Comparing Oil Degradation Efficiency and Bacterial Communities in Contaminated Soils Subjected to Biostimulation Using Different Organic Wastes

The use of organic wastes in bioremediation of oil-contaminated desert soils has received little attention, although their use is cost-effective. We evaluated the use of spent mushroom compost (SMC), poultry manure (PM), and urea in the stimulation of respiration activities and oil degradation in a polluted desert soil. Moreover, we followed post treatment shifts in bacterial community structure using MiSeq sequencing. The addition of SMC and PM resulted in a significant increase in the evolved CO₂ from 8.7 ± 1.9 to 25.7 ± 1.6 and to 23.4 ± 1.2 mg CO₂ g^-1 soil after 96 days of incubation, respectively. In contrast, changes in respiration activities after the addition of urea were insignificant. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that most of the alkanes (C₁₄-C₃₀) were degraded in all biostimulated soils at a rate of 0.12-0.19 mg g^-1 soil day^-1, which was significantly higher than in the untreated soil (P < 0.05). Bacterial community analysis showed that 87-94 % of total sequences in the original soil belonged to Firmicutes, Actinobacteria, and Proteobacteria. While the relative abundance of Firmicutes remained unchanged after the addition of PM (37-48 % of total sequences), it increased in the urea treatment (44-87 %) and dramatically decreased in the SMC treatment (0.5-4.5 %). The remaining bacterial groups were still detectable after the treatments, although no clear treatment-related shifts could be observed, due to the large difference in the relative abundance of the same bacterial groups among the same replicates. We conclude that the use of organic wastes could be one of the ways of combating petroleum pollution in desert soils.