Igor Cretescu

Characterization and remediation of soils contaminated with uranium

Environmental contamination caused by radionuclides, in particular by uranium and its decay products is a serious problem worldwide. The development of nuclear science and technology has led to increasing nuclear waste containing uranium being released and disposed in the environment. The objective of this paper is to develop a better understanding of the techniques for the remediation of soils polluted with radionuclides (uranium in particular), considering: the chemical forms of uranium, including depleted uranium (DU) in soil and other environmental media, their characteristics and concentrations, and some of the effects on environmental and human health; research issues concerning the remediation process, the benefits and results; a better understanding of the range of uses and situations for which each is most appropriate. The paper addresses the main features of the following techniques for uranium remediation: natural attenuation, physical methods, chemical processes (chemical extraction methods from contaminated soils assisted by various suitable chelators (sodium bicarbonate, citric acid, two-stage acid leaching procedure), extraction using supercritical fluids such as solvents, permeable reactive barriers), biological processes (biomineralization and microbial reduction, phytoremediation, biosorption), and electrokinetic methods. In addition, factors affecting uranium removal from soils are furthermore reviewed including soil characteristics, pH and reagent concentration, retention time.

Fractional Factorial Design Study on the Performance of GAC-Enhanced Electrocoagulation Process Involved in Color Removal from Dye Solutions

The aim of this study was to determine the effects of main factors and interactions on the color removal performance from dye solutions using the electrocoagulation process enhanced by adsorption on Granular Activated Carbon (GAC). In this study, a mathematical approach was conducted using a two-level fractional factorial design (FFD) for a given dye solution. Three textile dyes: Acid Blue 74, Basic Red 1, and Reactive Black 5 were used. Experimental factors used and their respective levels were: current density (2.73 or 27.32 A/m2), initial pH of aqueous dye solution (3 or 9), electrocoagulation time (20 or 180 min), GAC dose (0.1 or 0.5 g/L), support electrolyte (2 or 50 mM), initial dye concentration (0.05 or 0.25 g/L) and current type (Direct Current—DC or Alternative Pulsed Current—APC). GAC-enhanced electrocoagulation performance was analyzed statistically in terms of removal efficiency, electrical energy, and electrode material consumptions, using modeling polynomial equations. The statistical significance of GAC dose level on the performance of GAC enhanced electrocoagulation and the experimental conditions that favor the process operation of electrocoagulation in APC regime were determined. The local optimal experimental conditions were established using a multi-objective desirability function method.

Removal of heavy metal ions from aqueous solutions using low-cost sorbents obtained from ash

This study’s main objective was the development of effective low-cost sorbents for the removal of heavy metal ions from aqueous solutions. The influence of different factors on the sorption capacity of ash and modified ash as low-cost sorbents obtained by different methods was investigated. The synthesis of new ash-based materials was carried out at ambient temperature (20°C), 70°C, and 90°C, respectively, in an alkaline medium with NaOH concentrations of 2 M and 5 M, respectively, corresponding to a mixture with solid/liquid ratios of 1: 3 and 1: 5, respectively. The prepared materials (sorbents) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction, and BET surface measurement. Adsorption isotherms were determined using the batch equilibrium method. The results showed that these types of new materials displayed a good capacity to remove copper, nickel, and lead ions (29.97 mg of Cu2+ per g of sorbent, 303 mg of Ni2+ per g of sorbent, and 1111 mg of Pb2+ per g of sorbent) from aqueous solutions. The modified materials were prepared using an alkaline attack (a recognised method used in previous studies), but Romanian ash from a thermal power plant was studied for the above purpose for the first time. Hence, the factors which affect the sorption capacity of the prepared low-cost sorbents were determined and their behaviour was explained, taking into account the composition and structure of the new materials.

Photocatalytic Treatment of Rhodamine 6G in Wastewater Using Photoactive ZnO

The photocatalytic activity of zinc oxide, prepared by precipitation followed by calcination, was tested using rhodamine 6G as a rebel organic compound. The experiments were planned in order to allow an optimization procedure, by investigating the effects of different parameters such as the preparative method of the solid, amount of photocatalyst, pH of the reaction medium, and initial concentration of the dye. The results were compared with those obtained on P-25 Titania, and one of the samples had similar performances in terms of dye degradation degree, but needed higher pH values to prevent the photocatalyst degradation.

Bioelectro-Claus processes using MFC technology: Influence of co-substrate.

This work is focused on the removal of sulphide from wastewater using a two chamber microbial fuel cell, seeded with activated sludge and operated in semi-continuous mode. Two co-substrates were used in order to provide the system for carbon and nutrient source: actual urban wastewater and synthetic wastewater. Results show that sulphide is efficiency depleted (removals over 94%) and that electricity is efficiently produced (maximum power density is 150 mW m(-2)) meanwhile COD is also oxidised (removals higher than 60%). Sulphur and sulphate are obtained as the final products of the oxidation and final speciation depends on the type of co-substrate used. The start-up of the system is very rapid and production of electricity and polarisation curves do not depend on the co-substrate.

Nanosized spinel ferrites synthesized by sol-gel autocombustion for optimized removal of azo dye from aqueous solution

Nanosized spinel ferrites MFe2O4 (M = Ni, Co, and Zn) have been prepared by sol-gel autocombustion method using citric acid as a fuel agent. The materials are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The spinel ferrites have been applied for Congo-Red (CR) dye adsorption using batch technique. Different kinetic and equilibrium models have been fitted by nonlinear regression to analyze the adsorption data. In accordance with Langmuir isotherm, the maximum adsorption capacity at 293 K is 14.06mg/g for CoFe2O4 and 17.13 mg/g for NiFe2O4. The values of mean free energy determined from Dubinin-Radushkevich isotherm are higher than 8 (kJ mol-1), indicating a chemisorption mechanism. Based on the calculated thermodynamic parameters (free energy, enthalpy, and entropy) the adsorption of CR onto ferrites is a spontaneous and endothermic process. Response surface methodology has been applied to construct the multiple regression models for prediction of the adsorption capacity and removal efficiency. The model-based optimization has been performed using genetic algorithms and desirability function approach. The single-objective optimization has yielded a maximum value of color removal efficiency of 98.995%, using NiFe2O4 adsorbent. The multiobjective optimization has resulted in the improvement of both removal efficiency and adsorption capacity.

Electrochemical coagulation of treated wastewaters for reuse

Abstract In this work, the disinfection capability of electrocoagulation with iron and aluminium electrodes is studied. To do this, two different effluents of conventional municipal wastewater treatment plants (WWTP) are treated. Results show that electrocoagulation is able to reduce satisfactorily chemical oxygen demand, turbidity and nutrients and it allows increasing significantly the water quality. Likewise, it does not affect conductivity (just the contrary conventional coagulation–flocculation treatment) and helps to buffer pH in a value around 8. Precipitation, floc enmeshment and adsorption seem to be the primary mechanisms in this process. Regarding the variation of faecal coliforms, this technique behaves as a disinfection technology and allows increasing the efficiencies of WWTP processes in a very cheaper way. Energy consumption lower than 0.2 kWh m−3 is required to attain standard disinfection levels.

Multi-Objective Optimization of Indigo Carmine Removal by an Electrocoagulation/GAC Coupling Process in a Batch Reactor

A coupling process between Electrocoagulation (EC) and GAC was employed to separate dyes from aqueous solutions. The removal of an indigoid dye, namely C.I. Acid Blue 74, was tested. A novel approach for optimizing EC-based techniques is presented. In addition to maximizing removal efficiency, minimizing consumptions of energy and electrode materials were also targeted by means of multi-objective optimization in order to reduce the specific costs. A very good cost-efficiency feature of EC/GAC coupling process operated under optimal conditions to treat wastewater from dyestuff has been revealed. The independent variables considered were the current density, influent pH, contact time, granular activated carbon dose, and initial dye concentration. Simple maximization of color removal efficiency and multi-objective optimization were compared. Two different constraints were considered for each type of optimization. The determined costs outline the cheapness feature of the EC/GAC system as a potential dye wastewater treatment technology.

Treatment of Pesticides in Wastewater by Heterogeneous and Homogeneous Photocatalysis

The effect of different heterogeneous and homogeneous photocatalytic systems on the oxidative degradation of mepiquat chloride in aqueous solutions was investigated. In the case of heterogeneous reactions, the influence of five factors was studied: the type of catalyst, photocatalyst concentration, pH, pesticide concentration, and the presence of H2O2 and/or Fe3

A novel pulsed xenon flashlamp photoreactor and its potential applications in flow analysis with chemiluminescence detection

The pulsed xenon flashlamp as a source of UV-light in a flow analytical system is proposed. Milliseconds long, high energy pulses were applied to a suspension of photocatalyst (TiO2) in order to generate free radicals capable of participating in a luminol chemiluminescence reaction. Three commercially available TiO2 powders of different crystal structures and sizes were selected to prepare suspensions in an H2O2 solution or in ultrapure water. The preliminary results indicate that the induction of chemiluminescence signals using the proposed photoreactor is possible. The intensity of the chemiluminescence signals depends on the number of flashes applied and the composition of the irradiated suspension. The photoreactor described is compact, small in size and capable of saving reagents and energy. Additionally, the system allows us to obtain chemiluminescence signals with shorter irradiation time when compared to configurations employing classical low-pressure mercury lamps. The detailed characteristics of a flashlamp photoreactor and its potential applications in flow systems are discussed.