Disponibilidade e fracionamento do Cu, Pb e Zn num solo ácido da Galiza (NW Espanha) corrigido com um composto de resíduos sólidos urbanos

The potential availability and chemical fractionation of trace elements in soil after compost addition was studied in a laboratory incubation. An acid agricultural soil, developed on biotitic schists, was amended with two rates of a municipal solid waste compost (3% and 6% weight) or lime (2.5 g CaCO3 kg-1, calculated to raise soil pH to values close to those of the compost-amended soil), and incubated in the laboratory for five months. Compost addition increased the availability of Cu, Pb and Zn (measured in DTPA extract) with respect to the control, whereas lime reduced it. Compost amendment increased soil total Cu, Pb and Zn concentrations, and their chemical distribution, assessed by means of the BCR (Bureau Communautaire de Référence) fractionation scheme, was different for each element. Compost addition increased Pb in the reducible (iron oxide-bound) fraction, Cu in the organic and iron oxide fractions, and Zn in the soluble and reducible fractions. Lime did not change the fractionation or total concentrations of the metals analysed. The most problematic element in the compost-amended soil from an environmental point of view is Zn, because it was found in highly mobile forms, while for Cu and Pb this risk is lowSe estudió la disponibilidad potencial y el fraccionamiento químico de metales traza en el suelo tras la adición de compost en un experimento de laboratorio. Un suelo agrícola ácido, desarrollado sobre esquistos biotíticos, fue enmendado con dos dosis de un compost de residuos sólidos urbanos (3% y 6% en peso) e incubado en laboratorio durante cinco meses. Con fines comparativos, también se estudió el suelo enmendado con una dosis de cal (2,5 g CaCO3 kg-1) calculada para llevar el pH a valores próximos a los del suelo enmendado con compost. La enmienda con compost aumentó la disponibilidad de Cu, Pb y Zn con respecto al suelo sin enmendar, mientras que la cal tuvo el efecto contrario. El compost también incrementó las concentraciones totales de Cu, Pb y Zn, modificando su fraccionamiento químico, mientras que la cal no tuvo efecto en este sentido. La adición de compost aumentó la concentración de Pb en la fracción reducible (unido a óxidos), la de Cu en las fracciones oxidable (unido a materia orgánica) y reducible, y la de Zn en las fracciones soluble y reducible. El elemento más problemático en el suelo enmendado con compost es el Zn, al estar presente en formas de alta movilidad, en contraste con lo que sucede en el caso de Cu y PbEstudámos num ensaio laboratorial a disponibilidade potencial e o fracionamento químico de elementos metálicos vestigiais no solo após a adição de um material compostado. Usou-se um solo agrícola ácido, desenvolvido em xistos de biotite, ao qual se adicionaram duas doses de um composto de resíduos sólidos urbanos (3% e 6% em peso) e que foi incubado no laboratório duranteum período de cinco meses. Para comparação, o solo foi igualmente tratado com uma dose de calcário (2,5 g CaCO3 kg-1). A adição de composto aumentou a disponibilidade de Cu, Pb e Zn do solo testemunha, enquanto que o calcário teve o efeito oposto. O composto aumentou também as concentrações totais de Cu, Pb e Zn, modificando o seu fracionamento químico, enquanto que o calcário não produziu qualquer efeito. O composto aumentou a concentração de Pb na fracção redutível do solo, o Cu nas frações oxidáveis e redutíveis, e o Zn nas fracções solúveis e redutíveis. O elemento mais problemático no solo tratado com o composto foi o Zn, por estar presente sob formas de alta mobilidade, em contraste com o que aconteceu no caso de Cu e PbS

Heavy Metal Uptake of Lettuce and Ryegrass from Urban Waste Composts

Interest in using urban waste composts as amendments in urban agriculture is growing nowadays. However, concerns about the potential transference of pollutants present in urban waste to the food chain are very relevant when they are recycled for food or animal feed production. Thus, for the safe use of urban waste composts, it has to be assured that no risk of metal transference to plants from compost exists. In this work, the transference of heavy metals from urban waste composts to plants has been studied in an experiment with lettuce and Italian ryegrass, grown in substrates based on five metal-rich composts and a manure vermicompost (included for comparison). A two-month pot experiment was performed under controlled light and temperature conditions, and plant growth and uptake of Cu, Pb, Cd and Zn were analyzed. For both species, the concentration of metals in plant tissue followed the sequence Zn > Cu >> Pb ≈ Cd, the same as the metal concentrations in four out of the five composts. Plant concentrations of Zn, Cu and Cd increased with their concentrations in compost, whereas this relation was not observed for Pb. The ratio between element concentration in plant and compost were much higher for Zn, Cd and Cu than for Pb, showing the lower bioavailability of Pb with respect to other metalsThis research was funded by the Spanish Ministry of Economy and Competitiveness (MINECO), through a “Ramón y Cajal” fellowship, grant number RYC-2016-19286S

Utilization of Composts for Adsorption of Methylene Blue from Aqueous Solutions: Kinetics and Equilibrium Studies

Utilization of composts as low-cost adsorbents is an important application in the field of environmental remediation, but these materials have not yet been extensively used for dye removal. In this work, we have studied the characteristics of adsorption of methylene blue onto two composts (a municipal solid waste compost and a pine bark compost). Kinetics and equilibrium batch experiments testing the influence of adsorbent particle size, solution pH and ionic strength were performed. Both composts have a high adsorption capacity for methylene blue, similar to other low-cost adsorbents. Kinetics of adsorption followed a pseudo-first-order model, with maximum adsorption reached after a contact time of two hours. Equilibrium adsorption followed a Langmuir model in general. Reduction of particle size only increased adsorption slightly for composted pine bark. Increase in ionic strength had no effect on adsorption by municipal solid waste compost, but increased adsorption by composted pine bark. Modification of pH between 5 and 7 did not influence adsorption in any case. Overall, the results suggest that electrostatic interaction between the cationic dye and the anionic functional groups in the composts is not the only mechanism involved in adsorption. In conclusion, the use of composts for dye removal is a likely application, in particular for those composts presenting limitations for agricultural useThis research was funded by the Spanish Ministry of Economy and Competitiveness (MINECO), through a Ramón y Cajal fellowship, grant number RYC-2016-19286S

Potentially Toxic Trace Elements in the Urban Soils of Santiago de Compostela (Northwestern Spain)

With the objective of increasing information inorganic pollutants in urban soils in Spain, we studied the presence of Cu, Pb, Zn, Ni, Cr, and As in 55 soils in the city of Santiago de Compostela (northwestern Spain). The soils were developed over diverse parent materials (granites, gneiss, schists, and amphibolites) and present different land uses, urban grasslands, urban forests, urban allotment gardens, and peri-urban agricultural soils. Total trace element concentrations, analyzed by XRF of ground samples, were correlated to physicochemical properties of the soils, and the influence of land use, lithology, and location on the degree of pollution was explored. In most soils, trace element concentrations followed the sequence Zn (55–484 mg kg−1) > Pb (20–566 mg kg−1) > Cr (17–277 mg kg−1) > Cu (17–188 mg kg−1) > As (13–205 mg kg−1) > Ni (11–91 mg kg−1). The concentrations were overall higher than regional backgrounds, but not high enough to class the soils as contaminated according to the Spanish regulation. Accordingly, the geoaccumulation index values indicate that most soils present low to moderate pollution levels. Among the elements studied, Cu, Pb, and Zn were correlated between them, with their highest concentrations happening in soils of the green areas in the city center; Cr and Ni concentrations were related to lithology of the parent material, with the highest concentrations in soils developed over amphibolite; finally, As concentrations are higher in two precise points without a clear connection to a known source of pollutionThe authors gratefully acknowledge the support of the City Hall of Santiago de Compostela for the sampling for this study. Paradelo thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for his Ramón y Cajal fellowship (RYC-2016-19286)S

Potential use of composts and vermicomposts as low-cost adsorbents for dye removal: an overlooked application

The use of composts and vermicomposts as adsorbents is an important topic of study in the field of environmental remediation. These materials are rich in organic matter and have functional groups that can interact with organic and inorganic compounds. They also contain microorganisms that can promote biodegradation of organic substances. Composts that cannot be used for agronomic purposes (owing to e.g. low nutrient levels or phytotoxicity) may be valuable for soil remediation or pollutant removal. In this review, we discuss papers on this topic, with the objective of drawing attention to the potential use of composts/vermicomposts and to recommend further investigation on this subject. Few published studies have investigated the use of composts/vermicomposts to remove dyes and other coloured compounds. However, preliminary results show that these materials are potentially good adsorbents, at least comparable to other low-cost adsorbents, and that, in general, basic dyes are more efficiently removed than direct, reactive or acid dyes. The results of the works reviewed also show that dye removal takes place by adsorption mechanisms, in most studies following a Langmuir model, and that the kinetics of removal are fast and follow a pseudo-second order model. However, there remain several uncertainties regarding this application. For example, very few dyes have been studied so far, and little is known about the influence of the properties of composts/vermicomposts on the dye removal process. Moreover, the possible use of compost/vermicompost to enhance biodegradation processes has not been explored. All these questions should be addressed in future research.Postprint (author's final draft

Competitive removal of textile dyes from solution by pine bark-compost in batch and fixed bed column experiments

Compost from pine bark has been previously suggested as an effective low-cost biosorbent for different classes of textile dyes, although the existing studies have been performed in non-competitive batch conditions, so the effect of competition or adsorption in continuous-flow conditions has not been assessed. In this work, the removal of Basic Violet 10 (BV10) and Direct Blue 151 (DB151) by pine bark compost from single and bi-solute mixtures has been studied in batch and fixed-bed column experiments. Adsorption capacity of pine bark compost was three times higher for BV10 than for DB151 in batch conditions, where competition reduced the uptake of both dyes, with competition factors of 0.63 for DB151 and 0.82 for BV10. Dye adsorption capacity was lower in column than in batch tests, with 112.6 and 34.7 mg g−1 for BV10 and DB151, respectively, versus 127.1 and 42.1 mg g−1 in batch conditions. The presence of both dyes in solution also reduced their affinities with respect to non-competitive conditions in column tests, with saturation capacities of 71.6 mg g−1 for BV10 and 16.8 mg g−1 for DB151. The effect of competition between dyes was higher in columns than in batch conditions, with competition factors of 0.76 for BV10 and 0.59 for DB151. The column biosorbent was effectively regenerated using ethanol, thus enabling reuse in the practical application of compost for textile dye removal. The concentration of dyes in the eluted ethanol was higher than the influent concentration, what would give compost value for pre-concentration of textile dyesThe authors thank Mr. Bassem Nasrallah (Chemistry Department, Hashemite University, Jordan) for the continuous technical support represented by the spectroscopic analyses as well as the compositional analysis of the compost. Dr. Paradelo thanks the Spanish State Agency for Research (AEI) for his Ramón Cajal grant RYC-2016-19286, funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”S

Comparison of the sorption capacity of basic, acid, direct and reactive dyes by compost in batch conditions

Research on biosorption of organic dyes is an important subject for the development of clean technologies for the treatment of textile wastewater. In this work, the process of sorption of four textile dyes of different natures, namely Basic Violet 10 (BV10), Acid Red 27 (AR27), Direct Blue 151 (DB151) and Reactive Violet 4 (RV4) onto two composts, pine bark compost and municipal solid waste compost, has been studied. For this, sorption kinetics and equilibrium sorption at different solution pH values (3.0–7.0) and salinity (0–1.0 M KCl) conditions have been assessed in batch experiments. Sorption rates were relatively slow for BV10, reaching equilibrium only after 24 h, and faster for the rest: around 5–6 h for RV4 and AR27 and 2 h for DB151. Kinetics of dye sorption followed a pseudo-first order model, except that of DB151, which was better described by a pseudo-second order model. The sequence of adsorption capacity for both composts was as follows: BV10 > DB151 > RV4 > AR27. In general, dye sorption at the equilibrium was adequately described by the Langmuir model, what allows to estimate maximum retention capacities for each dye by the composts. At the best removal conditions, pine bark compost presented maximum sorption capacities of 204 mg g−1 for BV10, 54 mg g−1 for DB151, 23 mg g−1 for RV4, and 4.1 mg g−1 for AR27, whereas municipal solid waste compost showed maximum sorption of 74 mg g−1 for DB151, 38 mg g−1 for RV4, 36 mg g−1 for BV10, and 1.6 mg g−1 for AR27. Sorption increased at acid pH in all cases, likely because of modification of charges of the dyes and higher electrostatic attraction, whereas increasing salinity also had a positive effect on sorption, attributed to a solute-aggregation mechanism in solution. In conclusion, organic waste-derived products, like composts, can be applied in the removal of colorants from wastewater, although they would be more effective for the removal of basic cationic dyes than other types, due to electrostatic interaction with mostly negatively-charged compostsDr. Paradelo thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for his Ramón y Cajal fellowship (RYC-2016-19286)S

Estudo a escala de microcosmos de barreiras reativas permeáveis com serragem de granito e composto para o tratamento de água contaminadas com Cr (VI)

The permeable reactive barrier (PRB) is a technology developed for the removal of contaminants in groundwater. It consists of a screen perpendicular to the flow of contaminated groundwater filled with a material capable of adsorbing, precipitating or degrading pollutants. Several materials have been tested for their use as reactive substrates for the construction of PRBs. Waste materials are of particular interest for this purpose due to the possibility of their reuse and their generally lower cost. With this aim, the Cr (VI) retention capacity of filler material consisting either of pine bark compost (PB) or a 50% mixture of compost and granite powder (PB50) was evaluated using an experimental device specifically designed for this study, which reproduces a permeable reactive barrier at the laboratory scale. Percolation experiments were carried out with a solution of 100 mg L-1 Cr (VI) in 0.01M KNO3, followed by a leaching step with the saline background. The results show that compost is a highly efficient filler for permeable reactive barriers with almost 100% retention of Cr, whereas the retention efficiency of the mixture of PB50 oscillated between 18 and 46% during the experiment. The Cr retained by the filling material is strongly fixed, since no desorption was detected by leaching with the saline background, and concentrations in the standard Toxic Characteristic Leaching Procedure (TCLP) extracts were lower than 1 mg L-1. This behaviour minimizes the risk of release of the Cr retained by the material of the barrier in the event of it being traversed by water not contaminated with Cr. Modelling with Visual Minteq indicates that in the experiments with PB, the reduction of Cr (VI) to Cr (III) occurs and that Cr (III) is associated with dissolved organic matter, which is a form of lower toxicity than the initial Cr (VI) species. In turn, in the experiments with PB50, Cr (III) and Cr (VI) coexist and the oxidised form is not associated with dissolved organic matter, which suggests greater toxicity. The results indicate that pine bark compost is a potential candidate for use as filler material permeable reactive barriers.Las barreras permeables reactivas (BPRs) son tecnologías de eliminación de contaminantes en aguas subterráneas, que consisten en una pantalla perpendicular al flujo de agua subterránea contaminada, rellena de un material con capacidad de adsorber, precipitar o degradar los contaminantes. Se han evaluado diversos materiales reactivos como material de relleno de BPRs, siendo de especial interés la utilización de materiales residuales, por la posibilidad de su reutilización y, frecuentemente, menor coste. Con este fin se estudió la capacidad de retención de Cr (VI) de compost de corteza de pino (PB) y de una mezcla al 50% de compost y serrines graníticos (PB50), utilizando un dispositivo diseñado específicamente para este estudio, que reproduce una barrera permeable reactiva a escala de laboratorio. Para evaluar la retención se llevó a cabo un experimento de percolación con una disolución de 100 mg L-1 de Cr (VI) en KNO3 0,01M, seguido de una etapa de lavado con el fondo salino, para evaluar la liberación del Cr previamente retenido. Los resultados mostraron una gran eficacia del compost como material de relleno de BPRs, consiguiendo una retención de Cr cercana al 100%. La mezcla de serrín granítico y compost presentó una capacidad de retención que osciló entre el 18 y el 46% a lo largo del experimento. El Cr retenido por el material de relleno se encuentra fuertemente fijado, pues no se desorbe por lixiviación con la solución salina y las concentraciones en los extractos obtenidos mediante la aplicación del procedimiento estándar de lixiviación Toxic Characteristic Leaching Procedure (TCLP) fueron inferiores 1 mg L-1. Este comportamiento minimiza el riesgo de liberación del Cr retenido por el material de la barrera, en el supuesto de que fuera atravesada por un agua no contaminada con Cr. La modelización con Visual Minteq indica que, en los eluatos de los experimento con PB, se ha producido reducción de Cr (VI) a Cr (III), y éste se encuentra asociado con la materia orgánica disuelta, lo que sugiere una reducción de la toxicidad en comparación con la que presenta el Cr (VI) introducido en la solución de percolación. En los eluatos del experimento con PB50 se encuentran tanto Cr (III) como Cr (VI), y la forma oxidada no se encuentra asociada con la materia orgánica disuelta. Los resultados de este estudio indican que el compost de corteza de pino tiene un gran potencial para ser usado como material de relleno de barreras permeables reactivas.Entre as tecnologias desenvolvidas para a remoção de contaminantes em águas subterrâneas são as barreiras permeáveis reactivas (BPRs), as quais consistem de uma trincheira perpendicular ao fluxo das águas subterrâneas contaminadas, cheia com um material capaz de adsorver, precipitar ou degradar poluentes. Diversos matérias foram ensaiados como substratos reativos na construção de BPRs, sendo de interesse a utilização de materiais residuais, pela possibilidade de reutilização e, geralmente, menor custo. Para este fim foi avaliada a capacidade de retenção de Cr (VI) de um composto de casca de pinheiro (PB) ou uma mistura de 50% de composto e pó de serragem de granito (PB50), usando um dispositivo experimental que simula uma barreira permeável reactiva a escala de laboratorio. Experiências de percolação foram levadas a cabo com uma solução de 100 mg L-1 de Cr (VI) em 0,01MKNO3, seguida por um passo de lavagem com a solução salina. Os resultados obtidos mostram uma alta eficáciado composto, com uma retenção de 100% de Cr. A eficiência de retenção da mistura de serradura de grantito e de composto oscilou entre 18-46% ao longo do experimento. O Cr é fortemente retido pelo material de enchimento, não dessorvido por lixiviação com a solução salina, enquanto que as concentrações dos extractos obtidos pela aplicação do procedimento de lixiviação standar Toxic Characteristic Leaching Procedure (TCLP) eram inferiores a 1 mg L-1. Este comportamento reduz o risco de a liberação da carga de Cr retida pelo BPR o que poderia acontecer se águas limpas passan através da barreira. O modelado com Visual Minteq indica que nas experiências com PB ocorre redução de Cr (VI) a Cr (III), e que o Cr (III) está associado com a matéria orgânica dissolvida, que é uma forma de toxicidade mais baixa do que as espécies de Cr (VI) iniciais, enquanto nas experiências com PB50, Cr (III) e Cr (VI) coexistem, e o Cr (VI) não está associado com a matéria orgânica dissolvida, o que sugere uma maior toxicidade. Os resultados indicam que o composto de casca de pinheiro é um candidato potencial para utilização como material de enchimento de barreiras permeáveis reactivas.The study was funded by the Xunta de Galicia through the project entitled Avaliación do uso de materiais de caracter inerte e orgánico para o tratamento de augas contaminadas –Tradesol (09MDS005CT). The authors also thank Xunta Galicia-Feder for the financial support through "Axudas de Consolidación e Estruturación de Unidades de Investigación Competitivas. IN845B-2010/038 and GRC2014/028". Diego Martiñá Prieto wishes to acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness for his FPI Fellowship (BES-2011-044514)S

Impact des fumures organiques sur les rendements de la tomate et sur la densité des champignons à mycorhizes arbusculaires dans la zone de Saguiya (Niger)

La rhizosphère est très importante pour la croissance et les rendements des cultures et peut être affectée par des facteurs comme les pratiques agricoles ou les fertilisants. L’effet du type de fumure organique sur la densité des spores mycorhizogènes dans la rhizosphère de la tomate et sur les paramètres agronomiques a été évalué dans la zone de Saguiya (Niger). Le dispositif expérimental mis en œuvre comporte 48 parcelles traitées avec trois types de fumure organique (bouse de vache, bouse de chèvre et fumure de volaille) à trois niveaux de fertilisation (100%, 125% et 150%) en quatre replicats, pendant une campagne de trois mois. La variété de tomate exotique Tropimech a été cultivée avec suivi des paramètres agronomiques, et des échantillons du sol ont été prélevés pour l’extraction et le dénombrement des spores de champignons mycorhiziens arbusculaires (CMA). Le traitement T3 de l’essai 3 (soit 150% de la fiente de volaille plus matière organique) est le plus efficace parmi les traitements, avec 38 t ha-1 pour le rendement en fruits, 13 t ha-1 de rendement pour la partie foliaire et 6 t ha-1 pour la partie racinaire. Les principaux genres de spores CMA trouvés sont des Glomus sp, Gigaspora sp et Scutellospora sp. La densité de Scutelospora sp est aussi plus élevée pour le traitement avec fiente de volaille, avec une forte corrélation positive entre la densité des spores et les paramètres agronomiques. Les résultats ont montré que les fumures, en particulier la fiente de volaille, améliorent la fertilité du sol de cette région ainsi que la densité des spores CMA