Adaptability of microbial inoculators and their contribution to degradation of mineral oil and PAHs

Five dominant bacteria strains(Acetobacter sp., Alcaligenes sp., Micrococcus sp., Arthrobacter sp. and Bacillus sp.) and five fungi strains (Cephalosporium sp. I, Cephalosporium sp. Ⅱ, Aspergillus sp. Ⅰ, Aspergillus sp. Ⅱ and Fusarium sp.) isolated from petroleum-contaminated soil were used to assess the potential capability of mineral oil and PAH enhanced degradation separately and jointly using the batch liquid medium cultivation with diesel oil spiked at 1000 mg/L. The experiment was performed on a reciprocal shaker in the darkness at 25℃ to 30℃ for 100 d. The dynamic variation in the activity of microbial inoculators in each treatment and the degradation of the target pollutants during the period of experiment were monitored. Results showed a more rapid biodegradation of mineral oil and PAHs at the beginning of the experiment (about 20 d) by dominant bacteria, fungi and their mixture than that of the indigenous microorganisms, however, thereafter an opposite trend was exhibited that the removal ratio by indigenous microorganisms was superior to any other dominant treatments and the tendency lasted till the end of the experiment, indicating the limited competitive capability of dominant microorganisms to degrade the contaminants, and the natural selection of indigenous microorganisms for use in the removal of the contaminants. At the end of the experiment, the removal ratio of mineral oil ranged from 56.8 % to 79.2 % and PAHs ranged from 96.8 % to 99.1% in each treatment by microbial inoculators.