BIOREMEDIATION OF CERTAIN HEAVY METALS VIA COMPOST APPLICATION AND BIOFERTILIZATION

The main goal of this study is to investigate the effect of the composted plant residues and biofertilization on bioremediating certain heavy metals (Cd and Pb) applied to soil cultivated with maize plants. Four cellulose-decomposing bacterial strains were isolated and the highly efficient two strains i.e., Bacillus cereus and Proteus vulgaris were used in the composting process. The plant residues were composted for 60 days either under aerobic or anaerobic conditions. The plant residue samples were taken and analyzed during composting process at 0, 14, 28, 42 and 60 day for microbiological, physical and chemical analysis. Moisture content was maintained above 50% during the first 50 days of composting thereafter the compost was allowed to dry naturally to reach 30% at the final product under aerobic and 73% under anaerobic conditions. Under aerobic conditions, temperature of compost rose rapidly and reached its peak (61oC) after 4 days and lasted above 39oC more than 3 weeks. Under anaerobic condition temperature reached its peak of 35oC after 4 weeks and lasted of 23oC.Underaerobic and anaerobic condition the pH value was decreased within the first 14 day of composting to reach 6.0 and thereafter increased to 8.9 under aerobic and 7.5 under anaerobic condition. The organic matter and carbon content of plant residues were decreased gradually during the composting process under aerobic and anaerobic conditions. C:N ratio was narrowed rapidly to reach 13.0 under aerobic and 16 under anaerobic conditions. The macronutrient contents (N, P and K) were increased during the composting period and it was higher in aerobic than anaerobic conditions. The heavy metals content in the mature compost under aerobic and anaerobic condition were within the safe range. Under aerobic and anaerobic composting process, the number of microbial population i.e., total microbial count, cellulose-decomposers, fungi and actinomycetes were decreased gradually within the first 14 days. But it was less in anaerobic than aerobic conditions. Then the total microbial count and cellulose-decomposing microorganisms increased gradually up to 28 day of composting process. Fungi were continued to decline up to the end of process under aerobic and anaerobic conditions while actinomycetes disappeared after 14 day under anaerobic condition. After 42 day of composting under aerobic and anaerobic conditions, the number of microbial populations (total microbial count, cellulose-decomposers and fungi) re-decreased up to the end of composting process. A pot experiment included 24 treatments was carried out to evaluate the effect of resultant compost with ratio 1% or 3% and/or biofertilizer with Bacillus cereus in bio-remediating the harmful effects on maize plants cultivated in a soil artificially polluted with Cd and Pb. Application of compost with 1% or 3% in presence or absence B. cereus to the treatment receive 0.1% of PbCl2 or CdSO4 increased plants height, fresh and dry weights. At 0.5% of PbCl2 or CdSO4, maize plants completely failed to growth. Inclusion of compost with 1% or 3% alone or with biofertilizer to the treatment 0.5% of PbCl2 helped maize seedling to survive. This means that use of biofertilizer (B. cereus) and compost neutralize the toxic concentrations of lead and boosted maize plant growth. The present study recommended that the combined application of compost and biofertilizer could be considered a good option for remediation of the toxic influence of heavy metals