Abstract

Uncontrolled releases of petroleum compounds that are carcinogenic, mutagenic and are potent immunotoxicants into soil and groundwater poses a serious threat to human and animal health. Biodegradation of hydrocarbon-contaminated soils has been established as an efficient, economic, versatile and environmentally sound treatment. Ten indigenous microorganisms were isolated from contaminated soils using the enrichment technique. Five isolates with the highest degradation potentials under standard degradation conditions were identified asAcinetobacter calcoaceticus (LT₁ and ETS₂), Acinetobacter sp. (LT₁A),Citrobacter freundii (MRC₃) and Bacillus pumilus (JL_B). B. pumilus achieved 86.94% of diesel degradation in 2 weeks. Additional degradation assay was carried out in liquid media using 3 local commercial fertilizers as nutrient supplements in comparison with the Bushnell-Haas (BH) media. The results show that the addition of fertilizer F1 stimulated diesel degradation by all isolates especially B. pumilus while the addition of fertilizer F3 seemed to strongly inhibit the bacterial ability of diesel degradation. The inoculation with the consortia did not show a higher degradation potential than the individual isolate. The results strongly indicate that environmental conditions of the contaminated sites play a crucial role in the degradation even though additional diesel-degrader has been introduced into the contaminated site.

Key words: Diesel bioremediation, Bacillus sp, Acinetobacter calcoaceticussp., Citrobacter freundii.