Characteristics and behaviors of soluble microbial products in sequencing batch membrane bioreactors at various sludge retention times

The characteristics and behaviors of soluble microbial products (SMP) in sequencing batch membrane bioreactors (SBMBRs) were investigated at various sludge retention times (SRTs). SMP concentrations in SBMBRs reached a minimum at SRT of 40 days and were consistently higher than those in effluents. The extent of SMP accumulation was found to significantly increase with decreasing SRT. Similar molecular weight distributions of SMP in SBMBRs and in effluents were observed suggesting that SMP accumulation is not mainly because of size exclusion. Biomass associated products having a higher proportion of larger and more aromatic components appeared less prone to accumulate in SBMBRs than utilization associated products. Protein constituted a larger fraction of SMP than carbohydrate, especially at long SRTs and in effluents. The fouling potential of SMP was observed to be higher at shorter SRTs. Carbohydrate was speculated to be the major fraction of SMP possessing the highest potential to foul membranes and accumulate in SBMBRs.