Chemical and energy recovery alternatives in SWRO desalination through electro‐membrane technologies

Electro-membrane technologies are versatile processes that could contribute towards more sustainable seawater reverse osmosis (SWRO) desalination in both freshwater production and brine management, facilitating the recovery of materials and energy and driving the introduction of the circular economy paradigm in the desalination industry. Besides the potential possibilities, the implementation of electro-membrane technologies remains a challenge. The aim of this work is to present and evaluate different alternatives for harvesting renewable energy and the recovery of chemicals on an SWRO facility by means of electro-membrane technology. Acid and base self-supply by means of electrodialysis with bipolar membranes is considered, together with salinity gradient energy harvesting by means of reverse electrodialysis and pH gradient energy by means of reverse electrodialysis with bipolar membranes. The potential benefits of the proposed alternatives rely on environmental impact reduction is three-fold: (a) water bodies protection, as direct brine discharge is avoided, (b) improvements in the climate change indicator, as the recovery of renewable energy reduces the indirect emissions related to energy production, and (c) reduction of raw material consumption, as the main chemicals used in the facility are produced in-situ. Moreover, further development towards an increase in their technology readiness level (TRL) and cost reduction are the main challenges to face.This research was funded by MICIU (Spanish Government) under project CTM2017-87850-R. M.H.-G. research was funded by the Counseling of Universities, Equality, Culture and Sports (Cantabrian Government) under the Augusto González de Linares postdoctoral grant

Risk assessment of total petroleum hydrocarbons (TPHs) fractions

Leakages of oil products derived from petroleum can affect the environment, even causing risks to human. In order to study all the substances that usually are found in a petroleum leakage, it becomes interesting to apply the study to the Total Petroleum Hydrocarbons (TPH) fractions which have similar physico-chemical properties. The purpose of this paper is to perform a suitable risk specific site analysis for TPH fractions distribution and concentration, applying the RBCA (Risk Based Corrective Action) framework. As a case of study, this work is applied to a high populated area of a Spanish medium size city (Santander, approximately 182000 inhabitants). This simulation provides useful information about the pathways with higher risks, enabling to focus the analysis onto the parameters that mainly affect the risk assessment. This approach will simplify future site specific risk assessment and the corresponding decision making.The authors are grateful for the financial support provided by the Spanish MARM under project 276/PC08/2-01.2 and MICINN under project CTM2006-0317

Reverse electrodialysis: potential reduction in energy and emissions of desalination

Salinity gradient energy harvesting by reverse electrodialysis (RED) is a promising renewable source to decarbonize desalination. This work surveys the potential reduction in energy consumption and carbon emissions gained from RED integration in 20 medium-to-large-sized seawater reverse osmosis (SWRO) desalination plants spread worldwide. Using the validated RED system’s model from our research group, we quantified the grid mix share of the SWRO plant’s total energy demand and total emissions RED would abate (i) in its current state of development and (ii) if captured all salinity gradient exergy (SGE). Results indicate that more saline and warmer SWRO brines enhance RED’s net power density, yet source availability may restrain specific energy supply. If all SGE were harnessed, RED could supply ~40% of total desalination plants’ energy demand almost in all locations, yet energy conversion irreversibility and untapped SGE decline it to ~10%. RED integration in the most emission-intensive SWRO plants could relieve up to 1.95 kg CO2-eq m−3. Findings reveal that RED energy recovery from SWRO concentrate effluents could bring desalination sector sizeable energy and emissions savings provided future advancements bring RED technology closer to its thermodynamic limit.This research was funded by the LIFE programme (LIFE19 ENV/ES/000143) and the Spanish Ministry of Science, Innovation and Universities (RTI2018-093310-B-I00 and CTM2017-87850-R, and the FPI grant awarded to C.T., PRE2018-086454)

Electrodialysis with bipolar membranes for valorization of brines

Several industrial processes, such as desalination or neutralization, generate brines defined as concentrated solutions of salts in water, usually NaCl, typically discharged in the vicinities of the desalination plant or factory. To reduce the environmental impact and promote the valorization of the wasted resources, alternatives must be sought. Among sustainable alternatives for the recovery of brines, the possibility of using Electrodialysis with Bipolar Membranes (EDBM) is of interest, because it allows recovering brines as useful acids and bases. This review focuses on the discussion of the technical aspects of the EDBM as a means to treat streams rich in NaCl from reverse osmosis desalination and industrial processes in order to complete the direct delivery of chemicals for self-supply. The main environmental issues associated with desalination brine disposal are presented. The state-of-the-art of valorization of brines by EDBM to acids and bases is completed. This work concludes with an in-depth discussion of the technical, techno-economic and economic barriers that prevent the widespread use of EDBM technology.The authors gratefully acknowledge the funding for the projects CTQ2013-48280-C3-1-R-D and CTM2014-57833-R. Carolina Fernandez-Gonzalez also thanks the Spanish Ministry of Economy and Competitiveness for the FPI grant awarded BES-2012-053461

Selective lithium separation from desalination concentrates via the synergy of extractant mixtures

Seawater reverse osmosis (SWRO) desalination plants generate high volumes of concentrates, which contain, in addition to major salts, some elements of growing interest in minor concentrations. This is the case of lithium, highly demanded in the battery industry. In this work, the separation of Li+ from model SWRO brines has been evaluated by obtaining Li+ extraction curves with the combination of extractants DBM-TOPO and FDOD-TOPO, proving that both mixtures are capable of extracting Li+ under basic pH conditions, due to the keto-enolic tautomerism of the b-diketones. Li+ extraction values of 95.4 % for DBM-TOPO (pH = 12.2) and 100 % for FDOD-TOPO (pH = 9.0) were achieved. This behaviour was verified by the FT-IR analysis of the sample before and after the Li+ extraction. Finally, the selective separation of Li+ against other cations, such as Na+, K+, Mg2+, Ca2+ and Sr2+, present in the model brines at higher concentrations, was determined. Under mentioned experimental conditions, these cations are not extracted, reaching to Li+ selective separation close to 100 %. This study shows the first results on the selective extraction of lithium in complex SWRO brines, fostered through promising extractants mixtures showing a synergic effect towards Li+ in such multicomponent matrices.This research was developed in the framework of the projects PID2020-115409RB-I00, PDC2021-120786-I00 and TED2021-129874B-I00 financed by the Ministry of Science and Innovation (Spain). Elena Fernández-Escalante is grateful for the predoctoral contract PRE2021-100160

Hydrocarbons analysis for risk assessment in polluted soils

Policies for contaminated site management in Europe are evolving from total concentration-based of pollutants policies to risk-assessment policies. Leakages of petroleum products are usually composed of many different substances, usually grouped into the parameter Total Petroleum Hydrocarbons (TPH). However, to carry out a suitable risk assessment TPH must be divided into different fractions, according to their physicochemical properties. The purpose of this work is to develop an analytical method for the characterization of TPH fractions taking soils from a high populated area of a Spanish medium size city. Results allow determining which product was released depending on each fraction percentage and it can be compared to the regulation to determine the actions that must be performed. If the action is the risk assessment, TPH fractions are suitable for this task, enabling a detailed study of TPH risks for human health and the environment.The authors are grateful for the financial support provided by the Spanish MARM under project 276/PC08/2-01.2 and MICINN under project CTM2006-0317

Modeling of lactic acid rejection from lactose in acidified cheese whey by nanofiltration

The continuously increasing demand of lactic acid opens a window for the integration of membrane technology in the dairy industry, improving the sustainability by avoiding the use of large amounts of chemicals and waste generation. Lactic acid recovery from fermentation broth without precipitation has been studied by numerous processes. In this work, a commercial membrane with high lactose rejection and a moderate lactic acid rejection, enabling a permselectivity up to 40%, is sought to perform the simultaneous removal of lactic acid and lactose separation from the acidified sweet whey from mozzarella cheese production in a single stage. The AFC30 membrane of the thin film composite nanofiltration (NF) type was selected because of its high negative charge, low isoelectric point, and divalent ion rejection, as well as a lactose rejection higher than 98% and a lactic acid rejection lower than 37%, at pH 3.5, to minimize the need of additional separation steps. The experimental lactic acid rejection was evaluated at varying feed concentration, pressure, temperature, and flow rate. As the dissociation degree of lactic acid is negligible in industrially simulated conditions, the performance of this NF membrane was validated by the irreversible thermodynamic Kedem-Katchalsky and Spiegler-Kedem models, with the best prediction in the latter case, with the parameter values: Lp = 3.24 ± 0.87 L × m-2 × h-1 × bar-1 and = 15.06 ± 3.17 L × m-2 × h-1, and d = 0.45 ± 0.03. The results obtained in this work open the way for the up-scaling of membrane technology on the valorization of dairy effluents by simplifying the operation process and the model prediction and the choice of the membrane.Science and Innovation (Madrid, Spain; MCIN/AEI/10.13039/501100011033) and European Union “NextGenerationEU”/PRTR” under projects CTM2017-87850-R and EIN2020-112319 is gratefully acknowledged

Método para la extracción y concentración simultáneas de compuestos de fases líquidas utilizando membranas microporosas.

En este método la extracción y concentración de compuestos líquidos se realiza simultáneamente utilizando para ello un agente de extracción selectivo hacia el/los solutos que se quieren extraer. Este agente de extracción forma con el/los solutos complejos reversibles que se liberan en la etapa de concentración de modo que el agente de extracción es regenerado para ser utilizado de nuevo en el proceso. Ambas etapas de extracción y concentración se realizan utilizando membranas microporosas donde el contacto entre las fases se realiza en los poros de las fibras que se encuentran en el interior del módulo, de modo que se evita la dispersión de las fases y por tanto su posterior separación. Además se debe aplicar una ligera sobrepresión a la fase por la cual las fibras no están preferentemente impregnadas con objeto de evitar la dispersiónde las fases. El funcionamiento del sistema puede ser en continuo, discontinuo o semicontinuo.Solicitud: 009901559 (05.07.1999)Nº Pub. de Solicitud: ES2187311A1 (01.06.2003)Nº de Patente: ES2187311B2 (01.03.2005

A generalized disjunctive programming model for the optimal design of reverse electrodialysis process for salinity gradient-based power generation

Reverse electrodialysis (RED) is an emerging electro-membrane technology that generates electricity out of salinity differences between two solutions, a renewable source known as salinity gradient energy. Realizing full-scale RED would require more techno-economic and environmental assessments that consider full process design and operational decision space from the RED stack to the entire system. This work presents an optimization model formulated as a Generalized Disjunctive Programming (GDP) problem that incorporates a finite difference RED stack model from our research group to define the cost-optimal process design. The solution to the GDP problem provides the plant topology and the RED units´ working conditions that maximize the net present value of the RED process for given RED stack parameters and site-specific conditions. Our results show that, compared with simulation-based approaches, mathematical programming techniques are efficient and systematic to assist early-stage research and to extract optimal design and operation guidelines for large-scale RED implementation.This work was supported by the LIFE Programme of the European Union (LIFE19 ENV/ES/000143); the MCIN/AEI/10.13039/501100011033 and “European Union NextGenerationEU/PRTR” (PDC2021–120786-I00); and by the MCIN/AEI/10.13039/501100011033 and “ESF Investing in your future” (PRE2018–086454)

Monetizing environmental footprints: index development and application to a solar-powered chemicals self-supplied desalination plant

The assessment of the environmental greenness in the process industry has been quantified by means of the development of an integrated index, i.e., Monetized Footprint Index (MFI), based on the compilation and the integration of land, water and carbon footprint indicators. The MFI has been applied to assess the case study of a seawater reverse osmosis desalination with an integrated electrodialysis with bipolar membranes brine treatment. The MFI enables the evaluation of environmental burdens related to the chosen functional unit based on a weighting procedure, which integers land, water, and CO2 prices. It is neither a tool for the calculation of the production cost nor a sustainability analysis tool as it does not include social or economic indicators. Comparison between selected scenarios, based on the different sources of the requested electricity, grid mix (Spain and Israel, as examples), and photovoltaic solar energy (under a fixed solar irradiation), has been carried out. Maximum values of 0.30 €·m–3 and minimum values of 0.11 €·m–3 for the different scenarios have been obtained in the calculation of the MFI. Moreover, uncertainties in land, water and CO2 prices have been analyzed under a Monte Carlo simulation. This study concludes that MFI, being based on well-known environmental footprint indicators, can simplify and support the decision-making process.Support from MICINN under project CTM2014-57833-R is acknowledged. M.H.-G. thanks the MICINN for FPI grant BES-2015-07350 and the Erasmus+ program for the Student Mobility KA107 grant