Ana Urtiaga

Laboratory and pilot plant scale study on the electrochemical oxidation of landfill leachate

Kinetic data regarding COD oxidation were measured in a laboratory scale cell and used to scale-up an electro-oxidation process for landfill leachate treatment by means of boron-doped diamond anodes. A pilot-scale reactor with a total BDD anode area of 1.05 m(2) was designed. Different electrode gaps in the laboratory and pilot plant cells resulted in dissimilar reactor hydrodynamics. Consequently, generalised dimensionless correlations concerning mass transfer were developed in order to define the mass transfer conditions in both electrochemical systems. These correlations were then used in the design equations to validate the scale-up procedure. A series of experiments with biologically pre-treated landfill leachate were done to accomplish this goal. The evolution of ammonia and COD concentration could be well predicted.

Nitrate removal from electro-oxidized landfill leachate by ion exchange

Treatment of landfill leachates by electrochemical oxidation led to the complete removal of chemical oxygen demand and ammonium nitrogen. However, as result of the ammonium oxidation, the partial formation of nitrate ions was observed. Ion exchange technology was investigated as a polishing step in the treatment of landfill leachates. Removal of nitrate from aqueous solutions was studied using two selective anion exchangers: Purolite A 520E and Purolite A 300, under a fixed bed configuration. The following aspects of the ion exchange system were experimentally analyzed: (i) the influence of the presence of other competitive anions in solution, sulfate and chloride, during the loading step, (ii) the breakthrough point and resin saturation as a function of chloride concentration in the feed stream and, (iii) the efficiency of the regeneration step working with NaCl solutions at several concentrations. After a comparison of the experimental results, it was concluded that the resin Purolite A 300 showed a better behavior. Experimental analysis of the equilibrium isotherms made it possible to determine the equilibrium constant (K=3.21) and the maximum capacity (q(max)=183mgg(-1)), important parameters in the design of the treatment process.

Electrochemical treatment of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in groundwater impacted by aqueous film forming foams (AFFFs)

Laboratory experiments were performed to evaluate the use of electrochemical treatment for the decomposition of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), as well as other perfluoroalkyl acids (PFAAs), in aqueous film forming foam (AFFF)-impacted groundwater collected from a former firefighter training area and PFAA-spiked synthetic groundwater. Using a commercially-produced Ti/RuO2 anode in a divided electrochemical cell, PFOA and PFOS decomposition was evaluated as a function of current density (0-20 mA/cm(2)). Decomposition of both PFOA and PFOS increased with increasing current density, although the decomposition of PFOS did not increase as the current density was increased above 2.5 mA/cm(2). At a current density of 10 mA/cm(2), the first-order rate constants, normalized for current density and treatment volume, for electrochemical treatment of both PFOA and PFOS were 46 × 10(-5) and 70 × 10(-5) [(min(-1)) (mA/cm(2))(-1) (L)], respectively. Defluorination was confirmed for both PFOA and PFOS, with 58% and 98% recovery as fluoride, respectively (based upon the mass of PFOA and PFOS degraded). Treatment of other PFAAs present in the groundwater also was observed, with shorter chain PFAAs generally being more recalcitrant. Results highlight the potential for electrochemical treatment of PFAAs, particularly PFOA and PFOS, in AFFF-impacted groundwater.

Definition of a Clean Process for the Treatment of Landfill Leachates Integration of Electrooxidation and Ion Exchange Technologies

Abstract The aim of this work is the definition of a clean process for the treatment of landfill leachates by integration of efficient technologies, namely electrooxidation and selective ion exchange, that reduce the initial concentration of the pollutants and allow re‐use of the treated water. Treatment of the leachates by electrochemical oxidation using a boron doped diamond electrode led to complete removal of chemical oxygen demand and ammonium nitrogen. However, as a result of ammonium oxidation the partial formation of nitrate was observed. Ion exchange removal of nitrate was experimentally analyzed using the selective resin Purolite A520 E obtaining satisfactory results.

Development and validation of a dynamic model for regeneration of passivating baths using membrane contactors

This work aims at the development of a dynamic model for the mathematical description of facilitated transport separation processes carried out in membrane contactors where mass transport phenomena are coupled with chemical reactions. A general model that takes into account the description of all possible mass transport steps and interfacial chemical reactions is initially presented, allowing its application to a wide range of separation processes and operation conditions. The analysis of the specific system under study, regeneration of trivalent chromium spent passivating baths by removal of zinc using the emulsion pertraction technology, allowed to define several assumptions obtaining simplified models with minimum number of uncertain parameters and mathematical complexity. The final equations and parameters were validated with experimental data reported in a previous work (Urtiaga, Bringas, Mediavilla, & Ortiz, 2010).

Development and Validation of a Dynamic Model for Regeneration of Passivating Baths using Membrane Contactors

Abstract Selective liquid membranes have been traditionally employed for liquid/liquid and gas/liquid mass transfer in a wide range of applications. In particular, the Emulsion Pertraction Technology (EPT) using hollow fiber membrane contactors is a promising alternative to carry out the selective separation of metals from complex mixtures. However, the application of a new technology requires of reliable mathematical models and parameters that serve for design and optimization purposes allowing to accurate scale-up processes. This work reports the methodology for the development of a dynamic model to describe the kinetics of the EPT separation-concentration process applied to the regeneration of spent trivalent chromium-based passivating baths. The regeneration stage aims at the selective removal of Zn2+ dragged from previous steps in the plating line, not affecting the level of Cr3+ concentration in the passivating bath. In the case study the mathematical model was initially developed in a rigorous way and in a further analysis, a systematic method for its simplification was established. Then, the system of partial differential and algebraic equations obtained was integrated using the commercial software package ASPEN CUSTOM MODELER (from ASPENTECH) making possible the analysis of the model sensibility under different values of the operation variables. Finally, the model was validated with kinetic data obtained at laboratory scale.