Bioaccumulation of heavy metals during composting and vermicomposting processes of sewage sludge

Using of sewage sludge as an organic fertilizer is restricted by international standards because it contains heavy elements in addition to, pathogenic microorganisms. Therefore, this study aimed to use technology of both composting and vermicomposting to remove heavy elements from sewage sludge by using bio-accelerator (Trichoderma harzianum, Trichoderma viride and Phanerochaete chrysosporium,) and vermi worms (Eisenia fetida) individually or combined together. The results showed that the use of bio-accelerator and Eisenia fetida worms together had a significantly positive effect on reducting the concentration of heavy metals to the safe limit compared to the Egyptian code during the 12-week experiment period, where it decreased the available concentration of heavy metals (Lead, Nickel and Cadmium) from 6.429, 4.448 and 0.197 in the initial experiment to 0.213, 0.142 and 0.065 mg /kg in the final experiment, respectively. Also, total concentrations of heavy metals were reduced to 313.95, 210.40 and 10.85 for Pb, Ni and Cd (mg/ kg) initially; meanwhile, the final concentrations did not exceed either the Egyptian code limits or worldwide Standards. In addition, to improve quality (NPK) of organic fertilizers and safety represented the highest percentage of removal 72, 67 and 62% for Cd, Ni and Pb respectively. So, this technique for sewage sludge treatment is considered promising for production of quality organic fertilizer and safe environmentally.