Boron removal from seawater by electro-chemical treatment as part of water desalination

Abstract

Significant decrease of boron concentration during seawater desalination is one of the more difficult, consuming and expensive tasks. Average boron concentration in the Mediterranean Sea is 4 mg/l, and due to heavy use of wastewater in irrigation the Israeli Water Authority (Ministry of Health) demands boron reduction to 0.4 mg/l maximum. The current boron removal procedure is based on two-pass reverse osmosis (RO) membrane treatment that requires pH adjustment to dissociate boric acid into borate ion. The operation is expensive, energy consuming and calls for cheaper and reliable alternatives. The current research was initiated to explore the abilities of electro-flocculation (EF) to remove boron from seawater. The EF experiments were performed under batch electro-chemical reactor conditions with iron electrodes. Settling time and pH of the solution were selected as two main independent parameters. The obtained results suggest that significant boron reduction can be achieved without membrane separation technologies. The obtained drop from 4.2 to 0.8 mg/l boron after 10 min EF and 60 min sedimentation suggests that RO can be applied as a polishing stage only, needed to achieve the goal of 90% B retention. At the same time, the average 80% boron retention achieved by EF/sedimentation is encouraging and can be viewed as a valuable alternative to currently applied RO-based technology. The studies were performed on seawater from the Palmachim beach (near Rishon-Le-Zion, Israel) and were an important step in detection of possible boron removal mechanisms.