Fouling cake layer in a submerged anaerobic membrane bioreactor treating saline wastewaters: curse or a blessing?

摘要

The treatment of inhibitory (saline) wastewaters is known to produce considerable amounts ofnsoluble microbial products (SMPs), and this has been implicated in membrane fouling; the fate ofnthese SMPs was of considerable interest in this work. This study also investigated the contribution ofnSMPs to membrane fouling of the; (a) cake layer/biofilm layer, (b) the compounds below the biofilmcake layer and strongly attached to the surface of the membrane, (c) the compounds in the innernpores of the membrane, and (d) the membrane. It was found that the cake/biofilm layer was the mainnreason for fouling of the membrane. Interestingly, the bacteria attached to the cake/biofilm layernshowed higher biodegradation rates compared with the bacteria in suspension. Moreover, thenbacteria attached to the cake layer showed higher amounts of attached extracellular polysaccharidesn(EPS) compared with the bacteria in suspension, possibly due to accumulation of the released EPSnfrom suspended biomass in the cake/biofilm layer. Molecular weight (MW) analysis of the effluentnand reactor bulk showed that the cake layer can retain a large fraction of the SMPs in the reactor andnprevent them from being released into the effluent. Hence, while cake layers lead to lower fluxes innsubmerged anaerobic membrane bioreactors (SAMBRs), and hence higher costs, they can improventhe quality of the reactor effluent.