Image analysis procedure for studying Back-Diffusion phenomena from low-permeability layers in laboratory tests

In this study, the long-term tailing derived from the storage process of contaminants in low-permeability zones is investigated. The release from these areas in the groundwater can be considered a long-term source that often undermines remediation efforts. An Image Analysis technique is used to analyze the process and evaluate the concentrations of a tracer at different points of the test section. Furthermore, the diffusive flux from the low-permeability lenses is determined. To validate the proposed technique, the results are compared with samples, and the diffusive fluxes resulting from the low-permeability zones of the reconstructed aquifer are compared with a theoretical approach

Experimental and Numerical Study of Biochar Fixed Bed Column for the Adsorption of Arsenic from Aqueous Solutions

Two laboratory tests were carried out to verify the suitability of an Italian commercial biochar as an adsorbing material. The chosen contaminant, considered dissolved in groundwater, was As. The circular economic concept demands the use of such waste material. Its use has been studied in recent years on several contaminants. The possibility of using an efficient material at low cost could help the use of low-impact technologies like permeable reactive barriers (PRBs). A numerical model was used to derive the kinetic constant for two of the most used isotherms. The results are aligned with others derived from the literature, but they also indicate that the use of a large amount of biochar does not improve the efficiency of the removal. The particular origin of the biochar, together with its grain size, causes a decrease in contact time required for the adsorption. Furthermore, it is possible that a strong local decrease in the hydraulic conductibility does not allow for a correct dispersion of the flow, thereby limiting its efficiency

nZVI Mobility and Transport: Laboratory Test and Numerical Model

Zerovalent iron nanoparticles (nZVI) are becoming one of the most widely recommended nanomaterials for soil and groundwater remediation. However, when nZVI are injected in the groundwater flow, the behavior (mobility, dispersion, distribution) is practically unknown. This fact generally results in the use of enormous quantities of them at the field scale. The uncertainties are on the effective volumes reached from the plume of nZVI because their tendency to aggregate and their weight can cause their settling and deposition. So, the mobility of nanoparticles is a real issue, which can often lead to inefficient or expensive soil remediation. Furthermore, there is another aspect that must be considered: the fate of these nZVI in the groundwater and their possible impact on the subsoil environment. All these considerations have led us to propose an application of nZVI simulating the permeation technique through a laboratory experience, finalized to have a better, or even simpler description of their real behavior when injected in a flow in the subsoil. A two-dimensional laboratory-scale tank was used to study the dispersion and transport of nZVI. A nZVI solution, with a concentration equal to 4.54 g/L, was injected into glass beads, utilized as porous medium. The laboratory experiment included a digital camera to acquire the images. The images were then used for calibrating a numerical model. The results of the mass balance confirm the validity of the proposed numerical model, obtaining values of velocity (5.41 × 10−3 m/s) and mass (1.9 g) of the nZVI of the same order of those from the experimental tests. Several information were inferred from both experimental and numerical tests. Both demonstrate that nZVI plume does not behave as a solute dissolved in water, but as a mass showing its own mobility ruled mainly from the buoyancy force. A simple simulation of a tracer input and a nZVI plume are compared to evidence the large differences between their evolution in time and space. This means that commercial numerical models, if not corrected, cannot furnish a real forecast of the volume of influence of the injected nZVI. Further deductions can be found from the images and confirmed by means the numerical model where the detachment effect is much smaller than the attachment one (ratio kd/ka = 0.001). From what is reported, it is worthwhile to pay attention on the localization of the contaminants source/plume to reach an effective treatment and it is important to go further in the improvement of solution for the limiting the nanoparticles aggregation phenomenon

Reuse of mswi ba in the ceramic tiles production: An experimental industrial activity in latium region (central Italy)

The need of increasing the use of alternative materials, in construction and in production, is a current issue worldwide. At the same time, with regard to the treatment of waste, the management of bottom ash coming from Municipal Solid Waste Incineration, is an important issue all over the world, especially in Italy. In fact, the need for right management of ashes increases, which, in Italy, are almost always disposed of in landfills. This paper presents the environmental aspects of an industrial experiment, in Central Italy. In an industry, according with Government Institution, it was made an experimental industrial activity to produce ceramic tiles, using bottom ashes in the mixture with feldspatic sands and clays. In fact, comparison between the ashes composition and the traditional mixture one shows interesting affinity, from mineralogical and rheological point of view. This aspect is very interesting because it allows the reduction of the natural aggregates amount, used in the tiles production. In the industrial experiment the Municipal Solid Waste Incineration Bottom Ashes (MSWI BA), after storage, have been treated and then mixed with the other components of the mixture. After the mixing, ashes followed the traditional industrial production cycle. The first step of the experimental industrial activity consists in the sampling of the different materials that concern the production cycle. Subsequently, in agreement with the Regional Government Institution, the samples have been analyzed according to the tests present in the Protocol drawn up by CRITEVAT. In this regard, eco-toxicological and leaching tests on the different materials were carried out. Tests made on the final products, ceramics tiles produced adding MSWI BA to the traditional mixture, gave excellent results

An Integrated Approach to the Biological Reactor–Sedimentation Tank System

Secondary clarifiers are demanded to separate solids created in activated sludge biological processes to achieve both a clarified effluent and to manage the biological processes itself. Indeed, the biological process may influence the sludge characteristics, and conversely, the settling efficiency of the sedimentation basin plays an important role on the biological process in the activated sludge system. The proposed model represents a tool for better addressing the design and management of activated sludge system in wastewater treatment plants. The aim is to develop a numerical model which takes into account both the conditions in the biological reactor and the sludge characteristics coupled to the hydrodynamic behavior of a clarifier tank. The obtained results show that the different conditions in the reactor exert a great influence on the sedimentation efficiency

Assessment of zerovalent iron nanoparticle (nZVI) efficiency for remediation of arsenic-contaminated groundwater. Two laboratory experiments

Zerovalet iron nanoparticle (nZVI) technology has been found to be promising and effective for soil and groundwater remediation. This paper shows the results of two batch tests (Test A and Test B) carried out to assess the capacity of nZVI to remediate arsenic (As)-contaminated water. Test A, performed with batches of tap water contaminated by arsenic, with a concentration equal to 10 mg*L-1, showed a significant reduction of the As concentrations in solution, with a maximum removal rate up to 98% (Batch 3). Test A lasted 26 h. At the same time, Test B was performed with a sample of arsenic-contaminated sediment, with a concentration equal to 100 mg*Kg-1 (ca). Test B lasted 72 h. Test B also confirmed an excellent reduction of the As concentrations in solution, up to a maximum removal rate of 99% (Batch 3). These results show the effectiveness of nZVI for the remediation of water contaminated by arsenic. However, as the As–nZVI interaction time increased, there was a decrease in the available sites for arsenic immobilization, and so the As concentrations in solution became constant. In fact, as the dose of nZVI (mnZVI) used in the batches increased, the mass concentration of residue As in the solution at the equilibrium decreased (cAse) and therefore the concentration of As absorbed (cAs0–cAse) on the nZVI increased due to the immobilization action of the nanoparticles. The results show concentrations of As absorbed (cAs0–cAse) on the nZVI with a range between 5.10 mg*L-1 (mnZVI = 0.05 g) and 9.54 mg*L-1 (mnZVI = 0.5 g) for Test A, and with a range between 0.029 mg*L-1 (mnZVI = 0.05 g) and 0.058 mg*L-1 (mnZVI = 0.7 g) for Test B. Therefore, these results underline the need to monitor As concentrations during applications in the field, in order to verify the demand for injecting new active nanoparticles for arsenic removal

Experiment at laboratory scale to study the Back Diffusion phenomena from low permeability layers

Today the presence of contaminants in low permeability zones can represent a real limitation for a complete groundwater restoration. Low permeability layers store contaminants by molecular diffusion when plume of contaminant gets in touch with them, creating a concentration gradient between low and high permeability zones. After removal of the primary source of contamination, concentration gradient became inverse bringing a slow re-distribution of contaminant in groundwater (Back Diffusion). Therefore low permeability zones became a secondary source of contamination. This process is the primary cause of long-term plume tailing. Due to the enormous difficulties to carry out field tests, the experiments at laboratory scale assume an important role in the definition of the suitable mathematical relation to implement a correct treatment approach of these contamination scenarios. A Representation of the process was carried out using a Plexiglas tank and Sodium Fluorescein as fluorescent tracer. In the tank an aquifer represented by means of a high permeability layer with low permeability lenses was reproduced. The lenses were saturated with a solution containing dissolved Fluorescein and inside the aquifer was flushed clean water at different velocities to investigate the effects of pumping water on the low permeability lenses rate of release. An Image Analysis procedure based on the intensity of emitted light by the tracer is used to evaluate the concentration and the mass of Fluorescein released from low permeability zones. By this procedure different relations to estimate the duration of the phenomenon and the amount of mass release from the lenses are obtained. The results show a not-significant decrease of the time affected by Back Diffusion process and a slight increase of contaminants removal from low permeability lenses. The collected data demonstrate the need to manage the Back Diffusion phenomenon using alternative remediation technologies, such as groundwater circulation wells or thermal treatments

The LCA methodology for ceramic tiles production by addition of MSWI BA

Integrated waste management and sustainable use of natural resources are the basis of the Green Economy. In this context, the management of the Municipal Solid Waste Incineration Bottom Ashes (MSWI BA) is one of the current issue worldwide. This paper presents an application of the Life Cycle Assessment (LCA) procedure to the industrial production of ceramic tiles using bottom ashes in the mixture together with feldspathic sands and clays. The comparison between ashes and traditional mixture showed a similar mineralogical and rheological composition. In the reported procedure the MSWI BA, after storage, were treated to separate and to recover metals. The residual ashes were added to the mixture and then they followed the traditional industrial production cycle. Samples of the different materials were taken during the experimental industrial activity and leaching tests were carried out to verify the environmental compatibility of MSWI BA use to produce ceramic tiles. Results of the LCA show large environmental and energy benefits related to the proposed reuse of BA. Metals recovery and lower use of clay in traditional mixture allow to avoid emission of substances with a negative potential impact for environment. This study provides a sustainable alternative to the MSWI BA final disposal in landfill. In fact, MSWI BA are hazardous wastes which present complicated management and high disposal costsIntegrated waste management and sustainable use of natural resources are the basis of the Green Economy. In this context, the management of the Municipal Solid Waste Incineration Bottom Ashes (MSWI BA) is one of the current issues worldwide. This paper presents an application of the Life Cycle Assessment (LCA) procedure to the industrial production of ceramic tiles using bottom ashes in the mixture together with feldspathic sands and clays. The comparison between ashes and traditional mixture showed a similar mineralogical and rheological composition. In the reported procedure the MSWI BA, after storage, were treated to separate and recover metals. The residual ashes were added to the mixture and then they followed the traditional industrial production cycle. Samples of the different materials were taken during the experimental industrial activity and leaching tests were carried out to verify the environmental compatibility of MSWI BA use to produce ceramic tiles. The results of the LCA show large environmental and energy benefits related to the proposed reuse of BA. Metal recovery and lower use of clay in traditional mixture avoids emission of substances with a negative potential impact for environment. This study provides a sustainable alternative to the MSWI BA final disposal in landfill as MSWI BA are hazardous wastes that present complicated management and high disposal costs

Contaminant back-diffusion from low-permeability layers as affected by groundwater velocity: A laboratory investigation by box model and image analysis

Low-permeability lenses represent potential sources of long-term release when filled from contaminant solute through direct contact with dissolved plumes. The redistribution of contaminant from low to high permeability aquifer zones (Back-Diffusion) was studied. Redistribution causes a long plume tail, commonly regarded as one of the main obstacles to effective groundwater remediation. Laboratory tests were performed to reproduce the redistribution process and to investigate the effect of pumping water on the remediation time of these contaminated low-permeability lenses. The test section used is representative of clay/silt lenses (k ≈ 1 ∗ 10− 10 m/s/k ≈ 1 ∗ 10− 7 m/s) in a sand aquifer (k ≈ 1 ∗ 10− 3 m/s). Hence, an image analysis procedure was used to estimate the diffusive flux of contaminant released by these low-permeability zones. The proposed technique was validated performing a mass balance of a lens saturated by a known quantity of tracer. For each test, performed using a different groundwater velocity, the diffusive fluxes of contaminant released by lenses were compared and the remediation times of the low-permeability zones calculated. For each lens, the obtained remediation timeframes were used to define an analytical relation vs groundwater velocity and the coefficients of these relations were matched to grain size of the low-permeability lenses. Results show that an increase of the velocity field is not useful to diminish the total depletion times as the process mainly diffusive. This is significant when the remediation approach relies on pumping technology