Reduction of Heavy Metals Sludge by Vermicomposting Technique: Treatment of the Industrial Sludge by Earthworms

Two kinds of treatments were used in the current Book, namely, biological and chemical treatments, to reduce the concentration of four heavy metals (Al, Ni, Zn, and Pb) in the sludge collected from the electronic industry. A biological treatment called vermicomposting technique was employed to expose four different ratios of sludge (20, 50, 80, and 100%) mixed with goat manure and rice straw as a composting material to the earthworm species Eisenia fetida for four weeks. For the chemical technique, the sludge was washed with a mixture of two reagents (Na2 EDTA and Na2S2O5) at different volumes of washing solution (2.5, 5, and 7.5 mL to 1 g of sludge). The best reduction of heavy metals occurred in 7.5 mL with a percentage reduction of 5%, 12%, 16%, and 24% per gram sludge for Al, Ni, Zn, and Pb, respectively. Based on the findings, the vermicomposting technique shows greater potential over the chemical washing technique in reducing heavy metal concentration in electronic sludge.