Enhanced phosphorus bioavailability and heavy metal removal from sewage sludge ash through thermochemical treatment with chlorine donors

Direct application of sewage sludge ash (SSA) to agriculture is mostly prohibited due to its heavy metals and limited bioavailability. Thermochemical treatment of SSA with Cl-donors were carried out to remove heavy metals and enhance P bioavailability. MgCl2 and CaCl2 removed more heavy metal than other Cl-donors. Pb was completely removed followed by Cd, Zn, Cu. They also increased P bioavailability by the conversion of Al-P to Ca/Mg-P which was confirmed by chemical fractionation. XRD confirmed the conversion of AlPO4 to Ca-5(PO4)(3)Cl, Ca-3(PO4)(2), and Mg-3(PO4)(2) by the thermochemical treatment. (C) 2017 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.