Aquatic micro-pollutants removal with a biocatalytic membrane prepared by metal chelating affinity membrane chromatography

Abstract

Biocatalytic membranes are promising to remove micro-pollutants in aqueous environment due to their mild and green operation condition. However, more efforts need to be devoted to improving their removal efficiency and stability. In this study, metal chelating affinity membrane chromatography (MCAMC) was used to construct a biocatalytic membrane by selectively capturing laccase from a crude fermentation broth. Metal ions had a significant effect on the activity of the immobilized laccase and copper ion was the best choice. A pH of 4.5 was selected for laccase adsorption and its loading seemed the same under flow rates from 0.5 to 10mLmin−1 thanks to the inherent convective transport of membrane chromatography. The pH value and salt concentration in the storage buffer had an obvious effect on the stability of the immobilized laccase, and the prepared biocatalytic membrane retained 87% of initial activity after 20days storage. When applying such membrane to micro-pollutant removal (taking bisphenol A (BPA) as an example), a high BPA removal efficiency (99.3%) could be obtained. The biocatalytic membranes could be operated at a high flux of 50Lm−2h−1 without recycling the permeate into the feed, and its throughput and BPA removal rate were superior to the most results in the literature. However, BPA removal decline (from 99.6% to 56.6% after five cycles) occurred during the successive water treatment due to the membrane fouling caused by BPA polymerization products. Membrane regeneration could be achieved by simple elution-cleaning-reloading, and the laccase activity and BPA removal were fully recovered.