Adsorption of heavy metals in slow sand filters

Chemical contaminants at low concentrations are difficult to remove from water. Chemical precipitation, reverse osmosis and other methods become inefficient when contaminants are present in trace concentrations. The process of adsorption is one of the few alternatives available for such situations (Huang and Morehart, 1991). A number of adsorbent materials have been studied for their capacity to remove heavy metals, including activated carbon, activated alumina, ion exchange resins, crushed coals etc. Some of these materials, such as ion exchange resins are totally effective but expensive and others, such as coal and straw, are inexpensive but ineffective. Activated carbon is very effective in removing heavy metals, but is readily soluble under extreme pH conditions (Huang and Blankenship, 1989). Peat moss has been found as very effective in adsorbing heavy metals (Ho, 1995). In the present study Slow Sand Filters (SSFs) are tried to remove heavy metals and found very effective (Muhammad et al, 1997). Experimental results on the influences of process variables in removing heavy metals by SSFs demonstrated that adsorption was one of the mechanisms of the removal of heavy metals (Muhammad et al, 1997). To confirm this prediction/hypothesis, batch adsorption tests were carried out. This paper deals with the results of the batch adsorption tests to establish adsorption isotherms and adsorption capacity of the sand for the selected heavy metals.