Accumulation of Cu (II) and Pb (II) by biofilms grown on particulate in aquatic systems

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Abstract
Biofilms are believed to significantly influence the accumulation, transport and transformation of heavy metals. A system of bacterium‐ex opolysacchride (EPS)‐kaolinite (BEK) was used as a simulation of biofilm‐coated particle to discern the interaction of biofilms with Cu (II) and Pb (II). The adsorption for single metal ions and in the presence of two metals was interpreted using Freundlich isotherms. The distribution coefficients (Ka) of single ions were 270 for Cu2+ and 435 for Pb2+, indicating Pb (II) has a higher affinity for biofilms than Cu (II). Where both metals were present, Ka values were 413 for Cu2+ and 3.09xl04 for Pb2+, showing that the two metals competed for biofilm binding sites, with the adsorption of Pb (II) being favored. Metal adsorption was influenced by pH. Adsorption capacity increased with the elevated pH to maximums of 161.80±29.30 μg/g cell (dry weight) for Cu (II) at pH 5.0 and 112.30±26.74 ng/g cell for Pb (II) at pH 4.0. With the further increase of pH, the adsorption capacity decreased owing to the hydrolysis of metals ions and the detachment of EPS. Where both metals were present, an initial increase of metal adsorption with time was observed. Afterwards, the adsorption of Cu2+ and Pb2+ decreased from the individual maximums to 7603±970 μg/kg cell, 2240±310 μg/kg cell, respectively, suggesting that the metals seemed to be excluded from the biofilms because of their toxicity.