Novel approaches for valorisation of waste brines at pilot scale via electrodialysis with bipolar membranes

Minimum Liquid Discharge (MLD) schemes are gaining interest to comply with stricter discharge regulations and to recover useful resources. However, MLD schemes pose new challenges in terms of non-conventional operations in well-established industrial processes. As an example, Electrodialysis with Bipolar Membrane (EDBM), which valorises a saline solution through the production of acids and bases and requires large quantities of water, can be operated by sending a brine into the chemicals compartment instead of water. Thus, increasing the brine treatment capacity and reducing the water consumption of EDBM. The produced chemical solutions present a salt background, but it may become irrelevant for a variety of applications inside and outside MLD schemes. The present work evaluates such novel operating schemes at pilot scale, adopting the feed and bleed configuration. Three different scenarios, in which a brine is provided (i) to the acid compartment, (ii) to the base compartment and (iii) to both of them, were investigated and compared with a reference condition. The results showed a slight reduction in concentration (∼15 %) feeding one of the two compartments with the brine, while a more pronounced reduction (∼ 30 %) was observed feeding both compartments. This suggests that the environmental benefit is achieved at the cost of a performance reduction. Moreover, an innovative scheme, called Water Salt BackFlip (WS-BF), was proposed and tested. The WS-BF produced a high-purity base product and acid product with a lower salt content. Improved performance were observed, especially at high base target, in addition to the environmental benefits.