The Impact of Organic and Inorganic Amendments on Removal of Heavy Metals in Soils Polluted with Sewage Sludge
Application of sewage sludge on agricultural fields may increase the risk of soil contamination with heavy metals and could affect distribution of heavy metals in soil. The application of amendment is essential in order to reduce the harmful effects of sewage sludge applied to the soil. This study aimed to investigate the impact of organic and inorganic amendments on removal of heavy metals in the soils contaminated through sewage sludge application. Firstly, the sewage sludge was applied to the soil at levels of 0, 10, 20, 30, 40 and 50 tons per hectare, which increased heavy metal concentrations in the soil. Then, earthworm (Eisenia fetida) was added to the polluted soil in order to study the effect of organic amendments. The total concentration and fractionation of heavy metals, the weight and mortality of earthworm were evaluated after 42 days. Nanoparticles of Aluminium oxide was applied to the soil in order to study the effect of inorganic amendments. Earthworm activity caused a reduction in the total amount of Copper, Zinc, Nickel and Cadmium, while led to an increase in the total amount of Lead. Earthworms decreased all metals except Cadmium in the exchangeable fraction. The residual fraction of Zinc and Copper increased whereas the residual fraction of other three elements decreased. The total concentrations of heavy metals were decreased as a result of the aluminum oxide nanoparticles treatment. Heavy metals for Lead and Cadmium in exchangeable fraction were reduced by nanoparticles of aluminum oxide. The amount of all metals was decreased for organic fraction. The Lead and Cadmium were decreased in inorganic and residual fractions whereas other elements were increased. In general, the use of earthworms can be more effective than nanoparticles. The use of nanoparticles is not economic, while the presence of earthworms as soil organisms is very cost-effective.
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