GREEN ENERGY HARVESTING FROM CONCENTRATED SALTWORKS BITTERNS BY REVERSE ELECTRODIALYSIS

Abstract

Concentrated bitterns discharged from saltworks have extremely high salinity, often up to 300 g/L, thus their direct disposal not only can have harmful effect on the environment, but also generates a depletion of a potential resource of renewable energy. Here, reverse electrodialysis (RED), an emerging electrochemical membrane process, is introduced to capture the salinity gradient power (SGP) intrinsically conveyed by these bitterns also aiming at the reduction of concentrated salty water disposal. A RED unit at the laboratory scale has been adopted to study the SGP potential with different ion exchange membrane and different operating conditions. In particular, membranes supplied by Fujifilm, Fumatech, and Suez were tested, and results compared. The unit was fed with artificial hypersaline (5 mol/L) NaCl solution on one side, and with variable concentration of NaCl dilute solutions (0.01 – 0.1 mol/L) on the other. The influence of several operating factors has been also assessed, including the flowrate and the solutions temperature. In particular, increasing feed solutions temperature and velocity has been found to lower the sack resistance, which enhances the output performance of the RED stack. The maximum obtained power density (corrected to account for the effect of electrodic compartments), which can be relevant in 5 cell pairs laboratory stacks) reached around 8 W/m2cellpair, with FUJIFILM Type 10 membranes, temperature of 40°C and a fluid velocity of 3 cm/s (as empty channel, considering 270 mm thickness). Notably, results of the present study confirm the large potential for SGP generation from hypersaline brines, thus providing a useful guidance for the harvesting of SGP in seawater saltworks all around the world.