Pyrolysis of sewage sludge by electromagnetic induction: Biochar properties and application in adsorption removal of Pb(II), Cd(II) from aqueous solution.

Pyrolysis of sewage sludge was studied by electromagnetic induction (EMI) heating method and in a laboratory-scale reaction installation. Basic properties and adsorption of heavy metals Pb and Cd on biochar from EMI pyrolysis of sewage sludge was investigated. Experimental results indicate that EMI pyrolysis temperature was determined by the relationship between working voltage of EMI device and induction media. Biochar yield rate ranged from 89.7% to 51.2% at temperature from 300 to 600 °C. Elements, surface characterizations and micromorphology, thermogravimetric properties as well as gas evolution changed with increasing pyrolysis temperature. Hydroxyl groups were decomposed during EMI pyrolysis process. Heavy metals in biochar was leached through TCLP and higher leachability was obtained in biochar pyrolyzed at 400 °C compared to other biochar products. A higher adsorption removal efficiency of Pb and Cd was obtained by EMI pyrolyzed biochar. Langmuir and pseudo-first-order models were used for description of adsorption isotherm and kinetics.