Abstract
The effectiveness of Salinity Gradient Power - Reverse Electrodialysis (SGP-RE) in real practice is still not clearly defined due to the lack of specific studies in literature, being investigations in large part limited to pure NaCl solutions or aqueous mixtures of two salts. In this work, we experimentally assessed the impact of natural feed streams (collected from Licetto river and Tyrrenian sea in Amantea - Italy) in terms of Open Circuit Voltage (OCV) and power density (Pd) measured on a lab-scale SGP-RE stack prototype; results have been compared to those obtained when using NaCl solutions having equivalent ionic strength. Highest OCV (3.68 V and 4.09 V) and Pd values (0.46 and 1.41 W. m(-2)) were observed at temperature of 60 degrees C for real and synthetic feeds, respectively.
The extent of electrical resistances (ion exchange membrane/electrical double layer/diffusion boundary layer) was elucidated by electrochemical impedance spectroscopy (EIS); in particular, a critical effect of real solution on cation exchange membrane (CEM) resistance was detected. Additionally, ionic characterization of process effluents revealed the occurrence of uphill transport of multivalent ions Mg2+, Ca2+ and SO42+.