Reduction of Some Heavy Metals in Fibre Cement Roofing Sheet Waste-Contaminated Soil by Consortium of Bacteria and Fungi

Abstract

This research was carried out in order to ascertain the effectiveness of microbial remediation (bio-remediation) of environmental pollution by heavy metals from different sources in general and wastes from the manufacturing of fibre cement roofing sheets specifically. The concentrations of Cd, Cr, and Ni in fibre cement soil (0.11, 0.08 & 0.83), in dumpsite soil (4.17, 2.87 & 40.68) and in surrounding soil (2.11, 1.89 & 19.84) and soils outside the pollution area, control, (1.76, 0.89 & 14.17) mg/g respectively were determined using atomic absorption spectrophotometry. Preliminary results showed that the concentration of the heavy metals; Cd, Cr, and Ni were all higer than values recorded by the WHO/FEPA standard. Analysis of the variance of means between the heavy metals showed differences in the respective sampled soils (P= 0.209). The minimum inhibitory concentration (MIC) of the heavy metals on the test organisms of Bacillus sp, Rhizopus sp, proteus sp and microsporium canis were obtained by the Agar diffusion method from stock culture of isolates from fibre waste dumpsites at the Department of Microbiology, Delta State University Abraka. The MIC values for Ni on the respective test organisms were; 300, 150, 250 & 450, Cr; 250, 400, 350 & 450 while that for Cd was 900, 750, 900 & 700 μg/ml. Sterilized consortia of isolates inoculated with various combinations of bacteria and fungi were used to treat the experimental sampled soils. Concentrations of the respective heavy metals of the sampled soils were evaluated after the 1st and 12th week of treatments. Furthermore, the concentration of the respective heavy metals reduced in varying percentages between the 1st and 12th week of treatment and the results were also found to be significantly different statistically (t-calculated > t-critical). Overall, the percentage reduction in the heavy metal concentrations between the 1st and 12th week was higher in Cd and Cr (76.25% & 76.25%) respectively than in Ni (52.65%). This was an indication that microbial isolates were very effective in reducing heavy metals in fibre cement roofing sheet-wastes and from the environment.