Maria Gavrilescu

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.

Emerging pollutants in the environment: present and future challenges in biomonitoring, ecological risks and bioremediation

Emerging pollutants reach the environment from various anthropogenic sources and are distributed throughout environmental matrices. Although great advances have been made in the detection and analysis of trace pollutants during recent decades, due to the continued development and refinement of specific techniques, a wide array of undetected contaminants of emerging environmental concern need to be identified and quantified in various environmental components and biological tissues. These pollutants may be mobile and persistent in air, water, soil, sediments and ecological receptors even at low concentrations. Robust data on their fate and behaviour in the environment, as well as on threats to ecological and human health, are still lacking. Moreover, the ecotoxicological significance of some emerging micropollutants remains largely unknown, because satisfactory data to determine their risk often do not exist. This paper discusses the fate, behaviour, (bio)monitoring, environmental and health risks associated with emerging chemical (pharmaceuticals, endocrine disruptors, hormones, toxins, among others) and biological (bacteria, viruses) micropollutants in soils, sediments, groundwater, industrial and municipal wastewaters, aquaculture effluents, and freshwater and marine ecosystems, and highlights new horizons for their (bio)removal. Our study aims to demonstrate the imperative need to boost research and innovation for new and cost-effective treatment technologies, in line with the uptake, mode of action and consequences of each emerging contaminant. We also address the topic of innovative tools for the evaluation of the effects of toxicity on human health and for the prediction of microbial availability and degradation in the environment. Additionally, we consider the development of (bio)sensors to perform environmental monitoring in real-time mode. This needs to address multiple species, along with a more effective exploitation of specialised microbes or enzymes capable of degrading endocrine disruptors and other micropollutants. In practical terms, the outcomes of these activities will build up the knowledge base and develop solutions to fill the significant innovation gap faced worldwide.

Mixing studies in external-loop airlift reactors

Abstract The mixing behaviour of the liquid phase in two external-loop airlift reactors of laboratory and pilot scale, in terms of the mixing time and axial dispersion, was investigated. The mixing parameters were determined from the output curves to an initial Dirac pulse, using the classical tracer response technique, and analysed in relation to operating and geometrical parameters, such as vsGR, AD/AR, Hd and DR. Mixing in the external-loop airlift reactors under investigation was essentially correlated with the liquid circulation velocity. The specific sections of the airlift reactor have different mixing behaviour, so that the riser and downcomer can be analysed as plug flow with axial dispersion, whereas the top section approaches ideal mixing behaviour. A simple correlation between the specific mixing time and the operating and geometrical parameters was developed which can be used for design and scale-up purposes.

Residence time distribution of the liquid phase in a concentric-tube airlift reactor

Abstract The residence time distribution (RTD) analysis of liquid phase was performed in a concentric-tube airlift reactor of 0.07 m 3 nominal volume, regarded as a simple unit and discriminating its different sections (riser, downcomer, bottom zone and gas-liquid separator) using the tracer response technique. The reactor was operated in biphasic continuous flow of liquid and gaseous phase. The volumetric liquid inflow rate, Q 1 , and gas superficial velocity in the riser, ν SGR , were chosen as independent variables. RTD functions in the reactor, namely: the RTD distribution functions at the reactor exit, inclusively in normalized form, E ( θ ), the distribution ages inside the reactor, I ( θ ), the intensity of distribution, λ ( θ ), respectively, as well as the mean liquid residence time, and the variance of distributions were essentially used for liquid flow diagnosis in the reactor in two operational modes: with and without recirculation. The experimental results revealed that the investigated airlift reactor had a more uniform flow than the tubular and bubble column reactors and the flow defects proved a significant attenuation. These conclusions were confirmed by the single parameter flow models: axial dispersion and tank-in-series models. This fact has a great practical importance, especially in the biotechnological applications of the airlift reactors, where the aerobic cultures can be affected greatly by the flow deficiencies.

Cadmium tolerance and adsorption by the marine brown alga Fucus vesiculosus from the Irish Sea and the Bothnian Sea

Cadmium (Cd) uptake capacities and Cd tolerance of the marine alga Fucus vesiculosus from the Irish Sea (salinity 35 psu) and from the Bothnian Sea (northern Baltic, 5 psu) were quantified. These data were complemented by measurements of changes in maximal photosynthetic rate (P(max)), dark respiration rate and variable fluorescence vs. maximal fluorescence (F(v):F(m)). At concentrations between 0.01 and 1 mmol Cd l(-1), F. vesiculosus from the Bothnian Sea adsorbed significantly more (about 98%) Cd compared with F. vesiculosus from the Irish Sea. The photosynthetic measurements showed that the Bothnian Sea F. vesiculosus were more sensitive to Cd exposure than the Irish Sea algae. The algae from the Irish Sea showed negative photosynthetic effects only at 1 mmol Cd l(-1), which was expressed as a decreased P(max) (-12.3%) and F(v):F(m) (-4.6%). On the contrary, the algae from the Bothnian Sea were negatively affected already at Cd concentrations as low at 0.1 mmol Cd l(-1). They exhibited increased dark respiration (+11.1%) and decreased F(v):F(m) (-13.9%). The results show that F. vesiculosus from the Bothnian Sea may be an efficient sorption substrate for Cd removal from Cd contaminated seawater and this algae type may also have applications for wastewater treatment.

Forecasting municipal solid waste generation using prognostic tools and regression analysis

For an adequate planning of waste management systems the accurate forecast of waste generation is an essential step, since various factors can affect waste trends. The application of predictive and prognosis models are useful tools, as reliable support for decision making processes. In this paper some indicators such as: number of residents, population age, urban life expectancy, total municipal solid waste were used as input variables in prognostic models in order to predict the amount of solid waste fractions. We applied Waste Prognostic Tool, regression analysis and time series analysis to forecast municipal solid waste generation and composition by considering the Iasi Romania case study. Regression equations were determined for six solid waste fractions (paper, plastic, metal, glass, biodegradable and other waste). Accuracy Measures were calculated and the results showed that S-curve trend model is the most suitable for municipal solid waste (MSW) prediction.

Comparing environmental impacts of natural inert and recycled construction and demolition waste processing using LCA

AbstractConstruction and demolition wastes (C&DW) are usually recognized as not dangerous, but their accumulation can generate serious environmental problems. In spite of C&DW high potential to be reused/recycled, the practical procedures need to be assessed in terms of environmental consequences. The objective of this study is to quantify the environmental impacts of C&DW recycling/reuse, specifically in the production of aggregate 0/30 mm, comparative to those generated during the natural inert processing, in terms of global impacts addressing the whole process and for each technological phase. The analysis was carried out using Life Cycle Assessment methodology, assisted by SimaPro software, and based on primary data collected directly from the Italian Emilia Romagna region. Three methods were used for impact quantification: Eco-Indicator 99, EDIP/UMIP and Cumulative Energy Demand. The analysis revealed that the environmental impacts generated by C&DW recycling/reuse accounting for about 40% of the imp...

Experimental analysis and mathematical prediction of Cd(II) removal by biosorption using support vector machines and genetic algorithms

We investigated the bioremoval of Cd(II) in batch mode, using dead and living biomass of Trichoderma viride. Kinetic studies revealed three distinct stages of the biosorption process. The pseudo-second order model and the Langmuir model described well the kinetics and equilibrium of the biosorption process, with a determination coefficient, R(2)>0.99. The value of the mean free energy of adsorption, E, is less than 16 kJ/mol at 25 °C, suggesting that, at low temperature, the dominant process involved in Cd(II) biosorption by dead T. viride is the chemical ion-exchange. With the temperature increasing to 40-50 °C, E values are above 16 kJ/mol, showing that the particle diffusion mechanism could play an important role in Cd(II) biosorption. The studies on T. viride growth in Cd(II) solutions and its bioaccumulation performance showed that the living biomass was able to bioaccumulate 100% Cd(II) from a 50 mg/L solution at pH 6.0. The influence of pH, biomass dosage, metal concentration, contact time and temperature on the bioremoval efficiency was evaluated to further assess the biosorption capability of the dead biosorbent. These complex influences were correlated by means of a modeling procedure consisting in data driven approach in which the principles of artificial intelligence were applied with the help of support vector machines (SVM), combined with genetic algorithms (GA). According to our data, the optimal working conditions for the removal of 98.91% Cd(II) by T. viride were found for an aqueous solution containing 26.11 mg/L Cd(II) as follows: pH 6.0, contact time of 3833 min, 8 g/L biosorbent, temperature 46.5 °C. The complete characterization of bioremoval parameters indicates that T. viride is an excellent material to treat wastewater containing low concentrations of metal.

Modelling of liquid circulation velocity in concentric-tube airlift reactors

Abstract A mathematical model for riser liquid superficial velocity in a concentric-tube airlift reactor is proposed. The model is based on an energy balance incorporating acceleration coefficients to quantify deviations from ideal flow. The acceleration coefficients at the draft-tube and downcomer entrance are determined experimentally, based on static pressure profile measurements. The model could predict liquid velocities over a broad range, including an almost 50-fold variation of liquid circulation velocity and a four-fold change in reactor height. The model predictions agreed with the measurements to within ± 28%.

Modeling and simulation of high pressure water scrubbing technology applied for biogas upgrading

Depending on the end of use, the quality of biogas must be upgraded in order to utilize the maximum amount of energy necessary for proper applications. Upgrading biogas refers to the increase of methane concentration in product gas by removal of CO2, which increases its heating power. Several treatment technologies are available for biogas upgrading: high pressure water scrubbing (HPWS), pressure swing adsorption, membrane separation, chemical absorption, and gas permeation. Water absorption based on the physical effect of dissolving gases in liquids (HPWS) is a well-known technology and the most effective upgrading process, since provides a simultaneous removal of CO2 and H2S. This could ensure an increasing methane concentration and energy content per unit volume of biogas. In spite of this, few studies are published on biogas upgrading using pressurized water technology. In order to elucidate the performance of HPWS technology at industrial scale with the possibility of water regeneration and recirculation, effects of different operating parameters on the removal of undesired components from biogas were examined, based on modeling and simulation tools. For simulation, the commercial software tool Aspen Plus was applied. Equilibrium model was applied for simulating the absorption process. The simulation results were validated with experimental data from the literature. The results are summarized in terms of system efficiency, expressed as CH4 enrichment, methane loss, and CO2 removal. Finally, new data which can be further applied for scale-up calculations and techno-economic analysis of the HPWS process are provided.