It has been shown that the use of respirometry in biomass activation assessment is a sound approach because of the celerity, the reliability and the limited cost. Consequently it has been extended in to the assessment of biomass activation when it is exposed to antibiotics.

The present work is aimed at exploring carbon which was prepared by calcination of Cereal By-Product (CBP) and used as adsorbent for the removal of Chromium (VI) from a surface treating industry. The effects of various parameters such as adsorbent dosage, pH, contact time were studied. As the adsorption process is pH dependent, it showed maximum removal efficiency of Cr(VI) in the pH range of 6–8 for an initial chromium concentration of 132 mg/L. Effect of temperature on the equilibrium constant was studied and the thermodynamic parameters like standard Gibb's free energy (Δ G °), standard enthalpy (Δ H °) and standard entropy (Δ S °) were also investigated. The positive values of Δ H 0 and Δ G 0 indicated an endothermic and a non spontaneous thermodynamically adsorption, respectively. Pseudo second-order model was found to best represent the kinetics of Cr(VI) adsorption. Intraparticle diffusion studies show that the mechanism of adsorption was mainly dependent on diffusion. The Langmuir, Freundlich and Temkin isotherm were used to describe the adsorption equilibrium studies of calcinated cereal by-product at 20 °C. Temkin isotherm showed better fit than Freundlich and Langmuir isotherms. It was demonstrated that the removal effectiveness reached nearly 90.37% when using optimal conditions as used for the treatment of wastewaters containing chromium as a low cost alternative compared to commercial activated carbon and other adsorbents reported.

The plant world is an excellent source of active substances, which gives it an important antibacterial activity, often sought in alternative medicine and agri-food for the conservation of food. Our work focuses on the phytochemical study of a medicinal plant, Urtica dioïca (Urticaceae). The phytochemical screening of Urtica dioïca revealed the presence of secondary metabolites: flavonoids, tannins, mucilages and saponosides. Selective extractions revealed significant yields compared to studies conducted on the same species in other countries. The qualitative analysis of the extract by thin layer chromatography (TLC) revealed the presence of Flavonones, phenol acid and Luteolin-7-glucoside

Tanning factory is globally considered to be one of the most resource consuming and pollutants producing industries because it requires, for processing leather, large amounts of fresh water, chemical reagents, and energy, and in addition produces wastes, liquid as well solid, rich in organic matter and heavy metals (e.g., chromium). Such characteristics of tannery wastes make their biological treatment promising as well as challenging. This study deals with the effect of coagulation process as a pretreatment method on real tannery wastewater prior to anaerobic digestion (AD), with the aim of removing chromium and thus limiting its inhibitory effect on biological process. Different concentrations (100, 200, 400, 600, 800, and 1,000 mg=L) of the coagulant FeCl3 were tested, at pH 7.5, with an initial total chromium concentration of 150 mg=L. The efficiency of metal removal was in the range of 0.44–29.38%. Simultaneously, the chemical oxygen demand was reduced by 0.86–28.80%, with the detrimental effect of lowering the total biogas production potential from tannery wastewater. Nevertheless, coagulation pretreatment enhanced the AD process of tannery wastewater, resulting in an increase of the cumulative biogas production by 10% and in a reduction of the digestion time by approximately 25%, in comparison with untreated wastewater. After 37 days of incubation, the maximum specific cumulated volume of biogas produced from the wastewater pretreated with 800 mg=L of FeCl3 was 837 mL=g total volatile solids added with approximately 84% of methane.

In wastewater treatment, waste removal and biomass activity are important processes which need to be monitored for a good process control. The difficulties in the interpretation of the total COD, BOD and VSS measurements encouraged the development of respirometric methods for assessing the kinetic constants. Respirometry is an important technique in assessing biological reaction in wastewater treatment. K L a $${K_L}a$$ , depends on endogenous oxygen uptake rate (OURend), is a key constant in evaluating respirogram-specific parameters. Generally, OURend is assumed constant in the dissolved oxygen equations. However, it is not the case. Consequently, this paper deals with the influence of OURend calculations region on K L a $${K_L}a$$ determination, exogenous oxygen uptake rate (OURexo), total oxygen consumption and heterotrophic yield (Y H). It was shown that the value of OURend and K L a $${K_L}a$$ varied considerably, a maximum of 56%, depending on where to consider C fin, on the oxygen concentration variation curve. Even though, the variation on OURend and K L a $${K_L}a$$ is important its influence on Yo/x and Y H is attenuated to 7.5% and 6%, respectively. This may be due to the local nature of the first parameters (OURend and K L a $${K_L}a$$ ) and the global nature of the later ones. Moreover, this can be seen through the variation of the calculated amount of oxygen consumed (QThete) which is of the order 7.6%.

Respirometry is the measurement of the biological oxygen consumption rate under well-defined conditions. This technique is generally employed to determine the kinetic and stoechiometric parameters of biological processes, such as: the oxygen transfer coefficient KLa, the endogenous oxygen uptake rate OURend, exogenous oxygen uptake rate OURexo, the total oxygen uptake rate OURt; the substrate affinity constant (KS), the maximum growth rate (μmax) and the yield (YX/S). According to the literature, there is a large variability in the estimation of these kinetic and stoechiometric parameters, attributed to three key factors: the culture history, the parameter identifiability and the initial substrate to biomass ratio (S0/X0). KLa, depends on endogenous oxygen uptake rate OURend, is a key constant in evaluating respirogramme-specific parameters. Generally, OURend is assumed constant during dissolved oxygen variation. The effect of S0/X0 ratio on kinetic and stoechiometric parameters has only been partially studied. The goal of this study was to assess respirometrically the effect of various S0/X0 ratios (in the range of 0.01 to 0.23) on the kinetic and stoechiometric parameters of a heterotrophic activated sludge biomass (presence of ATU a nitrification inhibitor) and for both heterotrophic-autotrophic activated sludge biomass.

In recent years the uses of waste as a raw material for producting porous carbon have been widely employed in the purification of water and wastewater. The application of these carbons has bees considered also a major unit operation in the chemical and petrochemical industries. The purpose of this study is to characterize a natural adsorbent obtained from local cereals by products. This solid has been tested with organic pollutants (phenol, dyes) and inorganic pollutants (copper, zinc and cadmium) where he was given a good performance. The characterization is important to understand and identify the different phenomena of retention (adsorbent-adsorbate) as well as to the interpretation of the kinetic results. The characterization is focused on quantitative analysis (elemental analysis, BET), qualitative (RX, IR) and optical (SEM) in order to get an idea on the morphology and pore structure and active sites.

Aprocess forpurifyingaqueoussolutionscontainingheavyand toxicmetalssuch aschromiumhasbeen investigated. Hexavalent chromium compound is present at high concentration in the shovels and cranes factory, it is used in the electrodepositioncontainer; afterits reductionbysodiumbisulfites it changesinto trivalent chromium. The present work deals with the investigation and optimization of chromium (III) ions removal from aqueous solutions by complexation enhanced ultrafiltration using experimental and calculation approach; diamine tetra-acetic acid (EDTA) has been used as chelating agent for Chromium (III) complexation; in the first part the study of experimental optimum conditions of complexation reaction is carried out; the second one the calculation of optimum pH, initial concentration of chelating agent and the influence of chromium hydroxides forms on complexation reaction using MATLAB language has been determined. Its shown that the Complexation reaction is favoured at pH equal to 5.1, at excess EDTA concentration ([EDTA] 0 =0.095 M for [Cr(III)] 0 =0.003 M), at ordinary temperature (T=20°C), and 600 tr/min for agitation, trivalent chromium concentration at solution increases with ionic strengths, it also increases with high CaCO 3 values. The calculated pH, initial concentration of ligand and presence of chromium hydroxidesforms shows a littlevariation with experimental ones.

Restrictions concerning the disposal of waste waters are getting more severe, requiring a greater reliability for the waste water treatment plants as well as a better understanding and application of biological processes which depend of the hosting media. The use of respirometry, the principle of which is based on measuring the consumed amount of oxygen by a sample of activated sludge for the metabolism of a given amount of substrate, seems to be able to contribute to the improvement of the plant management. In fact, it enables the estimation of certain characteristic variables for a good process or the detection of the influence of the physico-chemical conditions such as pH, salinity, metal toxicity, etc. Obviously these conditions have an impact on the enzymatic reaction rates and hence on the metabolism and cell multiplication. In the present study, inhibition by chromium which is a major contaminant present in tanning, metallic surface treatment and other industries waste waters, is likely to neutralise the biomass, was studied by means of the respirometry technique to detect the immediate influence of this type of stress on the activity of microorganisms (autotrophic and heterotrophic), as well as on its purifying power and its aggregation morphology.

A process for purifying aqueous solutions containing heavy and toxic metals such as chromium has been investigated. Hexavalent chromium compound is present at high concentration in the shovels and cranes factory, it is used in the electrodeposition container; after its reduction by sodium bisulfites it changes into trivalent chromium. The present work deals with the investigation and optimization of chromium (III) ions removal from aqueous solutions by complexation enhanced ultrafiltration using experimental and calculation approach; diamine tetra-acetic acid (EDTA) has been used as chelating agent for Chromium (III) complexation; in the first part the study of experimental optimum conditions of complexation reaction is carried out; the second one the calculation of optimum pH, initial concentration of chelating agent and the influence of chromium hydroxides forms on complexation reaction using MATLAB language has been determined. Its shown that the Complexation reaction is favoured at pH equal to 5.1, at excess EDTA concentration ([EDTA]0=0.095 M for [Cr(III)]0=0.003 M), at ordinary temperature (T=20°C), and 600 tr/min for agitation, trivalent chromium concentration at solution increases with ionic strengths, it also increases with high CaCO3 values. The calculated pH, initial concentration of ligand and presence of chromium hydroxides forms shows a little variation with experimental ones.

The microorganisms growth kinetics is determined by the physical and chemical characteristics of the environment in which they find themselves and multiply; It is therefore essential to understand the effect of these environmental factors to master cell multiplication and hence the pollution biodegradation. Respirometry has been used in recent years in the laboratory as an assessment technique of microbial activity and an effect detector of the contamination (presence of toxic, stress, increase or decrease in pH, temperature variation .) on bacterial respiration and hence on the biological waste water treatment plant. In this study respirometry has been used as a relatively quick and efficient means to detect the effect of the presence of a salt of up to 5 g/l (low salt stress) on the degradation of carbon and nitrogen pollution and on bacterial floc aggregation.

The present study deals with the elimination of phenol by adsorption onto polyaniline coated silica gel, from synthesized aqueous solutions. The silica gel was coated by the polyaniline, a conducting and an electroactive polymer in order to modify its surface structure to improve its adsorption capacity. The study was carried out batchwise and the effect of important operating parameters like the contacting time, the initial concentration, the temperature and the pH was also investigated. The obtained results showed that the polyaniline coating of the silica gel surface did in fact improve the adsorption capacity of phenol.

Crown rust caused by Puccinia coronata f.sp. avenae is the most damaging disease on oat. This work analyzed the effects of temperature and illumination regime during different time of incubation on both spore germination and germ tube growth, using both analysis of variance (ANOVA) and response surface methodology (RSM). This study reveals that the maximum of germination approached 95% under dark conditions at 20°C. Similarly, the maximum germ tube length was 125±23 μm under dark conditions at the same temperature after 18 h. Both spore germination and germ tube growth were observed over a wider temperature range of 5 to 30°C. The darkness conditions seem to enhance significantly (P < 0.05) both the germination and germ tube growth. After 4 h of incubation, germination was significantly higher under darkness regime at 15, 20 and 25°C than under light conditions. The effect of darkness conditions on germ tube growth paralleled its effect on germination. Furthermore, the response surface methodology (RSM) was applied to determine the optimal conditions of temperature, time and illuminations conditions for both the germination process and germ tube growth of urediospores for P. coronata f.sp. coronata. Values for the optimal germination and germ tube growth were 20°C and 8 h under darkness conditions. Moreover, urediospores of P. coronata f.sp. coronata germination and germ tube growth had followed a quadratic response function on temperature (R² = 0.94 and 0.97). On the other hand, the experimental values were in good agreement with the predicted ones and the model was highly significant with the correlation coefficient R being 0.97 and 0.98, respectively for germination and germ tube growth. Key words : Puccinia coronata f.sp. avenae, temperature, time, illuminations conditions, germination process, germ tube growth, urediospores.

The present work reports a study on the test of olive stones as an adsorbent for removal of cation Cd(II) and the oxyanion Cr(VI) from aqueous solutions. The experimental elimination of the species has been carried out batchwise and the influence of certain physico-chemical parameters such as the contact time, the pH of the solution, the temperature, the solid to liquid ratio and the agitation speed has also been considered. The equilibrium adsorption capacity of the olive stones for the case of Cr(VI) follows the Langmuir model, whereas for the Cd(II) cations, the two models — Langmuir and Freundlich can be equally representative. The adsorption process has been found to be of pseudo second-order and the rate constants have been determined for both cations. The Gibbs free energy sign is negative for the adsorption of both cations, indicating that the process is spontaneous. Finally the olive stones retain chromium more than cadmium, but at optimal conditions, high removal percentages are reached for both cations.

La salinité des eaux souterraines pose un problème en zones arides et semi-arides, et détériore leur qualité. Le système aquifère mio-plio-quaternaire des hautes plaines sétifiennes est logé dans des formations argileuses et conglomératiques, et des calcaires lacustres. Il est interposé entre les séries telliennes au Nord et les séries hodnéennes au Sud. Il est essentiellement alimenté par les précipitations et par des failles conditionnant et favorisant l’écoulement des eaux souterraines. L’endoréisme est le caractère principal de la région. Pour la période d’observation prise en compte, la valeur moyenne de l’évapotranspiration réelle (E.T.R.) est souvent supérieure à 85 % des précipitations et celle du coefficient d’infiltration ne dépasse pas les 10 %. Les pompages d’essai exécutés dans la région montrent de bonnes transmissivités de l’ordre de 10-3 m2/s. L’étude temporelle et spatiale des paramètres physico-chimiques du système aquifère superficiel, suivie depuis 1991, leur représentation en matrice de corrélation et les rapports caractéristiques ont permis de définir les principaux traits caractérisant la salinité (teneur, origine et évolution) et de mettre en évidence les faciès hydrochimiques dominants. Les eaux de l’aquifère superficiel de la zone d’étude présentent une salinité moyennement à assez élevée. Cette dernière a même révélé une mauvaise potabilité. Lors de leurs trajets en profondeur, les éléments chimiques dans l’eau ont évolué en deux faciès dominants : chloruré sodique et sulfaté calcique. L’analyse chimique a donc montré la dominance des ions salifères (Na+, Cl-) et des ions du gypse (Ca 2+, SO4 2-) par rapport aux carbonates (Ca2+, HCO3 -).

Mathematical modeling of an ultrafiltration membrane separation process, based mainly on the transmembrane pressure (TMP), is undertaken in the present work. The main objective is the prediction of the permeate flux of a solution containing Dextran T500 through a cylindrical module. The proposed model incorporates the resistance-in-series model coupled with the equation describing the solute (Dextran T500) transport, as well as the continuity and Navier-Stokes equations for solution flow modeling. The model equations are solved using finite-volume numerical methods, with appropriate initial and boundary conditions. The effects of the TMP and the length of the membrane on the mean permeate flux were also investigated. The influence of the membrane dimensions (aspect ratio) on the relative dimensionless mean permeate flux, at different inlet TMPs and different solution concentrations, respectively, have also been considered. The variations of the TMP with the membrane length as well as the influence of the Peclet number on the solute surface concentration were also examined. The numerical results obtained are compared with experimental values reported in the literature, and in general, the agreement is satisfactory enough to encourage further refinement of the model.

Les fondations superficielles sont largement utilisees dans le domaine de la construction. L’etude de leur stabilite en particulier vis-a-vis du poinconnement constitue un aspect primordial dans le but de construire des fondations et des ouvrages plus fiables et economiques. Dans cet article, on propose une analyse semi-probabiliste de la stabilite des fondations superficielles vis-a-vis du poinconnement a l’etat ultime basee sur l’Eurocode 7. Cette nouvelle approche prend en consideration le caractere aleatoire des parametres d’influence (geometrie, sol, surcharge), notamment celui des parametres de cisaillement du sol. Une comparaison de cette approche semi-probabiliste avec des approches conventionnelles nationales (approches deterministes) est effectuee pour differents cas de chargement et differents types de sol.

The performance of refrigeration systems using absorption heat pumps depends mainly on the combination of two working fluids, i.e., the refrigerant and the absorbent. Consequently, this work presents a theoretical model for systematically testing pairs of absorbents and refrigerants with respect to key parameters such as the coefficient of performance (COP), the circulation ratio, etc. At this stage, the refrigerants considered were issued from combinations of a chosen set of functional groups, excluding the chlorine atom, for obvious reasons. The resulting compounds may or may not exist at all, but this does not prevent testing them theoretically. The absorbents were chosen as water or organic compounds commercially available. For the compound property estimation, the proposed technique is based on group contribution methods which have proven to be very suitable for this kind of problem, i.e., compound design. The method is very flexible, not costly in terms of computer time, and can be adapted to various situations. The results obtained are encouraging compared to some available experimental values reported in the literature.

Biological wastewater treatment occupies an important place in sanitary schemes and therefore in environmental protection. To master the efficiency of this type of process necessitates the comprehension of the treatability which consists of the study of oxygen transfer between different phases and degradation of the carbonaceous nitrogen and phosphate loads. Therefore, in the first part of the study the oxygen transfer was considered in a batch reactor configuration in order to find the global oxygen transfer coefficient (KLa) from the gaseous phase to the liquid phase and from the liquid phase to the solid phase. Starting with the determination of the KLa (gas–liquid) of clear water by the variation of the air flow and mixing velocity. The experimental results were modeled with correlation reported in literature. In fact, the air flow and mixing velocity are related to energy consumption. The determination of the exact amount of oxygen and mixing needed could be of great effect on energy savings in wastewater treatment plants.

The present study concerns the test of natural adsorbent obtained from a local cereal by-product as adsorbent for the removal of heavy metals such as Cu, Zn, and Cd ions from aqueous solutions. The solid support was used after calcinations at a temperature of 600 °C in exclusion of the air. The study was an opportunity to investigate the adsorption kinetics where equilibrium was reached after 30 min for the three metallic pollutants. The kinetic was of pseudo-second-order and controlled by intra-particle diffusion phenomenon. The isotherm of adsorption was also examined and showed a type C from Langmuir classification. The effect of important parameters such as the initial concentration and the contact time was also considered. The results showed a high retention capacity of the cereal by-product adsorbent, where yield values exceeding 90 % was reached for an initial concentration of 10 mg/L, at 20 °C, a mean size diameter of 0.1 mm, a mixing velocity of 600 rpm, a solid–liquid ratio of 10 g/L, a pH between 3 and 6, and a contact time of 2 h.

The population balance model is a useful tool for the design and prediction of a range of processes that involve dispersed phases and particulates. The inverse problem method for the droplet population balance model is applied to estimate coalescences parameters for two-phase liquid-liquid systems. This is undertaken for two systems, namely toluene/water and n-butyl acetate/water in a rotating disc contactor (RDC), using a droplet population balance model. In the literature, the estimation procedure applied to this problem is often based on the deterministic optimization approach. These methods generate instabilities near a local minimum, inevitably requiring information about the derivatives at each iteration. To overcome these limitations, a method providing an estimate for the coalescences parameters is proposed. It is based on a simple and adapted structure of the genetic algorithm, for this particular problem. The agreement between the experimental observations and the simulations is encouraging and, in particular, the models used have proven to be suitable for the prediction of hold-up and Sauter diameter profiles for these systems. Finally, these results demonstrate that the optimization procedure proposed is very convenient for estimating the coalescences parameters for extraction column systems.

The test and use of natural materials as adsorbents for the removal of various pollutants such as heavy metals from industrial wastewater is under constant development. Consequently this work concerns the study of copper adsorption by means of sawdust obtained as by-product from locally used wood. The copper retention study has been carried out batchwise where the influence of physico-chemical key parameters such as the solution pH, the temperature, the agitation speed, the initial concentration, the contacting time, the liquid to solid ratio and the ionic strength has been considered. A desorption study for the solid support regeneration has also been included. The equilibrium adsorption capacity of sawdust for copper has been obtained by using linear Freundlich and Langmuir isotherms. The results tend to explain the retention mechanism as an ion exchange process for binding the divalent metal ions to the sawdust.

The presence of various pollutant species such as heavy metals in soil and industrial wastewater constitutes a potential source of ground water pollution. Therefore preventive and protective actions are required and must be developed. In this study an abundant and a low cost natural clay is tested as liners for use in public landfills to prevent heavy metals propagating into the ground soil and eventually reaching the waters. As an illustrating example, a local type of clay has been tested with respect to its capacity to retain copper cations. The study has been carried out batchwise and the influence of physico-chemical key parameters such as the contacting time, the solution pH, the temperature, etc. has been considered, in order to optimise the clay copper retention. The obtained experimental results have been fitted according to the two known adsorption models of Langmuir and Freundlich. A kinetic study of the copper retention has also been carried out where the equilibrium time has been determined during the cation fixation process, as well as the reaction order enabling the determination of certain thermodynamic functions. In conclusion the clay used in this work, as adsorbent for metallic cations such as copper, has shown a great retention capacity clay, making it very suitable to be used as clay barriers in public landfills, for ground water protection.

A general model, based on double film theory, is developed to study absorption with chemical reactions. In the liquid film region, the model is a set of differential equations that describe the mass transfer accompanying several chemical reactions; the resolution of the system is achieved by the finite difference method using an implicit scheme combined with Newton's method. Continuity equations and equilibrium coefficients are exploited in the treatment of the bulk region, which is based on the Newton-Raphson method; the results are used directly as boundary conditions in the liquid film equations. Maxwell-Stefan equations have been used as a rigorous approach in this model.

The effect of certain physical parameters on retention of copper 11 by calcinated wheat by-products was studied. Other parameters that also have an effect were assessed macroscopically. The effect of pH was studied thoroughly and yielded interesting findings. At a final pH less than 6, precipitation of copper is excluded as an elimination process in the presence of the by-product. The retention process is very rapid at the beginning of the experiments, which is due to surface acid-base interactions (protonic exchange). The determination of the nature of the sites on the support material surface using Bohems' method at first and second a titration method showed an amphoteric nature of the surface material. The Bohems' method resulted in an acidic nature whereas the titration method indicated a basic nature of the surface sites.

Synthesised polyaniline coated onto silica gel and other natural materials such as peanut, almond, nut shells, apricot and olive seeds, etc., have been tested for the ability to retain metallic pollutants. Two adsorbents have been tested, namely silica gel and peanut shells, with copper as the metallic pollutant. In the absence of the polymer, both adsorbents have shown an extremely low capacity of retention, inversely to the case where they are coated with polyaniline, where the retention is very important. In fact the kinetic study of metal retention has shown that both polyaniline coated sorbents exhibit a rapid phase of adsorption before saturation is reached. However it should be noted that the peanut shells have shown a more rapid kinetic of retention than silica gel. The influence of different parameters like the contact time between the liquid and solid phases and the solution pH, on the capacity of retention, has been considered. The main result obtained from this study is that, macroscopically, the introduction of polyaniline onto the surface of silica gel and peanut shells, has largely improved the retention capacity of copper, practically from a zero value to nearly hundred per cent.