Berta Galán

Assessment of Self-Organizing Map artificial neural networks for the classification of sediment quality.

The application of mathematical tools in initial steps of sediment quality assessment frameworks can be useful to provide an integrated interpretation of multiple measured variables. This study reveals that the Self-Organizing Map (SOM) artificial neural network can be an effective tool for the integration of multiple physical, chemical and ecotoxicological variables in order to classify different sites under study according to their similar sediment quality. Sediment samples from 40 sites of 3 estuaries of Cantabria (Spain) were classified with respect to 13 physical, chemical and toxicological variables using the SOM. Results obtained with the SOM, when compared to those of traditional multivariate statistical techniques commonly used in the field of sediment quality (principal component analysis (PCA) and hierarchical cluster analysis (HCA)), provided a more useful classification for further assessment steps. Especially, the powerful visualization tools of the SOM, which offer more information and in an easier way than HCA and PCA, facilitate the task of establishing an order of priority between the distinguished groups of sites depending on their need for further investigations or remediation actions in subsequent management steps.

Membrane mass transport coefficient for the recovery of Cr(VI) in hollow fiber extraction and back-extraction modules

Abstract This work has been focused to the determination of the membrane mass transport coefficient in the simultaneous non-dispersive extraction and back-extraction of Cr(VI). Following the methodology previously reported by the authors for the kinetic modelling of hollow fiber extraction and back-extraction processes, considering the assumption that the overall mass transport resistance is dominated by the resistance in the organic membrane, when Aliquat 336 is used as carrier, and after the description of the interfacial chemical equilibrium in the extraction process (non-linear model, K eq = 0.35) and in the back-extraction process (linear model, H r = 3.6), it has been possible to describe successfully the experimental results obtaining the optimum value for the membrane mass transport coefficient, K M = 2.2 × 10 −8 m/s, which allows the design and optimization of the recovery of Cr(VI).

Separation of Cr(VI) with aliquat 336: Chemical equilibrium modeling

Abstract The separation of chromium(VI) from industrial wastewaters is of great interest mostly due to the high toxicity of this metal. Although the extraction of Cr(VI) with anionic extractants (and among them, quaternary ammonium salts) has been widely studied using different technologies, a suitable equilibrium model it has not been reported due to the complex behavior of the organic phase. In this work a general methodology for modeling of the chemical equilibrium of Cr(VI) is presented. Discrimination between mathematical models that take account of the nonideal behavior of the organic phase led to the selection of a one-parameter empirical function of the total extractant concentration. K = K ccn o. The parameter values estimated for this model are the equilibrium constant (Kp = 0.197) and the fitting parameter (n = 0.661). and they are used in the expression for the description of the extraction equilibrium: This equation can satisfactorily describe the experimental behavior of chromi-um(VI) extrac...

Potential influence of CO2 release from a carbon capture storage site on release of trace metals from marine sediment

One of the main risks of CCS (Carbon Capture and Storage) is CO(2) leakage from a storage site. The influence of CO(2) leakage on trace metals leaching from contaminated marine sediment in a potential storage area (Northern Spain) is addressed using standardized leaching tests. The influence of the pH of the leaching solution on the leachates is evaluated using deionized water, natural seawater and acidified seawater at pH = 5, 6 and 7, obtained by CO(2) bubbling. Equilibrium leaching tests (EN 12457) were performed at different liquid-solid ratios and the results of ANC/BNC leaching test (CEN/TS 15364) were modeled using Visual Minteq. Equilibrium tests gave values of the final pH for all seawater leachates between 7 and 8 due to the high acid neutralization capacity of the sediment. Combining leaching test results and geochemical modeling provided insight in the mechanisms and prediction of trace metals leaching in acidified seawater environment.

Evaluation through column leaching tests of metal release from contaminated estuarine sediment subject to CO2 leakages from Carbon Capture and Storage sites

The pH change and the release of organic matter and metals from sediment, due to the potential CO(2) acidified seawater leakages from a CCS (Carbon Capture and Storage) site are presented. Column leaching test is used to simulate a scenario where a flow of acidified seawater is in contact with recent contaminated sediment. The behavior of pH, dissolved organic carbon (DOC) and metals As, Cd, Cr, Cu, Ni, Pb, Zn, with liquid to solid (L/S) ratio and pH is analyzed. A stepwise strategy using empirical expressions and a geochemical model was conducted to fit experimental release concentrations. Despite the neutralization capacity of the seawater-carbonate rich sediment system, important acidification and releases are expected at local scale at lower pH. The obtained results would be relevant as a line of evidence input of CCS risk assessment, in an International context where strategies to mitigate the climate change would be applied.

Viability of the separation of Cd from highly concentrated Ni−Cd mixtures by non-dispersive solvent extraction

Abstract The separation of nickel and cadmium from highly concentrated solutions by means of non-dispersive solvent extraction (NDSX) has been studied in this work. Extraction and back-extraction processes were carried out simultaneously in a batch mode using two parallel modules and the organic phase flowing in a closed circuit. Starting with concentrations of 0.37 M of Cd and 0.37–0.68 M of Ni in the feed aqueous phase, 1 M of H 2 SO 4 in the back-extraction phase, and using D2EHPA as extradant, the viability of the separation-concentration of Cd from that mixture has been confirmed. Under the experimental conditions, the separation process was run at a constant rate of mass transport, thus leading to a selectivity factor in the concentration step ρ =67 mol Cd/mol Ni.

Kinetics of the recovery of Cd from highly concentrated aqueous solutions by non-dispersive solvent extraction

Abstract In this paper, the kinetics of the non-dispersive extraction and back-extraction of cadmium from high concentration aqueous solutions using D2EHPA as selective extractant are reported. Batch experiments were performed in order to analyse the influence of the initial Cd concentration in the feed, organic and back-extraction phases. The proposed kinetic model consists of a system of partial differential and algebraic equations describing the mass balances of Cd in the fluid phases of the hollow-fibre contactors and homogenisation tanks. The main hypothesis is that membrane mass transport controls the extraction kinetics. Two design parameters K m , membrane mass transport coefficient, and K eq , equilibrium parameter of the extraction reaction have been calculated from the correlation of the experimental results by the reported model. The comparison of experimental and simulated data confirmed the validity of the kinetic analysis.

Stabilization/solidification of an alkyd paint waste by carbonation of waste-lime based formulations.

The application of solvent-based paints by spraying in paint booths is extensively used in a wide range of industrial activities for the surface treatment of a vast array of products. The wastes generated as overspray represent an important environmental and managerial problem mainly due to the hazardous characteristics of the organic solvent, rendering it necessary to appropriately manage this waste. In this paper a solidification/stabilization (S/S) process based on accelerated carbonation was investigated as an immobilization pre-treatment prior to the disposal, via landfill, of an alkyd solvent-based paint waste coming from the automotive industry; the purpose of this S/S process was to immobilize the contaminants and reduce their release into the environment. Different formulations of paint waste with lime, lime-coal fly-ash and lime-Portland cement were carbonated to study the effect of the water/solid ratio and carbonation time on the characteristics of the final product. To assess the efficiency of the studied S/S process, metals, anions and dissolved organic carbon (DOC) were analyzed in the leachates obtained from a battery of compliance and characterization leaching tests. Regarding the carbonation of paint waste-lime formulations, a mathematical expression has been proposed to predict the results of the leachability of DOC from carbonated mixtures working at water/solid ratios from 0.2 to 0.6. However, lower DOC concentrations in leachates (400mg/kg DOC in L/S=10 batch leaching test) were obtained when carbonation of paint waste-lime-fly-ash mixtures was used at 10h carbonation and water to solid ratio of 0.2. The flammability characteristics, the total contents of contaminants and the contaminant release rate in compliance leaching tests provide evidence for a final product suitable for deposition in non-hazardous landfills. The characterization of this carbonated sample using a dynamic column leaching test shows a high stabilization of metals, partial immobilization of Cl(-), SO(4)(2-), F(-) and limited retention of DOC. However, the obtained results improve the previous findings obtained after the paint waste S/S using uncarbonated formulations and would be a useful pre-treatment technique of the alkyd paint waste prior to its disposal in a landfill.

An integrated mathematical model for chemical oxygen demand (COD) removal in moving bed biofilm reactors (MBBR) including predation and hydrolysis.

An integrated mathematical model is proposed for modelling a moving bed biofilm reactor (MBBR) for removal of chemical oxygen demand (COD) under aerobic conditions. The composite model combines the following: (i) a one-dimensional biofilm model, (ii) a bulk liquid model, and (iii) biological processes in the bulk liquid and biofilm considering the interactions among autotrophic, heterotrophic and predator microorganisms. Depending on the values for the soluble biodegradable COD loading rate (SCLR), the model takes into account a) the hydrolysis of slowly biodegradable compounds in the bulk liquid, and b) the growth of predator microorganisms in the bulk liquid and in the biofilm. The integration of the model and the SCLR allows a general description of the behaviour of COD removal by the MBBR under various conditions. The model is applied for two in-series MBBR wastewater plant from an integrated cellulose and viscose production and accurately describes the experimental concentrations of COD, total suspended solids (TSS), nitrogen and phosphorous obtained during 14 months working at different SCLRs and nutrient dosages. The representation of the microorganism group distribution in the biofilm and in the bulk liquid allow for verification of the presence of predator microorganisms in the second reactor under some operational conditions.

Separation and Concentration of Cr(VI) from Ground Waters by Anion Exchange using Lewatit MP‐64: Mathematical Modelling at Acidic pH

Abstract This work focuses on the study of the removal of Cr(VI) from ground waters and its concentration for reuse by anionic exchanger process using Lewatit MP‐64. Working with a ground water with high Cr(VI) level concentration (200–2000 mg/l), the viability of the two objectives under consideration: (i) Cr(VI) separation until 0.5 mg/l and (ii) concentration up to 5–20 g/l, was checked. After having established the viability, the homogeneous solid diffusion model combined with external mass transfer resistance has been used to describe the mathematical model of the anionic exchange process of Cr(VI) working at acidic pH (1.7).