Effect of ageing on the availability of heavy metals in soils amended with compost and biochar: evaluation of changes in soil and amendment properties

Remediation strategies using soil amendments should consider the time dependence of metal availability to identify amendments that can sustainably reduce available pollutant concentrations over time. Drying-wetting cycles were applied on amendments, soils and soil + amendment mixtures, to mimic ageing at field level and investigate its effect on extractable Cd, Cu, Ni, Pb and Zn concentrations from three contaminated soils. The amendments investigated were municipal waste organic compost and biochars. The amendments, soils and mixtures were characterised by their physicochemical properties at different ageing times. The amendments were also characterised in terms of sorption capacity for Cd and Cu. The sorption capacity and the physicochemical properties of the amendments remained constant over the period examined. When mixed with the soils, amendments, especially the compost, immediately reduced the extractable metals in the soils with low pH and acid neutralisation capacity, due to the increase in pH and buffering capacity of the mixtures. The amendments had a relatively minor impact on the metal availability concentrations for the soil with substantially high acid neutralisation capacity. The most important changes in extractable metal concentrations were observed at the beginning of the experiments, ageing having a minor effect on metal concentrations when compared with the initial effect of amendments

Changes in heavy metal extractability from contaminated soils remediated with organic waste or biochar

The effect of the addition of organic waste or biochar on the extractability of heavy metals (Cd, Cu, Ni, Pb and Zn) was assessed in five heavy metal-contaminated soils. The amendments studied were: municipal organic waste compost (MOW), green waste (GW), biochar derived from tree bark (BF) and biochar derived from vine shoots (BS). The amendments were added to the soil at 10% dose. A pHstat leaching test was applied to the soils and soil + amendment mixtures to assess the effects of the amendments on the extractable metal concentration at the initial pH and in the 2-12 pH range. MOW increased the DOC content in the mixtures for most soils, whereas the rest of amendments only increased the DOC content for the soil with the lowest DOC value. Moreover, in the mixtures obtained from soils with a low buffering capacity, the amendments increased pH (up to 3 units) and the acid neutralization capacity, thus decreasing the extractability of heavy metals at the initial pH of the mixtures. In a few cases, the amendments further decreased the concentrations of extractable metal due to an increase in the sorption capacity of the mixture, even though the soil had high initial pH and ANC values. MOW and GW generally led to larger decreases in metal extractability in the resulting mixtures than biochar, due to their higher sorption and acid neutralization capacities

Examining sorption of perfluoroalkyl substances (PFAS) in biochars and other carbon-rich materials

The use of carbon-rich sorbents to remove and/or immobilize perfluoroalkyl substances (PFAS) in contaminated environmental scenarios is attracting increasing interest. The identification of key sorbent properties responsible for PFAS sorption and the development of models that can predict the distribution coefficients (Kd) for PFAS sorption in these materials are crucial in the screening of candidate materials for environmental remediation. In this study, sorption kinetics, sorption isotherms, and the effects of pH, calcium concentration and dissolved organic carbon (DOC) content on PFAS sorption were evaluated in four representative carbon-rich materials: two biochars with contrasting properties, a compost, and charcoal fines rejected by the metallurgical industry. Subsequently, the sorption of seven PFAS with numbers of fluorinated carbons ranging from 4 to 11 was evaluated in a total of ten carbon-rich materials, including activated carbons, so as to build up a Kd prediction model. The sorption of PFAS increased with greater fluorinated chain length, suggesting that hydrophobic interactions play a major role in sorption and electrostatic interactions a minor one. These results were confirmed by a principal component analysis, which revealed that the CORG/O molar ratio and the specific surface area of the material were the two main sorbent properties affecting PFAS sorption. Furthermore, the DOC content in solution had a negative effect on PFAS sorption. Using this information, a simple Kd prediction model applicable to a wide range of materials and PFAS was developed, using only a few easily-derived physicochemical properties of sorbent (CORG/O molar ratio and SSA) and PFAS (number of CF2), and was externally validated with data gathered from the literature

Demonstrating sorption analogy of lanthanides in environmental matrices for effective decision-making: The case of carbon-rich materials, clay minerals, and soils

Examining the effect of lanthanide-contaminated wastes, which have the potential to impact to other environmental compartments, requires conducting interaction studies with soils, as feasible first receptors of lanthanide leachates, and, if necessary, with sorbent materials, such as clay minerals and carbon-rich materials, which can serve as natural barriers and immobilisation agents used in remediation strategies. In this context, it is relevant to have available and reliable data on solid–liquid distribution coefficients (Kd) to understand the lanthanide sorption in these environmental matrices. Moreover, confirming lanthanide sorption analogies permits filling data gaps and data extrapolation among different contaminated scenarios, and thus facilitate to have available input data for decision-making related to the impact of a contaminated site. In this study, we demonstrate for the first time an analogous sorption of La, Sm, and Lu in carbon-rich materials (i.e., biochar and activated charcoal), clay minerals and soils, through laboratory batch experiments. The obtained sorption Kd values revealed similar sorption patterns among the three lanthanides for each matrix tested, even at different initial lanthanide concentrations. In all matrices, the maximum Kd values exceeded 104 L kg−1, with a significant decrease when testing high lanthanide concentrations. The analogy was first confirmed by examining the Kd correlations for the La-Sm, Lu-Sm, and La-Lu pairs within each matrix, for which strong linear correlations were obtained in all cases. Data compilations were built with own and literature data, and derived cumulative distribution functions revealed statistically equal lanthanide distributions and Kd best estimates. In addition to this, Kd variability decreased when grouping the data according to significant material properties. For the first time, Kd (Ln) best-estimates for different scenarios and materials were proposed as input data for risk assessment models

Dependence of samarium-soil interaction on samarium concentration: Implications for environmental risk assessment

The sorption and desorption behaviour of samarium (Sm), an emerging contaminant, was examined in soil samples at varying Sm concentrations. The obtained sorption and desorption parameters revealed that soil possessed a high Sm retention capacity (sorption was higher than 99% and desorption lower than 2%) at low Sm concentrations, whereas at high Sm concentrations, the sorption-desorption behaviour varied among the soil samples tested. The fractionation of the Sm sorbed in soils, obtained by sequential extractions, allowed to suggest the soil properties (pH and organic matter solubility) and phases (organic matter, carbonates and clay minerals) governing the Sm-soil interaction. The sorption models constructed in the present work along with the sorption behaviour of Sm explained in terms of soil main characteristics will allow properly assessing the Sm-soil interaction depending on the contamination scenario under study. Moreover, the sorption and desorption K-d values of radiosamarium in soils were strongly correlated with those of stable Sm at low concentrations (r = 0.98); indicating that the mobility of Sm radioisotopes and, thus, the risk of radioactive Sm contamination can be predicted using data from low concentrations of stable Sm. (C) 2017 Elsevier Ltd. All rights reserved

Sorption of perfluoroalkyl substances in sewage sludge

The sorption behaviour of three perfluoroalkyl substances (PFASs) (perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutanesulfonic acid (PFBS)) was studied in sewage sludge samples. Sorption isotherms were obtained by varying initial concentrations of PFOS, PFOA and PFBS. The maximum values of the sorption solid-liquid distribution coefficients (Kd,max) varied by almost two orders of magnitude among the target PFASs: 140-281 mL g−1 for PFOS, 30-54 mL g−1 for PFOA and 9-18 mL g−1 for PFBS. Freundlich and linear fittings were appropriate for describing the sorption behaviour of PFASs in the sludge samples, and the derived KF and Kd,linear parameters correlated well. The hydrophobicity of the PFASs was the key parameter that influenced their sorption in sewage sludge. Sorption parameters and log(KOW) were correlated, and for PFOS (the most hydrophobic compound), pH and Ca + Mg status of the sludge controlled the variation in the sorption parameter values. Sorption reversibility was also tested from desorption isotherms, which were also linear. Desorption parameters were systematically higher than the corresponding sorption parameters (up to sixfold higher), thus indicating a significant degree of irreversible sorption, which decreased in the sequence PFOS > PFOA > PFB

Feasibility of using low-cost, byproduct materials as sorbents to remove heavy metals from aqueous solutions

This work investigates the sorption of heavy metals by low-cost, byproducts such as charcoal fines (CF), waste green sand, and rice husk ash, in order to examine the feasibility of their use as alternative filter materials for metal-contaminated waters. The sorption of Cd, Cu, Pb, and Zn was investigated in batch experiments and sorption isotherms were constructed. The three byproducts showed high metal removal efficiencies (>95%, regardless of the metal concentration tested). The highest metal sorption distribution coefficients were obtained for CF, with maximum values within the 105-106 L kg-1 range for all the target metals. The sorption isotherms were satisfactorily fitted using the Freundlich equation and a linear model, the latter only being valid for initial metal concentrations lower than 0.4 mmol L-1. Sorption reversibility was very low, with desorption yields lower than 2% and desorption distribution coefficients often higher than 106 L kg-1. The values of the sorption and desorption parameters indicated that the use of these materials, especially CF, could constitute a low-cost alternative for the remediation of contaminated waters

Remediation of metal-contaminated soils with the addition of materials. Part 2: Leaching tests to evaluate the efficiency of materials in the remediation of contaminated soils

The effect of the addition of materials on the leaching pattern of As and metals (Cu, Zn, Ni, Pb, and Cd) in two contaminated soils was investigated. The examined materials included bentonites, silicates and industrial wastes, such as sugar foam, fly ashes and a material originated from the zeolitization of fly ash. Soil + material mixtures were prepared at 10% doses. Changes in the acid neutralization capacity, crystalline phases and contaminant leaching over a wide range of pHs were examined by using pH(stat) leaching tests. Sugar foam, the zeolitic material and MX-80 bentonite produced the greatest decrease in the leaching of pollutants due to an increase in the pH and/or the sorption capacity in the resulting mixture. This finding suggests that soil remediation may be a feasible option for the reuse of non-hazardous wastes

Implementación de la metodología de estudio de casos en asignaturas de titulaciones de grado y máster de Química

​La implementación de la metodología de estudio de casos, impulsada por el programa RIMDA y la Facultad de Química de la Universitat de Barcelona en distintas asignaturas teóricas y prácticas de titulaciones de grado y de máster, ha supuesto una experiencia muy positiva tanto por los beneficios que, a nivel competencial, supone para los estudiantes trabajar con esta metodología, como por la reflexión conjunta de los profesores del equipo de trabajo sobre la actuación docente y su mejora.

Proyecto RIMDA-Química. Proyecto institucional de fomento de la calidad docente en la Facultad de Química de la Universidad de Barcelona

Se presenta el Proyecto Institucional de Fomento de la Calidad Docente de la Facultad de Química (Proyecto RIMDA-Química), promovido por el equipo decanal de la Facultad de Química y por el Vicerrectorado de Docencia de la Universidad de Barcelona (UB), en el marco del programa de Investigación, Innovación y Mejora de la Docencia y del Aprendizaje de la UB. El proyecto se centra en la aplicación de cinco metodologías de aprendizaje activo (Aprendizaje Basado en Problemas, Estudio de Casos, Aula Invertida (Just In Time Teaching y Team-Based Learning) y Aprendizaje-Servicio) en asignaturas teóricas y prácticas de titulaciones de grado y máster