The role of EPS in the foaming and fouling for a MBR operated in intermittent aeration conditions

Abstract

This work investigates the causes of foaming and fouling in an Intermittent Aerated – Membrane BioReactor (IA-MBR) used for wastewater treatment. The experiment was divided into three periods with different aerated regimes expressed with different taeration/tcycle ratio (Period I: 60 min/180 min, Period II: 80 min/180 min, Period III: 30 min/90 min). The advanced foaming tests used allow the study of the role of extracellular polymeric substances (EPSs) on foaming and fouling. In general, in the Periods I and II, good correlations between the EPSs and the Modified Scum Index without purification (MSI0) and the Foam Power were observed. The results shown that the filamentous microorganisms, which mainly grew in the Period III, play also a key factor in the foaming and fouling. In particular, when a net proliferation of filamentous bacteria occurred (during period III with a higher number of cycles per day) both EPSs concentration and filamentous abundance influence the modified scum index obtained after two purification steps (MSI2). Finally, the processing data show that the EPSs hampered also the membrane filtration but improve the pre-filtration action of cake layer. On the other hand, the co-presence of EPSs and filamentous bacteria reduced the effect o cake layer as pre-filter.