Bioremediation of heavy metals from artisanal crude oil refinery (Kpo-Fire) impacted soil using Bacillus flexus and Pseudomonas aeruginosa in Ngie Community, Degema Local Government Area, Rivers State, Nigeria

Abstract

The existence of heavy metals in “kpo-fire” impacted soil creates significant risks to human health and the ecosystem. In this study, the efficacy of the elimination of heavy metal from “kpo-fire” impacted soil was evaluated using bacterial treatments. The organisms (Bacillus flexus and Pseudomonas aeruginosa) used in the bioremediation setup were isolated from the impacted soil. Heavy metal analysis was carried out using an Atomic Absorption Spectrophotometer. The experimental setup involved the recreation of the contaminated soil sample in three (3) vessels labeled as: Flask A containing 300g of un-amended sample (control) to monitor natural process; Flask B containing 300g of sterilized sample; Flask C containing 300g of sample with Pseudomonas aeruginosa and Bacillus flexus. Soil baseline physicochemical composition was determined to have a pH of 6.18, Temperature of 29.2oC, Total Organic Carbon 7.58 mg/kg and Phosphate concentration 37.56 mg/kg. At the end of the investigation, experimental setup C, containing bacterial inocula was observed to possess the best bio-removal rates for Mercury (99.32%), Cadmium (77.59%), Boron (72.84%) and Arsenic (93.43%) after a 42-day period of study. Also, the concentrations declined from 1.05264mg/kg to 0.00621mg/kg for Mercury; Cadmium declined from 5.93mg/kg to 1.16mg/kg; Boron declined from 3.61mg/kg to 0.82mmg/kg and Arsenic declined from 2.78mg/kg to 0.16mg/kg. Molecular characterization revealed the contaminated soil had predominance of isolates with genomic molecular weight of 1,500 bp and the phylogenetic construct showed the bacterial isolates were Pseudomonas aeruginosa (MT023359), Bacillus flexus (MT023375) and Lysinibacillus macroides (MT023377). Statistical analysis revealed a strong positive correlation between the bacterial biomass and heavy metal removal. The synergistic parts played by bacterial consortia in the bio-removal of heavy metals from the polluted soil have been established and these potentials can be harnessed as a roadmap for eco-recovery of impacted environment in the Niger Delta. Bacillus flexus and Pseudomonas aeruginosa in consortium are efficient in remediation of kpo-fire contaminated soil.