Continuous hydrolysis of olive oil by Candida rugosa (CRL) lipase was studied in a two configuration of microporous hydrophilic membrane bioreactor. This two confuguration of module side stream and submerged membrane bioreactors is based on the separation of enzyme and products (or substrates) by a semipermeable membrane that creates a selective barrier. Permeable solutes can be separated from the reaction mixture by the action of a driving force (chemical potential, pressure, electric field) that is present across the membrane. Membranes are used in bioreactor exclusively as a matrix for immobilization of the enzyme, without any separation intentions.
In recent years, the functions of the membrane have been extended with the systematic use of these reactors in two-phase bioconversions. Membrane acts as a support for the interface between two distinct liquid phases. The membrane not only separates the phases, but also provides interfacial contact area and, together with the enzyme, acts as an interfacial catalyst. A complete retention of the enzyme within the system is the first and most important requirement for a successful continuous operation of a membrane bioreactor. Upon this retention, the enzyme becomes confined to a defined region of the membrane reactor, where reaction with the substrate occurs. The enzyme was immobilized on the shell side of the membrane and is usually entrapped inside the pores or membrane matrix. Olive oil and buffer solution, fed continuously through two compartments partitioned by membrane, caused reaction at the interface of lipase-adsorbed membrane and buffer solution. The hydraulic pressure in the oil phase was enough to maintain phase separation, an accurate pressure control was not necessary. This fact is an advantage with respect to membrane bioreactors for hydrolysis reaction.Fatty acid was obtained in a single phase without being mixed with components of other phases. The products resulting from reaction with contact with the substrate should permeate through the membrane pores, either by diffusion (induced by concentration gradient) or convection (usually induced by a pressure gradient). In this way a continuous removal of products from the reaction media is attained. At all mean residence times, countercurrent flow mode was superior to cocurrent one. The percent hydrolysis depended hyperbolically on the interfacial enzyme concentration.
The hydrolysis seemed to be limited by diffusion of fat or fatty acid through the micropores of the membrane into the lumen side. The lipase stability was significantly greater to the buffer solution in the submerged module rather than that of sidestream one. However, in the case of low-solubility precipitating products, complete rejection of solid products might turn out to be an unexpected advantage of these reactors.To improve the membrane area/reactor volume ratio in hollow-fiber submerged membrane bioreactor has introduced. As The low enzyme stability might adversely affect the cost of industrial scale bioprocesses but with the submerged configuration it could be minimize.
