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THE EFFECTS OF CLAY A M E N D M E N T AND COMPOSTING ON METAL SPECIATION IN DIGESTED SLUDGE LIANG QIAO

Australia, Australia (First received October 1995; accepted in revisedform September 1996) Abstract--Sewage sludge usually contains significant heavy metals that may limit its land application. Heavy metals in municipal solid waste have been shown to be less mobile by amendment with bauxite refining residue (red mud) prior to the composting process. | Wat. Res. Vol. 31 No. 5 pp. 951-964 1997 1997 Elsevier Science Ltd. All rights reserved _ _ Printed in Great Britain PII S0043-1354 96 00290-4 0043-1354 97 17.00 0.00 Pergamon THE EFFECTS OF CLAY AMENDMENT AND COMPOSTING ON METAL SPECIATION IN DIGESTED SLUDGE LIANG QIAO and GOEN HO Institute for Environmental Science Murdoch University Murdoch 6150 Western Australia Australia First received October 1995 accepted in revised form September 1996 Abstract Sewage sludge usually contains significant heavy metals that may limit its land application. Heavy metals in municipal solid waste have been shown to be less mobile by amendment with bauxite refining residue red mud prior to the composting process. In the present research a sequential step extraction was employed to investigate metal speciation into exchangeable bound to carbonate to Mn and Fe oxides to organic matter and in residue phase and the effect of red mud on metal speciation in compost of sewage sludge for Cr Cu Ni Pb and Zn. The effect of red mud addition and composting process on metal distribution in sewage sludge compost is significant. Red mud addition generally reduces metal leachability and therefore the potential hazard of releasing metals from sludge compost through adsorption and complexation of the metals on to inorganic components to different extents for the different metals. Red mud cannot desorb however metals bound to organic matter in the sludge. The composting process breaks down organic matter in the sludge and may release the heavy metals. The addition of red mud prior to the sludge composting binds the released metals on to the red mud for those not strongly readsorbed by the remaining organics Cu Ni and Zn . 199 7 Elsevier Science Ltd Key words bauxite refining residue red mud composting heavy metals metal mobility metal speciation sewage sludge INTRODUCTION In a previous experiment Qiao et al. 1993 the effect of bauxite refining residue red mud on the metal .