Electrospinning Nano-Fibers Supports for Enzymes to Remediate Wastewaters

Electrospinning (ES) is a powerful technology capable of producing submicron nonwoven fibres under high voltage, which can be used to create 2D and 3D structures of fibrous scaffolds with controllable compositions and diameters. The outstanding increase in specific surface area, typical of electrospun nanofibrous fabrics (ENFs), combined with high porosity, interconnected pore structure, possible chemical/physical functionalization and cost-effectiveness provide this technology enormous potential for creating materials with specific features for a variety of applications (medicine and healthcare, textile, energy, environment, air and liquid filtration, etc.). High efficient and effective filter media can be obtained, indeed, by using nanometre-sized fibres in the filter structure, so that tiny particles or droplets can be easily captured in the electrospun nanofibrous structured filters. Then, ENFs could even replace conventional water treatment membranes. Most applications of ENFs in wastewater remediation involve removal of contaminant particles, microorganisms and organic pollutants. In the latter case, adsorption features of specific polymer materials in ENFs are exploited. The properties of some extracellular enzymes in degrading pollutants and their employment in detoxifying wastewaters have been investigated in several studies. Laccase, tyrosinase and peroxidase are the enzymes more extensively studied. Very few studies to date, however, have immobilised these enzymes on ENFs. The aim of this study was to create a fabric employing ENFs where these three enzymes were encapsulated in suitable organic polymers. Some electrospinning techniques, e.g. coaxial electrospinning, were used to create ENFs where enzymes are somehow encapsulated within nanostructures, to protect them from interferences and inhibition from an external environment, but prevent also immobilisation through covalent binding of enzymes that can often reduce their kinetic properties. Two different strategies for ENFs were tested to create the "multi-enzyme fabric for pollutant removal" (PR-MEF): i) a blend scaffold and ii) a multi-layer fabric. Single enzymes and/or combinations were tested. Some classes of organic pollutants (e.g. monophenols, chlorinated phenols, aromatic amine, PAHs) were used as model wastewater contaminants, both singly and in combination, to simulate real wastewater conditions. Because of the strength of the nanofibre web may be too weak to be used in operations, the applicability of some sublayers (e.g. meltblown or spunbonded nonwoven fabrics) was tested, if necessary, to support nanofibres web. The morphological structure of ENFs, the encapsulation of enzymes, the kinetics of enzymes and the degradation rates of water pollutants were tested.