Temporal variations of membrane foulants in the process of using flat-sheet membrane for simultaneous thickening and digestion of waste activated sludge

Membrane foulants were extracted at different operation time in simultaneous sludge thickening and digestion reactors using flat-sheet membranes. Temporal variations of foulants were analyzed by three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy, gel filtration chromatography (GFC), particle size distribution (PSD) and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy. Results showed that during the first 4 days fouling was mainly assigned to internal membrane foulants (IMFs), and afterwards external membrane foulants (EMFs) increased dramatically. EEM analysis showed that both IMFs and EMFs changed during the operation. Cluster analysis demonstrated that the characteristics of IMFs were relatively similar; however, both quantity and properties of EMFs were changed. GFC analysis showed that EMFs contained more molecules with large molecular weight compared to IMFs. PSD analysis illuminated that particle size of EMFs gradually increased and was larger than that of IMFs. ATR–FTIR analysis indicated that the foulants on membranes consisted of polysaccharides and proteins.

► Temporal variations of membrane foulants in a novel membrane process were studied.
► Internal membrane fouling played a significant role in the first 4 days, and afterwards external fouling dominated.
► Internal foulants’ quantity was changed while both the quantity and the properties of external foulants were varied.
► Internal foulants molecular weight, external foulants particle size and foulants quantity all increased in the process.