Characterization of foaming and non-foaming sludge relating to aeration and the implications for membrane fouling control in submerged membrane bioreactors

Abstract

In this study, two parallel aerobic MBRs were operated with different aeration diffusers (coarse-bubble aeration vs. fine-bubble aeration). It was found that fine-bubble aeration would cause serious foaming in the MBR system. The specific filtration resistance (SFR) of non-foaming sludge was similar to that of the sludge suspension in the foaming MBR, but almost 2–3 times larger than that of the foaming sludge liquor from the top layer of the foaming MBR. The intermediate pore blocking was the dominant fouling mechanism in batch filtration tests. The filtration performance of the sludge mixtures was governed by the combined effect of several major factors. There were more smaller flocs, less soluble microbial products (SMP) and less bound extracellular polymeric substances (EPSs) in the foaming sludge samples. Interfacial interaction calculation showed that the foaming sludge had a weaker adhesion ability. Comparison of foaming sludge and overflow foaming sludge revealed that the degree of foaming could affect the filtration behavior and physicochemical properties of the foaming sludge. The findings regarding the combined effect of aeration bubble size on foaming and fouling gave some implications for foaming and fouling control. Since fine-bubble aeration was detrimental for foaming control but beneficial for fouling mitigation, the selection of the optimal aeration intensity and diffuser would be a potentially effective strategy for the membrane fouling and foaming control in the MBR system.