A capillary membrane bioreactor has been developed and tested for the removal of phenolic compounds from synthetic and industrial effluents. Polyphenol oxidase was immobilized on single capillary membranes in a small-scale bioreactor using two morphologically different polymeric membranes. One has a novel structure with no external supporting skin layer. This membrane allows greater flux and was shown to facilitate high efficiency in removal of reaction products from the reactor Using this high flux membrane, 949 mu mol phenolics were removed from a solution containing 4 mM total phenolics using 45 U polyphenol oxidase in 8 h as compared with 120 mu mol removed using non-immobilized enzyme which was inactivated (due to product inhibition) after 7 h. No precipitated melanoid products were observed in the permeate from the capillary membrane bioreactor, and in order to remove the colored quinone-type products of the reaction, a packed column containing chitosan was integrated into the system. Almost complete removal of the colored quinones and associated polymers from the permeate was observed.