Valorisation of Lignocellulosic Biomass Wastes for the Removal of Metal Ions from Aqueous Streams: A Review

Heavy metal pollution derived from anthropogenic activities is a relevant environmental threat nowadays due to their toxic nature, persistence and accumulation potential in the food chain. A wide variety of lignocellulosic-based biomaterials have been thoroughly assessed by the scientific community as sorbents for the removal of metals from aqueous streams. This kind of biomaterials, mainly constituted by lignin and cellulose, bear functional groups such as alcohol, ketone and carboxylates that provide active sorption points for the effective removal of heavy metals. The role of lignin in the sorption process is especially relevant, since this substance provides polyhydroxy and polyphenol functional groups—especially effective in the coordination of metals—and that provide ion exchange functionality to the material. Depending on their nature, these materials can be used either in their raw form or chemically modified form so as to enhance their sorption capacity and/or to achieve improved mechanical and mass transfer properties

Nickel removal from exhausted electroplatting baths by using vegetable wastes

During the last years our research group has been studying the use of industrial vegetable wastes as grape stalks and exhausted coffee to remove metals ions such as Ni(II), Cu(II), Pb(II), Zn(II), Cd(II) or Cr(VI) and Cr(III) in aqueous solution from the point of view to use these wastes as biosorbents in a low cost alternative to activated carbon for wastewater treatment. The optimal experimental conditions for the removal of each of these metal ions in synthetic solutions by using both biosorbents were determined in previous studies . In this work, the performance of grape stalks and exhausted coffee for the removal of nickel ions from an exhausted electroplating bath of a metal finishing industry from Barcelona (Spain) has been investigated. Batch and column experiments were carried out at room temperature by using grape stalk wastes (particle size 0.8-1.0 mm), meanwhile in the case of exhausted coffee, two different particle size ranges were used, 0.25-0.50 mm and 0.50-1.00 mm for batch and column experiments, respectively. Kinetics and equilibrium studies were carried out in batch mode to determine the equilibrium contact time and to obtain the sorption capacity of sorbents. The data in both studies have been treated by using different models. Column experiments were designed to establish the optimal condition for the treatment of the industrial wastewater. The experiments were performed in packed bed up flow columns of different internal diameter and bed depth in order to predict the transport and sorption parameters. In all column experiments the flow rate was around 11 mL h-1. From perspective of process modelling, the dynamic behavior was described in terms of breakthrough curves. The bed depth service time (BDST), Thomas and Yoon Nelson models were used to analyze the experimental data and to determine model parameters. Batch results show that about 1hour was the time needed to reach equilibrium when using grape stalks and around 15 h when using exhausted coffee. In the case of exhausted coffee, the pH solution decreased during the sorption process from initial pH 5,5 to lower pH than the corresponding pHpzc (point zero charge). To avoid this, pH solution was controlled to a constant pH 5,5 and the equilibrium were achieved in 1h. Kinetic data of both sorption processes fit pseudo-second order model, indicating that chemisorption could be rate limiting in the sorption step. Equilibrium data of nickel sorption onto grape stalks and exhausted coffee fit adequately Langmuir model, indicating monolayer coverage. Results showed that maximum sorption capacity of grape stalks (4,8 10-2 mmol/g; 2,84 mg/g) is slightly higher than exhausted coffee (2,9 10-2 mmol/g; 1,70 mg/g). The maximum nickel sorption capacity of both sorbents was reduced to 50% compared to maximum sorption capacity determined using synthetic Ni(II) solutions. Thus, grape stalks and exhausted coffee performance for the removal of Ni(II) from the studied industrial wastewater are negatively affected by the presence of other compounds in the industrial wastewater. In column experiments, the best results were obtained by using 2.8 cm internal diameter columns and bed depth 6 cm and 8 cm for grape stalks and exhausted coffee, respectively. Breakthrough curves were successfully modelled by the proposed columns models. The results obtained demonstrated that grape stalks sorption capacity was higher than exhausted coffee but this one presented a higher sorption rate.Postprint (published version

Valorització de residus vegetals procedents de processos industrials com a biosorbents per a l'eliminació d'ions metàl•lics d'afluents aquosos

L’objectiu d’aquest projecte és la valorització de residus vegetals procedents de processos industrials, com són el pinyol d’oliva, rapa del raïm, suro, marro de cafè, etc.,com a biosorbents per a l’eliminació de diferents ions metàl·lics, crom, arsènic, plom, cadmi, coure, níquel, etc., d’afluents aquosos.Peer Reviewe

Proposta didàctica. Encapsulació de pols de peles de mandarina en boles d'alginat de calci. Aplicació com a sorbent del blau de metilè

Les aigües residuals de la indústria tèxtil han estat estudiades al llarg del temps degut als problemes ambientals que genera el seu abocament a les aigües naturals. El blau de metilè és un colorant catiònic àmpliament utilitzat en la indústria de paper i del teixit. Tot i que no es considera un colorant molt tòxic, pot tenir diversos efectes nocius sobre els organismes vius i un cop inhalat pot causar diversos trastorns per a la salut humana. En aquesta experiència didàctica s'explica com encapsular pols d'un residu de fruita en alginat de calci i posteriorment s'ha estudiat la seva capacitat d'eliminació del blau de metilè en fase aquosa en funció de diferents temps de contacte. La següent experiència didàctica consta de cinc sessions amb una durada total de 16 hores que s'ha extret del treball de recerca dut a terme per un alumne de 1r de Batxillerat, Sergi Ortiz Aparicio.Waste water in the textile industry has been studied over time due to the environmental problems generated by its spillage in natural waters. Methylene blue is a catiònic dye widely used in paper colouring, cotton and wool dyeing, and coating for paper stock. Although it is not considered as a very tòxic dye, it can have various harmful effects on líving organisms and once inhaled it may cause several disorders to human health. In this study, removal capacities of aqueous methylene blue (MB) by different formats of tangerine peels have been investigated: hidrated, dehydrated and dust tangerine peels encapsulated in alginated beads have been investigated in function of diferent contact times. The following teaching experience consists of five sessions with a total duration of 16 hours. It has been inspired from a research work carried out by student in the 1st year of Batxillerat named Sergi Ortiz Aparicio.Las aguas residuales de la industria textil han estado estudiadas a lo largo del tiempo debido a los problemas ambientales que genera su vertido en las aguas naturales. El azul de metileno es un colorante catiónico ampliamente utilizado en la industria de papel i del tejido. A pesar de que no se considera un colorante muy tóxico, puede tener distintos efectos nocivos sobre los organismos vivos y, una vez inhalado, puede causar diversos trastornos para la salud humana. En esta experiencia didáctica se explica como encapsular polvo de un residuo de fruta en alginato de calcio y posteriormente se ha estudiado su capacidad de eliminación del azul de metileno en fase acuosa en función de distintos tiempos de contacto. La siguiente experiencia didáctica consta de cinco sesiones con una duración total de 16 horas que se ha extraído del trabajo de investigación llevado a cabo por un alumno de 1º de Bachillerato, Sergio Ortiz Aparici

Degradation of azo dyes by rapidly solidified metallic particles

Azo compounds are one of the most common families of dyes used in textile and leather treatments. An important step during the treatment of water polluted by these compounds, is the degradation of the compounds by decomposition of the -N=N- bonds, producing the de-colorization of the water. This de-colorization reaction can be activated by the presence of zero valent metallic particles. The metastable structures generated during rapid solidification tend to increase the chemical activity of the alloys. Recently, it has been discovered that the use of metallic particles in a metastable phase (amorphous or nanocrystalline) multiplies significantly the efficiency of the decolorization water-treatment step. Here we present the results obtained in the decolorization of water using alloys based on different metals (Fe, Mn, Ni and Al) produced by rapid solidification and posterior ball milling. For some Al-containing alloys the results show a fast reaction, even in neutral pH conditions. In this work, the efficiency of the different metastable alloys in the de-colorization process, the effects of the metastable structure and the processing conditions are presented and assessed.Peer ReviewedPostprint (published version

Dynamic light scattering plus scanning electron microscopy: usefulness and limitations of a simplified estimation of nanocellulose dimensions

Measurements of nanocellulose size usually demand very high-resolution techniques and tedious image processing, mainly in what pertains to the length of nanofibers. Aiming to ease the process, this work assesses a relatively simple method to estimate the dimensions of nanocellulose particles with an aspect ratio greater than 1. Nanocellulose suspensions, both as nanofibers and as nanocrystals, are subjected to dynamic light scattering (DLS) and to field-emission scanning electron microscopy (FE-SEM). The former provides the hydrodynamic diameter, as long as the scatter angle and the consistency are adequate. Assays with different angles and concentrations compel us to recommend forward scattering (12.8°) and concentrations around 0.05–0.10 wt %. Then, FE-SEM with magnifications of ×5000–×20,000 generally suffices to obtain an acceptable approximation for the actual diameter, at least for bundles. Finally, length can be estimated by a simple geometric relationship. Regardless of whether they are collected from FE-SEM or DLS, size distributions are generally skewed to lower diameters. Width distributions from FE-SEM, in particular, are well fitted to log-normal functions. Overall, while this method is not valid for the thinnest fibrils or for single, small nanocrystals, it can be useful in lieu of very high-resolution techniques.Peer ReviewedPostprint (published version

Green synthesis of Ag nanoparticles using grape stalk waste extract for the modification of screen-printed electrodes

The chemical synthesis of silver nanoparticles (Ag-NPs) by using an environmentally friendly methodology for their preparation is presented. Thus, considering that plants possess components that can act as reducing agents and stabilizers in nanoparticles' production, the synthesis of Ag-NPs by using an extract aqueous solution of grape stalk waste as a reducing and capping agent is studied. First, the total polyphenols and reducing sugars contained in the produced extracts at different conditions are characterized. After that, Ag-NPs are synthesized regarding the interaction of Ag ions (from silver nitrate) and the grape stalk extract. The effect of temperature, contact time, extract/metal solution volume ratio and pH solution in the synthesis of metal nanoparticles are also studied. Different sets of nanoparticle samples are characterized by means of Electron Microscopy coupled with Energy Dispersive X-Ray for qualitative chemical identification. Ag-NPs with an average diameter of 27.7 ± 0.6 nm are selected to proof their suitability for sensing purposes. Finally, screen-printed electrodes modified with Ag-NPs are tested for the simultaneous stripping voltammetric determination of Pb(II) and Cd(II). Results indicate good reproducibility, sensitivity and limits of detection around 2.7 µg L−1 for both metal ions

Proposta didàctica : obtenció de nanopartícules de plata a partir d'extracte de te verd

En els darrers temps ha adquirit gran importància la síntesi de nanopartícules metàl·liques a partir d'extractes naturals fornint mètodes de preparació més respectuosos amb el medi ambient (l'anomenada "síntesi verda"). Molts extractes de plantes s'han emprat per obtenir nanopartícules principalment de plata i or. Aquest treball proposa la utilització de te verd com a extracte a partir del qual sintetitzar nanopartícules de plata. Tot i que la bibliografia esmenta ja la síntesi de nanopartícules de plata amb te, tractarem d'aprofundir en les condicions experimentals en què té lloc. La caracterització de les nanopartícules es farà mitjançant la seva absorbància en la regió del visible. Aquesta proposta didàctica està destinada a alumnes de 4t ESO o batxillerat. Per tal de fer un seguiment de l'alumnat i una avaluació formativa de l'activitat es proposa que els alumnes facin un bloc explicatiu de cada etapa de la proposta didàctica.In recent times, the synthesis of metal nanoparticles from natural extracts has become veryimportant, providing more environmentally friendly preparation methods (the so-called "green synthesis").Many plant extracts have been used to obtain nanoparticles, mainly silver and gold. This work proposes theuse of green tea as extract to synthesize silver nanoparticles. Although the literature already mentions thesynthesis of silver nanoparticles with tea, we will try to go in deep into the experimental conditions in which ittakes place. The characterization of the nanoparticles will be done by their absorbance in the visible region.This didactic proposal is addressed to students of 4th ESO and "batxillerat" (upper-secondary education). Inorder to monitor the students and their formative evaluation of the activity, it is proposed to make anexplanatory blog of each stage of the didactic proposal.En los últimos tiempos ha adquirido gran importancia la síntesis de nanopartículas metálicas a partir de extractos naturales proporcionando métodos de preparación más respetuosos con el medio ambiente (la llamada "síntesis verde"). Muchos extractos de plantas se han empleado para obtener nanopartículas principalmente de plata y oro. Este trabajo propone la utilización de té verde como extracto a partir del cual sintetizar nanopartículas de plata. Aunque la bibliografía menciona ya la síntesis de nanopartículas de plata con té, trataremos de profundizar en las condiciones experimentales en las que tiene lugar. La caracterización de las nanopartículas se hará mediante su absorbancia en la región de lo visible. Esta propuesta didáctica está destinada a alumnos de 4º ESO o bachillerato. Con el fin de realizar un seguimiento del alumnado y una evaluación formativa de la actividad se propone que los alumnos hagan un blog explicativo de cada etapa de la propuesta didáctica

Cross-sectional assessment of nut consumption and obesity, metabolic syndrome and other cardiometabolic risk factors: the PREDIMED study

INTRODUCTION: Prospective studies have consistently suggested that nut consumption is inversely related to fatal and non-fatal coronary heart disease. Limited data are available on the epidemiological associations between nut intake and cardiometabolic risk factors. OBJECTIVE: To evaluate associations between frequency of nut consumption and prevalence of cardiometabolic risk factors [obesity, metabolic syndrome (MetS), type-2 diabetes, hypertension, and dyslipidemia] in a Mediterranean population at high cardiovascular risk. MATERIALS AND METHODS: Cross-sectional study of 7,210 men and women (mean age, 67 y) recruited into the PREDIMED study. MetS was defined by the harmonized ATPIII and IDF criteria. Diabetes and hypertension were assessed by clinical diagnosis and dyslipidemia (high triglycerides, low HDL-cholesterol, and hypercholesterolemia) by lipid analyses. Nut consumption was assessed using a validated food frequency questionnaire and categorized as 3 servings/wk. Control of confounding was done with multivariate logistic regression. RESULTS: Compared to participants consuming 3 servings/wk had lower adjusted odds ratios (OR) for obesity (0.61, 95% confidence interval 0.54 to 0.68; P-trend <0.001), MetS (0.74, 0.65 to 0.85; P-trend<0.001), and diabetes (0.87, 0.78 to 0.99; P-trend = 0.043). Higher nut consumption was also associated with lower risk of the abdominal obesity MetS criterion (OR 0.68, 0.60 to 0.79; P-trend<0.001). No significant associations were observed for the MetS components high blood pressure, dyslipidemia, or elevated fasting glucose. CONCLUSIONS: Nut consumption was inversely associated with the prevalence of general obesity, central obesity, MetS, and diabetes in subjects at high cardiovascular risk

Aprofitament de residus vegetals per a la concentració i separació d'ions metàl·lics de solucions aquoses

La adsorció sobre carbó actiu és un tractament habitual para a l'eliminació de metalls contaminants d'afluents aquosos. Amb la finalitat de reduir el cost dels tractament actuals s'està estudiant la utilització d'adsorbents de baix cost com a substituts dels sorbents convencionals que s'utilitzen usualment en els tractaments d'aigües. En aquesta tesi s'ha avaluat la possibilitat d'aprofitar diversos residus vegetals procedents de processos agrícoles o residus industrials, com a sorbents per a l'eliminació de metalls de solucions aquoses. En concret, el treball s'ha centrat en assolir dos grans objectius, primer de tot, conèixer la possibilitat d'utilitzar el pinyol d'oliva com a adsorbent de metalls divalents de solucions aquoses, com són el Cd(II), Cu(II), Ni(II) i Pb(II), i en segon lloc, avaluar la utilització de quatre residus vegetals (escorça de yohimbe, rapa de raïm, suro i pinyol d'oliva) per a l'extracció de Cr(VI) de solucions aquoses i utilitzar el residu vegetal més apropiat com a base per tal d'obtenir un nou sorbent, amb més bona morfologia per ser utilitzat en sistemes d'eliminació de Cr(VI) en continu. Les dades cinètiques d'adsorció es van tractar amb el model cinètic de pseudo-segon ordre, amb el que es van determinar la velocitat inicial d'adsorció dels metalls. Els models d'isotermes d'equilibri de Langmuir i Freundlich es van utilitzar per descriure els equilibris d'adsorció i calcular els paràmetres de les isotermes. En els assajos amb mescles binàries de metalls, els resultats es van tractar amb el model ampliat de Langmuir.En aquest treball s'ha determinat, primerament, que el pinyol d'oliva és un bon sorbent dels metalls divalents estudiats. S'ha determinat que l'adsorció dels metalls varia amb el pH de la solució i que la presència de sals en la solució provoca una davallada en l'adsorció. També es va determinar la competència en l'adsorció entre els metalls al realitzar assajos en mescles binàries.Amb els estudis d'extracció de Cr(VI) amb els quatre materials s'ha determinat que aquests vegetals poden adsorbir el Cr(VI) en solució, tot i que la rapa i la yohimbe són els materials que presenten unes capacitats d'adsorció més elevades. Les anàlisis amb espectroscòpia electrònica de Raig-X realitzats en la rapa de raïm i la yohimbe en contacte amb Cr(VI) varen demostrar la presència del metall en els dos estats d'oxidació, Cr(VI) i Cr(III), evidenciant la participació del mecanisme de reducció de Cr(VI) en l'adsorció del metall sobre els materials.Amb l'encapsulació de la rapa de raïm es va incrementar significativament la capacitat d'adsorció del metall respecta a la seva utilització en la forma original. Les dades experimentals es van tractar amb un model de difusió i es va determinar el coeficient de difusió en l'adsorció en el sorbent amb diferent percentatge de rapa en l'interior.Finalment s'han realitzat estudis preliminars d'adsorció de crom hexavalent en continu utilitzant columnes de petites dimensions farcides amb el sorbent format per boles de rapa encapsulada en alginat càlcic. En aquests assajos s'ha determinat l'efecte en l'adsorció de metall de diversos paràmetres d'operació, com la concentració inicial de metall, el cabal i l'alçada de llit. El model de transferència de matèria i difusió en columna emprat pel tractament de les dades experimentals va mostrar l'efecte de la concentració inicial i del cabal en els coeficients de difusió i transferència de matèria. El model BDST no va predir correctament el temps de servei en els diferents paràmetres d'operació experimentats a causa de la complexitat del procés d'adsorció. Amb aquests assajos preliminars s'han establert les bases de l'adsorció de Cr(VI) amb el nou sorbent en sistemes en continu amb la finalitat de realitzar estudis posteriors d'eliminació del metall en columnes de majors dimensions.Adsorption with activated carbon is a usual treatment to remove metals from wastewater. In order to reduce the cost of the treatment, several studies have been carried out to evaluate the use of low cost sorbents as an alternative to conventional sorbents used in wastewater treatment. In this work, the use of different vegetable wastes from agricultural or industrial processes has been evaluated as sorbents for metal removal from aqueous solutions. The aim of this work was to study first, the usefulness of olive stones as a sorbent for divalent metals such as Cd(II), Cu(II), Ni(II) and Pb(II) from aqueous solutions and then the use of four vegetable wastes (yohimbe bark, grape stalks, cork and olive stones) for the removal of Cr(VI) from aqueous solutions. The vegetable waste powder was encapsulated in calcium alginate to obtain spherical gel beads that were used in continuous flow process for Cr(VI) removal.In all sorption experiments, kinetic data were modeled by the pseudo-second order kinetic equation and determine the constants sorption rates. Langmuir and Freundlich model isotherms were use to describe sorption equilibrium data and to obtain the isotherm parameters. In binary mixtures, the extended Langmuir isotherm model was used. The results showed that olive stones are a good sorbent for studied divalent metal. Metal uptake was pH dependent and the presence of salts in solution provokes a decrease in metal uptake. A clear competence between metals to be adsorbed on the waste was observed in metal binary mixtures. Although results obtained in Cr(VI) removal studies show that the four studied wastes can adsorb Cr(VI), grape stalks and yohimbe bark wastes showed the best chromium sorption capacity. X-Ray Photoelectron Spectroscopy analysis on grape stalks and yohimbe chromium loaded samples put into evidence that both Cr(VI) and Cr(III) were sorbed on wastes surface indicating that Cr(VI) sorption process involves a redox reaction. The gel beads obtained when encapsulating grape stalks in calcium alginate showed a significant increase in Cr(VI) sorption capacity compared to the original grape stalks waste. A diffusion model was used to analyze the experimental data and to determine the diffusion coefficient for Cr(VI) sorption by beads containing different percentage of grape stalks encapsulated in calcium alginate. Finally, preliminary studies of Cr(VI) removal in continuous flow using the beads containing grape stalks powder gel in laboratory columns have been carried out. The effect of operating parameters such as feed metal concentration, flow rate and bed depth was studied. The mass transfer and diffusion model used to describe column data showed the effect of feed metal concentration and flow rate in both, diffusion and mass transfer coefficients, respectively. The bed depth service time model (BDST) failed in predicting the service time when changing operating parameters due to the complexity of the sorption process. With these preliminary column experiments we established the basis for Cr(VI) sorption by the proposed sorbent in continuous flow process for further development of the process to be used in higher scale columns