Membrane fouling in a fermentative hydrogen producing membrane bioreactor at different organic loading rates

In a lab-scale continuously running fermentative hydrogen producing membrane bioreactor (HPMBR), the properties of biomass, extracellular polymeric substances (EPS) and colloidal material in the mixed liquor along with their influence on the performance of submerged hollow-fiber membrane modules were investigated. Five experimental runs were conducted at organic loading rates (OLRs) of 4.0, 6.0, 13, 22 and 30 g COD L−1 d−1. As OLR increased, the biomass content, colloidal hydrophobicity and mean particle diameter increased. Additionally, the membrane fouled more rapidly as OLR increased. The bound and soluble EPS content of biomass in the HPMBR were higher than that found in a hydrogen producing system in CSTR mode and in an aerobic activated sludge system. At a constant permeate flux rate of 11.1 L min−1 m−2 and N2 sparging intensity of 4.26 L min−1 m−2, membrane fouling was characterized by two distinct stages: an initial stage characterized by a relatively faster fouling rate and a second stage where the fouling rate was slower. Both fouling rates increased with increased biomass concentration and colloidal zeta potential. Increases in pore clogging resistance Rcoll correlated to increased concentrations of colloidal proteins and polysaccharides. The observed relationships between the membrane fouling properties and the properties of biomass and colloids (including soluble EPS), accompanied by scanning electron and confocal microscopy examination of the fouled membrane surfaces suggest that colloid adhesion and biomass deposition were the two dominant membrane fouling mechanisms in the HPMBR system.