Micro-particles—A Neglected but Critical Cause of Different Membrane Fouling between Aerobic and Anaerobic Membrane Bioreactors

Abstract

Until recently, membrane fouling in anaerobic membrane bioreactors (AnMBRs) was generally understood based on and by extrapolating from well-studied aerobic membrane bioreactors (AeMBRs). Clearly, this will probably be unhelpful, as each contains different microbial ecology, particles/colloids, and soluble microbial products. In this paper, a comprehensive comparison was made between these two systems to understand their different sources of foulants and, hence, differences in fouling. Our results showed that worse fouling occurred in the AnMBR than in the AeMBR due to the different characteristics of bulk solutions. Filtration tests revealed that the bulk solution supernatant in the AnMBR contained more abundant micro-particles (0.45−10 μm, 69.4% of the total organics), exhibiting a much higher specific filtration resistance (1.56 × 10 15 m −1 /g TSS) and a unified modified fouling index value (4.56) than the AeMBR (36.4%, 2.17 × 10 12 m −1 /g TSS and 0.03, respectively). Based on Fourier transform infrared spectra combined with principal component analysis, the AnMBR foulants had functional groups similar to those of the micro-particles in the bulk solution, while the AeMBR foulants were more similar to extracellular polymeric substances of the bulk sludge. More interestingly, the microbial source tracking calculation utilizing 16S rRNA gene sequences showed that the micro-particles were an important source (22.6%) of the biocake microorganisms in the AnMBR but only contributed to 1.9% in the AeMBR. In contrast, the bulk sludge (67.7%) was determined to be a more dominant component of the biocake microorganisms in the AeMBR than in the AnMBR (38.7%). Our findings enable us to discriminate between the different sources of foulants in AnMBRs and AeMBRs and highlight the significance of micro-particles in anaerobic systems from abiotic and biotic aspects. It is clear in AnMBRs that a more sustainable form of treatment by reducing the micro-particles could be better for fouling control.

The stimulation of microbial activity by microplastic contributes to membrane fouling in ultrafiltration

“…It is indicted that the effect of PE microplastic on membrane fouling was more obvious than the microparticles in raw water. The presence of microparticles has already been shown to cause membrane fouling [38], but the pattern of membrane fouling exacerbation caused by microplastics need to be further explored. A control experiment was supplemented that the feed waters with 0.05% (w/v) sodium azide (NaN3) were used as controls variable, which can inhibit the regrowth of microorganisms (Fig.…”

Examination of Extracellular Polymer (EPS) Extraction Methods for Anaerobic Membrane Bioreactor (AnMBR) Biomass

“…What little information that does exist is often extrapolated from MBRs, which can vary significantly from AnMBRs. For example, a recent comparison by Yao et al [10] showed significantly more fouling in AnMBRs, significant differences in membrane fouling mechanisms, and different characteristics within extracellular polymeric substances (EPS) and soluble microbial products (SMP).…”

“…Membrane bioreactor fouling is primarily driven by EPS, which are a complex mixture of polysaccharides, proteins (structural proteins or exoenzymes), lipids/phospholipids, humic substances, and other intercellular polymers [1,10,11]. Unfortunately, the compositional, and functional details of EPS are not completely understood, while the literature has reported EPS characteristics [3,10,12]. EPS is also related to SMP, another major category of foulants.…”

“…There are multiple studies in the literature, which have examined the optimization of EPS extraction methods for aerobic bacteria (MBRs) [25,27,28]. However, there is limited information on EPS extraction methods suitable for anaerobic microorganisms proliferated in AnMBRs [10]. EPS characterization studies for AnMBRs have primarily employed extraction methods, which have been developed for MBRs, although the metabolism and EPS composition of aerobic bacteria is very different from methanogens and fermentative microorganisms.…”

Assessing membrane biofilm predevelopment strategies to improve anaerobic membrane bioreactor effluent quality. (c2022)

“…The difference in formation of biofilm is based on microbial groups, micro-particles, and soluble microbial products, which confer potential advantages attributed to AnMBRs. Indeed, these benefits include the reduction and removal of emerging contaminants, namely, organic micropollutants (OMPs) and antibiotic resistance genes (ARGs) (Sanguanpak et al, 2019;Yao et al, 2020). Thus, a major factor not to be overlooked in membrane biofilms dynamics is the presence of inherent microbial communities in anaerobic membrane biofilms.…”