## 2 Electro-Membrane Technologies: Current Status and Challenges
Among these limitations, membrane electrical properties and stability improvements, together with a cost reduction to be economically competitive, stand out. EDBM (Figure 1c) is a technology able to generate acids and bases from feed saline streams by the application of electric potential and the configuration of bipolar membranes (BM) besides the AM and CM in the cell stack. The key element of EDBM is the bipolar membrane, which role is the dissociation of water when an energy field is applied. In this sense, protons (H\({}^{+}\)) and hydroxyl ions (OH\({}^{-}\)) are generated and migrate to the acid and base compartment, respectively. EDBM applications for product purification and waste vaporization have been reported in the literature under different frameworks such as the  
Figure 1: Simplified diagram of the input, process, and products of the electro-membrane processes: (**a**) electrodialysis, (**b**) reverse electrodialysis, (**c**) electrodialysis with bipolar membranes, and (**d**) reverse electrodialysis with bipolar membranes. food industry (casein, protein isolates) [28]; however, its application in desalination brine management for the production of HCl and NaOH stands out [29; 30]. Nevertheless, further development of bipolar membranes towards improvements on the longevity (pH stability) and the unwanted co-ion leakages should be carried out in addition to a reduction of their synthesis cost in order to be competitive with the current technologies [31]. As with RED and ED, R-EDBM (Figure 1d) is the opposite technology to EDBM, so that, with a membrane stack configuration such as that used in EDBM, acidic and alkaline solutions are selectively transported, mixed, and neutralized, enabling the generation of electric energy. Energy could be recovered from brines by means of both RED and R-EDBM. Nevertheless, while RED is a well-developed to date technology, R-EDBM is still in the early development stages with few research publications, although its potential has been known for a long time. The couple EDBM and R-EDBM is presented as a sustainable energy storage system for RE surplus [32] configuring the so-called Acid-Base Flow Batteries. Thus, the acidic and alkaline solutions produced by EDBM will act as a charge for the battery that could be discharged in the neutralization by R-EDBM. As seen in Table 2, R-EDBM presents one order of magnitude higher power densities compared to RED; however, it is still at low TRL due to the limitations regarding the use of the bipolar membranes. More details regarding these technologies' application into the desalination industry are given in the next sections of this work. TRL is a method that describes the maturity of technology by using a nine-level scale from level 1--basic principles observed to level 9--actual system proven in an operational environment. Indeed, research and development under a certain technology favor moving up in the TRL scale. As seen in Table 2, the described electro-membrane technologies are at medium to high TRL. Both EDBM and R-EDBM are at lower TRL compared to ED and RED; however, research efforts carried out in the technologies and in their components such as BM will enable to achieve higher TRLs. Hence, desalination is a challenging industry for the integration of the EDBM and R-EDBM couple system with two approaches: (a) chemical recovery with the aim of achieving self-supply and (b) energy harvesting. Additionally, it could notably reduce the indirect emissions of CO\({}_{2}\) and other Greenhouse Gases related to energy consumption by its integration with RE. In particular, [PERSON] et al. [35] reports that the combination of solar PV energy and bipolar electrodialysis flow battery demonstrated the best environmental performance. 3 Alternatives for Electro-Membrane Technologies Integration for Brine Management in SWRO Facilities  
In this section, the different alternatives for electro-membrane technologies integration for brine management in SWRO facilities will be presented and discussed.