# A Review of the Water Desalination Technologies
## 4 Conclusions  
As shown, the seawater desalination sector has many chemical and physical methods capable to obtain the freshwater. Thermally driven solutions (MED, MSF) are historically the first techniques adopted, whereas today the technologies based on membranes (mainly RO) are quickly spreading worldwide. This makes the sector flexible according to the needs of the site. Table 2 summarizes the advantages and disadvantages of the systems described below.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Technology** & **Advantages** & **Drawbacks** & **Status** & **Ref.** \\ \hline \multirow{3}{*}{MED} & - High water quality & \multirow{3}{*}{Scaling on the pipes} & \multirow{3}{*}{Commercial} & [5, 22, 23, 24, 25, 27, 28, 29] \\  & - Low energy consumption & & & \\ \hline \multirow{3}{*}{MSF} & - Maintenance operations to remove the scaling are simpler than in MED & - High energy demand & \multirow{3}{*}{Commercial} & \\  & - High water quality & - High rated capacity & & \\ \cline{1-1}  & - High water quality & & & \\ \cline{1-1}  & - High rated capacity & & & \\ \hline \multirow{3}{*}{MVC} & - High water quality & \multirow{3}{*}{Low production capacity} & \multirow{3}{*}{Commercial} & [31, 32] \\  & - Low energy consumption & & & \\ \hline \multirow{3}{*}{RO} & - Only electrical demand & - Low investments & - Lower water quality & \\ \cline{1-1}  & - Coupling with many & - High costs for & \multirow{3}{*}{Commercial} & \\ \cline{1-1}  & renewable energy sources & - Modular structure of & & \\ \cline{1-1}  & plant & - Subject to biofouling & & \\ \hline \multirow{3}{*}{FO} & \multirow{3}{*}{Low thermal energy} & No drinking purpose & \multirow{3}{*}{Special application (hydration bags)} & \multirow{3}{*}{[28, 47, 48, 49, 50]} \\  & & (ammonia carbon & & \\ \cline{1-1}  & & dioxide) in industrial & & In development \\ \hline \multirow{3}{*}{NF} & \multirow{3}{*}{Low energy demand} & Produces soft water (a & \multirow{3}{*}{In development at the dual-stage unit for seawater} & \multirow{3}{*}{[2, 23, 36, 46, 52]} \\  & & diluted saline solution) & & \\ \hline \multirow{3}{*}{ED} & - High purity of & \multirow{3}{*}{- Only for brackish water (up to 2000 ppm)} & \multirow{3}{*}{Commercial} & \multirow{3}{*}{[10, 23, 24, 53]} \\  & - Energy consumption & & & \\ \cline{1-1}  & proportional to salt & & & \\ \cline{1-1}  & concentration & & & \\ \hline \multirow{3}{*}{CDI} & Potentially more efficient & Only for brackish water & \multirow{3}{*}{In development} & \multirow{3}{*}{[54, 55, 56, 57]} \\ \cline{1-1}  & & (up to 2000 ppm) & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Advantages and disadvantages of the main desalination technologies.  
The many technologies on the market guarantee products of varying quality and are distinguished by efficiency, but the RO unit represents the best available technology for desalination, according to the previous statistics, thanks to the reduced cost of the water production. Furthermore, the possibility to adopt electrical energy as input would simplify the coupling with renewable energy sources, thanks to the adoption of commercial technologies like photovoltaic panels and wind turbines [97; 98]. In this way, it is possible to install small desalination units on minor islands, hopefully supplied by renewable energy sources, in order to satisfy freshwater demand in a sustainable way [99; 100; 101].  
Conceptualization, D.C., V.F. and A.G.; formal analysis, V.F.; investigation, D.C.; data curation, D.C. and A.G.; writing--original draft preparation, D.C.; writing--review and editing, D.C. and A.G.; supervision, V.F. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
No external data.  
The authors declare no conflict of interest.