Biosorption of heavy metals by bacteria isolated from activated sludge

Twelve aerobic bacteria from activated sludge were isolated and identified. These included both Gram-positive (e.g., Bacillus) and Gram-negative (e.g. , Pseudomonas) bacteria. The biosorption capacity of these strains for thre e different heavy metals (copper, nickel, and lead) was determined at pH 5. 0 and initial metal concentration of 100 mg/L. Among these 12 isolates, Pse udomonas pseudoalcaligenes was selected for further investigation owing to its high metal biosorption capacity. The lead and copper biosorption of thi s strain followed the Langmuir isotherm model quite well with maximum bioso rption capacity (q(max)) reaching 271.7 mg of Pb2+/g of dry cell and 46.8 m g of Cu2+/g of dry cell at pH 5.0. Study of the effect of pH on lead and co pper removal indicated that the metal biosorption increased with increasing pH from 2.0 to 7.0. A mutual inhibitory effect was observed in the lead-co pper system because the presence of either ion affected the sorption capaci ty of the other. Unequal inhibitions were observed in all the nickel binary systems. The increasing order of affinity of the three metals toward P. ps eudoalcaligenes was Ni < Cu < Pb. The metal biosorptive potential of these isolates, especially P. pseudoalcaligenes, may have possible applications i n the removal and recovery of metals from industrial effluents.