Anaerobic co-digestion of municipal sewage sludge and fruit/vegetable waste: effect of different mixtures on digester stability and methane yield

There are different options for the management of fruit and vegetable wastes (FVWs), but the most environmental-friendly is the anaerobic digestion, because it allows an optimum recovery of materials and energy from the two by-products: biogas and digestate. Nevertheless, in many cases there are economic and technical problems that cause the selection of other alternatives. Frequently these wastes are produced in large quantities but only during few weeks of the year. In these cases, this is the most important economic problem, because large digesters that would be used only for short time periods every year would be required. In addition, a close control of the pH of the digester is required for this kind of residues, for which the hydrolysis is usually faster than the methanogenesis, so large concentrations of fatty acids should be prevented to maintain the adequate pH value for anaerobic digestion that should be neutral or slightly alkaline. Both problems can be simultaneously overcome by the co-digestion with other residues that are produced throughout the year. Among the benefits of co-digestion, one of the most important is the improvement in the feedstock characteristics, since it may allow a more equilibrate composition resulting in a better performance of the digester in treatment capacity, and a better quality of biogas and digestate. The co-digestion with other substrates with a complementary composition that are produced throughout the year and that are already managed by anaerobic digestion is probably the optimum management option. For these cases, if the existing anaerobic digester is oversized and allows the introduction of additional volumes of wastes, the mean retention time of the digestate should be maintained. Therefore, the anaerobic co-digestion of fruit and vegetable waste (FVW) and municipal sewage sludge (MSS) under mesophilic condition and a constant hydraulic retention time (20 d) is studied. The effects on digester performance of the FVW:MSS ratio and the organic loading rate (OLR) were examined. The OLR is the mass of volatile solids fed per volume of digestate and day.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

New Perspectives for Electrodialytic Remediation

Electrodialytic remediation has been widely used for the recovery of different contaminants from numerous matrices, such as, for example, polluted soils, wastewater sludge, fly ash, mine tailing or harbour sediments. The electrodialytic remediation is an enhancement of the electrokinetic remediation technique, and it consists of the use of ion-exchange membranes for the control of the acid and the alkaline fronts generated in the electrochemical processes. While the standard electrodialytic cell is usually built with three-compartment configuration, it has been shown that for the remediation of matrices that require acid environment, a two-compartment cell has given satisfactory removal efficiencies with reduced energy costs. Recycling secondary batteries, with growing demand, has an increasing economic and environmental interest. This work focusses on the proposal of the electrodialytic remediation technique as a possible application for the recycling of lithium-ion cells and other secondary batteries. The recovery of valuable components, such as lithium, manganese, cobalt of phosphorous, based on current recycling processes and the characterization of solid waste is addressed.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778045. Paz-Garcia acknowledges the financial support from the University of Malaga, project: PPIT.UMA.B5.2018/17. Villen-Guzman acknowledges the funding from the University of Malaga for the postdoctoral fellowship PPIT.UMA.A.3.2.2018. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Anionic species transport through the soil (Electromigration versus Electroosmosis): The case of EDTA

The use of EDTA as a complexing agent to extract metals from soil is common. We have tested this possibility for the remediation feasibility studies of a soil contaminated with lead, collected in the mining district of Linares (Spain), a region where the mining activity has been going on for more than 20 centuries. In this work, we have found that close to 100% of Pb is removed from the contaminated soil when EDTA is used in batch reactor experiments. However, almost no Pb is removed when EDTA is used as an enhancing agent in electrokinetic soil remediation of the same soil. The percentage of Pb removed is 0-10% and the analysis of soil after electrokinetic treatment indicates that more than 90% of Pb remains in the soil. Instead, the use of other mobilization agents that gave also good removal yields for the batch reactor experiments gave also important removals by EKR [1]. Usually it is assumed that the removal of toxic metals during EKR take place by electromigration, which is about one order of magnitude more important than any other transport process, such as electroosmosis, diffusion, etc. [2]. Nevertheless, we found that in EKR experiments enhanced with EDTA, the electroosmotic flow is very important and severely impairs the extraction of lead. The negative charge of the complex is probably the main reason for the different behavior relative to the other mobilization agents. REFERENCES: [1] M. Villen-Guzman, J.M. Paz-Garcia, J.M. Rodriguez-Maroto, C. Gomez-Lahoz and F. Garcia-Herruzo. Acid Enhanced Electrokinetic Remediation of a Contaminated Soil Using Constant Current Density: Strong vs. Weak Acid. Separation Science and Technology (in press; DOI 10.1080/01496395.2014.898306). [2] Y.B. Acar, and A.N. Alshawabkeh. Principles of electrokinetic remediation Environ. Sci. Technol. 27(13), 2638-2647. (1993).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Co-digestion of mixed sewage sludge and fruit and vegetables wastes effect of different mixtures on biogas yield

Disposal of fruit and vegetable wastes (FVWs) in landfill site cause serious environmental issues such as contamination of soil, air and ground water. These wastes contain large quantities of biodegradable organic fractions, with high moisture that facilitates their biological treatment. One of the best alternatives to landfill disposal of these wastes is the anaerobic digestion. Therefore, it is one of the most widespread stabilization processes of the sludge in municipal wastewater treatment plants (WWTP). Introduction of FVW in WWTP and co-digestion with mixed sludge (MS) could enhance biogas production and plant economic feasibility. A lab-scale experiment for the anaerobic co-digestion of FVW and municipal mixed sludge under mesophilic condition and 20 days hydraulic retention time is investigated. Initially the digester was fed with mixed sludge (MS) from wastewater treatment plants with an average organic loading rate (OLR) of 0.63 (g L–1 d–1). The co-digestion of mixed sludge and FVW was performed at various organic loading ratios (OLRs), between 0.63 and 5.5 (g L–1 d–1). The experimental specific biogas and methane productions are 0.656 L g–1 and 0.340 L g–1 respectively. Alkalinity and pH remains relatively constant regardless the introduction of different proportions of FVW in the mixture. Co-digestion, compared with the digestion of MS as single substrate, improves the biogas and methane production.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Electrodialytic Recovery of Cobalt from Spent Lithium-Ion Batteries

Contribución en congreso científicoRecycling lithium-ion batteries has an increasing interest for economic and environmental reasons. Disposal of lithium-ion batteries imposes high risk to the environment due to the toxicity of some of their essential components. In addition to this, some of these components, such as cobalt, natural graphite and phosphorus, are included in the list of critical raw materials for the European Union due to their strategic importance in the manufacturing industry. Therefore, in the recent years, numerous research studies have been focused on the development of efficient processes for battery recycling and the selective recuperation of these key components. LiCoO2 is the most common material use in current lithium-ion batteries cathodes. In the current work, an electrodialytic method is proposed for the recovery of cobalt from this kind of electrode. In a standard electrodialytic cell, the treated matrix is separated from the anode and the cathode compartments by means of ion-exchange membranes. A cation-exchange membrane (CEM) allows the passage of cations and hinders the passage of anions, while the behaviour of anion-exchange membrane (AEM) does the opposite. A three-compartment electrodialytic cell has been designed and assembled, as depicted in the figure. In the central compartment, a suspension of LiCoO2 is added. Different extracting agents, such as EDTA, HCl and HNO3, are tested to enhanced the dissolution and the selective extraction of the target metal. Dissolved cobalt-containing complexes migrate towards the cathode or the anode compartments depending on the ionic charge of the complexes. While cobalt extraction via extracting agents is an expensive treatment, as it requires the constant addition of chemicals, an efficient electrodialytic cell could allow the recirculation of the extracting agents and the economical optimization of the process.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778045. Paz-Garcia acknowledges the financial support from the University of Malaga, project: PPIT.UMA.B5.2018/17. Villen-Guzman acknowledges the funding from the University of Malaga for the postdoctoral fellowship PPIT.UMA.A.3.2.2018. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Anaerobic co-digestion of pear residues and sewage sludge using a CSTR digester. Influence of the feed procedure

Anaerobic co-digestion of pear residues with sewage sludge is feasible. Important differences are obtained from the two feed regimes tested, with better results for the so-called continuous feed. The organic loading rate (OLR) is the important parameter for the methane productionUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The use of available chemical equilibria software for the prediction of the performance of EKR

Risk assessment aims for the prediction of the mobility of contaminants, and these are usually based in lab essays together with mathematical modelling. Also the feasibility studies of most techniques, require similar tools. Frequently the lab characterization is based in the chemical fractionation of the contaminants based on their mobility under different chemical reagents. Probably the most frequent fractionation technique for heavy metal contaminated soils is the BCR [1]. The use of chemical equilibria software helps to understand the processes involved in the contaminant transport during electrokinetic remediation. Most mathematical models used for the simulation of electrokinetic decontamination assume local equilibrium between the chemicals present in the aqueous phase. In other cases also equilibrium is supposed between the chemical species present in the aqueous phase and the solid matrix. In this work, we compare the results of batch extraction experiments with those obtained using Visual MINTEQ [2]. This is a free software that allows a reliable simulation of the chemical processes involved in the water-soil systems such as solubility, sorption, etc. We found that even when the main contaminant behaviour is in accordance with the local equilibrium assumption, the mobilization of other metals, such as Ca and Mg, that are also present in important concentrations, are affected by kinetic limitations. These kinetic limitations have important effects in the overall behaviour of the system. Thus, if ignored, important flaws will appear in the predictions of the model with respect to those toxic species that could be considered to behave under local equilibrium. [1] M. Villen-Guzman, J.M. Paz-Garcia, J.M. Rodriguez-Maroto, C. Gomez-Lahoz and F. Garcia-Herruzo. Acid Enhanced Electrokinetic Remediation of a Contaminated Soil Using Constant Current Density: Strong vs. Weak Acid. Separation Science and Technology (in press; DOI 10.1080/01496395.2014.898306). [2] J.P. Gustafsson, Visual MINTEQ ver. 3.0beta. KTH Royal Institute of Technology, Dept. of Land and Water Resources Engineering, Stockholm, Sweden. (2010) http://www2.lwr.kth.se/English/OurSoftware/vminteq/index.htmlUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Modeling of Electrodialytic Treatment of Lithium-Ion Batteries

Lithium-ion batteries are currently present in most portable electronic devices and their use is rapidly growing in the field of electric vehicles and renewable energy storage. Many components in lithium-ion batteries are toxic and/or environmentally hazardous. Furthermore, some of them are expensive and listed as critical materials in terms of supply-chain risk. Therefore, the need to improve the recycling techniques for lithium-ion batteries is becoming a priority. Herein, we describe and present a model for the electrodialytic treatment of disposed lithium-ion batteries. Electrodialysis is a separation process based on the use of electric fields and ion-selective membranes. The electrodialytic cell can be designed in different configurations, to enhance the selective extraction of the target products. In a standard electrodialytic cell, the treated matrix is separated from the anode and the cathode compartments by means of anion- and cation-exchange membranes respectively. However, depending on the ionic charge and the specific chemistry of the matrix, different cell designs can be used. In the present work, different possible configurations are explored for the optimization of the extraction of key valuable components from spent lithium-ion batteries, taking into account the chemical properties of the system depending on the chosen extracting agent and cell configuration. The model presented here is based on a set of differential and algebraic equations consisting of a Nernst-Planck based continuity equations for each of the chemical species involved in the process, coupled with the electroneutrality and the local chemical equilibrium conditions. The numerical solution is performed using COMSOL Multiphysics, and the simulation results are compared with experimental data for model validation.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778045. Paz-Garcia acknowledges the financial support from the University of Malaga, project: PPIT.UMA.B5.2018/17. Villen-Guzman acknowledges the funding from the University of Malaga for the postdoctoral fellowship PPIT.UMA.A.3.2.2018. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

A Model for Electrodialytic Treatment of Lithium-Ion Batteries

New recycling processes for secondary batteries are needed to achieve sustainable use of natural resources. Indeed, many components in lithium ion batteries, such as cobalt and graphite, are in the European Union’s “Critical Raw Materials” list. Electrodialytic treatment of disposed lithium-ion batteries is a pioneer proposal for the selective recovery of some of these relevant elements. In this work, a model for the electrochemical technology of disposed batteries implemented using COMSOL Multiphysics is presented. The main aim of this model is the optimization of the extraction of valuable components from spent batteries and the prediction of experimental results, which entails a better understanding of the different process involved. The model is based on the Nernst-Planck- Poisson system of equations coupled with the local chemical equilibrium conditions. The model uses multi-scale discretization of the different components; including the assumed well-stirred compartments, the ion-exchange membranes and the diffuse double-layer at the surface of the membranes. Different cell configuration has been tested, and results were compared to experimental data for model validation.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. The authors acknowledge the financial support from the "Plan Propio de Investigación de la Universidad de Málaga" with project numbers PPIT.UMA.D1, PPIT.UMA.B1.2017/20 and PPIT.UMA.B5.2018/17. This work has also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778045