Study of Cadmium Removal from Environmental Water by Biofilm Covered Granular Activated Carbon

Abstract

The contamination of water by toxic heavy metals is a world-wide environmental problem. Discharges containing cadmium, in particular, are strictly controlled due to the highly toxic nature of this element and its tendency to accumulate in the tissues of living organisms. Low concentration (below 5 mg`/L) of cadmium is difficult to treat economically using chemical precipitation methodologies. Ion exchange and reverse Osmosis which can guarantee the metal concentration limits required by regulatory standards, have high operation and maintenance costs. The goal of this research was to determination of efficacy of using GAC, Biofilm and BAC columns to treat low concentration cadmium bearing water streams and was to determination of the effects of temperature and pH on the adsorption isotherms. Studies were conducted to delineate the effect of pH, temperature, initial Cd and adsorbent concentration on adsorption of Cd2+ by GAC, BAC and Biofilm. Breakthrough curves for removal of 0.5 mg/L Cd2+ by GAC, Biofilm and BAC columns at two contact times were plotted. Batch adsorption and column data are compared, pH is shown to be the decisive parameter in Cd removal for GAC but not for BAC or biofilter. Lagergren plots confirm applicability of first-order rate expression for adsorption of Cd by GAC, BAC and Biofilm. The adsorption coefficient (Kad) for BAC was 2-3 times greater than those with plain GAC. Bed Volumes of water containing 0.5 mg/L Cd2+ treated at breakthrough for GAC, Biofilm and BAC columns were 45, 85 and 180 BV respectively. BAC is more efficient than GAC in the removing of Cd from water environment.