ENHANCED BIO-REMOVAL OF CADMIUM FROM CONTAMINATED SOIL BY AUGMENTATION USING ELEPHANT GRASS RHIZOPHERIC BACTERIA

Abstract

The ability of bacteria associated with the rhizosphere of elephant grass to enhance removal of cadmium from contaminated soil was evaluated. Rhizosphere bacteria were isolated using the soil dilution plate method on nutrient agar, centrimide agar, yeast extract mannitol agar, and formulated media specific for Acidobacterium spp. and Azospirrillum spp. Isolated bacterial response to cadmium toxicity was tested at cadmium concentrations of 0.01, 0.1, 1.0 and 10 mg/L. Resistant isolates were further tested for their cadmium sorption capacity using Atomic Adsorption Spectrophotometer (AAS). Bacterial isolates with high tolerance and sorption capacity were subsequently inoculated as consortium and individually into duplicate soils samples planted with elephant grass containing 4000 g of soil in pots at concentration of 6.118 mg/Kg of cadmium. Same was done for uninoculated
contaminated control. Rhizosphere soil in pots was then monitored for 60 days for residual cadmium levels. Results showed that cadmium resistance and sorption were highest in Pseudomonas sp., Bacillus sp. and Azospirillum sp., among rhizosphere isolates. Generally, cadmium levels decreased with time in soil. Cadmium removal was in the order: Bacterial consortium > Bacillus sp. >
Pseudomonas sp. > Azosprillum sp. > Unaugmented (control) planted soils. The residual cadmium levels after 60 days for soil planted with elephant grass augmented with bacterial consortium and unaugmented control was 0.705 and 5.701 mg/Kg respectively. Bacteria associated with the rhizosphere of elephant grass thus enhanced the removal of cadmium from contaminated soil.