Solidification of Electroplating Wastewater Treatment Sludges with Cement

Abstract

At the São Paulo Metropolitan Area, the sludge resulting from treatment of electroplating industry wastewater is inadequately disposed of, generating environmental hazards. A possible way to solve this problem is the cementation of this sludge before disposal. From July,1986 to March, 1987, the authors developed laboratory tests on cementation of electroplating wastewater treatment sludges. Performed at the laboratories of Escola Politécnica of the University of São Paulo and of CETESB, tests were conducted with three types of cement produced in Brazil - CPC - Portland Cement, POZ-pozzolanic cement and CAF - blast furnace cement. The tests had the following steps:characterization of electroplating industry wastewater treatment sludge and study of the sludge - cement mixtures;preparation of sludge - cement mixtures with water/cement ratios of 0.3, 0.5 and 0.7;measurements of mixture consistency with Casagrande soil mechanics equipment;determination of leaching quality and resistance to compression of solidified specimen at the ages of 7 days, 28 days and 90 days;analytical determination of the sludge cement mixture;test for solubility in water at the age of 90 days;analytical determination of cyanide and heavy metals in the cure water of specimen. Results showed that solidification with cement is an efficient technology for the fixation of toxic metal ions such as Cd, Hg and Pb and other metals such as Cr, Ni, Cu or Zn present in large concentrations in electroplating wastewater treatment sludges. With the only exception of Al+++ the other metallicions determined in the leachate showed concentrations below drinking water standards. As to mechanical resistance after 90 days, the sludge - cement mixtures presented a performance similar to that of structural concrete.