Surface Properties of Biofouled Membranes from a Submerged Anaerobic Membrane Bioreactor after Cleaning

Abstract

The surface structural properties of biofouled membranes from a laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) treating kraft pulping evaporator condensate after cleaning were studied. A flat sheet polyvinylidene fluoride (PVDF) membrane was used for the study. Three different cleaning methods, physical cleaning (PC), maintenance chemical cleaning (MCC), and recovery cleaning (RC) were applied to the fouled membrane surface, and the treated membranes were subject to flux recovery and surface structural analysis by using spectroscopic methods, zeta potential measurement, attenuated total reflectance-Fourier transform infra red spectroscopy (ATR-FTIR), and advanced correlative microscopic methods, including confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Neither PC, MCC, nor RC methods restored the membrane permeability to initial conditions. Adhesion of a thin extracellular polymeric substance (EPS) layer, consisting of proteins and polysaccharides with a thicknesses of 4.0 µm, 5.3 µm, and 7.1 µm and roughness of 190 nm, 236 nm, and 273 nm was observed on RC, MCC, and PC treated membrane surfaces, respectively. Partial flux recovery was achieved with the MCC and RC methods. This was correlated to the reduction of the protein associated with the foulant. Polysaccharides were found to be the most stable and predominant EPS constituent in relation to protein on the biofouled layer of RC and MCC membrane surfaces.