1,721,011 research outputs found
Different approaches for incorporating bioaccessibility of inorganics in human health risk assessment of contaminated soils
Full text linkIngestion of soil represents one of the critical exposure pathways in the human health risk assessment (HHRA) framework at sites contaminated by inorganic species, especially for residential scenarios. HHRA is typically carried out through starting from the so-called “total concentration”, which is estimated from the fraction of inorganic species extracted from the soil using standardized approaches, i.e., microwave acid extraction. Due to the milder conditions, a smaller portion of the inorganics present in the soil is actually dissolved in the gastro-intestinal tract (bioaccessible fraction), and afterward reaches the bloodstream, exerting an effect on human health (bioavailable fraction). Including bioaccessibility in HHRA could then allow for the achievement of a more realistic assessment than using the total concentration. In this paper, the bioaccessible concentration of different inorganics in soil samples collected from a firing range was estimated by applying two in vitro tests, i.e., the Unified Barge Method (UBM) and the Simple Bioaccessibility Extraction Test (SBET). Moreover, different options for incorporating bioaccessibility in HHRA for the estimation of the cleanup goals were also applied and discussed. Despite the notable differences in terms of reagents and procedure between the two methods, the obtained results were quite close, with the SBET method providing slightly higher values. The role of the soil particle size distribution on the calculation of the cleanup goals accounting for bioaccessibility is also discussed
Assessment of the energy requirements for Co2 storage by carbonation of industrial residues. Part 1: definition of the process layout
No full textAbstractMineral carbonation is an ex situ CO2 storage option that could allow to fix large amounts of CO2 in a solid and thermodynamically stable form. Its feasibility has been proven at lab-scale both employing natural minerals or alkaline industrial residues. However the energy requirements of this process can be quite significant depending on the type of material and operating conditions adopted and thus represent a crucial factor for its full scale applicability. The focus of this paper is the assessment of the energy requirements of CO2 storage by accelerated carbonation of alkaline materials applying the direct aqueous route. From the analysis of the main studies on energy penalties associated to the carbonation process large differences were observed on the assumptions made, the selected layout and operating conditions, in particular for alkaline residues. In addition most of the evaluations were carried out considering only experimental tests performed with high liquid to solid ratios (slurry phase route) while specific evaluations for tests with liquid to solid ratios lower than 1 (wet route) were not carried out. The overall aim of this study is to estimate the energy duties required to store the CO2 emissions of a small-medium size power plant (20 MW) by carbonation of different types of residues (steel slags and waste incineration residues) applying either the slurry phase or wet routes. In this paper the layouts of the proposed carbonation processes are presented and discussed
Combined Fenton-like oxidation and CO2 sparging for the treatment of groundwater contaminated by organic compounds.
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Combinazione di ossidazione chimica e CO2 sparging per il trattamento di acque di falda contaminate
No full textHorizontal permeable reactive barriers with zero-valent iron for preventing upward diffusion of chlorinated solvent vapors in the unsaturated zone
No full textChlorinated solvents are extensively used in many activities and hence in the past decades impacted a large number of sites. The presence of these contaminants in groundwater is challenging particularly for the management of the vapor intrusion pathway. In this work we examine the potential feasibility of using horizontal permeable reactive barriers (HPRBs) placed in the unsaturated zone to treat chlorinated solvent vapors emitted from groundwater. Zero-valent iron (ZVI) powders, partially saturated with water and characterized by different specific surface areas (SSA), were tested, alone or mixed with sand, in lab-scale batch reactors using TCE as model compound. Depending on the type of iron powder used, a reduction of TCE concentration in the vapor phase from approximately 35% up to 99% was observed after 3 weeks of treatment. The best performance in terms of TCE reduction was obtained using the ZVI characterized by the intermediated values of the specific surface area (SSA). This finding, which is in contrast with the results generally observed in in aqueous solutions, was tentatively attributed to a non-selective higher reactivity of the fine-grained iron samples with water and dissolved oxygen (with a consequent iron passivation) or to the occurrence of a diffusion-limited reaction kinetics. Based on the first-order kinetic degradation rate constants estimated from the experimental data, a horizontal barrier of 1 m containing ZVI or a mixture of ZVI and sand can potentially lead to an attenuation of TCE vapors over 99%
Storage of carbon dioxide captured in a pilot-scale biogas upgrading plant by accelerated carbonation of industrial residues
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Assessment of a carbonation-based CO2 utilization process for the valorization of CFBC ash
No full textThis work assesses a combined accelerated carbonation and wet granulation treatment applied to circulating fluidized bed combustion fly ash with the aim of producing secondary aggregates for civil engineering applications and of achieving a net storage of CO2. The experiments were carried out at both a laboratory scale and larger scale, and the effects of the CO2 content of the gas flow (40 or 100%), temperature (from 25 to 60 degrees C), and the use of an alkaline activator solution as binder for the granulation process were investigated. Specifically, the particle size distribution, aggregate crushing value, leaching behavior, and CO2 uptake of the products after 28 days curing under ambient air were analyzed. In addition, the energy requirements of the process were estimated on the basis of the results of the larger scale tests and were used to calculate the CO2 emissions of the process to estimate the net CO2 avoided that could be achieved per kilogram of produced aggregate. The carbogranulation process allowed us to achieve a relevant increase in particle size with respect to the starting material. The conditions that yielded the best performance in terms of product properties (both technical and environmental) and the maximum amount of CO2 avoided (above 75 g of CO2/kg aggregate) was the carbogranulation treatment performed at 60 degrees C with water as binder and a gas phase containing 40% CO2. Although the products obtained employing the alkaline activator solution presented a lower mobility of trace elements of potential environmental concern and generally a higher CO2 uptake compared to the granules produced with water as granulation binder, the carbon footprint of the additives (sodium silicate in particular) would make the process carbon positive, even considering the CO2 avoided by replacing natural aggregates
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