Improved Boron Rejection Using Electrocoagulation as a Pretreatment of Swro Desalination Lines: Unveiling Performance, Removal Mechanism, and Cost-Energy Analysis

Abstract

This study aimed to evaluate the applicability of the electrocoagulation process as a pretreatment for boron mitigation before seawater desalination through reverse osmosis. Batch experiments were conducted to investigate several operational parameters on the boron removal from synthetic and real seawater, including current density, electrolysis time, aluminum dissolution, initial pH, initial boron concentration, and the presence of other ions. Increasing the current intensity initially accelerates the dissolution of aluminum and the adsorption of boron, but beyond a certain point it leads to the rapid formation of large particles of ineffective aluminum hydroxide with a reduced capacity to adsorb boron. Generally, boron is best removed (72%) at a current density of 16.67 mA.cm-2, electrolysis time of 90 min, pHi 8, and initial boron content of 5 mg.L-1. Nevertheless, the real application to seawater has been challenging due to the complexity of the matrix and competitive adsorption with ions like magnesium, resulting in lower deboronation rates. Regarding EDS, XRD, and FTIR analysis, it confirmed the reduced content of boron in solid samples from synthetic seawater at 20 mA.cm-² compared to 16.67 mA.cm-², indicating the formation of less efficient crystalline boehmite. Kinetic studies demonstrated adherence to Lagergren's pseudo-first-order mechanism and the adequacy of the intraparticle diffusion model, suggesting the transport of boron molecules from the aqueous phase to the Al(OH)3 surface, and then diffused into the pores. Finally, the electrocoagulation process remains an economical and sustainable pretreatment for efficient boron removal from seawater, paving the way for high-quality freshwater production in water-scarce regions.

Keywords: seawater, Boron removal, Electrocoagulation process, Performance analysis, Kinetics modeling, Cost-energy analysis