Enzyme Immobilized LbL Membranes: Application Towards Pollutant Degradation and Value Added Transformation

Bio-inspired membrane with immobilized enzymes on it provides versatile platforms for applications ranging from environmental remediation to generation of value added chemicals from waste. Despite associated environmental concerns, the existing techniques for remediating pollutants in water consist of both physical and chemical means mostly using heavy metals. To offer bioremediation as an alternative option, we herein demonstrate a layer-by-layer approach to immobilize laccase enzyme into functionalized membranes. This mode of membrane functionalization provides a synergistic platform for pollutant degradation where leaching of heavy metals into the environment is unacceptable. The enzyme-functionalized membrane was characterized by a wide variety of spectroscopic and microscopic techniques including ATR FT-IR, SEM imaging and XPS analysis and more. The stability of the enzyme in both solution phase and on membrane phase was studied. Enzyme showed a loss of some 65% of initial activity in the solution phase after weeks of use, whereas the membrane-bound enzyme lost only a negligible percentage of activity in the same time span. Activity of these biomimetic membranes towards dechlorination of 2,4,6-trichlorophenol (TCP) is demonstrated under pressure driven continuous flow mode. Up to 80% of the initial TCP was degraded at optimum flow rate. The membrane was exposed to rigorous cycles of TCP exposure to study its long term activity and reusability. The primary results reveal that our laccase-functionalized membrane lost only 14% of its initial activity in a period of 25 days. Finally, the reusability of the membrane as a support material was also demonstrated by detaching and re-immobilizing the enzyme on the membrane-polymer domain for at least two consecutive cycles.

We have further extended the layer-by-layer approach to fabricate multienzyme functionalized membrane reactor for bioconversion of lignin model compound involving enzymatic reactions. Three different enzymes (glucose oxidase, peroxidase and laccase) were immobilized into functionalized PVDF membranes. This novel membrane reactor couples the in-situ generation of hydrogen peroxide to oxidative conversion of a lignin model compound, guaiacylglycerol-B-guaiacylether (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. GGE conversion product analysis revealed formation of oligomeric oxidation products with peroxidase, which might be potential hazard to membrane bioreactors. These oxidation products could be further degraded by laccase enzymes in the multienzymatic membranes explaining the potential of multienzyme membrane reactors.

We acknowledge the support from NSF-EPSCoR program for carrying out this research.