Application of Bipolar Membrane Electrodialysis in Environmental Protection and Resource Recovery: A Review

Recovery of ammonia nitrogen from simulated reject water by bipolar membrane electrodialysis

Ammonia monohydrate (NH3·H2O) is an important chemical widely used in industrial, agricultural, and pharmaceutical fields. Reject water is used as the raw material in self-built bipolar membrane electrodialysis (BMED) to produce NH3·H2O. The effects of electrode materials, membrane stack structure, and operating conditions (current density, initial concentrations of the reject water, and initial volume ratio) on the BMED process were investigated, and the economic costs were analyzed. The results showed that compared with graphite electrodes, ruthenium-iridium-titanium electrodes as electrode plates for BMED could increase current efficiency (25%) and reduce energy consumption (26%). Compared with two-compartment BMED, three-compartment BMED had a higher ammonia nitrogen conversion rate (86.6%) and lower energy consumption (3.5 kW· h/kg). Higher current density (15 mA/cm2) could achieve better current efficiency (79%). The BMED performances were improved when the initial NH 4 + concentrations of the reject water increased from 500 mg NH 4 + /L to 1000 mg NH 4 + /L, but the performance decreased as the concentration increased from 1000 mg NH 4 + /L to 1500 mg NH 4 + /L. High initial volume ratio of the salt compartment and product compartment was beneficial for reducing energy consumption. Under the optimal operating conditions, only 0.13 $/kg reject water was needed to eliminate the environmental impact of reject water accumulation. This work indicates that BMED can not only achieve desalination of reject water, but also generate products that alleviate the operational pressure of factories.

Advancements in Bipolar Membrane Electrodialysis Techniques for Carbon Capture

Bipolar membrane electrodialysis (BMED) is a promising technology for the capture of carbon dioxide (CO2) from seawater, offering a sustainable solution to combat climate change. BMED efficiently extracts CO2 while generating valuable byproducts like hydrogen and minerals, contributing to the carbon cycle. The technology relies on ion-exchange membranes and electric fields for efficient ion separation and concentration. Recent advancements focus on enhancing water dissociation in bipolar membranes (BPMs) to improve efficiency and durability. BMED has applications in desalination, electrodialysis, water splitting, acid/base production, and CO2 capture and utilization. Despite the high efficiency, scalability, and environmental friendliness, challenges such as energy consumption and membrane costs exist. Recent innovations include novel BPM designs, catalyst integration, and exploring direct air/ocean capture. Research and development efforts are crucial to unlocking BMED's full potential in reducing carbon emissions and addressing environmental issues. This review provides a comprehensive overview of recent advancements in BMED, emphasizing its role in carbon capture and sustainable environmental solutions.

Modeling and Validation of a LiOH Production Process by Bipolar Membrane Electrodialysis from Concentrated LiCl

Electromembrane processes for LiOH production from lithium brines obtained from solar evaporation ponds in production processes of the Salar de Atacama are considered. In order to analyze high concentrations' effect on ion exchange membranes, the use of concentrated LiCl aqueous solutions in a bipolar membrane electrodialysis process to produce LiOH solutions higher than 3.0% by mass is initially investigated. For this purpose, a mathematical model based on the Nernst-Planck equation is developed and validated, and a parametric study is simulated considering as input variables electrolyte concentrations, applied current density, stack design, process design and membrane characteristics. As a novelty, this mathematical model allows estimating LiOH production in a wide concentration range of LiCl, HCl and LiOH solutions and its effect on the process, providing data on final LiOH solution purity, current efficiency, specific electricity consumption and membrane performance. Among the main results, a concentration of 4.0% to 4.5% by LiOH mass is achieved, with a solution purity higher than 95% by mass and specific electrical energy consumption close to 4.0 kWh/kg. The work performed provides key information on process sensitivity to operating conditions and process design characteristics. These results serve as a guide in the application of this technology to lithium hydroxide production.