In Situ Formation of a Biocatalytic Alginate Membrane by Enhanced Concentration Polarization

A thin alginate layer induced on the surface of a commercial polysulfone membrane was used as a matrix for noncovalent immobilization of enzymes. Despite the expected decrease of flux across the membrane resulting from the coating, the initial hypothesis was that such a system should allow high immobilized enzyme loadings, which would benefit from the decreased flux in terms of increased enzyme/substrate contact time. The study was performed in a sequential fashion: first, the most suitable types of alginate able to induce a very thin, sustainable gel layer by pressure-driven membrane filtration were selected and evaluated. Then, an efficient method to make the gel layer adhere to the surface of the membrane was developed. Finally, and after confirming that the enzyme loading could remarkably be enhanced by using this method, several strategies to increase the permeate flux were evaluated. Alcohol dehydrogenase (EC 1.1.1.1), able to catalyze the conversion of formaldehyde into methanol, was selected as the model enzyme. An enzyme loading of 71.4% (44.8 μg/cm(2)) was attained under the optimal immobilization conditions, which resulted in a 40% conversion to methanol as compared to the control setup (without alginate) where only 10.8% (6.9 μg/cm(2)) enzyme was loaded, with less than 5% conversion. Such conversion increased to 60% when polyethylene glycol (PEG) was added during the construction of the gel layer, as a strategy to increase flux. No enzyme leakage was observed for both cases (with/without PEG addition). Modeling results showed that the dominant fouling mechanism during gel layer induction (involving enzyme entrapment) was cake layer formation in the initial and intermediate phases, while pore blocking was the dominant mechanism in the final phase. Such mechanisms had a direct consequence on the type of immobilization promoted in each phase. The results suggested that the strategy proposed could be efficiently used to enhance the enzyme loading on polymer membranes.