Removal and recovery of heavy metals by bacteria isolated from activated sludge treating industrial effluents and municipal wastewater

A total of nineteen metal-resistant and non-resistant bacteria from activat ed sludge treating both metal-contaminated industrial effluents and municip al wastewater were isolated and identified. These included both Gram-positi ve (e.g. Micrococcus) and Gram-negative (e.g. Pseudomonas) bacteria. The bi osorption capacity of these strains for five different heavy metals (copper , nickel, zinc, lead and chromium) was determined at pH 5 and initial metal concentration 100 mg/L. Pseudomonas pseudoalcaligenes and Micrococcus lute us were found to be capable of removing significant amounts of copper and l ead. Hence, they were selected for further investigations. Langmuir adsorpt ion isotherms adequately represented the distribution of copper and lead fo r both species. The study of pH effect on metal removal for both species in dicated that the metal biosorption increased with increasing pH from 2 to 6 . The effect of competing cations on biosorption of P. pseudoalcaligenes wa s studied. Sulphuric acid (0.05 M) was the most efficient desorption medium among the eleven reagents tested. Over 90% of copper sorbed on the cells o f M, luteus could be recovered by washing with 0.05 M sulphuric acid within five minutes. The biosorbent was used for at least five biosorption and de sorption cycles without loss of copper removal capacity. Immobilization of M. luteus in 2% calcium alginate and 10% polyacrylamide gel beads increased copper uptake by 61%.