In situ formation of oil-suspended particulate matter aggregate during flushing activities

Abstract

After the collision of the Singapore-registered oil tanker, Wu Yi San into the oil terminal of Yeosu port, approximately 800 tons of oil mixture was released from the ruptured pipelines. Emergency oil spill responses were performed to recover and clean the spilled oil in a short period of time. However, considerable amounts of residual oils were found along a beach located 2 km from the accident site during a monitoring program a year after the spill. In an attempt to remediate the residual oil, the beach was subject to consecutive flushing: seawater under high pressure was repeatedly applied over residual oil-sediment mixtures. Resuspended residual oils were collected through snares and adsorption pads. During the flushing operation, large amounts of suspended particulate matters (SPM) were also resuspended, which promoted oil-SPM interactions, providing favorable conditions for formation of oil-SPM aggregate (OSA). In situ formation of OSA was identified by microscopic and chemical analysis. Large size multiple droplet type OSA was dominant. Mass balance of resuspended oil in various forms was estimated by laboratory OSA simulation using natural seawater and spilled oil. The percentage of surface oil slick, neutral buoyancy OSA, and negative buoyancy OSA were calculated as 52.2±10.7, 32.2±9.8, and 15.6±3.5%,respectively. The neutral buoyancy OSA remained stable for more than 3 months, which might be sufficienter and clean the spilled oil in a short period of time. However, considerable amounts of residual oils were found along a beach located 2 km from the accident site during a monitoring program a year after the spill. In an attempt to remediate the residual oil, the beach was subject to consecutive flushing: seawater under high pressure was repeatedly applied over residual oil-sediment mixtures. Resuspended residual oils were collected through snares and adsorption pads. During the flushing operation, large amounts of suspended particulate matters (SPM) were also resuspended, which promoted oil-SPM interactions, providing favorable conditions for formation of oil-SPM aggregate (OSA). In situ formation of OSA was identified by microscopic and chemical analysis. Large size multiple droplet type OSA was dominant. Mass balance of resuspended oil in various forms was estimated by laboratory OSA simulation using natural seawater and spilled oil. The percentage of surface oil slick, neutral buoyancy OSA, and negative buoyancy OSA were calculated as 52.2±10.7, 32.2±9.8, and 15.6±3.5%,respectively. The neutral buoyancy OSA remained stable for more than 3 months, which might be sufficient