Original Articles: 2011 Vol: 3 Issue: 1
Abatement of toxic heavy metals from highway runoff using sawdust as adsorbent
The possible use of sawdust as biosorbent has been successfully utilised to remove heavy metal ions from highway runoff. It is noted that increase in Pb2+ concentration and pH, caused the increase in adsorption capacity of sawdust. In relation to this, a decrease in sawdust dose results in a higher metal loading on the sawdust. The adsorption isotherms of heavy metals fit the Langmuir or Freundlich model reasonably well. The order of heavy metal adsorption is Pb2+ > Cu2+ > Zn2+. A high concentration of co-existing ions such as Ca2+ and Mg2+ depresses the adsorption of heavy metal. Dissolved organic matter (DOM) has a significant influence on metal adsorption. In studies involving column, a long breakthrough time is observed for heavy metals according to the ion selectivity on sawdust. The metal adsorption capacity per sawdust mass in column is lower than that obtained in batch equilibrium tests, which is possibly due to the insufficient residence time and diffusion limitation of the metal. Flushing of the column saturated with heavy metals by 0.1M CaCl2 solution results in the elution of a highly concentrated metal within shortened pore volumes, implying that sawdust could be re-used for the treatment of heavy metals.