Biodegradation of bisphenol a on an enzyme modified nanofibrous membrane for water treatment

M.Sc. (Chemistry)Abstract: Water scarcity has become a major constraint globally. This situation has been further aggravated by the introduction of harmful foreign substances into most natural water systems. Among these highly toxic pollutants, bisphenol A (BPA) has raised a lot of environmental concerns in recent years. BPA is an active endocrine disrupting pollutant that disturbs the normal functioning of hormones in human beings and animal thus resulting in various health challenges. Traditional wastewater treatment methods have shown some limitations towards complete removal of BPA, especially at trace levels. This has compelled researchers to device better methods that can effectively remove BPA from water. The use of environmentally friendly enzymes, with high selectivity and reaction rates as compared to most chemical catalysts, have proven to be efficient in the biotransformation of emerging micro-pollutants, such as BPA. This research therefore presents, for the first time, the biotransformation of an endocrine disrupting pollutant (bisphenol A) using a laccase immobilized dendritic Hyperbranched polyethyleneimine/polyethersulfone (HPEI/PES) nanofibrous membrane. Laccase enzymes from Rhus vernificera were covalently bound on HPEI/PES electrospun nanofibrous membranes and used for the removal of BPA from water. The laccase enzyme was anchored on the dendritic membranes through the abundant peripheral amine groups in the hyperbranched polyethyleneimine (HPEI) using glutaraldehyde as a cross-linker. The membranes were characterised with attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), ultraviolet-visible (UV-Vis) spectroscopy, correlative light and electron microscopy (CLEM), and atomic force microscopy. Furthermore, contact angle analyses, pure water flux measurements and rejection analyses were carried out. Liquid chromatography-mass spectrometer (LCMS) was used to monitor the degradation by products. CLEM showed that the enzymes were uniformly dispersed on the nanofibers while SEM analysis revealed that the nanofibers had an average diameter of 354±37 nm..