The process of thermodialysis and the efficiency increase of bioreactors operating under non-isothermal conditions

When a catalytic membrane is employed in a non-isothermal bioreactor its activity increases as a direct function of the applied temperature gradient and decreases when both average temperature or substrate concentration increase. To know the physical cause responsible for this behaviour substrate fluxes have been studied under isothermal conditions (diffusion) and non-isothermal conditions (thermodialysis). Strong analogies between the behaviour of the catalytic membrane and the substrate fluxes produced by the process of thermodialysis have been observed. By introducing diffusive and thermodiffusive substrate fluxes in appropriate mass balance equations the substrate concentration profiles into the catalytic membrane have been deduced by computer simulation. In absence of catalysis and under non-isothermal conditions the profiles are higher than the ones corresponding under comparable isothermal conditions, while the contrary occurs in the presence of catalysis. The percentage increases of enzyme activity, calculated by the curves of the substrate concentration profiles, show the same temperature and concentration dependence than those actually observed with the catalytic membrane. The role of thermodialysis in affecting the enzyme activity in non-isothermal bioreactor has been discussed and demonstrated. (C) 2000 Elsevier Science B.V. All rights reserved.