Novel biodegradation system for bisphenol A using laccase-immobilized hollow fiber membranes.

Radiation-induced graft polymerization was applied to prepare membranes for multilayer immobilization of laccase, which has biodegradation ability for bisphenol A (BPA). Glycidyl methacrylate (GMA) was grafted onto porous polyethylene membranes as the monomer of polymer brushes, and aminoethanol (AE) was introduced to the grafted GMA membrane, creating unfolded polymer brushes that serve as a good support for multilayer immobilization of laccase. The objectives of this study were as follows: adjustment of space velocity (SV) for optimum performance; enhancement of stability in organic media through moisture retention; biodegradation of BPA at continuous operation; and investigation of the effects of redox mediators. Laccase and membrane activities were increased at higher SVs as a result of stronger substrate transport. The 1.85% moisture retention as a result of high-density AE containing polymer brushes demonstrated the improved stability of immobilized laccase over free laccase in methanol-containing solutions. BPA was removed with an activity of 0.11 mol/h/kg-membrane. The effects of three major laccase mediators on BPA oxidation was studied, and only 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) was shown to increase the oxidation of BPA to 100% at low SVs. Improved stability of laccase and high removal rates in the continuous biodegradation of BPA were achieved by the presented method.