Electric field forward osmosis (EFFO) for efficient oil-in-water emulsion separation and fouling mitigation in shipboard bilgewater

Abstract

Bilgewater, an oily wastewater generated from ships, poses a major environmental concern due to the difficulty of separating stable oil-in-water emulsions containing surfactants and cleaning agents. Conventional treatment technologies often fail to meet the discharge limit of 15 ppm oil, requiring multiple polishing units and chemical use. This study investigates electric-field forward osmosis (EFFO) as an energy-efficient, chemical-free approach for bilgewater treatment using polyamide thin-film composite (PA-TFC) membranes. The effects of applied electric potentials (-0.1 V and - 1.0 V) on water flux, fouling, and reverse salt flux (RSF) were examined using standard bilge mix (SBM) stabilized with an anionic surfactant (sodium dodecyl sulfate, SDS) or a non-ionic cleaner (Type 1). Mineral oil (MO) was used as a control. Applying a negative electric field (-0.1 V and 1.0 V) significantly increased water flux (Jw) by 25-50 % and improved flux recovery to above 90 % after physical cleaning compared with conventional FO (0 V). The enhancement was attributed to electrostatic repulsion between negatively charged oil droplets and the cathodic membrane surface, which reduced fouling layer compaction. Specific RSF values (Js/Jw) decreased under EFFO operation, indicating improved selectivity. Scanning electron microscopy confirmed thinner, less compact fouling layers under electric-field conditions. The results demonstrate that EFFO effectively mitigates membrane fouling while maintaining stable long-term performance. This study highlights EFFO as a sustainable and scalable bilgewater treatment strategy suitable for shipboard and marine environments where seawater can serve as a natural draw solution.