Brine Valorisation via Extensive Operation of a pilot-scale ElectroDialysis with Bipolar Membranes (EDBM)

Nowadays, human activity tackling fresh-water scarcity by desalination plants leads to the production of waste hypersaline streams which are discharged directly into the sea. According with this, EU policy ruled conventional disposal strategies unsustainable because of their harmful effect on the environment, forcing stricter discharge regulations and increased interest in recovery of useful resources from brine. To address this problem, the development of new technologies able to valorize waste streams could lead to several benefits such as the reduction of pollutants discharge and the extraction of valuable products which can be reused inside the industrial process. At this regard, Electrodialysis with Bipolar Membrane (EDBM) has been recently proposed as a promising method for the efficient removal of salt ions from concentrated saline solutions through the production of alkaline and acid streams. Furthermore, acids and bases derived from EDBM are often of sufficient purity for utilization in various industrial processes such as pH adjustment and neutralization reactions. Despite this, EDBM unit has never been investigated in industrial relevant scenarios using as a feed real brine coming from desalination plants. In the present work, the influence of the saline stream composition and the implementation of different operating strategies have been investigated in a pilot scale EDBM unit. In particular, a long-run experimental campaign has been conducted to assess the performance of the unit with both artificial and real brines. During the test has been also tested the effect of two different control strategies, flowrate and pressure control, to evaluate the impact of the internal leakage in the stack performances at fixed target of the alkaline product. At the same time, different steady state conditions have been analysed varying the outlet flow-rates and the supplied power to demonstrate the flexibility and stability of the process to provide several products specifications. The results have shown how the behavior of the unit strongly depends on the control strategy adopted rather than the feed employed. Indeed, for the same feed, a wide range of CE (between 20-90%) and SEC (between 1.5-7 kWh kg-1) have been found for both base and acid. This study revealed the EDBM a very suitable technology in an industrial context where acid and base streams can be re-used inside the plant, aiming to ensure waste valorisation and circularity of the whole process.