Role of hemoglobin in hemoglobin-based remediation of the crude oil-contaminated soil

Highlights: • Hemoglobin (Hb) imposed a selective force on surfactant-producing bacterial species. • Hb application promoted TPH removal in the aged crude oil-contaminated soil. • Hb-based biocatalytic reaction removed TPH from the crude oil-contaminated soil. • Bacterial community structure recovered better after the biocatalytic reaction. • Hb-based remediation can be a viable option for crude oil-contaminated soils. This study investigated the changes in the indigenous microbial community structure with hemoglobin (Hb) application to determine the role of Hb in Hb-based remediation of crude oil-contaminated soil. The phylogenetic diversity of the bacterial community showed that the Hb addition selected surfactants-producing species, thereby, promoting TPH degradation. The significant increase in the CO₂ generation, which can be related to the increase in the bacterial abundance inferred from the 16S rRNA gene copy number, supports the enhanced TPH degradation with Hb application. The similar residual TPH concentrations in the presence of only hydrogen peroxide (H₂O₂) and both Hb and H₂O₂ suggested that the role of Hb as a catalyst was not as significant as the role of Hb as a nutrient. Also, in the presence of H₂O₂, a greater recovery of the microbial community structure was observed with the double Hb injection than the single Hb injection. Overall, this study shows that the Hb-based remediation strategies via microbial metabolism can be successfully applied to remediate the crude-oil contaminated Kuwaiti soil.