Hybrid multi-chamber system for enhanced removal of boron during water treatment/desalination without chemical usage

Abstract

The efficiency of boron removal during water treatment and desalination is insufficient to meet the water quality standard set by the World Health Organization. Boron can exist in its two natural forms in water, depending on the water pH. At low and high pH, boron tends to exist as boric acid and borate ion, which are neutral and negatively charged, respectively. In this study, we developed a multi-chamber boron control system. For the control group (nanofiltration (NF) and reverse osmosis (RO)), the pH was controlled to enhance the boron removal efficiency. As expected, the boron removal efficiency at pH 11 (RO: 95–98%, NF: 91%) was higher than that at pH 8 (RO: 85–87%, NF: 80%). Additionally, activated carbon was introduced in the developed system (forward osmosis-NF/RO hybrid processes within the draw-solution chamber). Powdered activated carbon was more effective than granulated activated carbon in adsorbing boron molecules, with the maximum adsorption capacities (qm) of the former and latter being 2.33 and 1.33 mg g−1, respectively. A simple economic analysis was performed to determine the applicability of the multi-chamber boron control system for the economical production of high-quality water with minimal boron concentration. The unit cost of the multi-chamber boron control system (0.26 USD ton−1) was significantly lower than that associated with single NF and RO processes (0.64–1.62 USD ton−1). The multi-chamber boron control system thus represents an economical alternative that can achieve a higher product water quality compared with existing processes.