Heavy Metals Removal in a Horizontal Rotating Tubular Bioreactor Tonči Rezić & Michaela Zeiner & Božidar Šantek & Srđan Novak Received: 29 July 2009 / Accepted: 31 March 2010 / Published online: 28 April 2010 # Springer Science+Business Media B.V. 2010 Abstract Mixed microbial culture was isolated from heavy metal-contaminated ground soils located inside iron, vinyl and cement factory area. Isolated mixed microbial culture was used for the heavy metal ions (Fe 2+ , Cu 2+ , Ni 2+ and Zn 2+ ) removal process in horizontal rotating tubular bioreactor (HRTB). In this research, the effect of bioreactor process parameters on the bioprocess dynamics in the HRTB was studied. Results of this research have shown that profiles of heavy metals concentration were gradually reduced along HRTB at all combinations of bioreactor process parameters [inflow rates (0.5–2.0 Lh -1 ) and rotation speed (5–30 min -1 )]. Hydrodynamic conditions and biomass sorption capacity have main impact on the metal ions removal efficiency that was varied in the range of 38.1% to 95.5%. Notable pH gradient (cca 0.7 pH unit) along the HRTB was only observed at the inflow rate of 2.0 Lh -1 . On the basis of obtained results, it is clear that medium inflow rate (F) has higher impact on the heavy metal removal process than bioreactor rotation speed (n) due to the fact that increase of inflow rate was related to the reduction of equilibrium time for all examined metal ions. Fur- thermore, equilibrium times for all metal ions are significantly shorter than medium residence times at all examined combinations of bioreactor process parameters. The main impact on the biofilm sorption capacity has covalent index of metal ions and biofilm volumetric density. The sorption capacity of sus- pended microbial biomass is closely related to its concentration. Results of this research have also shown that the removal of heavy metals ion can be successfully conducted in an HRTB as a one-step process. Keywords Horizontal rotating tubular bioreactor . Heavy metals (Fe 2+ , Cu 2+ , Ni 2+ and Zn 2+ ) . Mixed microbial culture . Biological treatment List of symbols c M,0 inflow concentrations of metal ion (kg m -3 ) c M,out outflow concentration of metal ion (kg m -3 ) c M,f concentration of metal ion in biofilm phase (kg m -3 ) c M,L concentrations of metal ion in the liquid phase (kg m -3 ) c x,f biofilm volumetric density (kg m -3 ) c x,L biomass concentration in the liquid phase (kg m -3 ) D ef effective diffusion coefficient of metal ion in biofilm (m 2 h -1 ) Water Air Soil Pollut (2011) 214:343–355 DOI 10.1007/s11270-010-0428-7 T. Rezić : B. Šantek (*) : S. Novak Department of Biochemical Engineering, Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6/IV, Zagreb HR-10000, Croatia e-mail: bsantek@pbf.hr M. Zeiner Department of Analytical and Food Chemistry, Faculty of Chemistry, University of Vienna, Vienna, Austria