OPTIMISATION OF BIOSTIMULATION BY USING DIFFERENT NUTRIENT RATIOS TO IMPROVE BIOREMEDIATION OF PETROLEUM CONTAMINATED SOIL

Abstract

Petroleum contamination of sandy soils is a severe environmental problem in Libya, but relatively little work has been carried out to optimize the bioremediation of such heavily contaminated soil, particularly at a pilot scale. This study assessed the effect of varying nutrient (NPK) levels and types (urea) on bioremediation of diesel contaminated soil by a combination of chemical and toxicological analyses. Varying nutrient C:N:P ratios were used 100:10:10, 100:10:1, 100:1:1 and 100:1:0.1 that contained both NPK fertilizer and urea as an extra source of nitrogen. The optimum C:N:P ratio found was 100:10:1 (and urea was found to be a good nutrient source). In this study, approximately 69% TPH removal was achieved. The amounts of petroleum removed as revealed by chemical analysis appeared to correspond well to bacterial counts and the residual toxicity of soil as estimated by the Microtox assay. The highest amounts of nutrients used (C:N:P ratio of 100:10:10) did slightly reduce bioremediation effectiveness. GC analysis revealed that hydrocarbons of chain length C9-C20 were most effectively removed and that the higher chain length petroleum compounds (>C20) remained in the soil. Overall, the work demonstrated the clear potential of nutrient stimulation to reduce levels of hydrocarbons present and to reduce the soil toxicity.