BIOAUGMENATION OF SOIL CONTAMINATED WITH STEEL MILL COKE TAR SLUDGE

Waste disposal of soil contaminated with coke tar sludge is a problem for steel mills. Coke tar sludge primarily contains coal dust, naphthalene, benzene, toluene, ethylbenzene and xylene (BTEX). In the past, the common method of disposal was incineration. However, incineration is very expensive. Bioremediation can clean-up the soil and save the steel mills money and virtually eliminate “cradle to grave“ liability.Working with a major international steel mill, RMC Bioremediation developed a bioremediation program to solve the disposal problem of contaminated soil. The solution was to treat the tar sludge soil with bioaugmentation in a landfarm.Bioaugmentation is the technique of applying specially cultured microbes that metabolize the tar into environmentally safe water and carbon dioxide. In addition to the application of microbes, a colloidal surfactant and nutrients were utilized. The surfactant helps break down the tar sludge so the microbes can metabolize the waste more efficiently. Nutrients are applied to insure the microbes have the proper components to colonize the soil.A landfarm is the most often used bioremediation technique to treat surface contaminated soil. As the name implies, this technique involves tilling and watering the soil to maintain proper conditions for biodegradation to occur. Tilling provides oxygen for the microbes and facilitates mixing of the bioremediation products.Before starting the landfarm, RMC Bioremediation performed a Biotreatability Study. The purpose of the Study was to confirm the main issues of bioremediation:Is the compound readily biodegradable.Is there a compound present that would inhibit microbial growth.Which type of active bioremediation, biostimulation or bioaugmentation, would be required.To determine which environmental factors such as the soil pH, nutrients and soil moisture needs to be monitored.From the results of the Biotreatability Study, RMC Bioremediation verified the main components of tar sludge can be used as a food and energy source for the microbes and identified the operating conditions for the landfarm. This information was used to estimate project costs and the time required to reduce the naphthalene to less than 100 mg/kg and BTEX to less than 1.0 mg/kg.Initially the soil was tilled to fracture the large clods of tar sludge and dirt. Next, a surfactant was sprayed on the soil to break up the tar sludge. The following day, the liquid nutrients and microbes were applied and the soil was tilled to mix in the products.