A novel integrated membrane bioreactor-stirred tank bioreactor system for simultaneous biodegradation of bisphenol A contaminated wastewater and biopolyol production: An approach towards circular bioeconomy

Abstract

The present work examined the biodegradation of bisphenol A (BPA) under batch and continuous modes using hydrocarbonoclastic bacterium, Pseudomonas aeruginosa PR3. The strain showed great biodegradation potential under batch shake flask and stirred tank reactor. Bacterial growth was considerably inhibited at initial BPA concentrations > 50 mg/L. Further, membrane bioreactor (MBR) for BPA biodegradation was also evaluated under different inlet BPA concentration and hydraulic retention time (HRT) and the maximum BPA removal efficiency of 94.4 % was attained with an influent BPA concentration of 25 mg/L at 5 d of HRT. MBR also showed better performance under shock loading conditions. Identification of BPA biodegraded pathways was also performed using liquid chromatography-mass spectrometry, elucidating the different metabolites and end products formed. A subsequent enhancement in BPA removal efficieny was also observed owing to the microfiltration system of MBR that was applied to separate bacterial biomass from effluent. The maximum removal efficiency was further enhanced to 98.5 % under the same operational schedule. As the strain has the ability to produce extracellular diol synthase enzyme which transforms oleic acid into the biopolyol 7,10-dihydroxy-8(E)-octadecenoic acid, the effluent containing the enzymes was supplemented with 1 % (v/v) oleic acid under whole cell and cell-free approaches. Cell-free technique showed an enhanced bioconversion efficiency in comparison to the traditional whole cell approach. Further, the produced biopolyol was characterized using Fourier transform infrared spectroscopy, thermogravimetry, differential scanning calorimetry, and 1H nuclear magnetic resonance analyses and also depicted the antibacterial activity.