# Reverse Electrodialysis: Potential Reduction in Energy and Emissions of Desalination
## 2 Methods  
### Scenarios for RED Implementation: SWRO Desalination Plants  
We simulated RED system energy retrieval from a low saline stream, reversibly mixed with the concentrate effluent of 20 medium-to-large capacity SWRO desalination plants distributed worldwide (Table 1). For each location, we set average values of concentrate feed concentration, temperature and flow rate according to seasonal records reported in the literature. The volume and concentration of the concentrate effluent, if not readily available, were estimated solving mass balance for each SWRO plant according to (i) the overall RO configuration; (ii) the water recovery rate RR--i.e., the volume of desalted water to feed water volume--and (iii) the product water and feed seawater salinity. Appendix C details more information on SWRO desalination plants.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**ID**} & **SWRO** & **SEC** & **Capacity** & \multicolumn{2}{c}{**Concentrate**} \\  & **Plant** & **(kWh m\({}^{-3}\))** & **T** (\({}^{\circ}\)**C**) & **(m\({}^{3}\) day\({}^{-1}\))** & **(mol L\({}^{-1}\))** & **(m\({}^{3}\) m\({}^{-3}\))\({}^{1}\)** \\ \hline
1 & Al Dur & & & & \\  & [30] & 5.4 & 28 & 218,000 & 1.33 & 1.53 \\
2 & Barcelona & & & & \\  & [31] & 4.2 & 19 & 200,000 & 1.23 & 1.39 \\
3 & Beni Saf & & & & \\  & [32,33] & 4.1 & 25 & 200,000 & 1.16 & 1.13 \\
4 & Carlsbad & & & & \\  & [34,35] & 3.6 & 18 & 190,000 & 1.14 & 1.24 \\
5 & El Coloso & & & & \\  & [36] & 4.3 & 17 & 45,630 & 1.25 & 1.00 \\
6 & Fujairah I & & & & \\  & [37] & 4.5 & 29 & 170,500 & 1.10 & 1.44 \\
7 & Fukuoka & & & & \\  & [38, 39, 40] & 5.5 & 20 & 50,000 & 1.49 & 0.76 \\
8 & Glen Rocky & & & & \\  & [41,42] & 3.0 & 20 & 1400 & 1.06 & 1.50 \\
9 & Kindasa & & & & \\  & [43] & 4.6 & 27 & 34,000 & 1.36 & 1.09 \\
10 & Los Cabos & & & & \\  & [44,45] & 3.5 & 20 & 20,736 & 1.04 & 1.04 \\  & Maspalomas & & & & \\
11 & II & 3.8 & 20 & 26,184 & 1.67 & 0.67 \\  & [46,47] & & & & \\  & Mundo & & & & \\
12 & Nobo & 4.2 & 27 & 10,200 & 1.54 & 0.72 \\  & [46] & & & & \\
13 & Nemmeli & 3.9 & 28 & 150,000 & 1.21 & 1.22 \\  & Qingdao & & & & \\
14 & Baifa & 3.5 & 24 & 100,000 & 0.86 & 1.45 \\  & [48] & & & & \\
15 & Sadara & 4.4 & 27 & 148,800 & 1.40 & 1.33 \\
16 & SingPring & & & & \\  & [50,51] & & & & \\
17 & Sonck & & & & \\  & [52, 53, 54] & 3.5 & 27 & 540,000 & 1.06 & 1.24 \\
18 & Sydney & & & & \\  & [54, 55, 56] & 3.9 & 20 & 250,000 & 1.13 & 1.38 \\
19 & Tampa Bay & & & & \\  & [57,58] & 3.4 & 32 & 95,000 & 1.13 & 0.75 \\
20 & Wonthaggi & 4.2 & 16 & 450,000 & 1.11 & 1.40 \\ \hline \hline \end{tabular}  
* \({}^{1}\) Concentrate effluent volume per m\({}^{3}\) of total permeate produced.  
\end{table}
Table 1: Scenarios for RED implementation: Specifications of seawater reverse osmosis (SWRO) desalination plants. Data from [1,6].  
The proper pairing of SWRO concentrate effluent with a low salinity stream will be a decisive factor in RED's feasible implementation. Hence, we computed the inlet diluate's concentration and flow rate with the RED system mathematical model to maximize the net power output of the RED stack. The optimal concentration range (35-55 mM) is of practical occurrence and may be obtained from natural resources--e.g., estuaries, river basins or anthropogenic ones--for instance, by blending a secondary wastewater effluent 1-20 mM [15; 19; 21] with a more saline stream as seawater or a 2 nd RO pass' concentrate effluent.