Exploring the use of Indigenous Microorganism for the Removal of Cadmium Contaminated Soil

Abstract

This work deals on cadmium concentration remediation of (70.21mg/kg) in soils in Nigeria to below maximum allowable 3 mg/kg specified for safe agriculture by standards to ensure that farm products close to area of mining are safe for human beings. Three indigenous organisms: Bacillus subtilis (B. subtilis), Escherichia coli (E. coli) and Proteus mirabilis (P. mirabilis) were engaged for the remediation study. The organisms were isolated and cultured. Optimum weights of the distinct organisms were inoculated in 4g soils each conditioned with optimum values of pH, temperature, stirring frequency and nutrient in thirty-six 50 ml beakers; and experimented for residual cadmium ion at times 5, 10, 15, 20, 25, 30 and 35 days in triplicate with Atomic Absorption Spectrophotometer. Cadmium removal was a big task for the organisms within the experiment time frame of 5 to 35 days. The organisms either do not have great expertise for cadmium removal or the initial concentration of 70.21 mg/kg was too high for the organisms to bring the concentration to below the maximum allowable of 3 mg/kg early enough. In addition, the rapid drop in concentration with experiment time suggested a longer experiment time to achieve cadmium pollution control provided equilibrium has not been exceeded, the influence of the selected organisms on cadmium removal from the soil sample. Along the experiment time, no organism could remove cadmium to control level apart from B. subtilis at time 35 days with an efficiency of 96.10 % and residual concentration of 2.74 mg/kg. In the case of P. mirabilis and E. coli, high efficiency seemed not to necessarily effect control. This is obvious from efficiency (85.05%) of removal by P. mirabilis and 79.35 % of removal by E. coli. At these respective high efficiencies, the residual concentrations of cadmium were 10.50 mg/kg and 14.42 mg/kg for removal by P. mirabilis and E. coli respectively. These efficiencies were not sufficient for cadmium pollution control but for it abatement.