The biodegradation of pentachlorophenol (PCP), the most toxic among chlorophenols, was extensively investigated in solid-liquid two-phase bioreactors (according to Box-Behnken experimental design) to demonstrate the feasibility of this technological platform. Process performance optimization for the subsequent scale up was also performed. The process was catalysed by an acclimated microbial consortium and the partitioning phase consisted of Hytrel 8206 polymer. The virtuous combination of polymer uptake/release and microbial biodegradation allowed achieving practically complete biodegradation efficiencies and rates in the range of 4.0-7.8 mg/(L h) for PCP concentrations up to 100 mg/L far above those previously tested. Detected biodegradation rates are one order of magnitude higher than the ones reported for suspended biomass reactors. A regression model based on 3 independent variables (initial PCP and biomass concentration and polymer-to-water ratio) was formulated to predict the volumetric biodegradation rate. The significance of independent variables and their interactions was tested by the analysis of variance (ANOVA) with 95% confidence limit. The model resulted adequate and the polymer-to-water ratio was identified as the most significant factor affecting the system response. Maximization of the biodegradation rate has been achieved for PCP concentration of 100 mg/L, biomass concentration of 1 gVSS/L and polymer-to-water ratio of 9%. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.