Temporal changes in extracellular polymeric substances on hydrophobic and hydrophilic membrane surfaces in a submerged membrane bioreactor

Abstract

Membrane surface hydrophilic modification has always been considered to mitigating biofouling in membrane bioreactors (MBRs). Four hollow-fiber ultrafiltration membranes (pore sizes ∼0.1 μm) differing only in hydrophobic or hydrophilic surface characteristics were operated at a permeate flux of 10 L/m(2) h in the same lab-scale MBR fed with synthetic wastewater. In addition, identical membrane modules without permeate production (0 L/m(2) h) were operated in the same lab-scale MBR. Membrane modules were autopsied after 1, 10, 20 and 30 days of MBR operation, and total extracellular polymeric substances (EPS) accumulated on the membranes were extracted and characterized in detail using several analytical tools, including conventional colorimetric tests (Lowry and Dubois), liquid chromatography with organic carbon detection (LC-OCD), fluorescence excitation - emission matrices (FEEM), fourier transform infrared (FTIR) and confocal laser scanning microscope (CLSM). The transmembrane pressure (TMP) quickly stabilized with higher values for the hydrophobic membranes than hydrophilic ones. The sulfonated polysulfone (SPSU) membrane had the highest negatively charged membrane surface, accumulated the least amount of foulants and displayed the lowest TMP. The same type of organic foulants developed with time on the four membranes and the composition of biopolymers shifted from protein dominance at early stages of filtration (day 1) towards polysaccharides dominance during later stages of MBR filtration. Nonmetric multidimensional scaling of LC-OCD data showed that biofilm samples clustered according to the sampling event (time) regardless of the membrane surface chemistry (hydrophobic or hydrophilic) or operating mode (with or without permeate flux). These results suggest that EPS composition may not be the dominant parameter for evaluating membrane performance and possibly other parameters such as biofilm thickness, porosity, compactness and structure should be considered in future studies for evaluating the development and impact of biofouling on membrane performance.

Characterization of the Fouling Layer on the Membrane Surface in a Membrane Bioreactor: Evolution of the Foulants’ Composition and Aggregation Ability

“…Higher PN content on the membrane surface during the steady membrane fouling stage was also reported in a previous report [8]. Matar et al investigated the temporal changes in EPS on hydrophobic and hydrophilic membrane surfaces in a lab-scale MBR; they found that the same type of organic foulants developed over time on the different membrane surface and the PN dominated the EPS components [8]. Regardless of microbe metabolism within the biofouling layer, the increment of PN at this stage was likely mainly caused by adsorption from the buck liquor by the initial fouling layer.…”

“…A significant increase in PN was observed for S2, which constituted about 74.11% of the total EPS. Higher PN content on the membrane surface during the steady membrane fouling stage was also reported in a previous report [8]. Matar et al investigated the temporal changes in EPS on hydrophobic and hydrophilic membrane surfaces in a lab-scale MBR; they found that the same type of organic foulants developed over time on the different membrane surface and the PN dominated the EPS components [8].…”

“…Several authors reported that the cake layer was considered as the dominant foulant and the cake resistance was the major membrane resistance, accounting for about 85% of total resistance [6,7]. In general, EPS have been recognized as the main fouling components of the fouling layer in MBRs, resulting in an increase in TMP [8,9]. Therefore, the dynamic variations of EPS composition have a significant correlation with the TMP development.…”

“…The resulting interaction energy between foulants and membrane can be divided into two types: (1) the attachment strength between initial foulants and the virgin membrane; and (2) the self-aggregation strength between foulants [14,15]. Matar et al reported that the initial fouling layer developed quickly on the different types of membrane surfaces and then the fouling selection of the membrane-surface chemistry reduced since the membrane lost its intrinsic affinity [8]. Therefore, further understanding of the self-aggregation ability between foulants is indispensable to mitigate membrane fouling.…”

The Effect of Membrane Material and Surface Pore Size on the Fouling Properties of Submerged Membranes

“…However, contradictory results have been reported. For example, Matar et al [17] studied the effect of hydrophobic and hydrophilic membrane surfaces in MBR, and their results showed that fouling behavior in MBR processes are much less dependent on hydrophilicity than previously thought. Choi et al [18] reported that pore structure had a greater influence on the development of membrane fouling than the hydrophilicity of the membrane surface.…”