Pilot study on ex situ bioremediation of diesel-contaminated soil using bioaugmentation and biostimulation

Soil at a site that recently was contaminated by diesel was investigated to apply different enhanced bioremediation processes at a pilot scale of 0.5m ³ biopiles. The indigenous microbial concentration was measured at the range of 10⁵ CFU/g soil that meaned the biodegradation would be happened. After two months of soil stabilization, a certain amount of diesel was applied again to these four acclimated biopiles at the level of 4,500 to 5,000 mg TPH-d/kg dry soil. Same dosages of the enriched diesel-degrading bacteria, rhamnolipid, and BH nutrients were applied to BA1, BS, and NE biopiles. A second run of landfarming was evaluated with same performance indicators. Within the first 30 days, the plate counting of existed soil culture was measured at the range of 10⁶ to 10⁷ CFU/g soil. The ratios of TPH-d degrading colonies (HDB) to total plate count (HAB) were enhanced with 9% in Ct, 49% in NE, 45% in BA1, and 42% in BS, respectively. Therefore, the TPH-d removal efficiencies achieved at different levels in these four biopiles, Ct=15%, NE=74%, BA1=77%, BS=40%. Bioremediation performance was promoted by bioaugmentation, while the biosurfactant addition (BS) attainted fair performance. The indigenous biopile (Ct) was still inhibited by the high loading of diesel with 3,600 mg TPH-d/kg dry soil. First-order reaction rate constant K values (day^-1) were evaluated as BAl(0.0592)>NE(0.0442)>BS(0. 0205)>Ct(0.0065). Molecular biomonitoring methods were developed to identify the diesel-degrading bacteria existing in all biopiles: DGGE electrophoresis showed the predominant group was Pseudomonas sp. presented in three biopiles of NE, BA1 and BS. This pilot study of three months of biopile farming approved that bioaugmentation and biostimulation could enhance the bioremediation of TPH-d-contaminated soil.