1,721,047 research outputs found
Sequestering ability of landfill leachate towards toxic metal ions
No full textThe great part of municipal solid wastes is worldwide stored in sanitary landfills. The interaction of organic and inorganic wastes with rainwater produces in the landfill a leachate of extremely variable composition. It depends on several variables such as the type of wastes, the age of landfill, the pH, the redox potential, etc [1-2]. Four are the recognized categories of pollutants in landfill leachate: inorganic macrocomponents, dissolved organic matter (DOM), heavy metals and xenobiotic organic compounds [3]. In particular, heavy metals (arsenic, cadmium, copper, lead, mercury, etc.) are usually present at concentration of few ppb and up to some ppm.
A variable but consistent fraction of DOM is constituted by humic and fulvic-like compounds, formed through a series of biological and chemical processes that involve DOM, especially during the methanogenic phase of wastes decomposition [3]. The great number of binding sites in humic like substances, mainly carboxylic and phenolic groups, are responsible of the high sequestering ability of leachate towards metal ions. As consequence, the speciation scheme of all the toxic metal ions contained in the landfill is strictly influenced by the amount and composition of DOM fraction in leachate.
Due to the imperfections or the possible damages of landfill liners, the leachate can contaminate superficial and ground waters in proximity of the landfill causing serious environmental pollution and human health risks. In a previous study the presence and the amount of landfill leachate, also in trace, on some groundwater samples collected in proximity of Bellolampo landfill was evaluated [4]. The obtained results showed a leachate concentration of ~ 130 μg L-1. Landfill of Bellolampo is a solid waste sanitary landfill near Palermo (Sicily). The landfill has been created in 1960s and become a controlled dump site in 1980s. Previous ICP-OES measurements on Bellolampo leachate have been shown a Pb, Cd and Cu concentrations in the ranges 0.05 - 2.3, 0.02 - 0.12 and 0.02 - 0.6 mg L-1 respectively.
The environmental and health risks related to the presence of toxic heavy metal ions in leachate depends on the species that metals form with the other components and at the conditions of the contaminated groundwater, with particular attention to the amount of free metal ions, the most dangerous among their possible species in aqueous solution.
For this reason, the study of the sequestering ability of landfill leachate towards toxic metal ions is of fundamental importance to establish the environmental impact of leachate contamination. Here we present a potentiometric and voltammetric (Differential Pulse Anodic Stripping Voltammetry, DP-ASV) study on the acid-base properties and on the sequestering ability of leachate samples collected in Bellolampo landfill towards Cd(II), Pb(II) and Cu(II) ions. The voltammetric and potentiometric titrations were carried out in NaCl aqueous solution, at I = 0.1 mol L-1 in order to simulate the mean experimental conditions typical of groundwaters. The acid – base properties of the filtered leachate were compared to those of the soluble fraction of humic substances, with carboxylic and phenolic groups as main binding sites of the macromolecules. Two units namely leach1 and leach2 containing COOH and phenol OH groups, respectively were considered and the Diprotic Like model has been used to process the ISE-H+ potentiometric data [5].
The voltammetric titrations of toxic metal ions solutions with leachate (diluted or as it is) were carried out adjusting the pH of titrand solutions at 5. The results shown an appreciable sequestering ability of leachate towards the heavy metal ions considered and an estimation of the metal complexes stability has been done by calculating rough metal – leachate formation constants
Hydrocarbons removal from wastewater by adsorption onto biochar from Posidonia oceanica
Full text linkEnvironmental pollution by petroleum derivatives is a very current topic. In particular, low concentration of this kind of pollutants can seriously compromise the life of animals and plants of aquatic ecosystems [1]. For this reason, recent environmental legislation imposes severe restriction to oil-in-water content for overboard discharge with concentration limits from 15 to 5 ppm [2]. The shipping industry is trying to adapt to these directives by equipping ships with cleaning treatment devices in which there are several oil removal steps. Usually, the last step of bilge water treatment is based on adsorption onto suitable adsorbent materials that must be able to remove the last and most dispersed oil fraction reducing its concentration within legal limits. In this work, a biochar obtained from pyrolysis of Posidonia oceanica, a Mediterranean sea plant, has been tested as adsorbent material of a synthetic bilge water. The pristine biochar (BCP) was tested as it was and after two chemical activation treatments with sulfuric acid (BCA) and potassium hydroxide (BCB). The adsorbent materials have been characterized by using different techniques (TGA, SEM-EDAX, FT-IR, etc) and their adsorption capacity was studied by batch and column experiments. Oil concentration measurements were performed by using: HPLC-FLD and TOC techniques
Modelling the dependence on medium, ionic strength and temperature of N-acetyl-L-cysteine acid-base properties, and its interactions with Na+, Mg2+, Ca2+ and Zn2+
No full textN-acetyl-L-cysteine (NAC) is the acetylated precursor of L-cysteine, and it is strictly related to glutathione activity. NAC is used in medicine since more than 30 years, primarily as a mucolytic, though its properties are exploited in the treatment of many diseases, such as acute poisoning by acetaminophen (restoring protective levels of glutathione), HIV, contrast-induced nephropathy, type-2 DM (diabetes mellitus), and it also looks promising in the treatment of several psychiatric disorders [1]. This resulted in a huge number of scientific contributions published during the years on NAC (searching in some scientific databases, more than 10000 papers appear).
As expected, most of them are focused on the biological and therapeutic activity of NAC, while relatively few data are reported on the solution chemistry of this molecule, despite the thorough knowledge of its acid-base and coordination behaviour are of fundamental importance for the understanding of its properties in aqueous solution, as biological fluids are. Moreover, the relatively few thermodynamic data available (necessary to assess the speciation of this ligand in the system under study) are reported in single, specific conditions, while it is well known that the most of biological fluids (and natural waters) are, from a chemico-physical perspective, multielectrolyte aqueous solutions of very variable composition, ionic strength, and temperature [2].
Therefore, in this contribution we report the results of an investigation on the modelling of the acid-base properties of NAC in different ionic media (sodium and tetramethylammonium chlorides and tetraethylammonium iodide) at different ionic strengths (0 < I / mol dm-3 ≤ 3.0) and temperatures (283.15 ≤ T / K ≤ 318.15). Due to their importance from a biological perspective, we also report the results on the binding ability of NAC towards Na+, Mg2+, Ca2+ and Zn2+ in NaClaq at T = 298.15 K and different ionic strengths (0 < I / mol dm-3 ≤ 2.0). Surprisingly, despite the importance of these cations and their involvement in many biological mechanisms strictly connected with NAC activity, to our knowledge almost no data (only some for Zn2+) are present in literature on these interactions. The dependence on medium, ionic strength and temperature of the protonation and complex formation constants obtained has been modelled by classical approaches, such as the Extended Debye-Hückel (EDH), Specific ion Interaction Theory (SIT), Pitzer, and by the van’t Hoff equation
Evaluation of adsorption ability of Cyclodextrin-Calixarene Nanosponges towards Pb2+ ion in aqueous solution
Full text linkDifferent cyclodextrin-calixarene nanosponges (CyCaNSs) have been characterized by means of FFC-NMR relaxometry, and used as sorbents to remove Pb2+ from aqueous solutions. Considering that the removal treatments may involve polluted waters with different characteristics, the adsorption experiments were performed on solutions without and with the addition of background salts, under different operational conditions. The adsorption abilities and affinities of the nanosponges towards Pb2+ were investigated by measuring the metal ion concentration by means of Inductively Coupled Plasma Emission Spectroscopy (ICP-OES) and Differential Pulse Anodic Stripping Voltammetry (DP-ASV). The acid-base properties of nanosponges and of metal ion as well as their interactions with the other interacting components of the systems have been considered in the evaluation of adsorption mechanism. Recycling and reuse experiments on the most efficient adsorbents were also performed. On the grounds of the results obtained, post-modified CyCaNSs appear promising materials for designing environmental remediation devices
HYDROCARBONS REMOVAL FROM BILGE WATER BY ADSORPTION ONTO ACTIVATED BIOCHAR FROM POSIDONIA OCEANICA
Full text linkThe normal operations carried out on the boats during navigation generate waste waters such as oily bilge water. The latter is the aqueous mixture of potential pollutants of different origins and types: oily fluids, lubricants and greases, cleaning fluids and other wastes that accumulate in the lower part of the vessel [1,2]. The current legislation provides that they can be discharge directly into the sea if the concentrations of some components are below the expected limits. In particular, with regard to oil / hydrocarbons contamination, the current regulatory limit is 15 mg L-1 of total hydrocarbons. The present work starts from a public/private partnership funded by a grant of the Ministry of Economic Development (MiSE). Among the aims of the project, novel methods shall be tested for the reduction of hydrocarbons concentration at values below 5 mg L-1. Moreover, instrumental techniques able to quickly measure the required low hydrocarbons concentration were tested. Among the different steps of bilge water treatment in pilot plant (coagulation, flotation, centrifugation, adsorption etc.), the latter requires the use of adsorbent materials able to reduce the oily concentration below the legal limits. Here we have hosen, optimized and tested materials obtained from bio-oil production waste, a biochar obtained by pyrolysis of Posidonia oceanica, a marine plant widespread in the Mediterranean sea. means of acid or alkali treatments. Moreover, a commercial activated carbon (Filtrasorb 400) has been used for comparison purpose. Synthetic bilge waters were prepared following the reference standards [3] for the preparation of test fluids (used to test the bilge separator plant), containing DMA (distillate marine fuel) and SLS (sodium lauryl sulfate). Batch adsorption isotherms were carried out without ionic medium and at different ionic strengths in NaCl in order to evaluate the effect of salinity on the adsorption ability of dsorbent materials. The same adsorbents were tested by column experiments. In particular, a bench pilot system was built (Figure 1.) and breakthrough curves were obtained changing amount of adsorbent material in column, flow rate, initial DMA and surfactant concentrations. Several instrumental techniques (turbidimetry, TOC, HPLC-QQQ and HPLC-FLD) have been used to measure surfactant and hydrocarbon concentrations in experimental samples. The batch experimental data were fitted with the most used isotherm models (Langmuir, Freundlich, Sips) and important considerations were made on the breakthrough curves of column experiments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Effect of pH Variations on the Properties of Cyclodextrin‐Calixarene Nanosponges
Full text linkThe pH-responsive properties of cyclodextrin-calixarene nanosponge co-polymeric materials have been investigated. In particular, ISE-H+ potentiometric titrations were carried out in order to evaluate the acid-base properties and the actual amount of ionizable sites present in the materials. Moreover, the relevant pH-dependent adsorption abilities were evaluated towards a set of selected model organic pollutant molecules by means of adsorption tests and by studying the corresponding adsorption isotherms. The latter ones could be suitably described by means of the Freundlich model. The whole of the experimental results enabled us to clarify some general aspects of the microscopic behavior of the nanosponges considered
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