Solid-Liquid Two Phase Partitioning Bioreactors as a tool for xenobiotic biodegradation: case study of 4-nitrophenol M. ConcettaTomei 1* , M.Cristina Annesini 2 , Vincenzo Piemonte 2 , Sara Rita 1 , Andrew J. Daugulis 3 1* Water Research Institute, C.N.R., Via Salaria km 29.300, CP10-00016 Monterotondo Scalo (Rome) Italy, E-mail: tomei@irsa.cnr.it 2 Department of Chemical Engineering Materials Environment, Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy 3 Department of Chemical Engineering, Queen’s University, Kingston Ontario Canada K7L 3N6 In this paper the performance of two phase liquid-solid systems applied to the removal of xenobiotics was investigated. 4-nitrophenol, a typical representative of substituted phenols, was chosen as the target compound. Three polymers, a polyether-ester copolymer Hytrel 8206, a poly-caprolactone polyester Tone P797 and a polyethylene- vinyl acetate copolymer Elvax were utilized in batch kinetic tests. The best performance was obtained with Hytrel, and this polymer was also employed as the partitioning phase in a lab scale sequencing batch reactor. In all cases in the two phase systems, even if operated with a very low polymer content (~ 5%), the biomass was exposed to 4- nitropheol concentrations that are significantly lower if compared to the one-phase aqueous system with consequent drastic reduction of the toxic effect of 4-nitrophenol, and of the reaction times. A process model was also set up and applied to analyze the performance of the system in different operating conditions. 1. Introduction Biological processes are attractive as “green” remediation strategies for xenobiotic removal from aqueous environments but they have a major limitation due to substrate toxicity that can significantly reduce process efficiency and the applicable substrate load. In order to overcome these limitations an extremely promising technology based on the use of two phase partitioning bioreactors (TPPBs) has been proposed: the basic principle is to partition the toxic substrate between the aqueous phase containing the micro-organisms and an organic phase which has typically been comprised of an immiscible solvent. This configuration allows control of substrate delivery (from the solvent to the water phase) that is determined by the degradation kinetics and the maintenance of thermodynamic equilibrium (Daugulis, 2001). This approach is suitable for pure cultures but when mixed cultures are employed (i.e. in industrial wastewater treatment) a reduced efficiency can result by the parallel biodegradation of the solvent arising from biomass acclimatization. Solid polymers beads have recently been