摘要：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.
