The Inhibitive Effect of Gmelina arborea Fruit Extract on Biocorrosion Induced by Sulphate-reducing Bacteria

Microbial activities contribute significantly to the global economic burden of corrosion. The sulphatereducing bacteria (SRB) are major cause of biocorrosion in anoxic environments. This study investigated the corrosion inhibition efficiency of Gmelina arborea extracts against corrosion of carbon steel caused by SRB isolated from injection and produced water from Bonga oilfield. The SRB isolation, antimicrobial assay and corrosion experiments were carried out in a Coy anaerobic chamber. The isolates were identified based on the microscopic and physiologic characteristics as Desulfovibrio spp. The minimum inhibitory concentration (MIC) for G. arborea ethanol extract (GAEE) against the isolates was 0.85 g/ml and 0.93 g/ml for G. arborea aqueous extract (GAAE). The highest reduction in SRB population was observed with the MIC of extracts potentiated with 50 PPM D-Tyrosine and the least reduction was with half strength of the extract (0.5xMIC). For the 14-day test, the least inhibition efficiencies were 28.88%I and 31.01%I at 40oC for GAAE and GAEE respectively and the highest were 92.95%I and 94.63%I at 20oC for GAAE and GAEE potentiated with D-Tyrosine respectively. Similarly, for 28-day test, the least inhibition efficiencies were 22.62%I and 24.29%I at 40oC and the highest was 85.58%I and 90.28%I at 20oC for GAAE and GAEE potentiated with D-Tyrosine respectively. Adsorption mechanism of the extracts on the steel obeyed the Langmuir adsorption model at temperature between 20°C - 40°C with extract concentrations range of 0.5-2.5 g/ml. Adsorption mechanism of the extracts on the steel obeyed the Langmuir adsorption model. G. arborea contains compounds that inhibit the growth and corrosion activities of SRB. These phytochemicals can be harnessed as green inhibitors in the control of SRB in the oilfield.