Pulsed electrodialysis for demineralisation of oil refinery wastewater: bench-scale optimisation and scaling mitigation.

The integration of electrodialysis (ED) into zero liquid discharge (ZLD) schemes for industrial wastewater requires improved energy efficiency and scaling control. This study investigates the application of a pulsed electric field (PEF) mode in ED for the treatment of model and real refinery wastewater. PEF is a promising method for intensifying mass transfer and mitigating polarisation phenomena in the presence of complex mixtures of salts, petroleum products, and surfactants. Key parameters - average current density (5-10 mA/cm2), frequency (500 ± 20 Hz), and duty cycle (2) - were optimised to minimise specific energy consumption and membrane scaling. The novelty of this research lies in the comparative analysis of pH stability and energy efficiency between DC and PEF modes under high-fouling conditions typical of the oil and gas industry. Compared to direct current (DC) at the same average current density, the PEF mode reduced specific energy consumption by 1.2-2.2 times and increased the desalination rate by 1.6-2.0 times. Furthermore, PEF mode stabilised the pH in the concentrating chamber, leading to a significant reduction in inorganic scaling, as confirmed by qualitative and quantitative observations. High removal efficiency of heavy metal ions (Fe, Cr) were achieved at the optimal pulse frequency. The treated real wastewater met international quality standards for industrial reuse, demonstrating the potential of PEF-ED as a robust stage in advanced treatment systems for complex industrial effluents.