Preparation, characterization of enzyme immobilized membranes and modeling og their performances

Abstract

The objective of this thesis study is to prepare active and stable urease (URE) immobilized membranes for the efficient removal of urea and to predict the performances of these membranes under pressure. Two commercially available ultrafiltration membranes namely Poly (acrylonitrile-co-sodium methallyl sulfonate) copolymer (AN69) and polyethyleneimine (PEI) deposited AN69 membranes (AN69-PEI) were used as supporting materials on which urease is immobilized by means of physical adsorption using layer-by-layer self assembly method or chemical attachment using N-ethyl-N.-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and Nhydroxysuccinimide (NHS) coupling agents as a zero crosslinker. During physical immobilization (pH 7.4), the effect of polyelectrolyte type on the activity of immobilized urease was compared between PEI and chitosan (CHI) cationic polyelectrolytes where urease was located either on top of the polyelectrolyte layer (AN69-PEI-URE or AN69-CHI-URE) or between two polyelectrolyte layers in a sandwiched form (AN69-PEI-URE-PEI or AN69-CHI-URE-CHI). The results reveal that the amount of urease immobilized on AN69 membranes are similar and slightly higher than the amount adsorbed on the activated AN69 surface by chemical attachment (AN69-C-URE). The maximum reaction rate was observed with AN69-PEI-URE membrane while the maximum retained activity during storage time was determined with AN69-C-URE membrane. Under dynamic conditions, the hydraulic permeabilities of the commercial and urease immobilized membranes were found similar and the highest urea conversion was achieved with the AN69-PEI-URE-PEI membrane. At the end of 450 minutes of filtration under pressure, the catalytic activity of AN69-C-URE membrane was completely preserved. The mathematical model developed can correlate the experimental filtration data quite well.