Bioremediation of creosote-contaminated soil in South Africa by landfarming

Aims: To determine the combined effects of biostimulation and bioaugmentation in the landfarming of a mispah form (lithosol; food and Agriculture Organisation (FAO)) soil contaminated with >310 000 mg kg(-1) creosote with a view to developing a bioremediation technology for soils heavily contaminated with creosote. Methods and Results: The excavated soil was mixed with 2500 kg ha(-1) dolomitic lime and 2000 kg ha(-1) mono-ammonium phosphate (MAP) before spreading over a treatment bed of shale reinforced with clay. Sewage sludge (500 kg) was ploughed into 450 m(3) of contaminated soil in the second and sixth months of treatment. A further 1000 kg ha(-1) MAP was added to the soil at the end of the fifth month. Moisture was maintained at 70% field capacity. Total creosote was determined by the US Environmental Protection Agency (EPA) method 418.1 and concentrations of selected creosote components were determined by gas chromatography/flame ionisation detection (GC/FID). Total creosote was reduced by more than 90% by the 10th month of landfarming. The rate of reduction in creosote concentration was highest after the addition of sewage sludge. The three-ring PAHs were more slowly removed than naphthalene and the phenolic compounds. The four- and five-ring PAHs, although persist until the end of treatment, were reduced by 76-87% at the end of the experiment. Conclusions: A combination of biostimulation and bioaugmentation during landfarming could enhance the bioremediation of soils heavily contaminated with creosote. Significance and Impact of the Study: The study provides information on the management of a combination of biostimulation and bioaugmentation during landfarming, and contributes to the knowledge and database necessary for the development of a technology for bioremediating creosote-contaminated land.