Extracellular polymeric substances (EPS) are reported to be the major foulant in membrane bioreactor (MBR) processes. It is important to understand the EPS fractions which cause irreversible fouling to reduce operation cost and energy consumption in MBR. In this study, we developed polarity-molecular weight profiling, in which EPS components were plotted on two-dimensional matrix of its polarity and molecular weight, and applied it to investigate EPS of bulk sludge and cake layers from a labscale MBR. The EPS components were also characterized via three-dimensional excitation-emission matrix (3D-EEM) spectroscopy. The result showed that hydrophilic substances as large as 100 − 670 kDa was found only in loosely-bound EPS (LB-EPS) of bulk sludge but not in that of cake layers nor in permeate. Hydrophobic substances smaller than 20 kDa were mainly found in soluble microbial products (SMP) in bulk sludge. Hydrophilic substances larger than 670 kDa was mainly found in tightly-bound EPS (TB-EPS) of bulk sludge and in LB-and TB-EPS of cake layers. These findings suggest that, after conditioning of micropores of virgin membrane by hydrophobic substances smaller than 20 kDa in SMP, hydrophilic biopolymers as large as 100 − 670 kDa in bulk sludge clog the narrowed micropores inside membrane, causing irreversible fouling.

Quorum sensing is recently considered to play important roles in biological wastewater treatment processes. This study aimed to investigate diversity of N-acyl homoserine lactones (AHL) among biological wastewater treatment processes and their locations. We analyzed and quantified 10 AHL in activated sludge at wastewater treatment plants (WWTPs) by Fourier transform mass spectrometry (FTMS) and by bioassay on thin-layer chromatography (TLC). Sludge samples were taken at seven WWTPs in Japan and in Thailand, which were chosen to compare different process types including a pilot-scale membrane bioreactor process. Various AHL were detected in activated sludge, suggesting the presence of quorum sensing activity in many practical WWTPs. Detection of AHL by LC-FTMS was much more sensitive than by TLC bioassay, because TLC bioassay was implied to be affected by the presence of quorum quenching molecules in activated sludge. With LC-FTMS analysis, AHL, which has short straight chain in the acyl group, were more abundant. Especially, C 4 -HSL, C 7 -HSL, and C 8 -HSL were detected widely independent of locations and process types. AO processes had higher AHL productivity than other processes.npj Clean Water (2019) 2:11 ; https://doi.