1,721,004 research outputs found
Portable low-cost measurement system development for self-potential (SP) monitoring in severe environmental conditions
No full textIn the field of environmental sciences self-potential (SP) data are generally considered as promising and reliable to investigate subsurface properties, especially for their ease of acquisition and simplicity in making qualitative interpretations. Self-potential is a passive method consisting in the measurement of the electric potential at a set of measurements stations. SP anomalies usually indicate the presence of a source of current in the ground due to subsurface disturbances. In order to fulfill such requirements we developed a measurement setup with the main advantages of being portable, low cost, rugged, sufficiently accurate and optimized for low power consumption
Trattamento elettrocinetico di sedimenti di dragaggio portuale contaminati da metalli pesanti: il progetto LIFE+ "SEKRET"
Full text linkLa contaminazione dei sedimenti di fondo, che interessa molti porti e corpi idrici in cui si svolgono attività commerciali e produttive, è un problema emerso da qualche decennio ed oggetto di crescente attenzione. Nei porti e canali navigabili, sottoposti ad attività di dragaggio per garantire il mantenimento delle profondità prescritte per la navigazione, il livello di contaminazione si ripercuote direttamente sugli oneri di gestione del dragaggio, che risultano notevolmente accresciuti al superamento delle soglie di contaminazione prescritte. Ad oggi, molte delle tecniche di trattamento di matrici contaminate da metalli pesanti risultano troppo onerose per l'applicazione ai sedimenti di dragaggio, in particolare per quelli a struttura limo-argillosa, che sono caratterizzati da bassa permeabilità ed elevato potere tampone. Il trattamento elettrocinetico presenta in queste circostanze il campo ideale di azione, mostrando ottime potenzialità anche per il trattamento dei sedimenti di dragaggio. Tuttavia, nonostante i numerosi test di laboratorio citati in letteratura, le applicazioni in piena scala sono ancora limitatissime, essendo ben consolidata la sola applicazione al trattamento di terreni. Il progetto LIFE+ SEKRET ("Sediment ElectroKinetic REmediation Technology for heavy metal pollution removal") ha come obiettivo di dimostrare l'applicabilità di tale tecnica al trattamento di sedimenti marini di dragaggio contaminati da metalli pesanti, attraverso la realizzazione di un impianto dimostrativo in un'area dedicata nel porto di Livorno, che tratterà 150 m3 di sedimenti di dragaggio. In tale realtà vengono infatti regolarmente dragati circa 100.000 m3/anno di sedimenti, in parte contaminati da Cd, Cr, Cu, Ni, Pb e Zn poco oltre i valori soglia di contaminazione. Il progetto si pone l'obiettivo di evidenziare i vantaggi ambientali ed economici di questa soluzione rispetto ad altre tecniche di trattamento o al trasferimento in discarica del materiale contaminato
Model-based optimization of field-scale electrokinetic remediation of marine sediments
Full text linkSeveral technologies are available for the remediation of contaminated marine sediments, most of which derived from soil remediation techniques, such as sediment washing, thermal treatment, chemical oxidation, bioslurry processes and biopiles. The applicability of such technologies is strongly affected by specific characteristics of sediments which can adversely influence both operation and removal efficiency. Unfortunately, none of available technologies is effective when main pollution is represented by heavy metals and when sediment matrix is characterized by low hydraulic permeability. These conditions pose severe limitations to remediation efficiency, as most decontamination techniques available for treating high-permeability soils are not effective for fine-grained matrices. In this context, electrokinetic remediation is widely recognized as an efficient technique for removing a broad range of contaminants from low-permeability soils and sediments .
Despite this technique has demonstrated being very promising for the remediation of marine sediments, the selection of the best operating conditions remains elusive, due to the variety of mechanism involved. Complicating factors include the high complexity of sediment matrix and the strong non-linearity of the processes occurring during electric field application. Complexity is one of the main limiting factors to the spread of electrokinetic remediation technology for "real-world" applications. Complexity directly affects the reliable prediction of achievable results and induces technical challenges when the technique is implemented at the field scale [4]. A thorough understanding of the mechanisms involved in electrokinetic remediation through experimental studies is always needed, for an appropriate design of full-scale treatment schemes. In some cases, the prescribed laboratory experiments can get excessively time consuming, and modelling could become a necessary tool to assess the main remediation parameters and predict achievable results. Despite several mathematical models have been developed to predict electrokinetic extraction of contaminants, their application to plant design and optimization is still unavailable.
This work presents a model-based approach for the optimization of field-scale electrokinetic processes, including the possibility of estimating optimum design parameters and minimizing the costs. We developed a numerical model to simulate the electrokinetic remediation of real contaminated sediments characterized by a heterogeneous solid matrix and aged heavy metal pollution. The numerical model couples a transport model able to simulate electromigration and electroosmosis with a geochemical model, which calculates aqueous speciation, precipitation-dissolution, adsorption and surface complexation reactions. Laboratory-scale experiments were carried out to calibrate and validate the model. The model was able to reproduce experimental data with adequate accuracy. We identified the acid buffering capacity as the most significant factor for the extraction of heavy metals from the sediments as their speciation and mobility were strictly dependent on sediment capacity to prevent the pH shift to the acidic range.
The developed model was then “scaled up”, to reproduce electrokinetic processes occurring at field scale, considering a typical field setup consisting of vertical electrodes arranged on a rectangular grid. A parametric study was performed to evaluate the influence of electrode distance and sediment properties on treatment costs. The simulations allowed us to calculate time-dependent contaminant removal rate and to define cost curves for each set of parameters. The resulting curves of total cost were obtaining by summing up all individual costs. A clear point of minimum could be identified in each case, corresponding to the optimum set of parameters which minimized the costs.
In conclusion, we strongly believe that the methodology and results obtained can be employed as a valuable tool to support evaluation and design of electrokinetic remediation systems
Flood risk assessment of land pollution hotspots
Full text linkAmong the risks caused by extreme events, the potential spread of pollutants stored in land hotspots due to floods
is an aspect that has been rarely examined with a risk-based approach. In this contribution, an attempt to estimate
pollution risks related to flood events of land pollution hotspots was carried out. Flood risk has been defined
as the combination of river flood hazard, hotspots exposure and vulnerability to contamination of the area, i.e.
the expected severity of the environmental impacts. The assessment was performed on a geographical basis, using
geo-referenced open data, available from databases of land management institutions, authorities and agencies.
The list of land pollution hotspots included landfills and other waste handling facilities (e.g., temporary storage,
treatment and recycling sites), municipal wastewater treatment plants, liquid waste treatment facilities and contaminated
sites. The assessment was carried out by combining geo-referenced data of pollution hotspots with flood
hazard maps. We derived maps of land pollution risk based on geographical and geological properties and source
characteristics available from environmental authorities. These included information about soil particle size, soil
hydraulic conductivity, terrain slope, type of stored pollutants, the type of facility, capacity, size of the area, land
use, etc. The analysis was carried out at catchment scale. The case study of the Arno river basin in Tuscany (central
Italy) is presented
Spectral induced polarization for monitoring electrokinetic remediation processes
No full textElectrokinetic remediation is an emerging technology for extracting heavy metals from contaminated soils and sediments. This method uses a direct or alternating electric field to induce the transport of contaminants toward the electrodes. The electric field also produces pH variations, sorption/desorption and precipitation/dissolution of species in the porous medium during remediation. Since heavy metal mobility is pH-dependent, the accurate control of pH inside the material is required in order to enhance the removal efficiency. The common approach for monitoring the remediation process both in laboratory and in the field is the chemical analysis of samples collected from discrete locations. The purpose of this study is the evaluation of Spectral Induced Polarization as an alternative method for monitoring geochemical changes in the contaminated mass during remediation. The advantage of this technique applied to field-scale is to offer higher resolution mapping of the remediation site and lower cost compared to the conventional sampling procedure. We carried out laboratory-scale electrokinetic remediation experiments on fine-grained marine sediments contaminated by heavy metal and we made Spectral Induced Polarization measurements before and after each treatment. Measurements were done in the frequency range 10− 3–103 Hz. By the deconvolution of the spectra using the Debye Decomposition method we obtained the mean relaxation time and total chargeability. The main finding of this work is that a linear relationship exists between the local total chargeability and pH, with good agreement. The observed behaviour of chargeability is interpreted as a direct consequence of the alteration of the zeta potential of the sediment particles due to pH changes. Such relationship has a significant value for the interpretation of induced polarization data, allowing the use of this technique for monitoring electrokinetic remediation at field-scale
Decontaminazione elettrocinetica di sedimenti marini in vasca di colmata: risultati preliminari di un'applicazione pilota
No full textLa bonifica elettrocinetica viene proposta come tecnica di rimozione di vari contaminanti, in particolare metalli pesanti, da matrici come terreni o sedimenti caratterizzate da bassa permeabilità idraulica. La sua implementazione più comune applica un campo elettrico alla matrice da trattare mediante coppie di elettrodi collocati in pozzetti a pareti porose in cui viene fatta circolare acqua opportunamente condizionata. Il campo elettrico provoca l’elettrolisi di tali soluzioni, generando un fronte acido, che avanza dagli anodi ai catodi favorendo il desorbimento e la mobilizzazione dei contaminanti, e un fronte basico che avanzando in senso opposto ostacola tale processo e viene dunque contrastato dosando acidi al catolita. Le reazioni di elettrolisi, gli agenti condizionanti e i fenomeni di trasporto dovuti al campo elettrico arricchiscono gli elettroliti dei contaminanti rimossi e di altri macroelementi, rendendo necessaria una loro gestione per: 1. evitare rischi di precipitazione sugli elettrodi, sulle pareti dei pozzetti elettrodici o nella matrice da trattare; 2. impedire la possibile inversione dei processi di trasporto e il conseguente rischio di ricontaminazione della matrice trattata; 3. contenere l'incremento di conduttività elettrica degli elettroliti e della soluzione interstiziale che riduce il rendimento di rimozione e causa inutile dispendio di energia elettrica. La letteratura scientifica, essenzialmente focalizzata sul trattamento del mezzo poroso, raramente considera l’implementazione a scala reale e le problematiche di gestione degli elettroliti. Pertanto, il presente contributo è mirato ad analizzare le opzioni di gestione e di trattamento degli elettroliti evidenziandone tecniche, criticità ed aspetti economici
Multispecies reactive transport modelling of electrokinetic remediation of harbour sediments
Full text linkWe implemented a numerical model to simulate transport of multiple species and geochemical reactions occurring during electrokinetic remediation of metal-contaminated porous media. The main phenomena described by the model were: (1) species transport by diffusion, electromigration and electroosmosis, (2) pH-dependent buffering of H+, (3) adsorption of metals onto particle surfaces, (4) aqueous speciation, (5) formation and dissolution of solid precipitates. The model was applied to simulate the electrokinetic extraction of heavy metals (Pb, Zn and Ni) from marine harbour sediments, characterized by a heterogeneous solid matrix, high buffering capacity and aged pollution. A good agreement was found between simulations of pH, electroosmotic flow and experimental results. The predicted residual metal concentrations in the sediment were also close to experimental profiles for all of the investigated metals. Some removal overestimation was observed in the regions close to the anode, possibly due to the significant metal content bound to residual fraction
Resistivity imaging during electrokinetic remediation of sediments: practical challenges in the field
Full text linkThe use of geophysical techniques such as electrical resistivity and impedance tomography have proven to be
effective for the investigation and monitoring of a variety of environmental processes.
This study investigates the possibility of using resistivity imaging to monitor the progress of electrokinetic
remediation, a decontamination process based on electrochemical methods.
The resistivity is a parameter of great theoretical and practical interest. On one side, resistivity is strictly related
to the pore fluid composition and provides information about the chemical state of the material subjected to
remediation. On the other side, knowing the evolution and distribution of resistivity is of practical importance both
at the design stage and during operation because it directly affects the electrical energy expenditures.
Monitoring of electrokinetic processes both in laboratory and in field is usually carried out by point measure-
ments and sample collection from discrete locations. Resistivity imaging is effective in providing low-cost,
non-destructive, high space and time resolution mapping.
During electrokinetic remediation an electric field is applied to the contaminated matrix to extract the pollutants.
In the field, array of electrodes are generally employed to apply the electric field, arranged in a two-dimensional
grid. The electrodes are installed inside wells to allow the circulation of electrolytes employed to enhance the
extraction of the pollutants.
In this study we describe the practical challenges both in the measurements and in the data processing encountered
during the tomographic imaging of marine sediments subjected to electrokinetic remediation in a 150 m3 ex-situ
treatment plant.
In such system there are a number of constraints to overcome in order to obtain an effective tomographic image
of the sediments: (1) the electric field applied for remediation cannot be powered off, thus this field represents
the source for current injection for the resistivity measurements, (2) the applied electric field signal is irregular
and noisy because it is generated by high power current regulators, (3) the environment is extremely corrosive and
special care must be taken choosing the electrode material, (4) a number of disturbances, such as the influence of
the wells and pipes on the electric field distribution must be taken into account, (5) the electric field is generated
by all the electrode couples operating simultaneously (the current injection is produced by multiple electrodes)
Ligand-enhanced electrokinetic remediation of metal-contaminated marine sediments with high acid buffering capacity
Full text linkThe suitability of electrokinetic remediation for removing heavy metals from dredged marine sediments with high acid buffering capacity was investigated. Laboratory scale electrokinetic remediation experiments were carried out by applying two different voltage gradients to the sediment (0.5 and 0.8 V/cm) while circulating water or two different chelating agents at the electrode compartments. Tap water, 0.1M citric acid and 0.1M ethylenediaminetetraacetic acid (EDTA) solutions were used respectively. The investigated metals were Zn, Pb, V, Ni and Cu. In the unenhanced experiment the acid front could not propagate due to the high acid buffering capacity of the sediments; the production of OH- ions at the cathode resulted in a high-pH environment causing the precipitation of CaCO3 and metal hydroxides. The use of citric acid prevented the formation of precipitates but solubilisation and mobilisation of metal species were not sufficiently achieved. Metal removal was relevant when EDTA was used as the conditioning agent and the electric potential was raised up to 0.8 V/cm. EDTA led to the formation of negatively charged complexes with metals which migrated toward the anode compartment by electromigration. This result shows that metal removal from sediments with high acid buffering capacity may be achieved by enhancing the electrokinetic process by EDTA addition when the acidification of the medium is not
economically and/or environmentally sustainable
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