Effect of different extraction methods on bound EPS from MBR sludges. Part I: Influence of extraction methods over three-dimensional EEM fluorescence spectroscopy fingerprint

Abstract

Membrane bioreactor (MBR) technology is quickly increasing. It has been widely reported that extracellular polymeric substances (EPS) play important roles in membrane fouling. Therefore, it is essential to know in depth the characteristics and behaviour of EPS to improve MBR operation. EPS can appear as supernatant and bound EPS, and the latter have to be extracted from flocs. For this, some extraction methods have been developed. In this paper, a comparison among four methods of EPS extraction was done, using three activated sludges coming from different MBRs. Results show that cationic exchange resin (CER) extracted 1.1–2.2 times more than formaldehyde + NaOH, 1.1–1.5 times more than formaldehyde + NaOH + sonication, and 1.1–6 times more than thermal treatment. With regard to the study using excitation–emission matrix (EEM) fluorescence spectroscopy to characterize the fluorescence signals of EPS, the fluorescence spectra showed the presence of protein-derived compounds in all EPS extracted. Additionally, humic-like substances were found when formaldehyde was used in the EPS extraction. Also, it was found that the peak intensity strongly depended on the EPS concentration.