Immobilization of laccase from Trametes versicolor on a modified PVDF microfiltration membrane: characterization of the grafted support and application in removing a phenylurea pesticide in wastewater

Laccase immobilization onto a hydrophilic PVDF microfiltration membrane and its application for removing a herbicide derivative, N′,N′-(dimethyl)-N-(2-hydroxyphenyl)urea (2-HF), from waste water were studied. 2-HF was transformed via an oxidation reaction catalyzed by laccase mostly into an insoluble product, which was simultaneously separated by filtration through the membrane. The microfiltration membrane used to graft laccase was treated with hydrazine to form a hydrazide group on its surface, which further reacts with the oxidized carbohydrate groups of the enzyme, leading to a covalent immobilization of laccase. Contact angle measurements by the sessile drop technique and X-Ray photoelectron spectroscopy followed the successive modifications of the membrane. Streaming potential measurements as a function of the pH led to determine the IEP of the grafted membrane at 4.1±0.5. This value is representative of the IEP of the laccase mixture produced by the white rot fungus Trametes versicolor. 2-HF removal experiments were performed in a microfiltration module. The performance of the laccase grafted membrane was evaluated for different enzyme loading rates. It was shown that laccase grafted membrane with a 60 cm2 effective microfiltration area transformed 200 ml of a 2-HF 0.1 g/l solution within less than 5 min. The main transformation product, an insoluble dark purple precipitate, was retained by the membrane.