Biocatalytic productivity of alcohol dehydrogenase (ADH) in membrane bioreactor: effect of pH

The present study is to evaluate the effect of pH value on enzyme loading rate in membrane and to examine the effect of pH on permeate flux, observed rejection, filtration resistances and fouling mechanisms. Immobilization enzymes are necessary for increasing the biocatalytic efficiency. The main beneficial of immobilization of enzymes are enhancing productivity and enabling re-usability of enzymes which can be able by using enzyme membrane reactor. However, fouling is the main issues on membrane reactors and compromise the performance of the membrane in terms of separation efficiency and permeate flux. The fouling mechanisms are pore blocking, surface adsorption, cake formation and biological fouling. The membrane fouling and enzyme immobilization have sharing a number of similarities. So that, it can conclude deliberate promotion of fouling might be used as strategy for enzymes immobilization. In present study, pH values of 5.7, 7 and 8 are adjusting in order to evaluate effect of parameter (pH) in to the enzyme immobilization by using dead-end filtration. Besides that, mass balance was used in order to calculate the immobilization enzyme on the membrane surface. The concentration of ADH and NADH are measured by using spectrophotometer at absorbance 280 nm and 340 nm respectively. Then, the results were shows at low pH during immobilization the enzyme was liable to accumulate on the membrane surface due to the electrostatic adsorption and reduced the stability on enzyme. While when the solution of enzyme at high pH value (away from IEP) during immobilization, the membrane and enzyme was negatively charged and lead to much lesser accumulation on the membrane surface due to the strongest of electrostatic repulsion. Therefore, it will induce to lower fouling on the membrane. At the neutral pH (near IEP), the hydrogen bonding between enzyme and membrane was stabilized and might be lead to maintain the enzyme activity.