Performance of conventional drinking water treatment following dispersant remediation of an oil spill in surface water

Physical remediation such as the use of booms has been applied for most oil-spill cleanup activities in surface water. The application of dispersants has been controversial primarily due to the unknown impacts on drinking water sources. This study investigated changes in surface water quality following dispersant application to crude oil spills and the subsequent impact on the efficiency of ballasted flocculation, a physicochemical treatment process applied in many drinking water treatment plants (DWTP). Contamination of surface water was performed in the presence of crude oil concentrations (109 ± 13 mg/L) with and without dispersants. Water quality parameters such as turbidity and UVA254 were monitored and ballasted flocculation efficiency was assessed based on water quality as well as the removal of oil droplets, residual dispersant, and petroleum hydrocarbons as total organic carbon (TOC). Results showed that the measured water quality parameters except TOC are unsuitable indicators of petroleum hydrocarbon contamination in surface water. However, TOC lacked sensitivity when used in settled water to detect hydrocarbon contaminants. Although ballasted flocculation efficiency was not limited by the presence of crude oil and low dispersant concentrations when an optimized alum dose was applied (41 mg dry alum/L), the process was unable to remove other dispersant-related compounds that are not identifiable by the monitored water quality parameters. Measured concentrations of these compounds in settled waters were above the U.S. EPA's aquatic life benchmark (40 μg/L). Findings would be beneficial to DWTP in their efforts to upgrade their treatment processes and prepare oil-spill contingency plans.