Analysis of Multi-Salt Transport and Salt Leakage Pathways in Bipolar Membrane Electrodialysis for Brine Valorization

Bipolar membrane electrodialysis (BMED), a process which converts a concentrated saline feed into acidic, basic, and desalinated streams, has promising applications across resource recovery and brine valorization. BMED can be used to produce valuable acids and bases from reverse osmosis or nanofiltration concentrate while desalinating the waste brine and reducing disposal costs. In the first part of this thesis, we assess the feasibility of applying BMED to the nanofiltration permeate of groundwater that contains a high concentration of nitrate and sodium chloride. We analyze the transport of different ions in the mixed solution and compare the performance of the mixed salt permeate to an idealized single salt feed. BMED was shown to be just as effective at producing acid and base from the composition of polluted groundwater composition as from a single salt solution. BMED appears to be a feasible means to create value from and reduce the volume of waste brine in this application. The second part of this thesis examines the transport of salt impurities in the produced acid and base stream. BMED membranes allow small amounts of salt leakage that lower the purity and value of the acid and base generated. Impurities in the base stream may originate from the feed stream or the acid stream. While the total concentration of impurities in the base stream can be tracked, in conventional BMED operation pinpointing the origin of those impurities is not possible without making presumptions. A novel membrane stack and method is proposed for distinguishing between and measuring the flux of salt leakage from the acid and feed streams into the base stream (the same analysis is also done for the acid stream). For feed concentrations between 0.25-2.25 M and current densities from 10-100 mA/cm2, the impurity fluxes from the two sources are always the same order of magnitude and neither is negligible. Furthermore, lowering the feed stream concentration and operating at a higher current density decreased the net flux of impurities, resulting in a higher acid and base purity.

Name thesis:degree_name

Master

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Mechanical Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2024

Author dc:creator

• Wegmueller, Jakob Max

Advisor dc:contributor.advisor

• Lienhard, John H.

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
• Copyright retained by author(s)

Licence dc:rights.uri

• https://creativecommons.org/licenses/by-nc-nd/4.0/

Handle dc:identifier.uri

https://hdl.handle.net/1721.1/155859

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/155859