Ukiwe, L.N., J.I, A., A.E, E., C.I.C, A. and S.I, I. 2008. Chemical and Biological Leaching Methods to Remove Heavy Metals from Sewage Sludge: A Review. JOURNAL OF ADVANCES IN CHEMISTRY. 4, 3 (Dec. 2008), 509–517. DOI:https://doi.org/10.24297/jac.v4i3.948.