Electrodialysis with bipolar Membranes for the sustainable production of chemicals from seawater brines at pilot plant scale

Abstract

In recent years, the global demand of fresh water has increased rapidly. Various, thermal and membrane, desalination processes have been developed to meet the growing demand of fresh water supply. However, these have the disadvantage of producing a brine twice as concentrated respect to the starting seawater, which is generally discharged into the sea causing serious damage to the marine ecosystem. Electrodialysis with bipolar membranes (EDBM) is an highly innovative technology, capable of producing acidic and basic solutions starting from the corresponding saline solution. In this way there is a double benefit, both environmental, linked to the valorisation of the brines from the desalination processes, and economic, since these reagents can be used by various equipment installed in the same production site. Even though, to the best of the author's knowledge, there are no applications of this technology on a semi-industrial scale in the literature. The aim of this work was therefore focused on the testing of an EDBM unit at the pilot scale both in continuous and discontinuous mode and at different current densities (200-500 A m-2). Particularly, the EDBM unit was operated under three different process configurations , namely closed-loop, feed & bleed, and fed-batch. At lower applied current density (200 A m-2), the closed-loop had a lower Specific Energy Consumption (SEC) (1.4 kWh kg-1) and a higher Current Efficiency (CE) (80%). When the current density was increased (300–500 A m-2), the feed & bleed mode was found to be more appropriate due to its low values of SEC (1.9–2.6 kWh kg-1) as well as high values of Specific Production (SP) (0.82–1.3 ton y-1 m-2) and current efficiency (63–67%). These results showed the effect of various process configurations on the performance of the EDBM, thereby guiding the selection of the most suitable process configuration when varying the operating conditions and representing a first important step towards the implementation of this technology at industrial scale.