Application of xylene-degrading bacteria in the treatment of soil contaminated with petroleum hydrocarbons - A comprehensive laboratory to pilot-scale analysis.

Petroleum hydrocarbons, including both aliphatic (gasoline, mineral oil) and aromatic compounds (BTEX), are known for their harmful effects on ecosystems and human health. Despite many studies, large-scale treatment of contaminated soils continues to be challenging, especially at lower temperatures. The use of metabolically-versatile, psychrotolerant, cold-active microorganisms, seems a promising, cost-effective and eco-friendly solution to boost remediation rates. In this study, a suitable microbial consortium was prepared and tested both in lab- and pilot-scale. To achieve the best bioremediation results, bacterial strains were isolated from BTEX-contaminated soil and then tested for the desired traits over a wide range of conditions. Of 5 preselected strains, 3 Pseudomonas strains capable of denitrification and aerobic/anaerobic degradation of hydrocarbons (up to 41.53±7.39 %), further characterized by a broad temperature (4-37 °C), pH (3-4 to 11) and salinity (0-8 %) tolerance, as well as resistance to freezing, were selected. Physiological studies were supported by genetic analyses, which indicated the presence of both alkB and xylM genes, and excluded similarity of the strains to the known opportunistic pathogens. To further confirm the applicability of the consortium, lab-scale analyses were followed by comprehensive pilot-scale tests on ~5 m biopile/biocell, at different conditions. The results revealed increased efficacy of the consortium in bioremediation, when compared to biostimulated indigenous strains, for volatile hydrocarbons (93 % vs 88 %) and mineral oil (23 % vs 15 %), as well as 175 % and 136 % acceleration of remediation for the respective compounds in terms of time needed to complete the process. Moreover, the high survivability and metabolic activity of the consortium at different temperatures indicate the possibility of its year-round use for bioremediation of soil contaminated with petroleum hydrocarbons. The study proves the potential of specialized bacteria in the removal of pollutants, and emphasizes the role of bio-based strategies in addressing complex environmental challenges and remediation of contaminated sites.