Bioremediation potential of diesel-contaminated Libyan soil

• Bioremediation of diesel contaminated Libyan soil using Bacillus, pea straw was assessed.
• Pea straw treatment resulted in the highest degradation of TPH (96.1%).
• Metagenomics showed that necrophytoremediation led to shifts in microbial community.

Bioremediation is a broadly applied environmentally friendly and economical treatment for the clean-up of sites contaminated by petroleum hydrocarbons. However, the application of this technology to contaminated soil in Libya has not been fully exploited. In this study, the efficacy of different bioremediation processes (necrophytoremediation using pea straw, bioaugmentation and a combination of both treatments) together with natural attenuation were assessed in diesel contaminated Libyan soils. The addition of pea straw was found to be the best bioremediation treatment for cleaning up diesel contaminated Libyan soil after 12 weeks. The greatest TPH degradation, 96.1% (18,239.6 mg kg−1) and 95% (17,991.14 mg kg−1) were obtained when the soil was amended with pea straw alone and in combination with a hydrocarbonoclastic consortium respectively. In contrast, natural attenuation resulted in a significantly lower TPH reduction of 76% (14,444.5 mg kg−1). The presence of pea straw also led to a significant increased recovery of hydrocarbon degraders; 5.7 log CFU g−1 dry soil, compared to 4.4 log CFU g−1 dry soil for the untreated (natural attenuation) soil. DGGE and Illumina 16S metagenomic analyses confirm shifts in bacterial communities compared with original soil after 12 weeks incubation. In addition, metagenomic analysis showed that original soil contained hydrocarbon degraders (e.g. Pseudoxanthomonas spp. and Alcanivorax spp.). However, they require a biostimulant (in this case pea straw) to become active. This study is the first to report successful oil bioremediation with pea straw in Libya. It demonstrates the effectiveness of pea straw in enhancing bioremediation of the diesel-contaminated Libyan soil.