Consequence of Anacardium occidentale and Garcinia kola Extracts on Sulphate Reducing Bacteria and Corrosion of Mild Steel

Abstract

The effect of Anacardium occidentale (Cashew) leaf and Garcinia kola (bitter kola) seed extracts on the corrosion of mild steel in Sulfate Reducing Bacteria (SRB) environment. Enrichment of SRB was achieved by anaerobic incubation of waste water sample from gutter along old market road Owerri, Imo State Nigeria in BmA medium and BmA medium without iron. Weight loss method was used to determine corrosion. The specific growth rate and cell biomass of SRB in batch culture was determined. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extracts were also determined using standard methods. Results showed measurable weight loss of mild steel samples as a result of corrosion by SRB. Garcinia kola extract had inhibitory effect on SRB at concentrations above 50mg/ml while Anacardium occidentale extract showed no inhibition capacity at 200mg/ml. The MIC for the Garcinia kola extract was at 50mg/ml and MBC at 100mg/ml while there was no observable MIC and MBC value for Anacardium occidentale extract. The cell biomass of the SRB in a batch culture containing Garcinia kola extract was observed to decrease over time, while Anacardium occidentale extract showed an increase in cell biomass with no decrease over time. Garcinia kola extract also reduced the specific growth rate of SRB significantly while Anacardium occidentale extract did not show any significant reduction in the specific growth rate of the SRB cultures. Garcinia kola may have potentials for use in the development of benign natural products for mitigation of microbial induced corrosion of mild steel.