Functional Determinants of Extracellular Polymeric Substances in Membrane Biofouling: Experimental Evidence from Pure-Cultured Sludge Bacteria

Abstract

The aim of this work was to better understand the roles of extracellular polymeric substances (EPS) in membrane biofouling at the single-strain level. In the present study, a total of 23 bacterial strains were isolated from a sludge sample. The EPS extracted from pure-cultured bacteria were assessed for their fouling potentials and were simultaneously analyzed using Fourier transform infrared spectroscopy (FTIR). Further, the impact of calcium on the chemical composition of EPS and membrane fouling behavior was investigated in a strain-dependent manner. The EPS of the 23 bacterial strains exhibited different IR features for protein and polysaccharide regions. In addition, an α-1,4-glycosidic linkage (920 cm) and amide II (1,550 cm) correlated very well with the fouling potentials of all pure-cultured bacteria. In contrast to low-fouling strains, medium- and high-fouling strains exhibited two distinct peaks at 1,020 cm (uronic acids) and 1,250 cm (-acetyl), which accelerate membrane fouling given their gelling capacities. In the presence of calcium, the fouling potential of a high-fouling strain ( sp. strain JSB10) was profoundly reduced ( < 0.0005) due to the binding activity of an α-1,4-glycosidic linkage and amide II with calcium. However, the impact of calcium on a low-fouling strain ( sp. strain JSB21) was insignificant. Two-dimensional FTIR correlation spectroscopic (2D-FTIR-COS) analysis further revealed that the susceptibilities of functional groups to calcium largely relied on the composition and abundance of the above-described functional groups in EPS. These findings suggest that bacterial strains with different fouling potentials exhibit varied responses to calcium. Membrane biofouling is one of the main challenges for the operation of membrane-based processes used for water and wastewater treatment. This study revealed the functional determinants of EPS in membrane biofouling of 23 bacterial strains isolated from a full-scale membrane bioreactor (MBR) plant. We found that an α-1,4-glycosidic bond, amide II, and uronic acids of EPS significantly correlated with the fouling potentials of bacteria. The roles of these EPS groups in membrane fouling were impacted by calcium resulting from EPS-calcium interactions. In addition, our results also demonstrated that any perturbations in the sludge bacterial community in MBRs can lead to varied filtration potentials of the bulk liquor.

Ecological insights into the underlying evolutionary patterns of biofilm formation from biological wastewater treatment systems: Red or Black Queen Hypothesis?

“…Thus, the higher biofilm formation potentials of strains from surface‐attached aggregates might not be attributed to growth rates. The varying biofilm potentials of these isolated strains could be associated with the phenotypes of the strains, such as extracellular polymeric substances (EPS) production (Karunakaran & Biggs, 2011; Maddela et al, 2018; Vanysacker, Boerjan, Declerck, & Vankelecom, 2014) and mobility (Xia, Chen, Chen, Qian, & Liu, 2018). We recently found that the functional groups of Amide II and α‐1,4‐glycosidic linkage largely determined the biofouling process of the bacterial strains (Maddela et al, 2018).…”

“…In this study, 40 strains were isolated from two microbial aggregates (Figure 1a, Step 1). Twenty strains were isolated from 8‐day‐old surface‐attached aggregates (SA1‐20) in a glass flow cell chamber (IBI Scientific) using activated sludge from a laboratory MBR as the source community; the other 20 strains were isolated from mobile aggregates (MA1‐20) from a full‐scale MBR plant (Guangzhou, China) with the sludge retention time of approximately 15–20 days (Maddela, Zhou, Yu, Zhao, & Meng, 2018). Herein, strains from each aggregate had previously coexisted and adapted to each other for several days: 8 days for SA1‐20 and 15–20 days for MA1‐20.…”

“…In this study, 40 strains were isolated from two microbial aggregates ( Figure 1a The isolation and identification of these strains followed the description of Maddela et al (2018), and details are available in the supplementary material. For similarity analysis, the 16S Ribosomal RNA (rRNA) sequences were blasted online (http://www.ncbi.nlm.nih.…”

Fouling of membranes in membrane bioreactors for wastewater treatment: Planktonic bacteria can have a significant contribution

“…Interestingly, Arcobacter and several other genera observed in the sludge supernatant are known to be abundant in raw wastewater (Kristensen, Nierychlo, Albertsen, & Nielsen, 2020; Saunders, Albertsen, Vollertsen, & Nielsen, 2016), so their presence indicate that some of these influent bacteria were not removed by higher organisms such as ciliates or bound to the flocs (Ali et al, 2019; Eikelboom, 2000; Kristensen et al, 2020). Therefore, these free‐living bacteria, which are continuously supplied with the influent wastewater, act as small colloids in bulk water with a size of 0.5–3 µm (Maddela, Zhou, Yu, Zhao, & Meng, 2018; Snaidr, Amann, Huber, Ludwig, & Schleifer, 1997). The bacterial strain chosen for the model suspension belongs to the family Pseudomonadaceae, which has been found in wastewater influent (Saunders et al, 2016).…”

“…This would indicate that the immigrating bacteria, which are not absorbed by the sludge flocs, might play a key role in initial fouling. After initial adhesion, the fouling potential of bacteria may be species/strain‐dependent and some features shared by key fouling‐causing bacteria (Ishizaki, Fukushima, Ishii, & Okabe, 2016; Maddela et al, 2018) Hence, future studies should further investigate how specific influent planktonic cells contribute to initial membrane fouling and how this can be mitigated. In addition, as it is shown that a significant part of measured soluble EPS may be planktonic cells, it is suggested for further studies to include bulk water cell count in the analysis of MBR sludge fouling potential.…”