Microbial corrosion inhibition of mild steel by Bacillus thuringiensis

The mechanism of microbial corrosion inhibition cannot be linked to a single biochemical reaction or particular species or group of microbes. Some microorganisms are able to both cause and inhibition corrosion. Studies on the effect of Bacillus thuringiensis on the corrosion behaviour of mild steel were carried out using gravimetric and atomic force microscopy (AFM) analysis. The mild steel coupons 2 x 2x 2 cm in size were suspended with a cotton thread which passes through a hole in each coupon, inoculated with the bacterium and incubated aerobically. The coupons were retrieved at 10 days intervals progressively for 60 days and analyzed. The result revealed that B. thuringiensis inhibited the corrosion of mild steel. The corrosion rate showed clear decrease in rate from 0.45 mpy after 10 days to 0.03 mpy after 60 days of exposure to B. thuringiensis when compared to a significant increase in corrosion rate observed (from 0.67mpy after 10 days to 3.98 mpy after 60 days) for mild steel not exposed to the bacterium respectively. The AFM analysis showed a wavy pattern of corrosion on the surface of the metal not exposed to the bacterium coupled with some peaks and valley formed as a result of uneven deposition of corrosion products. B. thuringiensis was very effective in inhibiting mild steel corrosion in aerobic environment.