Treatment of Brackish Water RO Brine via Bipolar Membrane Electrodialysis

Abstract

Due to the demand for acid and base in brackish water reverse osmosis (RO) desalination plants located in remote areas and the difficulty of transporting acid and base, bipolar membrane electrodialysis (BMED) was employed to convert brackish water RO brine into acid and base on site. The effects of operating parameters (i.e., initial salt content, current density, content of electrode solution, and initial HCl and NaOH contents) on the BMED performance for batch processing of brackish water RO brine were investigated with NaCl solutions. The operating conditions were optimized via the response surface methodology. Using the actual RO concentrate from a brackish water desalination plant as the feed solution for BMED after softening pretreatment, an acid of 0.7 mol/L and a base of 0.6 mol/L were produced in three BMED cycles, and the salt content in the feed compartment decreased from 19.8 to 4.1 g/L in each cycle. While the acid and base produced on site can be used for membrane cleaning and pH adjustment of the RO influent water, the residual salt solution from the BMED can be pumped to the RO system to maximize utilization of the water resources. The purities of the acid and base produced were 91.1 and 97.2%, respectively, and the total process cost was estimated at $1.69/kg NaOH.

Asymmetric chloride-mediated electrochemical process for CO2 removal from oceanwater

“…However, the high cost of bipolar membranes might impede the commercialization of the process, and these architectures present risks of toxic redox-couples leaking into the oceanwater. 41 We describe here a new approach based solely on electrochemical modulation of the pH to initially release the CO 2 and then to alkalize the treated water before it is returned to the ocean. This approach does not require expensive membranes or addition of chemicals, is easy to deploy, and does not lead to formation of byproducts or secondary streams.…”

“…However, the high cost of bipolar membranes might impede the commercialization of the process, and these architectures present risks of toxic redox-couples leaking into the oceanwater. 41…”

Origin of Limiting and Overlimiting Currents in Bipolar Membranes

“…Bipolar membranes (BPMs) represent a distinct class of ion exchange membranes with the unique ability to electrochemically dissociate water into protons and hydroxide ions . These membranes have become increasingly attractive for the production of acid/base and for emerging environmental applications which aim to phase out the dosing of harsh chemicals for pH regulation − as well as other applications at the water-energy nexus. − Specifically, BPMs are ion exchange membranes with two oppositely charged layers: an anion exchange layer (AEL) and a cation exchange layer (CEL). Due to such a composite structure, the function of a BPM is not selective ion separation as neither anions nor cations can ideally pass both layers of the membrane.…”

Decreasing Seawater Desalination Footprint by Integrating Bipolar-Membrane Electrodialysis in a Single-Pass Reverse Osmosis Scheme

“…It stems from these studies ,− that BMED is a potentially eco-friendly, cost-effective method for SWRO brine management, yet techno-economical barriers and the lack of sufficient knowledge still limit the application of BMED on an industrial scale . Indeed, very few studies ,,, have included an economic evaluation related to the production of an acid and base from SWRO brine by BMED. Thiel et al emphasized that using real SW concentrated streams (pretreated by NF or other methods) is critical for determining the techno-economic feasibility of BMED.…”