Enhanced microbial hydrocarbon biodegradation as stimulated during field-scale landfarming of crude oil-impacted soil

Abstract

The study investigated microbial population dynamics and petroleum hydrocarbon degradation during 56-day landfarming bioremediation of crude oil-polluted soil at a Community in Niger Delta Nigeria. Landfarming involved the addition of fresh top soil from unpolluted soil to the polluted soil followed by periodic ploughing. Active oleophilic bacteria identified by 16S rRNA sequencing were screened with 2,6-dichlorophenol indophenol (DCPIP) redox indicator for their degradation profile. Physicochemical parameters monitored during landfarming included the extractable Total Petroleum Hydrocarbons (TPH), Polycyclic Aromatic Hydrocarbons (PAHs), pH and heavy metals. TPH was more than 9000 mg/kg which exceeded the Department of Petroleum Resources’ (DPR's) intervention value of 5000 mg/kg. Total viable counts of culturable heterotrophic and hydrocarbon utilizing bacteria in the polluted soil pre-landfarming were between 0.2 and 0.5 × 103 cfu/g. Monitoring of microbial population dynamics on days 0, 9, 18, 36 and 56 revealed an increase in hydrocarbon utilizing bacterial population from 104 up to 107 cfu/g which correlated significantly (R = 0.88; p = 0.05) with TPH reduction to below 700 mg/kg by day 56 when bioremediation experiment ended. Pseudomonas aeruginosa was the most efficient diesel degrader which showed 100% DCPIP decolourization. Acinetobacter, Myroides, Pseudomonas and Bacillus were central in the degradation of the long chain hydrocarbon fraction in the spill site. The fungal classes recovered included Eurotiomycetes, Saccharomycetes and Sordariomycetes. The findings from this study showed that the addition of virgin top soil to a compromised and chemically stressed soil is a green and eco-friendly strategy for enriching microbial degradative activities without addition of chemical fertilizers