Study of mass transfer and biocatalyst stability for the enzymatic degradation of anthracene in a two-phase partitioning bioreactor

In this study the optimal experimental conditions for the degradation of a polycyclic aromatic hydrocarbon in an enzymatic two-phase partitioning bioreactor (TPPB) were investigated. The immiscible organic phase was comprised of silicone oil, acting as a pollutant reservoir for anthracene. This compound underwent degradation by the enzyme versatile peroxidase (VP) produced by the white-rot fungus Bjerkanderaadusta. Mass transfer coefficients (kLa) and enzymatic deactivation constants (kD) were determined in the TPPB system. The effects of operational parameters such as solvent viscosity (10, 20 and 50 cSt), agitation rate (200, 250 and 300 rpm) and addition of the non-ionic surfactant Triton X-100 (below its critical micelle concentration, CMC) on the mass transfer and enzymatic decay were investigated. It was ascertained that there was superior enzymatic stability at high values of viscosity. The addition of surfactant below CMC displayed the dual benefit of increasing mass transfer of the substrate fivefold from the organic to aqueous phase whilst also creating a protecting effect upon VP. Optimized conditions led to an 88% oxidation of anthracene after 38 h.