Use of sludge from wastewater treatment plants as adsorbents for removal of heavy metal ions from water

Abstract

The sludge from municipal and industrial wastewater treatment plants were used as adsorbents for removal of heavy metal ions from water. Both of sewage sludge were obtained from activated sludge bilolgical treatment processes. The adsorption studies were performed using batch method and the adsorption efficiency of both sludge for Cd(II), Ni(II) and Pb(II) ions were compared under influence of certain parameters. The residual metal concentrations were determined by FASS. The result from surface characterization and elemental analysis indicated that both sludge had low surface area and consisted of carbonaceous substances. The results from adsorption studies showed that suitable contact time for removal of Cd(II), Ni(II) and Pb(II) ions were 1 hour and the suitable pH values werre 7 for Cd(II) and Ni(II), and 5 for Pb(II), respectively. The adsorption of the metal ions on both sewage sludge fit well Langmuir model and the adsorption kinetics followed the pseudo-second-order kinetics. It was observed that an increase in adsorbent resuluted in an increase in removal effciencies and a faster adsorption rate. The maximum adsorption capacities of Cd(II), Ni(II) and Pb(II) ions were 0.140, 0.053 and 0.171 mmol g-1 by municipal sludge, and 0.147, 0.064 and 0.150 mmol g-1 by industrial sludge, respectively. The adsorbents were applied to remove the metal ions in real wastewater containing 8.3 mg L-1 of Cd(II), 5.1 mg L-1 of Ni(II) and 27.4 mg L-1 of Pb(II) ions and the total removal of the metal ions was obtained when using 2 g mg L-1 of sludge. The result from sequential extraction indicated that metal distributed in different fractions of the sewage sludge, and mostly in the residual fraction. The results from the standard leaching ttest showed that the concentrations of metal in the leachate were greater than the total threshold limit concentration (TTLC) for all metals. Therefore, the used sludge was classified as hazardous waste. All of the results showed that the adsorbents derived from municipal and industrial sludge have a good potential to be used as adsorbents for removal of Cd(II), Ni(II) and Pb(II) ions in water. However, the used adsorbents had to dispose correctly.