Bilgewater management in marine vessels: a systematic literature review of marine vessel bilgewater and treatment options

Bilgewater is a mixture of oil, water, suspended solids, and other contaminants that collects in the lower inside areas of marine vessels and its discharge into the marine environment contributes to ocean pollution. Due to its complex composition and ecological impacts, effective management is critical. This systematic review examined existing research on bilgewater composition and assesses available treatment technologies to identify knowledge gaps and options for treatment. The Scopus database was searched for studies published between 1980 and 2025 that examined bilgewater treatment or its chemical and microbiological characteristics. Studies lacking independent validation or functioning as commercial promotion were excluded to minimise bias. A total of seventy-seven studies were examined. These revealed significant heterogeneity in bilgewater's chemical and microbiological profiles across vessels, sampling locations, and environmental conditions. Microbiological analysis identified the presence of hydrocarbon-degrading bacteria, corrosion-associated species, and potentially pathogenic species. Bilgewater treatment approaches included biological, electrochemical, filtration, coagulation, and multi-barrier systems, each with distinct advantages and limitations. The variability of bilgewater composition highlights the need for standardised assessment methods and guidance on which treatment systems are most effective in different situations. Future research is also needed to understand the interplay between the chemical and microbial characteristics of bilgewater and to investigate the removal of trace metals, non-indigenous species, pathogenic bacteria, and emulsified oil. Addressing these challenges is imperative to developing robust regulations and innovative control solutions.