Electrodialytic Removal of Cadmium from Brackish Water: Effects of Operating Parameters

The continuous increase of environmental regulations make interesting to find effective and efficient methods for processing effluents containing metal ions. This research focuses on cadmium removal from brackish water by an electro-membrane process: The electrodialysis. Experiments were carried out on synthetic brackish water solutions and using a laboratory scale electrodialysis system. The influence of several parameters on process efficiency was investigated. The efficiency of this process was assessed by the determination of five parameters: The demineralization rate, the removal rate and the transport flux of cadmium, the current efficiency and the specific power consumption. The applied voltage, the feed flow rate, the pH and cadmium initial concentration of the feed solution have a significant effect on the process efficiency and mainly on the cadmium transfer from dilute to concentrate compartment. In contrast, feed ionic strength seems to affect only the SPC and not the R(Cd)

Energy generation and storage by salinity gradient power: A model-based assessment

Three energy storage systems based on mixing and desalination of solutions with different salt concentrations are presented, namely, reverse electrodialysis, pressure retarded osmosis and capacitive Donnan potential, coupled to their corresponding desalination technologies: electrodialysis, reverse osmosis and membrane capacitive deionisation. Conceptual mathematical models are used to assess power densities and efficiency, and to address the influence on the performance of factors such as temperature and residence time. The maximum power densities for electrodialysis, osmotic and capacitive energy storage systems are calculated as 4.69, 4.83 and 0.503 W m−2, respectively, at 25 °C and residence time of 20 s, corresponding to an average fluid velocity of 5 mm/s. In order to achieve competitive economic energy (in the EU) with this power density, the membrane price needs to be lower than 2.9, 3.0 and 0.31$m−2, for each of the technologies. Utilisation of waste heat to increase the temperature to 60 °C increases the power density to 8.54, 6.04 and 0.708 W m−2, which allows for 25$ m−2), and over 80% and 40% higher price (5.2 and 0.43$ m−2) for the ionic exchange membrane used in the electrodialytic and capacitive energy storage system respectively, while still having economic energy production. Advantages and disadvantages of the proposed energy storage systems are discussed, along with the cost evaluation for each technology.publishedVersion© 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/)

Separation Of Bioactive Peptides From Whey Hydrolysate Using Electrodialysis With Ultrafiltration Membrane: A Pilot-Scale Study And Investigation On Process Parameters

A tryptic hydrolysis of whey protein isolate has generated 19 peptides from β-lactoglobulin source, out of 27 peptide sequences detected under HPLC-MS. Amongst 19 peptides, 12 were detected as anionic peptides and 5 as cationic peptides. The aim of this work was to investigate the process parameters for fractionating bioactive peptides from protein hydrolysate by pilot-scale electrodialysis with ultrafiltration membrane (EDUF) unit. Preliminary tests were performed to evaluate process parameters. A pressure-flow relation was studied for establishing no transmembrane pressure. Protein hydrolysate was fractionated during 60 minutes by EDUF on a pilot-scale EUR6 module. Under a constant pH of 6 and electric field strength of 0.7 V/cm, peptide migration rates of 0.57 ± 0.25!!/!!ℎ and 0.29 ± 0.09!!/!!ℎ were achieved in anionic and cationic peptides recovery compartments respectively. An experiment was also further investigated under two electric field conditions: pulsed electric field (PEF) and reverse polarity (RP) to observe the effect on migration rate and selectivity. Total migration rates were found to be 0.51 ± 0.05 and 0.38 ± 0.15 !/!!ℎ under PEF and RP conditions, respectively. An application of PEF and RP were able to separate selectively few of peptides. Peptide migration rate and selective separation of peptides found to be strongly depended on electric field strength and pressure/flow rate in each compartment. It is the low electric field and relatively higher pressure that hinders the simultaneous separation of anionic and cationic peptides in their respective compartment. To our knowledge, it was the first attempt to study separation of bioactive peptides from whey protein isolate in a pilot scale EDUF module

Novel Separation Methods using Electrodialysis/Electrodeionization for Product Recovery and Power Generation

The use of electrodialytic separations for the purification of products has been a vital technique for the past 50 years in the chemical industry. Originally used for demineralization and desalination, electrodialysis and its counterparts have expanded to assist in product purification, waste and hazard removal, and power generation. This research focused on the development of high purity organic acids purification with low power requirements. Work resulted in the development of a new type of electrodialysis process, specifically the use of ionic liquids as a secondary solvent for the development of dual solvent electrodialysis. Through dual solvent electrodialysis, ions were recovered and concentrated from products streams while enacting a solvent change. This allowed the requirements and scope of secondary purification steps to be greatly reduced and, in some cases, no longer necessary. Application of ion exchange wafers further improved separation performance of dual solvent electrodialysis. This electrodeionization technique resulted in separation efficiencies and power consumption levels similar to those of commercially implemented organic acid recovery methods with reduced complexity. Additional efforts in power generation through a technique known as reverse electrodialysis were also pursued and a discussion on the implication technology on meeting future energy demands will presented. Through this research, new avenues and applications for electrodialytic separation are now possible

Mass transfer in the electrodialytic desalination of brackish water and a correlation of experimental data with theory

The object of this work is an experimental investigation into the possibility of obtaining an increase in mass transfer in the electrodialysis of brackish water by altering the physical character of the selective membrane, and a correlation of experimental mass transfer data with theory --Introduction, page 1

Electrokinetic treatment of environmental matrices. Contaminants removal and phosphorus recovery

There is a need to develop viable techniques for removal and recovery organic and inorganic compounds from environmental matrices, due to their ecotoxicity, regulatory obligations or potential supplies as secondary materials. In this dissertation, electro –removal and –recovery techniques were applied to five different contaminated environmental matrices aiming phosphorus (P) recovery and/or contaminants removal. In a first phase, the electrokinetic process (EK) was carried out in soils for (i) metalloids and (ii) organic contaminants (OCs) removal. In the case of As and Sb mine contaminated soil, the EK process was additionally coupled with phytotechnologies. In a second phase, the electrodialytic process (ED) was applied to wastes aiming P recovery and simultaneous removal of (iii) toxins from membrane concentrate, (iv) heavy metals from sewage sludge ash (SSA), and (v) OCs from sewage sludge (SS). EK enhanced phytoremediation showed to be viable for the remediation of soils contaminated with metalloids, as although remediation was low, it combines advantages of both technologies while allowing site management. EK also proved to be an effective remediation technology for the removal and degradation of emerging OCs from two types of soil. Aiming P recovery and contaminants removal, different ED cell set-ups were tested. For the membrane concentrates, the best P recovery was achieved in a three compartment (3c) cell, but the highest toxin removal was obtained in a two compartment (2c) cell, placing the matrix in the cathode end. In the case of SSA the best approach for simultaneous P recovery and heavy metals removal was to use a 2c-cell placing the matrix in the anode end. However, for simultaneous P recovery and OCs removal, SS should be placed in the cathode end, in a 2c-cell. Overall, the data support that the selection of the cell design should be done case-by-case

Electrodialytic recovery of rare earth elements from coal ashes

Fundação para a Ciência e a Tecnologia, I.P., Portugal, UIDB/04085/2020 (Research unit CENSE “Center for Environmental and Sustainability Research”). Fundação para a Ciência e a Tecnologia is also acknowledged for N. Couto Contract established under Individual Call to Scientific Employment Stimulus (CEECIND/04210/2017).Rare earth elements (REE) are critical raw materials crucial for modern technologies and used in a variety of industries. There is a need of investment in REE recovery from secondary sources. The present work was designed to assess the potential of the electrodialytic process to recover REE from coal ash. The content of REE was evaluated in bituminous and anthracite ash. Anthracite presented higher REE concentration (447 ppm vs. 138 ppm) and a triple concentration of critical REE compared with bituminous ash. Anthracite ash was treated aiming to test the REE recover potential, including differences between light REE (LREE) and heavy REE (HREE) fractions as well as the specific recovery of REE with high criticality. A two-compartment electrodialytic cell was tested with the matrix placed in the anode compartment and a cation-exchange membrane separating the compartments. Experiments lasted a maximum of 7 days applying different current intensities and pH adjustment in the catholyte (≈ 2). Three main steps are observed in the removal process 1) REE solubilization - from the solid to the liquid phase (anolyte); 2) REE mobilization - movement from the anolyte towards the cathode end; 3) REE removal - presence in the catholyte. The extent of each step observed for the REE depends on their individual position in the periodic table with HREE removal being more regulated by step 1 and LREE by step 2. At the best tested conditions (50 mA, 3 days, pH adjustment), more than 70% of REE were extracted from the ash with the catholyte enclosing up to ≈ 50% of LREE and HREE. Combining the high criticality of neodymium with its high concentration in anthracite coal ash (65 ppm), the electrodialytic treatment is highly recommended to concentrate this REE in the catholyte. The results demonstrated the proof-of-concept for electro-assisted extraction of REE from anthracite coal ash, opening perspectives to a selective recovery of these elements from secondary sources.authorsversionpublishe

Recuperação de fósforo de digestato de resíduos urbanos com vista à sua valorização como fertilizante

Phosphorus (P) is a vital nutrient for plant development and food production. It is a key fertilizer constituent and no feasible substitute has been found yet. P is mainly obtained from phosphate rock, which is a non-renewable resource. This raises the critical issue of ensuring a continuous supply of P-fertilizers to feed mankind in the future. Therefore, it is of utmost importance to promote the circularity of P by recycling and recovering P from waste streams. The municipal solid waste (MSW) digestate is the result of the anaerobic digestion of MSW. It contains P but also contaminants, so currently it is mostly sent to landfill. This raises the question of how feasible is the extraction of P from MSW digestate for the production of a high-quality fertilizer. The present research is focused on MSW digestate utilization as a secondary P resource. In this PhD thesis, the extraction of P from MSW digestate using the electrodialytic (ED) process combined with struvite formation is explored for the first time. The ED process allows the separation of anions (e.g. PO4 3-) and cations (e.g. metals like Cu2+) present in MSW digestate by selectively transporting them across ion-exchange membranes under the influence of an electric field. Considering this extraction principle, P extraction experiments were conducted at lab-scale attempting to reach three purposes: i) extraction of the P available in the MSW digestate, ii) optimization of the energy performance of the ED process and iii) improvement of ED process, allowing also to recover nitrogen (N) from MSW digestate. The ED-extracted P was used for the synthesis of secondary struvite (MgNH4PO4·6H2O), through chemical precipitation. Alternative sources of N and magnesium (Mg) needed for the synthesis of struvite were explored, named seawater (as Mg source) and N contained in the MSW digestate itself. Acting as a slow-release fertilizer, struvite releases nutrients to the soil along the time. The agronomic efficacy of the secondary struvite, obtained using the P extracted from MSW digestate was assessed, first in incubation trials (to study the evolution with time of P in the soil) and then in pot trials, where plant growth in struvite fertilized soils and in soils fertilized with a commercial fertilizer was compared. The research findings show that up to 90% of P present in MSW digestate could be extracted using ED and converted to struvite. Being a negatively charged specie, P moved from the MSW digestate and concentrated in the anolyte solution when a 50 mA electric current (1.0 mA cm-2) was applied. During ED process, the extraction of P was strongly dependent on the pH of MSW digestate, and a low pH (2.5-3.0) was needed to enhance the P solubilization from the MSW digestate. This was achieved by using the electrochemical reaction occurring at the anode (originates H+ ions), thus avoiding the addition of chemicals. The benefit of this electrochemical reaction was fundamental for the implementation of another strategy for P extraction: a dual-stage approach. In the first stage, the electrode (+) was placed in contact with the MSW digestate, causing a faster acidification of the digestate while P remains in this compartment. When the pH reached 3 in the MSW digestate suspension, the electrode (+) was moved into the anolyte compartment and the solubilized P migrated from the MSW digestate compartment to the anode compartment. This strategy effectively reduced the time required for the ED extraction of P (to 7 days) and consequently decreased the energy consumption (≈30%). The extraction of another important nutrient, N, from MSW digestate was also pursued by adding a gas permeable membrane (GPM) to the cathode of the ED cell, while the extraction of P was taking place. N moved from the MSW digestate into the cathode compartment as NH4 + (by electromigration), and there it was converted to gaseous NH3 and collected by the GPM into a clean N solution, leaving behind the heavy metals at the cathode solution. The clean N solution was subsequently used with success as a source of N in the synthesis of secondary struvite. The combination of these two membrane technologies - ED and GPM - for simultaneous extraction of P and N was explored in this work for the first time, and contributed to the sustainability of the synthesis of secondary struvite. The secondary struvite produced in this work using P recovered from MSW digestate proved to be of high quality, even when alternative materials were used instead of synthetic ones during its precipitation. Its action as an effective P biofertilizer is similar to that of a commercial synthetic fertilizer. The major outcome of this work is the proof of concept of an innovative process that combines ED and GPM for the recycling of P from MSW digestate. The contaminant-free biofertilizer, produced at lab scale, widens the possibilities for the large scale recycling of P and for the implementation of efficient strategies to close P-nutrient cycling, thus contributing to a more sustainable resource management.O fósforo (P) é um nutriente vital para o desenvolvimento das plantas e a produção de alimento. É um dos principais constituintes dos fertilizantes e até ao momento ainda não foi encontrado nenhum outro elemento que o possa substituir. O P é obtido principalmente da rocha fosfatada, que é um recurso não renovável. Isto suscita uma questão fundamental sobre como garantir um fornecimento contínuo de P para a produção de fertilizantes fosfatados necessários para produzir alimento para a humanidade, no futuro. Portanto, é de extrema importância promover a circularidade do P por meio da sua reciclagem e da recuperação a partir de fluxos de resíduos. O digestato de resíduo urbano (RU) é o resultado do processo de digestão anaeróbia. Este contém P, mas também contaminantes, pelo que atualmente, o digestato de RU é na maioria das vezes encaminhado para aterro. Isto levanta a questão de saber quão viável é a extração do P do digestato de RU para a produção de um fertilizante de elevada qualidade. O presente trabalho de investigação é focado na utilização do digestato de RU como um recurso secundário de P. Nesta tese é explorada pela primeira vez a extração de P do digestato de RU utilizando o processo electrodialítico (ED) combinado com a precipitação de estruvite. O processo ED permite a separação de aniões (p. ex. PO4 3-) e catiões (p. ex., metais como Cu2+) presentes no digestato de RU, transportando-os seletivamente através de membranas de troca iónica, sob a influência de um campo elétrico. Considerando este princípio, as experiências de extração de P foram realizadas à escala laboratorial, tendo em conta três objetivos: i) a extração do P disponível no digestato de RU, ii) a otimização do desempenho energético do processo ED e iii) a melhoria do processo ED através da conjugação com a recuperação do azoto (N) do digestato de RU. O P extraído durante o processo ED foi utilizado para a síntese de estruvite secundária (MgNH4PO4·6H2O), através do processo de precipitação química. Para a síntese desta estruvite foram exploradas fontes alternativas de N e magnésio (Mg), nomeadamente a água do mar (como fonte de Mg) e o N contido no próprio digestato de RU. A estruvite é um fertilizante de libertação lenta, o que significa, que fornece nutrientes ao solo ao longo do tempo. A eficácia agronómica da estruvite secundária, obtida com o P extraído do digestato de RU, foi avaliada, primeiramente em ensaios de incubação (para estudar a evolução do P no solo, ao longo do tempo) e depois em ensaios em vaso, onde o crescimento da planta num solo fertilizado com estruvite e num solo fertilizado com um fertilizante comercial foi comparado. Os resultados mostram que cerca de 90% do P que está presente no digestato de RU pode efetivamente ser extraído através do processo ED e convertido em estruvite. Por ser uma espécie carregada negativamente, o P foi extraído do digestato do RU e foi concentrado no anólito, após ter sido aplicada uma corrente elétrica de 50 mA (1,0 mA cm-2). Durante o processo ED observou-se que a extração de P era fortemente dependente do pH do digestato de RU, e que era necessário um pH baixo (2,5-3,0) para aumentar a sua solubilização. Isto foi conseguido através da utilização da reação eletroquímica que ocorre no ânodo (origina iões H+ ), o que evitou a adição de produtos químicos. Os efeitos benéficos desta reação eletroquímica foram fundamentais para a implementação de uma outra estratégia para a extração de P: uma extração em duas fases. Na primeira etapa, o elétrodo (+) foi colocado em contato com o digestato de RU, o que causou uma acidificação mais rápida do digestato enquanto o P permaneceu neste compartimento. Quando o pH da suspensão de digestato de RU atingiu o valor de 3, o elétrodo (+) foi movido para o compartimento do anólito e o P que tinha sido solubilizado durante a primeira etapa migrou do compartimento de digestato de RU para o compartimento do anólito. Esta estratégia permitiu uma redução efetiva do tempo necessário para a extração de P pelo processo ED (para 7 dias) e, consequentemente, uma diminuição do consumo de energia (≈30%). A extração de outro nutriente importante, o N, do digestato de RU também foi realizada, ao mesmo tempo que ocorria a extração de P, adicionando uma membrana permeável a gases (GPM) ao cátodo da célula electrodialítica. O N era extraído do digestato de RU para o compartimento do cátodo, na forma de ião NH4 + (por electromigração), e lá era convertido em NH3 gasoso e capturado pela GPM produzindo uma solução limpa rica em N, deixando para trás os metais pesados na solução do cátodo. A solução limpa rica em N foi subsequentemente usada com sucesso como fonte de N na síntese de estruvite secundária. A combinação destas duas tecnologias de membrana - ED e GPM - para extração simultânea de P e N foi explorada neste trabalho pela primeira vez, e contribuiu para a sustentabilidade da síntese de estruvite secundária. Neste trabalho, a estruvite secundária produzida utilizando o P recuperado do digestato de RU apresentou uma elevada qualidade, mesmo quando durante a sua precipitação foram utilizados materiais alternativos em vez de materiais sintéticos. A sua ação como um biofertilizante fosfatado foi semelhante à de um fertilizante sintético comercial. O principal resultado desta tese é a prova de conceito de um processo inovador que combina a técnica electrodialítica com uma membrana permeável a gases para a reciclagem de P a partir do digestato de RU. O biofertilizante livre de contaminantes, produzido à escala de laboratório, amplia as possibilidades para a reciclagem do P em larga escala e para a implementação de estratégias eficientes para fechar o ciclo do nutriente P, contribuindo assim para uma gestão mais sustentável dos recursos.Programa Doutoral em Ciências e Engenharia do Ambient