Removal of tetracycline by electrocoagulation: Kinetic and isotherm modeling through adsorption

International audienceThe use of antibiotics and growth hormones in human and veterinary medicine has a significant effect on the quality of surface and groundwater. The relevance of an electrocoagulation (EC) process for the removal of an antibiotic selected because of its wide application, high solubility in water, high residual toxicity and an absence of biodegradability, was examined in this study. Metal hydroxides generated during EC were used to remove tetracycline (TC) from aqueous solution. The knowledge regarding the removal mechanism of this substance has not been investigated up to now. Experiments were carried out in a batch electrochemical reactor using aluminum electrodes. The removal of TC was relatively fast and equilibrium was reached within 15 min. The effects of the main operating parameters were examined and showed that irrespective of the initial concentration and for pH ranging from 3 to 10, maximum removal efficiency remained close to 99%; while a sharp decrease was recorded at pH 2 (10% removal). The results of this study also showed that the removal of TC from water was strongly affected by the current intensity. The mechanism of electrocoagulation was modeled using isotherm models and showed that the Sips isotherm matched satisfactorily experimental data, suggesting monolayer coverage of adsorbed molecules and assumed a quasi-Gaussian distribution energy owing to the high correlation also found for the Toth model. In addition, adsorption kinetic studies showed that the EC process followed a pseudo-second-order kinetic model at the various current densities, pH and initial antibiotic concentrations considered

Photocatalytic Degradation of Oxytetracycline in Aqueous Solutions with TiO2 in Suspension and Prediction by Artificial Neural Networks

International audienceIn this study, the photocatalytic degradation of oxytetracycline (OTC) in aqueous solutions has been studied under different conditions such as initial pollutant concentrations, amount of catalyst, and pH of the solution. Experimental results showed that photocatalysis was clearly the predominant process in the pollutant degradation, since OTC adsorption on the catalyst and photolysis are negligible. The optimal TiO2 concentration for OTC degradation was found to be 1.0 g/L. The apparent rate constant decreased, and the initial degradation rate increased with increasing initial OTC concentration with the other parameters kept unchanged. Subsequently, data obtained from photocatalytic degradation were used for training the artificial neural networks (ANN). The Levenberg–Marquardt algorithm, log sigmoid function in the hidden layer, and the linear activation function in the output layer were used. The optimized ANN structure was four neurons at the input layer, eighteen neurons at the hidden layer, and one neuron at the output layer. The application of 18 hidden neurons allowed to obtain the best values for R2 and the mean squared error, 0.99751 and 7.504e–04, respectively, showing the relevance of the training, and hence the network can be used for final prediction of photocatalytic degradation of OTC with suspended TiO2

Sorption of hexavalent chromium ion onto a strong basic anion exchanger: equilibrium isotherms and kinetic studies

International audienceHexavalent chromium can contaminate drinking water resources and should therefore be removed from industrial waste effluents. The use of ion exchange resin was examined in batch tests to remove Cr (VI) from acidic solution by Amberlite IRA 410. Equilibrium data were analyzed and modelled using Freundlich and Langmuir adsorption isotherms and the results showed that the adsorption behaviour of Cr (VI) could be accurately described by means of a Langmuir model. The monolayer adsorption capacity was found to be 222.2 mg g-1 at an optimum pH of 3. The Lagergren pseudo-first-order and pseudo-second-order models were used to represent kinetic. Results showed that the sorption kinetics data followed a pseudo-second order model. It was also found that pore diffusion played an important role in the adsorption, and intra particles diffusion was the rate-limiting step during the first 30min for Cr (VI) concentrations in the range of 10 - 200 mg L-1

Doxycycline Removal by Solar Photo-Fenton on a Pilot-Scale Composite Parabolic Collector (CPC) Reactor

In this study, the solar photo-Fenton (SPF) process was investigated for the degradation of doxycycline (DOX) using a solar compound parabolic collector (CPC) reactor and a borosilicate serpentine tube with an irradiated volume of 1.8 L. The influence of the operating parameters, such as H2O2, Fe2+ dosage, and DOX concentration, was investigated. The optimum H2O2, Fe2+ dosage, and DOX concentration were found to be 4, 0.1, and 0.06 mM, respectively. The results of photo-Fenton experiments fitted the pseudo-first-order kinetic equation (R2 = 0.99). The efficiency of the treatment under optimized conditions was analyzed by an HPLC analysis of the samples, chemical oxygen demand (COD), and total organic carbon (TOC). The results obtained showed that the solar photo-Fenton process achieved a DOX degradation of 95.07%, a COD elimination of 81.43%, and a TOC elimination of 73.05%. The phytotoxicity tests revealed a 73.32% decrease in the germination index of watercress seeds, demonstrating that the SPF process minimizes the toxicity of the chemical and did not have any negative impact on plant growth. Overall, the results of this study suggest that SPF is a promising technology for the removal of doxycycline from wastewater

Removal of an antibiotic, tetracycline hydrochloride, by adsorption onresin Amberlite RC 120

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Sorption of hexavalent chromium metal onto Amberlite IRA 410 - equilibrium isotherms and kinetic studies

International audienceThe removal of chromium (VI) from aqueous solution by a strong anion exchanger Amberlite IRA 410 was studied. Batch mode experiments were conducted to study the effect of the initial concentration of Cr (VI) and the equilibrium isotherms. The sorption process of chromium (VI) was tested with Freundlich, Langmuir and Khan models, and the results showed that sorption behaviour of chromium (VI) followed a Langmuir isotherm, namely a monolayer sorption onto the resin surface. The sorption capacity was determined to be 153.8 mg/g. Elovich, Ritchie and the pseudo-second order models were tested to represent kinetic data and the equation parameter values were evaluated. It was found that the sorption kinetics followed a pseudo-second order model in the concentration range 0-100 mg/l, while above 100 mg/l the Ritchie model matched experimental kinetic data. In addition, the capacity of sorption increased for increasing initial Cr(VI) concentration. The thermodynamic parameters for the sorption process have been evaluated. The entropy change ΔS was found to be 318.4 J/K/mol, the heat of adsorption (enthalpy change) ΔH was 85.2 kJ/mol indicating the endothermic nature of the adsorption process, and a decrease of the Gibbs free energy (ΔG) for increasing temperatures indicated the spontaneous nature of the process

Removal of chromium VI from wastewater by combined electrocoagulation sorption processes

International audienceThe elimination of hexavalent chromium from synthetic effluents in a batch stirred electrocoagulation cell with aluminum electrodes coupled with a sorption process using red onion skin adsorbent is addressed. The effect of process variables such as medium pH and adsorbent concentration was investigated in an attempt to optimize the removal capacity. Adsorption and electrocoagulation were first considered separately, with maximum Cr(VI) removal yields of 47 % and 78 %, respectively, at pH 2. When combining the two processes, a removal of 97 % of the total Cr(VI) in a pH range of 3-6 was achieved. The almost total elimination observed for the considered pollutant demonstrated the feasibility and the synergistic effect of the coupled process

Integration of electro coagulation and adsorption for the treatment of tannery wastewater - The case of an Algerian factory, Rouiba

International audienceTanneries have a severe impact on the water quality if they are rejected without treatment. Indeed, they contain not only an important amount of biodegradable compounds, like proteins and fats, but also non-readily biodegradable wastes, such hydrolyzed piles and toxic heavy metals like chromium, the most toxic, which is extensively used for skin tanning. The main problem associated with this anthropogenic contamination is chromium toxicity for living organisms. To reduce the pollution of tannery wastewaters, the development of efficient processes from a technical and an economical point of view is needed. To this aim the efficiency of coupling electrocoagulation (EC) and adsorption (AD) in terms of COD removal, turbidity decrease and residual chromium (VI) amount was examined in this wor

Assessment of the biodegradation of doxycycline by biostimulation with addition of glucose, phenol or/and copper

International audienceDoxycycline, an antibiotic, is largely used in human and veterinary medicine. The conventional treatment with activated sludge is not very efficient. Laccase appeared to be the main enzyme secreted essentially by white rot fungi as Trametes versicolor and Phlebia fascicularia on the degradation of xenobiotic compounds from the pharmaceutical industry. The main purpose of this study was to enhance the biodegradation of doxycycline through activated sludge combined with addition of glucose as a carbon co-substrate to improve the growth of the microbial population present in the activated sludge, phenol as a laccase mediator, copper as a cofactor and inductor for laccase production. The enhancement of the biodegradation of doxycycline was 50, 90, 68 and 83% greater respectively with the addition of glucose, copper, phenol and with a mixture of the compounds after 14 days of treatment at 25°C. Compared with the biotic control (activated sludge alone), a 30% increase for the test with the addition of phenol was observed

Hexavalent chromium removal from an aqueous solution by means ofan hybrid process coupling biosorption and electrocoagulation

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