## 2 Electro-Membrane Technologies: Current Status and Challenges
### Alternative A0--Direct Brine Disposal  
This alternative, A0, depicted in Figure 2, is the baseline scenario considered, and it represents the current \"business as usual\" in regard to SWRO brine management and relies on the direct discharge of brine to the receiving water bodies as other proposed alternatives are far from being technically, socially, economically, or environmentally feasible [37]. Likewise, it was considered that the receiving media was capable of the assimilation and correction of the high concentrations of brines; thus, no environmental impact was associated with this direct disposal. Since marine organisms live in an osmotic balance with their environment, flora and fauna in the surroundings of brine discharges may be affected due to alterations in the physicochemical characteristics of the media, mainly salinity and temperature [38]. In this sense, the perspective on brines has undergone an evolution as the desalination capacity and the associated brine disposal increased [39; 40; 41; 42].  
Firstly, remarkable research efforts have been made to document and quantify the environmental impacts of brine disposal on the receiving marine media [43; 44; 45; 46; 47; 48; 49; 50; 51; 52]. These studies concluded that typical discharge concentrations are higher than the desired disposal concentrations [53]. Although there are few legislations regarding brine disposal, several authors have been working on the development of systems for brine management. The initial strategies carried out to reduce the environmental impacts associated with brine disposal were the development of more efficient discharge systems at the time of facilitating the dilution of the brine itself in the receiving media, such as the mixing with other effluents (for example, cooling water from power plants or wastewater) and the use of systems that modify the discharge, such as diffusers or jets [37; 54]. Next, the strategies were focused on minimizing the discharge volumes, many of them based on the evaporation of water,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Alternative Code** & **RED** & **EDBM** & **R-EDBM** \\ \hline A0 & ✗ & ✗ & ✗ \\ A1 & ✗ & ✓ & ✗ \\ A2 & ✓ & ✗ & ✗ \\ A3 & ✗ & ✓ & ✓ \\ A4 & ✓ & ✓ & ✗ \\ A5 & ✓ & ✓ & ✓ \\ \hline \hline \end{tabular}
\end{table}
Table 3: Electro-membrane technologies employed for each alternative.  
which requires large areas [4]. More recently, efforts in the development of Zero Liquid Discharge (ZLD) systems which combine different techniques in order to manage, reduce, and even make brines profitable and able to reintroduce them into the supply chain, have been made. Several technologies have been reported for brine management; however, emerging technologies which additionally are able to generate valuable products have been highlighted in the literature [55]. Thus brines, considered as waste until now, become a raw material, in accordance with the Circular Economy principles [56]. As an example, SAL-PROC [57] processes are able to sequentially extract different salts such as yeso gypsum, sodium chloride, magnesium hydroxide, calcium chloride, calcium carbonate, and sodium sulfate from brines. Emphasis has been placed on emerging technologies such as vacuum membrane distillation, membrane distillation coupled with crystallization, direct osmosis, and electrodialysis for the recovery of existing salts [58]. In addition, desalination brines have been identified as a potential source for the extraction of metals [9; 59], many of them considered to be critical raw materials. European projects such as Sea4 value [60] or SEArcularMine [61] aim to recover the material from saline waste streams.  
Therefore, the following alternatives will propose the management and use of brines in such a way as to avoid the environmental burdens associated with their direct discharge (alternative A0 from Table 1) and, in turn, the harvesting of high value-added products which can be used in situ in the desalination facility.