Restoration of copper-contaminated wastewater through bacterial biosorbents

Nowadays accumulation of heavy metals (HM) in water bodies represents a serious environmental and human health threat. Mechanisms of water decontamination exploit bacterial exopolymeric substances (EPS) as active surfaces for binding HM cations. Biofilm formation on microporous carriers inoculated with specific metal-resistant bacterial strains, can represent an operative implementation with respect to planktonic systems to be applied in the upscale of wastewater treatment systems. The aim of the present study is to investigate the feasibility of using a copper-resistant (MIC of 476 mg L-1) Serratia plymuthica strain As3-5a(5) in a biofilm-based system to remove Cu(II) from electroplating wastewaters. The strain was previously characterized for EPS production (90 mg g-1 d.w.) and biofilm formation. In non-proliferating cell planktonic system, it removed up to 92% of Cu(II) from a 200 mg L−1 solution and 90% from Cu contaminated (30 mg L-1) wastewater. Metal desorption achieved by 0.1 M nitric acid was in the order of 50%. In different biofilm-based systems strain As3-5a(5) exhibited various Cu(II) removal within 4-minute contact time: 42% when on calcium alginate beads, 55% on perlite gardening substrate and 92% on sintered glass beads. In sintered glass beads column systems, As3-5a(5) biofilm removed up to 92% of Cu(II) in solution. EPS production, quantified either by extraction and spectrophotometric method and by specific Concanavalin-A fluorescent lectin analysis in flow cytometry, was higher from cells grown for 24 than 72 hours whereas maximum metal adsorption was achieved after 72 hours of incubation. As determined by NMR analysis, the prevalent monosaccharides were mannose and rhamnose at all incubation times. Data obtained so far indicate that S. plymuthica strain As3-5a(5) is promising for the development of a biofilm-based system to eliminate heavy metals from industrial wastewaters. Beside this, further work is necessary to understand the role of EPS or other cellular outer layers in metal binding. This could be of help for optimizing the strain ability in larger scale bioreactors.