Metals and suspended solids in the effluents from in-water hull cleaning by remotely operated vehicle (ROV): Concentrations and release rates into the marine environment

An increase in the use of ROVs for in-water hull cleaning (IWC) has led to the need to understand the risks to the marine environment posed by the release of IWC effluents. The primary objective of this research is to investigate the characteristics of wastewater generated during IWC, specifically concerning suspended solids (SS) and metal concentrations, and their release rates and total load to the environment. The IWC effluents contain substantial amounts of SS and metals, with Cu and Zn being the most prevalent. These metals are predominantly associated with fine antifouling paint particles, posing a potential risk of secondary pollution upon release into the marine environment. While the treatment systems demonstrated effectiveness in reducing SS and particulate metals, achieving complete removal of dissolved and particulate metals below ambient levels proved to be challenging. To mitigate environmental risks, this study proposes, based on the particle size analysis, the implementation of multistage filtration systems with an optimal filtration pore size for the effluent treatment. In conclusion, we highlight the potential environmental risks of IWC activities. As most metals have a strong affinity towards particles in wastewater, effective removal of particles is essential to alleviate environmental stress at IWC sites.