Continuous fixed-bed column studies to remove polycyclic aromatic hydrocarbons by degrading enzymes immobilized on polyimide aerogels

Abstract

The main sources of polycyclic aromatic hydrocarbons (PAHs), entering aquatic environments are industrial discharges, petroleum spills, combustion of fossil fuels, urban runoff, and atmospheric deposition. For the biodegradation of PAHs, the use of biocatalysts, such as enzymes, is an environmentally friendly method. Despite this, it is necessary to immobilize the enzymes to facilitate their recovery and reusability, as well as to prevent their loss. Using covalent bonding, (PAHs) degrading enzymes including naphthalene and catechol 2,3 dioxygenase enzymes were immobilized on modified polyimide aerogels. Covalent immobilization of enzymes on surface-modified polyimide aerogels resulted in around 9- and 6-fold lower enzyme leaching for naphthalene and catechol 2,3 dioxygenase enzymes compared to enzyme immobilization using adsorption. The Fourier Transform Infrared Spectrum (FT-IR) confirmed the enzyme immobilization and aerogel modification. SEM images indicated completely different textures for surface-modified aerogel attributed to the presence of functional groups after surface modification that enhanced enzyme loading. The removal capacity (∼20mganthracenegaerogel) of enzyme loaded aerogel was determined to select an appropriate range for column tests. Finally, the effects of flow rate, size of aerogels and inlet concentration of anthracene on the removal efficiency of pollutants were examined. Using the derived model as a basis for prediction, in terms of removal efficiency, the highest result was achieved to be 84.01% at a flow rate of 22 mL min−1, initial concentration of 34 mg L−1and aerogel size of 2 cm while under these conditions, the removal efficiency was experimentally measured to be 87.14 %. A fixed-bed column packed with enzyme-loaded aerogel for the removal of PAHs provides novel insight into the application of aerogel base materials for water treatment and PAH removal with possibilities of scaling up for larger applications.