Development and Evaluation of an Exogenous Bioaugmentation Framework Using an Immobilized Mixed Bacterial Consortium for the Remediation of Hydrocarbon-Contaminated Soils

Improving the quality of oil-contaminated soils remains a critical challenge, and bioaugmentation using allochthonous bacteria offers promising perspectives. This study proposes a framework for exogenous bioaugmentation using a bacterial consortium, composed of strains from diverse climates, immobilized in alginate beads and combined with calcium peroxide as an oxygen-releasing compound. Two conditions were tested: freshly prepared beads (BA) and lyophilized beads (LA). Their performance was compared to natural attenuation (NA) and to landfarming coupled with bioaugmentation using a free autochthonous consortium. Hydrocarbon degradation was assessed through total petroleum hydrocarbon (TPH) and alkane depletion (GC-MS), microbial community dynamics (amplicon sequencing), and abundance of the alkB gene (qPCR). In three months, the BA treatment achieved a 44% TPH reduction, outperforming LA (34%) and NA (10% less than BA). However, LA induced a marked increase in alkB gene copies and microbial biomass at the end of the experiment, suggesting greater long-term potential. Dominant genera varied across treatments: Rhodococcus in NA, Gordonia in BA, and Pseudomonas in LA. In parallel, the autochthonous consortium achieved up to 80% oil degradation. This study demonstrates the viability of lyophilized microbial consortia in scalable, ready-to-use formulations and provides an operational methodology for exogenous bioaugmentation as a tool for the remediation of hydrocarbon-contaminated soils.