Diesel biodegradation and the effect of application frequency were investigated in artificially contaminated soils (loam soil and sea sand) amended with commercial fertilizers and the effect of application frequency. Two sets of four equal portions (2 kg each) of diesel-contaminated soils were amended with 10% (w/w) of 2 different commercial fertilizers at 4 different but regular intervals for up to four times during a 7-week study period. The microcosms were then incubated at 30°C and sampled weekly. One sterilized soil microcosm contaminated with 10% (v/w) diesel and supplemented with 10% (w/w) fertilizer and one naturally attenuated microcosm served as controls. The amount of diesel remaining in each sample was determined using the Soxhlet extraction method and compared to the amount of diesel present in the same sample at day 0. The quantities of hydrocarbon contents in the supplemented samples and the controls were determined by GC-MS. The total heterotrophic population of each sample was also monitored. The population increase was found to correspond to the higher diesel degradation percentage in the study on sea sand. A significant enhancement (p<0.05) of diesel degradation was observed after the supplementation of fertilizers especially in sea sand compared with those in both controls. There were no significant differences in diesel degradation with the fertilizer application frequency. In conclusion, supplementation of diesel contaminated soils with commercial fertilizer results in a significant increase on diesel biodegradation. Additional supplementation did not further stimulate the degradation under the same conditions.
Key words: Diesel, bioremediation, fertilizers, application frequency.
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