Characterization of membrane fouling in submerged ceramic membrane photobioreactors fed with effluent from membrane bioreactors

• Three SCMPBRs were operated at 72-, 24- and 6.5-h HRT.
• Membrane fouling rate increased with lower operating HRTs through increased of SMPc.
• At long HRT (72 h), hydrolysis was induced in cake layer formed on membrane surface.
• At short HRT (6.5 h), fouling occur via cake layer compaction at high convection rate.
• Macromolecular compound contributed more to membrane fouling than soluble compound.

The effect of hydraulic retention time (HRT) on the membrane fouling behavior of submerged ceramic membrane photobioreactors (SCMPBRs) fed with effluent from a submerged ceramic membrane bioreactor (SCMBR) was investigated. The effluent from a SCMBR was continuously fed to three SCMPBRs operated at different HRTs (72, 24, and 6.5 h) for a period of 100 d. Results of the effect of mixed liquors characteristics on fouling showed that mixed liquor suspended solids (MLSS), zeta potential and extracellular polysaccharides (EPS) were not the key factors leading to various fouling behaviors for the SCMPBRs. Membrane fouling rates increased with lower operating HRTs through increased production of carbohydrates in soluble microbial product (SMP). The transmembrane pressure (TMP) value of SCMPBR6.5h exceeded 30 kPa after 68 d of operation, while the TMP of SCMPBR72h and SCMPBR24h were relatively constant throughout the 100 d. Different membrane fouling phenomena were observed at different HRTs. It was noted that biological reactions (e.g., hydrolysis) were induced on the biofilm/biocake layer formed on the membrane surface when operating SCMPBR at long HRT (i.e., 72 h). For SCMPBR operating at short HRT (i.e., 6.5 h), fouling layer and active layer developed on the membrane surface facilitated sieving of colloidal particles and organics. The detailed composition of the organic compounds on membrane foulants in the SCMPBR6.5h showed that carbohydrates and proteins were the major foulants. The finding of much higher organic in non-filtered membrane foulant samples as compared to filtered samples together with the findings from membrane fouling resistance distribution, molecular weight distribution (MWD) and particle size distribution (PSD) indicated that macromolecular compounds contributed more to membrane fouling than those small molecular compounds or soluble compounds.