Bioremediation of heavy metal-contaminated effluent using optimized activated sludge bacteria

Removal of heavy metals from contaminated domestic-industrial effluent using eight resistant indigenous bacteria isolated from acclimatized activated sludge was investigated. Molecular identification using 16S rDNA amplification revealed that all strains were Gram-negative among which two were resistant to each of copper, cadmium and cobalt while one was resistant to each of chromium and the heavy metal mixture. They were identified as Enterobacter sp. (Cu 1 ), Enterobacter sp. (Cu 2 ), Stenotrophomonas sp. (Cd 1 ), Providencia sp. (Cd 2 ), Chryseobacterium sp. (Co 1 ), Comamonas sp. (Co 2 ), Ochrobactrum sp. (Cr) and Delftia sp. (M 1 ) according to their resistance pattern. Strains Cu 1 , Cd 1 , Co 2 and Cr were able to resist 275 mg Cu/l, 320 mg Cd/l, 140 mg Co/l and 29 mg Cr/l respectively. The four resistant strains were used as a mixture to remove heavy metals (elevated concentrations) and reduce the organic load of wastewater effluent. Results revealed that using the proposed activated sludge with the resistant bacterial mixture was more efficient for heavy metal removal compared to the activated sludge alone. It is therefore recommended that the proposed activated sludge system augmented with the acclimatized strains is the best choice to ensure high treatment efficiency and performance under metal stresses especially when industrial effluents are involved.