Two-Phase Partitioning Bioreactors (TPPBs) have traditionally been used to partition toxic concentrations of xenobiotics from a cell-containing aqueous phase by means of an immiscible organic solvent and to deliver these substrates back to the cells on the basis of metabolic demand and the maintenance of thermodynamic equilibrium between the phases. A limitation of TPPBs, which use organic liquid solvents, is the possibility that the solvent can be bioavailable, and this has therefore limited organic liquid TPPBs to the use of pure strains of microbes. Solid polymer beads have recently been introduced as a replacement for liquid organic solvents, offering similar absorption properties but with the capability to be used with mixed microbial populations. The present work was aimed at identifying a polymer with a greater capacity for and more rapid uptake and release of phenol for use as the second phase in a mixed culture TPPB. Polarity and hydrogen bonding capabilities between polymer and phenol were considered in the screening and selection process of candidate polymers. Hytrel (a copolymer of poly(butylene terephthalate) and butylene ether glycol terephthalate) polymer beads, offered improved capacity (19 mg phenol/g polymer at a fixed initial phenol concentration of 2000 mg/L) and a greater diffusivity (1.54 x 10(-7) cm(2)/s) when compared to the capacity and diffusivity of previously used EVA (ethylene vinyl acetate) beads (12.4 mg phenol/g polymer and 3.73 x 10(-9) cm(2)/s, respectively). Hytrel polymer beads were then used in a TPPB for the investigation of various substrate feeding strategies (fed-batch, bead replacement, and concentrated spikes of phenol), with rapid and complete phenol degradation shown in all cases.