Fouling control mechanism by suspended biofilm carriers addition in submerged ceramic membrane bioreactors

Membrane fouling has been the main concern deterring widespread applications of membrane bioreactors. In this study, porous suspended biofilm carriers were introduced to submerged ceramic membrane bioreactors (SCMBR) treating domestic wastewater to explore its effectiveness in alleviating membrane fouling. Results showed that biofilm carriers addition was effective in mitigating cake formation on the membrane surface that, in turn, helped to retard membrane fouling in SCMBR. The SCMBR without carriers had 2.7 times higher cake resistance and 1.5 times higher total resistance than the corresponding values observed in the SCMBR with carriers, indicating that the addition of biofilm carriers in SCMBR decreased the cake resistance by 72.7% over a similar period of operation. Both higher concentration of biomass and inorganic matters in the cake layer facilitated a more rapid TMP increment in the SCMBR without carriers. The liquid chromatography–organic carbon detector (LC–OCD) results indicated that a higher concentration of low molecular weight compounds (less than 1000) in the cake layer contributed to the faster fouling development observed in the SCMBR without carriers. The excitation–emission matrix florescence spectra of the cake layer showed the existence of two obvious protein-like substance peaks at the wavelength of Ex/Em=250–270/380–390 nm and Ex/Em=250–260/420–430 nm in both SCMBRs. However, relative dominance of the protein-like substance was relatively higher in the SCMBR without carriers, with an intensity of 284.9 occurring at the first peak and an intensity of 244.7 at the second peak, which confirmed that higher biopolymer contents were detected in the cake layer of the SCMBR without carriers. Other characteristics of the cake as well as the biomass suspensions were also evaluated in this study.

Highlight
► Fouling control mechanisms by biofilm carrier addition were elucidated in SCMBR.
► Biofilm carrier addition could effectively retard membrane fouling.
► Advanced technologies (EEM and LC–OCD) are useful to examine cake compositions.
► Higher contents of biopolymers and inorganics in cake accelerate membrane fouling.
► Polysaccharide in biomass EPS and cake layer was the dominant fouling factor.