Nickel and copper biosorption by EPS producing Ensifer adhaerens strain As3-5a

Anthropogenic and industrial activities are responsible for environment contamination through the release of toxic heavy metals. Recent studies have reported that microbial biofilms producing extracellular polymeric substances (EPS) contribute significantly to heavy metals removal due to the capacity of EPS to bind and sequester heavy metals from industrial effluents. In the present work, an EPS producing bacterial strain, affiliated to Ensifer adhaerens, was characterized and used in biosorption experiments, in order to implement Nickel and Copper removal process from electroplating wastewaters. Ensifer adhaerens was grown in Luria Broth (LB) medium in a 5L bioreactor. At defined sampling times (24, 48 and 72 hours), cultural broths were deposited onto cellulose acetate membranes. Nickel (50 mg/L) and Copper (200 mg/L), provided as distilled water solutions as well as electroplating wastewaters, were passed through the biomass-activated filters. Abiotic systems were also prepared in order to monitor abiotic losses of heavy metals. Nickel and Copper analysis were conducted by inductively coupled plasma mass spectroscopy (ICP-MS). Twenty four hours-grown biomass removed from water solutions 6.12 mg/L of Nickel and 132.17 mg/L of Copper, separately. When both present in bimetallic water solution, the two metals were removed more efficiently: Ni 25.15 mg/L and Cu 174.03 mg/L. When electroplating wastewater was passed through the biomass-activated filter the removal of Nickel was 17.56 mg/L in the absence of Copper, and of 22.48 mg/L of Nickel and 204 mg/L of Copper in the presence of a bi-metallic wastewater. When the biomass was grown in EPS not inducing conditions, heavy metal removal was not observed, suggesting their role in the process. The high biosorption potential of Ensifer adhaerens strain As3-5a in single and bi-metal systems indicates that the EPS producing strain may be exploited as eco-friendly and low-cost biotechnology for the clean-up of industrial effluents from nickel and copper.