A fence that eats the weed: Alginate lyase immobilization on ultrafiltration membrane for fouling mitigation and flux recovery

Abstract

Polysaccharide fouling poses a significant challenge in the widespread application of membrane filtration for water purification. In order to mitigate the problem, a polysaccharide-degrading enzyme alginate lyase (Alg L; EC 4.2.2.3) was successfully immobilized on cellulose acetate ultrafiltration membrane using a dead-end filtration unit. Attenuated total reflectance Fourier transform infrared microscopy confirmed covalent linkage of the Alg L to the membrane. HPLC and Alg L activity studies confirmed that Alg L in immobilized form was enzymatically active. Even after 21 d, Alg L in immobilized form retained 80% of its original activity, compared to its free counterpart, which retained only 20% of its original activity. In fouling experiments using tap water containing 50 mg L−1 alginate, a simple backwash could remove the fouling on Alg L immobilized membrane, but not that on the control membrane. Atomic force microscopic analysis and bright field microscopic images of the fouled test membrane after backwash showed significant removal of fouling, while fouling on the control membrane remained largely intact. The immobilized Alg L remained active even after 10 runs of fouling-backwash cycle. The present antifouling technology using immobilized enzyme is suitable for keeping ultrafiltration membranes clean without the use of toxic chemical biocides.