Biological treatment of mineral oil in a salty environment

Abstract

Mineral oil may be spilled into the marine or coastal environment through the discharges of ballast and bilge water, dry docking activities and tanker and non-tanker accidents to contaminate both of the seawater and coastline, especially in harbors. The unsuitable storage and disposal of wasted mineral oil may also contaminate saltified soil or brackish groundwater that have been polluted by salty wastes or intruded by seawater in coastal areas. In order to clean those contaminated sites, the mineral oil must be removed from the salty environment. In this study, a lab-scale aerobic biofilter-biotrickling tower system packed with particulate plastic media (1.5 cm, hexagon in shape) was used to treat the salty artificial wastewater polluted by mineral oil (diesel fuel) mixed with chemical dispersant (CPC OD-10) and inorganic nutrients. The volatile organic compounds (VOCs) escaped from the biofilter due to aeration was then treated by the biotrickling tower of the treatment system. According to the experimental results, the optimal removal efficiencies of the emulsified diesel in this salty water was found to be 95% controlled under concentrations as high as 1000 mg TOC/L of diesel in the influent and volumetric loading rate of 1.5 kg TOC/m3-day. The biodegradation rate constant (k) was measured to be 0.169 hr–1 for a first-order reaction assumed. As to the removal efficiency for VOCs, a low percentage of 68.2% was measured due to short hydraulic retention time (10 seconds) applied to the tower. However, only a small fraction (7.9%) of total amounts of diesel was measured as VOCs. The chemical dispersant used in this study was biodegradable, which could be used as a surfactant to emulsify the mineral oil into seawater for biological treatment. Due to short HRT applied to this aerobic biofilter-biotrickling tower treatment system, both the surface area and reactor volume required to build this treatment equipment are thus decreased to make it more easily set up in a mobile ship or truck. Thus, we may treat the mineral oil in marine or any other salty environment more conveniently.