Abstract
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.
Highlights
Integration of enzymatic catalysis with membrane technology has attracted growing attention to facilitate functionalized membranes as bioreactors [1,2,3,4]
The functionalized membranes were characterized by ATR FT-IR, FIB-scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and water permeability studies to assess the success of polymerization of PAA in the pores of PVDF membranes
The functionalized membranes were used for oxidative degradation of the lignin model compound guaiacylglycerol-β-guaiacyl ether (GGE)
Summary
Integration of enzymatic catalysis with membrane technology has attracted growing attention to facilitate functionalized membranes as bioreactors [1,2,3,4]. On the other hand, encourage emerging technologies incorporating multienzyme systems, making catalytic strategies operative and sophisticated [7,8,9]. Immobilized multienzymatic systems that exploit the selectivity of biocatalysts have been developed from time to time [10,11]. In this respect, functionalized membranes with porous support and functional polymer matrices may be an ideal platform for multiple enzyme immobilization and aid in developing bioreactors for enzymatic reactions [12,13]. The highly abundant polymer, lignin, deserves more attention than only getting used for low-value applications such as low-grade
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