Removal of tetracycline in enzymatic membrane reactor: Enzymatic conversion as the predominant mechanism over adsorption and membrane rejection

The presence of micropollutants such as dyes, pharmaceuticals, personal care products or estrogens in water and wastewater might have an adverse effect on the environment and human beings. There is thus an emerging need to detect and remove these compounds from wastewater and water. Our study, which is strongly embedded in the scientific trend of development of novel, efficient and eco-friendly methods for removal of micropollutants, concerns fabrication of novel biocatalytic membranes with immobilized laccase for degradation of tetracycline. Biocatalytic membranes were prepared in normal mode using pressure-driven laccase immobilization and in reverse mode using reverse-fouling enzyme immobilization. Both biocatalytic membranes showed over 70% activity retention and exhibited over 80% of initial activity after 20 days of storage. The use of the produced systems facilitates removal of over 70% of tetracycline at pH from 3 to 5 from solution at concentrations up to 5 mg L^-1 in a in flow-through mode at a pressure of 3 bar. However, 89% removal efficiency of antibiotic was observed with the membrane in normal mode. The results highlight that a high biodegradation rate was attained due to synergistic action of membrane rejection, adsorption by polydopamine and membrane, and enzymatic conversion where laccase oxidation was the most pronounced. Due to application of membrane separation, a final effluent of significantly lower toxicity was obtained compared to the parent solution. The data presented indicate that the biocatalytic membranes produced could be considered as promising environmental tools for removal of micropollutants from wastewater and water bodies.