Project Title: "Determination of the mass transfer coefficients in a two phase partitioning enzymatic reactor for the degradation of recalcitrants"
Author: Alejandro Javier Pedezert Nunez de Moraes, Universidad de la Republica2, Uruguay
Host Supervisor: Juan M. Lema Rodicio, Universidade de Santiago de Compostela1, Spain
A. Pedezert2, G. Eibes1, M.T. Moreira1, G. Feijoo1 and J.M. Lema1
The mass transfers of anthracene and enzyme stability of Manganese Peroxidase (MnP), produced by the white rot fungus Bjerkandera adusta, were studied in a Two Phase Partitioning Bioreactor (TPPB). The organic solvent assayed was Silicon Oil, varying the viscosity (10, 20 and 50 cSt) and the agitation rate (200, 250 and 300 rpm). In addition, two surfactants were tested as possible mass transfer rate enhancers, Triton X-100 and Tween 80. First, for surfactant selection, activity stability was determined in the presence of both in parallel, with concentrations form 0.25 up to 1.0 times their Critical Micellar Concentration (CMC). Both diminished the grade of exponential decay for enzyme activity and Triton X-100 was chosen based on the greater enhancement of MnP’s stability observed. Stability diminished as surfactant’s concentration was put up however, the decay constant was in every case smaller than its’ similar for the aqueous solution. Furthermore, optimum surfactant concentration was chosen (0.25 CMC). It was also determined that the addition of Ca2+ to the solution increased MnP’s thermal stability in the biphasic system even when only 100 μM of the ion were added. A concentration screening was then performed and results showed that the optimum concentration was 1 mM (20% slower decay than the control). Apparently superior concentrations affected MnP’s stability because of the ionic force generated. No tendency was found to correlate the decay constant with the specific power of agitation (P/VT) and oil viscosity. The reason for no obvious trend may be due to the use of different crude enzyme in the different experiments. Although, the stability enhancement due to the presence of Triton X-100 was confirmed in every case, as well as the Ca2+ protective effect over the enzyme.
Concerning mass transfer of anthracene, it was observed that its’ rate was improved by the addition of the surfactant. However, the saturation capability was not improved. Besides, the mass transfer coefficient increased as specific power of agitation was raised and as oil’s viscosity decreased. A pair of equations was obtained for this process, as potential functions of oil viscosity and the specific power of agitation. Each is a semi empirical equation as it was determined from experimental data but correlated taking to acknowledge typical mass transfer equations. For the purely aqueous solution the equation is kLa = 3.913μ-0.1187(P/VT)1.013 with r2 = 0.8714. For the 0.25 CMC of Triton X-100 the equation is kLa = 13.900μ-0.3385(P/VT)1.039 with r2 = 0.9439.
