We have developed an integrated, multienzyme functionalized membrane reactor for bioconversion of a lignin model compound involving enzymatic catalysis. The membrane bioreactors were fabricated through the layer-by-layer assembly approach to immobilize three different enzymes (glucose oxidase, peroxidase and laccase) into pH-responsive membranes. This novel membrane reactor couples the in situ generation of hydrogen peroxide (by glucose oxidase) to oxidative conversion of a lignin model compound, guaiacylglycerol-β-guaiacyl ether (GGE). Preliminary investigation of the efficacy of these functional membranes towards GGE degradation is demonstrated under convective flow mode. Over 90% of the initial feed could be degraded with the multienzyme immobilized membranes at a residence time of approximately 22 s. GGE conversion product analysis revealed the formation of oligomeric oxidation products upon reaction with peroxidase, which may be a potential hazard to membrane bioreactors. These oxidation products could further be degraded by laccase enzymes in the multienzymatic membranes, explaining the potential of multi enzyme membrane reactors. The multienzyme incorporated membrane reactors were active for more than 30 days of storage time at 4 °C. During this time span, repetitive use of the membrane reactor was demonstrated involving 5–6 h of operation time for each cycle. The membrane reactor displayed encouraging performance, losing only 12% of its initial activity after multiple cycles of operation.

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Published in Polymers, v. 10, issue 4, 463, p. 1-13.

© 2018 by the authors. Licensee MDPI, Basel, Switzerland.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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This research was supported by an NSF KY EPSCoR grant (Grant No: 1355438) and by NIH-NIEHS-SRP (Award Number P42ES007380).

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The following are available online at http://www.mdpi.com/2073-4360/10/4/463/s1: Figure S1: Comparison of the degradation of GGE with laccase and multienzyme immobilized membranes in flow-through experiments as studied by UV-Vis spectroscopy. Experiments were performed at a temperature of 22 °C and a pH of 5.6, Figure S2: Degradation of GGE (initial GGE concentration 3.1 mM) with the PVDF-PAA-PAH-ENZ membrane in a flow-through experiment as studied by HPLC, Figure S3: Plot of GGE concentration (initial GGE concentration 3.1 mM) as passed through the PVDF-PAA-PAH membrane in a flow-through experiment as studied by HPLC. This is to show that with no enzyme present on the membrane, GGE could not be degraded. Furthermore, only a minimal (~5%) or no absorption of GGE onto the membrane matrix was observed, Figure S4: Mass spectrum of the GGE permeate degraded by a laccase immobilized membrane, Figure S5: Mass spectrum of the GGE permeate degraded by an HRP immobilized membrane, Figure S6: Mass spectrum of the GGE permeate degraded by a multienzyme immobilized membrane, Figure S7: Solution phase activity of (a) laccase and (b) HRP used for immobilization.

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Supporting Information: Figure S1-S7.