HEAVY METAL INTERACTIONS WITH ACTIVATED SLUDGE PARTICULATES

Interactions of heavy metals Ag(I), Cd(II), Co(II), Cr(III), Cu(II), Hg(II), Ni(II), Pb(II), and Zn(II) with secondary and tertiary activated sludge particulates were investigated using sludge samples collected from four full-scale municipal wastewater treatment plants. Batch equilibrium metal uptake experiments were conducted. Results showed that most heavy metals except Ni(II) and Co(II) are very adsorbable. Results also showed that pH significantly affects metal uptake. The pH-independent adsorption constants were determined using the metal distribution model that considers the effect of pH on metal uptake. Results showed that, for the same metal ion, the adsorption constants determined using different activated sludge samples have the same order of magnitude, therefore these constants can be normalized. The normalized adsorption constants (log KS) of Ag(I), Cd(II), Co(II), Cr(III), Cu(II), Hg(II), Ni(II), Pb(II), and Zn(II) for activated sludge particulates are, respectively, 6.7, 4.2, 3.0, 5.8, 5.6, 6.6, 3.2, 6.1, and 4.7. Based on the adsorption constants and the field pH and SS conditions, the metal distribution in mixed liquor samples can be calculated. Results showed that the calculated metal distribution results are in good agreement with the measured metal distribution data in the field sample.