Methanogenic biodegradation of crude oil storage tank sludge enhances bio-corrosion of mild steel
Methanogenic biodegradation of crude oil sludge was investigated using chemical and molecular approaches. 16S rRNA gene sequences recovered from the samples revealed significant presence of Marinobacterium (63%), Pseudomonas (3%), acetotrophic Methanosaeta (16%) and hydrogenotrophic Methanobacterium (5%). The resident microbial community was able to reduce the gravimetric weight of residual oil by 65.5% (with complete degradation of C5–C17 n-alkane fractions) in non-amended samples and 94.13% (with complete degradation of C5–C25 n-alkane fractions) in substrate-amended samples during the 60-day incubation period. As biodegradation progressed, acetotrophs consume acetate at the rate of 0.41 mM/day−1 while hydrogenotrophs consume hydrogen at the rate of 0.59 mM/day−1. Respective volume of methane produced and corrosion rates observed were higher in highly biodegraded samples (3.60 mmol/0.084 mm/year) than lesser biodegraded samples (1.64 mmol/0.018 mm/year). Our results showed that the resident methanogenic archaea were largely responsible for the anaerobic biodegradation of hydrocarbons in crude oil sludge and biodegradation was enhanced with substrate amendment, which further accelerated the corrosion rates of mild steel coupons. Considering the relatively high number of facultatively anaerobic Marinobacterium and significant presence of Pseudomonas in the sequenced data, we speculate that the bacteria were at least partially responsible for biodegradation of crude oil components potentially acting as syntotrophic organisms with methanogens to convert crude oil to methane and subsequently enhance corrosion rates of mild steel coupons.
KeywordsMethanogenic biodegradation Acetotrophs Hydrogenotrophs Crude oil sludge Syntrophy
This work was supported by grants from the Nigerian Petroleum Technology Development Fund (PTDF). We acknowledge the earlier DNA analysis and pyrosequencing of oily sludge samples carried out with grants from Gerrit Voordouw, University of Calgary, Alberta Canada.
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Conflict of interest
The authors declare that there is no conflict of interest.
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