Abstract:
Rapid industrialization and urbanization have resulted in the generation of large quantities of aqueous effluents, many of which contain high levels of toxic heavy metals and xenobiotics that pollute groundwater and soil of affected farmlands. Heavy metals are not biodegradable and as such not removed from the soil but rather accumulate and persist in soil reservoirs, consequently entering the food chain and exerting toxic effects on living organisms. Copper and lead which exert toxic effects even at very low concentrations are common constituents of the Nigerian crude oil and consequently are found in its effluent. Research has shown that removal/recovery of these metals (through bioaccumulation/biosorption by bacteria) is an attractive alternative to traditional physicochemical techniques. Microorganisms tolerant to metals are often isolated from areas of high metal loading, suggesting that metal tolerance or resistance is an adaptive response to excessive metal exposure. In this study, crude oil effluent was analyzed for copper and lead contents and both metals were found to show concentrations higher than the U.S Environmental Protection Agency (EPA) and the Compendium of Environmental Laws for African Countries (CELAC) recommended environmentally accepted standards. Microorganisms were isolated from the effluent and from the effluent-contaminated soil from the site. The largest/most successful colony was subsequently characterized. Through morphological and biochemical tests, it was identified as Bacillus subtilis. Four test groups of mineral salt media containing copper only (Group A), lead only (group B), copper + lead (Group C) and no lead or copper (Group D, control) set at different pHs of 5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0 for each group were used. The organism was standardized and found to contain 6.0 x 108 Bacillus subtilis cells per ml of suspension. Five ml of the organism was inoculated into each experimental medium. The absorbance change (turbidity) of the mineral salt media were measured at 540nm on the 10th, 17th and the 24th days - the evaluation criteria for microorganism growth and adaptation in the used media. The experimental media showing the highest growths for each group was analyzed for residual copper and lead. Also, the bacterial biomass from these media were harvested and analyzed for recovered lead and copper. Results showed that Group D had the highest growth, followed by Group B, Group A and lastly Group C. The organism grew most at pH 7.5 - 8.0. The experimental media that showed the highest growths for each group, when analyzed for residual copper and lead had no trace of metals, implying complete biosorption by the B.subtilis. B.subtilis is therefore recommended for removal of lead at pH 7.5 - 8.0 in crude oil pollution.
