Bioremediation of Petroleum Hydrocarbons by Using a Two-Step Inoculation Composting Process Scaled-Up from a Mineral-Based Medium: Effect of Biostimulation of an Indigenous Bacterial Strain

Abstract

The effect of stimulation of an indigenous bacterial strain on the performance of a two-phase composting process scaled-up from a mineral-based medium for bioremediation of petroleum sludge (PS) was investigated. After isolating Acinetobacter radioresistens strain KA2 from PS containing high levels of total petroleum hydrocarbons (TPH), the potential of the strain for crude oil degradation was measured in the mineral-based medium. Then, it was inoculated twice into the composting system included seven in-vessel reactors containing different initial C/N/P ratios and various amounts of mature compost. The process duration consisted of the first 8 weeks as the first-phase composting (FPC) and the final 8 weeks as the second-phase composting (SPC). A total TPH removal of 72–88% reached after the two-phase composting. The first and second-order rate constants were respectively, 0.060–0.071 day−1 and 0.002–0.005 g kg−1 day−1 in the FPC runs and 0.114–0.209 day−1 and 0.009–0.046 g kg−1 day−1 in the SPC experiments. The results indicated the superiority of nitrogen (N) in enhancing the intrinsic potential of the strain in TPH removal. The study demonstrated the effectiveness of stimulation of the strain in PS bioremediation through the two-phase composting.