Résumé: Wastewater laden with toxic pollutants, such as chromium (Cr), can hurt humans, the environment, and aquatic life if not properly treated. The present work proposes to study the elimination of 100 mg/l of Cr(VI) ions from a synthetic wastewater effluent using a dynamic electrocoagulation process employing aluminum electrodes. The influences of several parameters are explored for the electrocoagulation process effectiveness in terms of Cr removal yield. This was done within the following ranges: current density (5-22 mA/cm2), initial pH (2-7), and chromium concentration (25-150 mg/l). A settling step was followed to determine the total suspended solids content and the sludge volume index after electrocoagulation treatment. Depending on the operating conditions, the data of specific electrical energy consumption were employed to determine the best operating parameters of the process efficiency. Furthermore, data analysis (Scanning Electron Microscope, Fourier Transform Infrared spectroscopy, X-ray diffraction analysis, and X-ray fluorescence) of sludge formed after electrocoagulation showed an amorphous nature with a high content of aluminum and function groups that should have a potential to be utilized as coagulant/sorbent in wastewater treatment.

Résumé: Municipal and industrial wastewater treatment plants produce large amounts of sludge containing high levels of organic, chemical, and microbial pollutants. Unless stabilized completely and discharged safely, they may become potential pollution sources threatening soil and water bodies. This study investigated H2O2 oxidation and electrocoagulation as pretreatments to improve stabilization of an urban sludge. The H2O2 oxidation was optimized with respect to H2O2 dosage and initial sludge pH-H2O2. Batch electrocoagulation experiments were conducted using aluminum, iron, and zinc electrodes to investigate the effect of treatment period, current density, and pH. The effectiveness was compared in terms of solubilization of sludge, disintegration degree, and reduction of total solids. Sludge settling velocity after disintegration by both H2O2 oxidation and electrocoagulation were measured with respect to the operating conditions. The obtained results indicated that the high rate of sludge disintegration (63.3%) was obtained with aluminum electrodes, which has lower operating costs than iron and zinc electrodes. The H2O2 oxidation reached a maximum disintegration degree of 50%. Additionally, with aluminum and iron electrodes, sludge settleability was enhanced with both H2O2 oxidation and electrocoagulation.

Résumé: This work aims to evaluate the adsorption capacity of an abundant natural diatomite (ND) to remove the azo dye carmoisine, known as a harmful emerging organic pollutant. Indeed, to the best of our knowledge, no results were reported on this subject. The ND was characterized by FTIR, XRD, and SEM/EDX analyses. The experimental study of adsorption was carried out in batch mode. Results showed that ND adsorbent is mainly composed of silica. A fraction of calcite and ankerite was also identified. It is a porous material with a specific surface of about 41 m2.g-1 and with a hydroxyl surface functional group -OH. Adsorption results showed that adsorption process on ND is found to be effective in removing the carmoisine colorant. The adsorption capacity is strongly affected by the adsorbent and adsorbate contents, the solution pH, the work temperature, and the water hardness and mineralization. At room temperature, optimal experimental conditions for the highest adsorption capacity (12 mg.g-1) were colorant concentration 50mg.L 1, pH 2, contact time 30min, and ND content 1 g.L-1. Modeling study has showed that experimental results are well modeled by the Freundlich isotherm in multilayer adsorption. The reaction kinetics are pseudo-second order, and the thermodynamic parameters indicated that the nature of the adsorption process is endothermic and spontaneous.

Résumé: This manuscript demonstrates the ability to remove toxic hexavalent chromium species from aqueous solutions through adsorption in batch system using a cost-effective raw sludge (RS). The physico-chemical properties of the raw sludge were evaluated by scanning electron micro-scope/energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, and X-ray fluorescence. The RS was found to be rich in amines and carboxylic groups, which may induce strong surface interactions with Cr(VI) ions in the solution and exhibit a porous morphology suitable for the fixation of Cr(VI) ions. The effects of adsorbent amount, contact time, initial Hexavalent chromium [Cr(VI)] concentration, pH and temperature on the adsorption of Cr(VI) were studied. Under the optimized operating conditions (initial Cr(VI) concentration = 20 mg/L, pH = 2, contact time = 60 min, temperature = 30°C) produced a maximum removal rate of 80.9% and maximum adsorption capacity of 9.84 mg/g. The equilibrium data fitted well to the Langmuir and Dubinin–Radushkevich adsorption isotherm models. The kinetic data showed good compliance with a pseudo-second-order rate model. The thermodynamic parameters indicated that the Cr(VI) removal by RS is an endothermic process with positive entropy was feasible spontaneously by an increase in the temperature. Based on the obtained results, the tested waste product sewage sludge can provide a low-cost means for the removal of Cr(VI) from synthetic effluents.

Résumé: Electrokinetic (EK) treatment of soil/sludge contaminated with metallic and organic pollutants has proven its success concerning efficiency and cost. The study carried out in the laboratory aimed at the feasibility of this technology for the simultaneous elimination of aluminium and sulphates from sludge obtained from the clarification of industrial dairy wastewater by coagulation-flocculation with aluminium sulphate. Work in this area is scarce due to the presence of bacteria in the sludge. The EK reactor comprises three compartments: the anode, the cathode, and the central part, which contains the sludge to be treated. A constant voltage of 15 V is applied between two platinum wire electrodes immersed in each electrolytic compartment. The EK treatment employed gave satisfaction despite the bacterial front in the 3/5 of reactor sludge fractions. Indeed, the removal rates are approximately 72% for aluminium and 92% for sulphates with current values below 5 mA, and relatively low energy consumption and cost (648 kWh/ton and 25.9 $/ton of sludge, respectively). For EK transport, the absence of hydraulic convection exerted on the sludge would favour the displacement of aluminium and sulphates by electromigration. Electroosmosis also contributes to this displacement. Thereby, analysis of sludge after this EK treatment predicts a possible valorisation but after liming. The sludge is rich in nutrients with low heavy metals concentrations. Although the study is more interesting for aluminium because of its toxicity, the behaviour of sulphates suggests the possibility of using EK to decontaminate soils or sludge from anions like nitrates, chlorides, etc.

Résumé: Dairy industrial wastewater is characterized by high chemical oxygen demand (COD) and other pollution loads. In this study, simulated dairy wastewater (SDW) was treated for turbidity and COD elimination via electrocoagulation (EC) with aluminum electrodes. COD concentration was not completely abated and exceeded allowable Algerian direct discharge limits. To enhance rate parameter pollution removal, electrocoagulation (EC) was combined with adsorption (AD) under the same operational electrocoagulation conditions. A full factorial design was employed to determine the optimum operating conditions for dairy wastewater treatment by electrocoagulation used separately or coupled with granular activated carbon (GAC). Current density, initial pH, and GAC mass were chosen as the controlling process parameters and examined at three levels. The results showed that EC reduced turbidity and COD from SDW to 98.75% and 78.09%, respectively, when pH = 4 and with current densities of 20.83–27.77 mA/cm2. The EC/AD process enhanced turbidity reduction to 99.39% and COD removal to 87.12% when small masses of GAC (0.5 to 1.5 g) were used at the lowest applied current density level of 13.38 mA/cm2. In comparison to classical electrocoagulation using aluminum electrodes in a batch system, coupling electrocoagulation to adsorption technique achieved faster removal of pollutants with lower operating costs. Operating costs of the EC/AD process for turbidity and COD removals were calculated as 0.360 €/ m3 and 0.746 €/m3 vs. 0.494 €/m3 and 0.692 €/m3 for the EC process. Correlations with the experimental data for the EC process were R2 = 95.78% for turbidity and R2 = 96.22% for COD removal. For the coupled EC/AD they were R2 = 96.61% for turbidity and R2 = 95.48% for COD removal.

Résumé: Dairy wastewater constitutes an essentially organic polluting load. Considering the environmental nuisances generated, treatment is essential. In the present study, two treatment techniques recognized for their easy and inexpensive applications have been optimized on real water from a local dairy industry namely electrocoagulation (EC) and adsorption on Opuntia ficus-indica powder: OFIP. The application of the cactus species for water treatment is relatively recent, even less for the adsorption process. The characteristic of this biomaterial, with high potential for recovery and available in many countries all year round, lies in the fact that it has considerable adsorbing power on its surface sites. Whether in EC or adsorption on OFIP, the results of monitoring the parameters continuously (chemical oxygen demand (COD), turbidity) and punctual (biochemical oxygen demand(BOD5), Kjeldahl nitrogen, phosphorus, fat) are satisfactory. All the parameters measured after these treatments have values that meet the local standardization requirements for industrial aqueous residues. For comparison purposes, the EC gives turbidity (99%) and COD (80%) reduction rates higher than those of adsorption on OFIP but an operational cost 10 times more. However, given the advantages and disadvantages of each technique, the choice of the application of one or the other process requires a compromise to be made in relation to the objectives sought.

Résumé: The electrocoagulation (EC) process is an efficient and low-cost system for the purification of wastewater. The aim of this work was to investigate the efficiency of two types of aluminum (Al) electrodes (Al alloy and pure Al electrodes) for the treatment of synthetic semi-skimmed milk wastewater. Turbidity, chemical oxygen demand (COD), and concentration of Al species were monitored during the experiments. The effect of various parameters, such as current density and type and nature of the electrode were examined. The results showed that Al alloy electrodes exhibited a higher efficiency than pure Al electrodes. A quasi-total reduction of turbidity and a removal of approximately 58% of the COD were achieved within 24 min at pH 7 and a current density of 14.3 mA.cm−2. It was also observed that the removal performance was not affected by the state of the electrode surfaces (polished) under the same operating conditions.

Résumé: Electrocoagulation process was applied for the removal of Acid Red 14 in bath essays. Under optimal operating conditions: current density of 70 mA/cm², 60–90 min of reaction, natural pH, and an initial concentration of 50 mg/L, the decolorization and COD removal efficiencies were 95% and 90%, respectively. The electrical energy consumption was 110 kWh/kgAR.14removed. These experimental results are well modeled by the Langmuir and Freundlich isotherms and follow first-order reaction kinetics. The thermodynamic parameters indicated that the nature of the adsorption process was endothermic and spontaneous. The mud formed after electrocoagulation was characterized by FTIR and SEM coupled to EDS.

Résumé: The objective of this study is the removal of lead from aqueous solution by electrosorption on carbon prepared from lignocellulosic natural residue “date stones”. The electrosorption efficiency was evaluated after the thermally treatment of the raw material at 900 °C. Adsorption of lead from aqueous solution by activated carbon electrodes was investigated through electrosorption experiments by changing potentials from ±0.05 to ±0.5 V/SCE. The results allow to observe that the application of a negative potential (−0,13 V) increases the adsorption capacity until 17.71 mg/g, while a positive potential (+0,13 V) released lead from the activated carbon up to 17.02 mg/g, showing the reversibility of the sorption process. The effect of pH and cycles number on the elestosorption process was studied. The experimental results concluded that the better adsorption efficiency (97.5%) was obtained when pH is 5. Furthermore, it was confirmed that the recycling process of adsorption/desorption could be conducted for seven adsorption-desorption cycles.

Résumé: This present study focuses on the evaluation of the effectiveness and the feasibility of a combined treatment between the electrocoagulation (EC) and the adsorption on an activated carbon in grains (GAC) in a continuous mode. The peculiarity of this work is that the experiments are conducted with real wastewater from an industrial dairy. This combined treatment first required an optimization of the EC followed by an adsorption. For each of these techniques, different influential operating parameters such as the current density, the reaction time, the GAC dose, the initial turbidity of water … etc., have been studied. The Turbidity and the COD have been continuously analyzed, while the phosphorus, the BOD 5 , TSS, nitrogen and the grease have been punctually analyzed, and this happened before and after the water treatment.

Résumé: The present study is carried out to remove chromium and turbidity from tannery wastewater using the electrocoagulation process with aluminum electrodes. This experimental study is carried out using a batch system. The applied pilot comprises a reactor containing two parallel metal electrodes (Al). The latter are connected as monopolar, and a different potential is applied between them. Several working parameters, such as applied potential difference, electrolysis time, active electrode surface, interelectrode distance, and the pH of the medium have been studied to achieve higher removal efficiency. The treatment reached a maximum reduction of 99% for turbidity and 93% for chromium under the following conditions: 15 V applied potential difference, 45 cm2 electrode surface, 1 cm interelectrode distance, pH 6.1 raw water, and a contact time of 90 min. Given the treatment efficiency obtained in this study, electrocoagulation process has the potential to be used for the cost-effective removal of wastewater pollutants.