Highly effective antibiotic mineralization via laccase-immobilized nanocomposite beads coupled with fungal phycoremediation

This study investigated the synthesis and characterization of laccase (LAC)-activated ZnONPs-CS-PVPP and Ag@ ZnONPs-CS-PVPP composite beads and their application in removal of tetracycline (TET) and ciprofloxacin (CIP). Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) showed that the doped silver nanoparticles (AgNPs) were spherical globules on the ZnO nanoplates (ZnONPs) and d-spacings of 0.146 nm and 0.148 nm were obtained for ZnONPs and Ag@ ZnONPs respectively. Characterization of composite beads using Fourier transform infrared (FTIR) showed N H, O H and C O stretches responsible for amine, alcohol, carboxylic and amide groups which could be responsible for interaction with the antibiotics during adsorption. Significant removal of antibiotics by enzyme-free and enzyme-enriched beads where 65 % and 72 % removal of TET and 65 % and 60 % removal of CIP were achieved with enzyme free beads. Addition of laccase enzyme to the beads increased the removal of CIP to 85 % for both ZnONPs-CS-PVPP and Ag@ ZnONPs-CS-PVPP beads. LC-MS analysis showed that degradation of TET could be due to hydration of alkene groups followed by elimination of amide, hydroxyl and amine functional groups or ring opening with subsequent hydrolysis or elimination of amide groups. For CIP, decarboxylation and loss of cyclo-propane and diazinane rings as well as fluoride elimination were proposed. Antibiotic activity demonstrated a decrease in activity for CIP through decreased zones of inhibition over time while total loss of growth of P. aeruginosa was observed after 1 h degradation of TET. Further mineralization of the degraded byproducts was achieved via phycoremediation using Aspergillus sp , demonstrating the potential of this biocatalyst-fungal system for the effective removal of antibiotics from wastewater. • Laccase enzyme was successfully immobilized on synthesized ZnONPs-CS-PVPP and Ag@ZnONPs-CS-PVPP composite beads. • The biocatalyst demonstrated superior catalytic activity in degradation of tetracycline and Ciprofloxacin in wastewater. • Phycoremediation using Aspergillus sp. was used to achieve mineralization of the degradation by-products. • The plausible mechanisms of degradation of tetracycline and Ciprofloxacin were proposed • The antibiotic activity of tetracycline, ciprofloxacin and degradation byproducts was evaluated.