High performance removal of chlorophenols from an aqueous solution using an enzymatic membrane bioreactor.

Organochlorides and particularly chlorophenols are environmental pollutants that deserve special attention. Enzymatic membrane bioreactors may be alternatives for efficiently removing such hazardous organochlorides from aqueous solutions. We propose here a novel enzymatic membrane bioreactor comprising an ultrafiltration membrane GR81PP, electrospun fibers made of cellulose acetate, and laccase immobilized using an incubation and a fouling approach. Configurations of this biosystem exhibiting the highest catalytic activity were selected for removal of 2-chlorophenol and 4-chlorophenol from aqueous solution in an enzymatic membrane bioreactor under various process conditions. The highest removal of chlorophenols, at 88% and 74% for 2-chlorophenol and 4-chlorophenol, respectively, occurred at pH 5 and 30 ºC in the GR81PP/cellulose acetate/laccase biosystem with enzyme immobilized by the fouling method. Furthermore, the GR81PP/cellulose acetate/laccase biosystem with enzyme immobilized by the fouling method exhibited significant reusability and storage stability compared with the biosystem with laccase immobilized by the incubation method. The mechanism of enzyme immobilization is based on pore blocking and cake-layer formation, while the mechanism of chlorophenols removal was identified as a synergistic combination of membrane separation and enzymatic conversion. The importance of the conducted research is due to efficient removal of hazardous organochlorides using a novel enzymatic membrane bioreactor. The study demonstrates the biosystem's high catalytic activity, reusability, and stability, offering a promising solution for environmental pollution control.

Synergistic action of laccase treatment and membrane filtration during removal of azo dyes in an enzymatic membrane reactor upgraded with electrospun fibers.

Nowadays, the increasing amounts of dyes present in wastewaters and even water bodies is an emerging global problem. In this work we decided to fabricate new biosystems made of nanofiltration or ultrafiltration membranes combined with laccase entrapped between polystyrene electrospun fibers and apply them for decolorization of aqueous solutions of three azo dyes, C.I. Acid Yellow 23 (AY23), C.I. Direct Blue 71 (DB71) and C.I. Reactive Black 5 (RB5). Besides effective decolorization of the permeate stream, the biosystems also allowed removal of dyes from the retentate stream as a result of enzymatic action. The effect of pH and applied pressure on decolorization efficiencies was investigated, and pH 5 and pressure of 2 bar gave the highest removal efficiencies of 97% for AY23 and 100% for both DB71 and RB5 from permeate solutions while decolorization of retentate for RB5 reached 65% under these conditions. Almost 100% decolorization of all dyes was achieved after three consecutive enzyme membrane cycles. Decolorization was shown to be due to the synergistic action of membrane separation and bioconversion. The biocatalytic action also enabled significant reduction of permeate and retentate toxicity, which is one of the biggest environmental health issues for these types of streams.

An enzymatic membrane reactor for oligodextran production: Effects of enzyme immobilization strategies on dextranase activity.

An enzymatic membrane reactor (EMR) with immobilized dextranase provides an excellent opportunity for tailoring the molecular weight (Mw) of oligodextran to significantly improve product quality. However, a highly efficient EMR for oligodextran production is still lacking and the effect of enzyme immobilization strategy on dextranase hydrolysis behavior has not been studied yet. In this work, a functional layer of polydopamine (PDA) or nanoparticles made of tannic acid (TA) and hydrolysable 3-amino-propyltriethoxysilane (APTES) was first coated on commercial membranes. Then cross-linked dextranase or non-cross-linked dextranase was loaded onto the modified membranes using incubation mode or fouling-induced mode. The fouling-induced mode was a promising enzyme immobilization strategy on the membrane surface due to its higher enzyme loading and activity. Moreover, unlike the non-cross-linked dextranase that exhibited a normal endo-hydrolysis pattern, we surprisingly found that the cross-linked dextranase loaded on the PDA modified surface exerted an exo-hydrolysis pattern, possibly due to mass transfer limitations. Such alteration of hydrolysis pattern has rarely been reported before. Based on the hydrolysis behavior of the immobilized dextranase in different EMRs, we propose potential applications for the oligodextran products. This study presents a unique perspective on the relation between the enzyme immobilization process and the immobilized enzyme hydrolysis behavior, and thus opens up a variety of possibilities for the design of a high-performance EMR.

Tailor-made novel electrospun polystyrene/poly(d,l-lactide-co-glycolide) for oxidoreductases immobilization: Improvement of catalytic properties under extreme reaction conditions.

Immobilized enzymes find applications in many areas such as pharmacy, medicine, food production and environmental protection. However, protecting these biocatalysts against harsh reaction conditions and retaining their enzymatic activity even after several biocatalytic cycles are major challenges. Properly selected supports and type of surface modifier therefore seem to be crucial for achieving high retention of catalytic activity of immobilized biomolecules. Here we propose production of novel composite electrospun fibers from polystyrene/poly(d,l-lactide-co-glycolide) (PS/PDLG) and its application as a support for immobilization of oxidoreductases such as alcohol dehydrogenase (ADH) and laccase (LAC). Two strategies of covalent binding, (i) (3-aminopropyl)triethoxysilane (APTES) with glutaraldehyde (GA) and (ii) polydopamine (PDA), were applied to attach oxidoreductases to PS/PDLG. The average fiber diameter was shown to increase from 1.252 µm to even 3.367 µm after enzyme immobilization. Effective production of PS/PDLG fibers and biomolecule attachment were confirmed by Fourier transform infrared spectroscopy analysis. The highest substrate conversion efficiency was observed at pH 6.5 and 5 for ADH and LAC, respectively, and at 25 °C for enzymes attached using the APTES + GA approach. Improvement of enzyme stabilization at high temperatures was confirmed in that relative activities of enzymes immobilized onto PS/PDLG fibers were over 20% higher than those of the free biomolecules, and enzyme leaching from the support using acetate and MES buffers was below 10 mg/g.