Genotypic identification of oil-degrading bacterial isolates and physicochemical characterisation of produced water from the El-Faragh gas field in Libya

Abstract

Produced water is generated from subsurface formations during crude oil production in oil and gas fields.  Produced water samples from the El-Faragh gas field in the Al-Wahat district in northeastern Libya were collected to study its bacterial community structure. Since the physicochemical properties are crucial indicators for the level of pollution in the water, selective parameters of water samples such as pH, salinity, electrical conductivity, total dissolved solids (TDS), sulphate, phosphate, carbonate, bicarbonate, hardness, heavy metals (Ba, Ni, Cr, Cu, As, Fe, Pb, Cd, Se, Sr and Zn), total petroleum hydrocarbons (TPHs), Benzene, Toluene, Ethylbenzene and Xylene (BTEX) were analysed. Radioactive contamination was also evaluated using radiological scanning devices to measure the activity of alpha (α) and beta (β) particles and gamma (ɣ) rays. In this work, for the first time, the microbial community of the El-Faragh gas field was studied based on 16S rRNA analysis using a universal bacterial oligonucleotide primer set. The results showed that the produced water analysed in the current study contained high concentrations of salts (8443 ± 42.75 mg/L of TDS), TPHs (98.5 ± 2.18 mg/L), BTEX (97.03 ± 0.2 ppm) and heavy metals (Ba 2.42 ± 0.26 ppm, Fe 79.5 ± 0.95 ppm, Se 3.49± 0.39 ppm, Cd 0.02 ± 0.002 ppm and Sr 39 ± 0.36 ppm). Two petroleum-degrading bacterial strains were isolated and were found to be closely related to Microbacterium ureisolvens strain CFH S00084 with 98.96% gene sequence similarity and Exiguobacterium aquaticum strain IMTB-3094 with 99.36% gene sequence similarity. This study recommends that further culture-independent techniques, such as whole genome sequencing are still required.

Key words: produced water; El-Faragh gas field; M. ureisolvens strain CFH S00084; E. aquaticum strain IMTB-3094; Libya.