Advances and gaps in bilge water treatment for water reuse

The diagram summarizes bilgewater’s environmental and societal threats, oil weathering and emulsion formation, and electrocoagulation, membrane, biological, and hybrid treatments. Bilge water is estimated to account for a substantial fraction of oily wastewater discharged from marine vessels. It is a complex effluent composed of seawater, lubricants, fuels, detergents, solvents, and solid particles. This review provides a comprehensive analysis of bilge water characteristics, environmental and socioeconomic impacts, and current treatment technologies. Emphasis is placed on quantifying pollutants, with reported oil content ranging from 36 to 976 ppm, pH values between 6.8 and 9.0, and chemical oxygen demand (COD) levels reaching up to 12,800 ppm. The environmental hazards of untreated bilge water include severe ecological harm, risks to seabirds and marine biodiversity, and contamination of fisheries and tourism sectors, contributing to economic losses in coastal communities. Treatment strategies are categorized into electrochemical, membrane-based technologies, and biological processes. Hybrid systems, combining techniques such as electrocoagulation and reverse osmosis, have demonstrated superior pollutant removal efficiencies exceeding 99% for oil, turbidity, and total dissolved solids. Furthermore, although AI use in bilge water treatment remains underexplored, AI-based image analysis and machine learning models have shown potential to predict emulsion stability, thereby optimizing treatment design and monitoring. Hybrid systems achieved the highest removal efficiencies; however, several limitations still require further investigation, including cost, energy consumption, membrane lifetime and fouling in membrane-based systems, and regulatory compliance for marine oily wastewater remediation.