Elsevier

Chemosphere

Volume 268, April 2021, 129364
Chemosphere

The structural and functional properties of polysaccharide foulants in membrane fouling

https://doi.org/10.1016/j.chemosphere.2020.129364Get rights and content

Highlights

  • The spatial configuration of foulant molecule is significant in membrane fouling.

  • The resistance of gel layer is controlled by interaction of polysaccharide foulant.

  • Cations may change the interaction of polysaccharide foulant.

  • Mass-transfer model is more suitable for interpreting of crossflow filtration data.

Abstract

Polysaccharide foulant is known to play a crucial role in membrane fouling, however the detailed influential mechanisms and the pertinence to specific structure of polysaccharides, as well as intermolecular interactions among them with and without divalent cation are still indistinct. In this study, seven polysaccharides including agarose, sodium alginate, carrageenan, pectin, starch, sodium carboxymethylcellulose (CMC) and xanthan gum, with different chain and molecular structures, were used as model foulants to investigate the role of structural and functional features of polysaccharides in membrane fouling. Two Hermia’s models (classical and mass-transfer models) as well as the resistance-in-series model were used to analyze the fouling mechanism. Results show that the spatial configuration of foulant molecule is significant in membrane fouling which actually controls the resistance of gel layer formed on membrane. Polysaccharides with different properties show distinct fouling mechanisms which are in accordance with the four models described by Hermia respectively. Cations may change the interaction of polysaccharide foulant which further leads to the structural change of the gel layer. It turns out that mass-transfer model is more suitable for interpreting of crossflow filtration data. So far, little has been known about the effects of molecule structure of polysaccharides on membrane fouling. In this paper, we provide a basic database for polysaccharide fouling which will work as a theoretical basis for finding more effective measures to prevent and control membrane fouling.

Introduction

Membrane separation technology has been extensively applied in water and wastewater treatment thanks to its high efficiency and energy saving (Oinuma et al., 1994; Sheikholeslami, 1999; Matin et al., 2020). However, the fouling problem is always one of the main challenges for the application of membrane technique (Yu et al., 2019; Zhang and Jiang, 2019). Membrane fouling refers to the phenomenon that suspended particulate colloidal particles or dissolved macromolecules of organic matter are deposited on the surface of the membrane or adsorbed in the membrane pores in the process of membrane separation, resulting in the reduction or blockage of the membrane pores and irreversible decrease of membrane flux. Although various roles of organic foulant in membrane systems have been increasingly recognized, consensus cannot be reached if we don’t have enough knowledge about the fundamental structural features of organic foulants (Wang et al., 2017; Khan et al., 2020). Polysaccharide is the most common component of organic foulants, with extremely high molecular weight as well as gel properties and compositional diversity. Previous studies reveal that extracellular polymeric substances (EPS) often affect the properties and functions of activated sludge as well as the membrane separation process (Ji et al., 2020; Teng et al., 2020). Because of its unique structure with intermolecular cross-linking chains, polysaccharide is easy to cause more serious membrane fouling than other substances in EPS (Barzeev et al., 2015; Meng et al., 2015b; Meng and Liu, 2016). Usually, the fouling propensities of organic foulants are attributed to their functional groups, which are believed to play a significant role between foulant-foulant interaction and foulant-membrane interaction. However, recent studies have shown that the fouling tendencies of polysaccharides depend on not only their functional groups but also other properties such as spatial configuration and the morphology of foulants (Farias et al., 2014; Meng et al., 2020).

Polysaccharide shows an extensive diversity of nature and properties and such original characteristic may be an important reason leading to the controversy in understanding the mechanisms of membrane fouling. For example, Meng et al. (2018) demonstrated the fouling propensities of polysaccharide were structurally different by testing two different polysaccharides and their mixtures. In order to give a clear explanation to the fouling problem, it is crucial to establish a detailed database of reference polysaccharides from important categories. The mathematical model which has received much attention from researchers recently can be an efficient method in exploring fouling mechanism and it is very important to find a suitable fouling model for membrane filtration process.

Many more recent methods include artificial neural network (ANN), genetic programming (GP) models, membrane pore blocking models and cake layer models for evaluating membrane fouling mechanisms (Griffiths et al., 2014). However, most of them have some problems, such as the lacking of application method, high workload and high demand for computing facilities. Nowadays, the two models above the Hermia are the most widely used, but they still have such problems as that the conclusions are inconsistent and the application is unclear. In order to discuss the applicability and accuracy of the two models and interpret the membrane fouling problems and technical obstacles caused by polysaccharides, seven representative polysaccharides samples were employed as models for the present experiment. Above-mentioned polysaccharides are widespread in feed water in membrane system due to its wide application in food and textile industry. In this work, we investigated the relationship between flux decline and polysaccharide properties in UF-crossflow, and polysaccharide-Ca2+ interactions were probed to reveal the underlying membrane fouling mechanisms. Two models with different mass-transfer processes at typical feed water, Hermia’s mathematic model and resistance-in-series model, were used as polysaccharide analysis models. Our study represents the effort to delineate polysaccharides which can be classified into different categories and to explain their fouling properties on UF performance.

Section snippets

Experiment materials

Commercial polyethersulfone (PES) ultrafiltration membrane, AMFOR INC, Beijing, molecular weight cut off (MWCO) 20 kDa, effective surface area of 42 cm2; calcium chloride, Beijing Chemical Plant, AR; BSA224S precision electronic balance, Sartorius; ultra-pure water system (referred in this experiment), Millipore Simplicity; RP-1DN magnetic stirrer, As One; GS6202 electronic balance, Shinko Denshi; CF042A filter plant, Sterlitech; KH–500B ultrasonic cleaner, Kunshan Hechuang ultrasonic

The fouling mechanism of various polysaccharides

The filtration curves of different polysaccharides are shown in Fig. 1. It can be seen that agarose and starch led to continuous permeation decline over the whole filtration period. Under the same operation condition, the least flux decline during the 120min filtration test can be seen when the feed contained agarose only; while for the most flux decline, the feed contained starch. Agarose is known to be peculiarly gelatinous, but the gels are fragile and easily get synaeresis due to the

Conclusion

Although remarkable progress has been made in recent years, questions related to membrane fouling mechanism and related technique challenges haven’t been properly addressed. The current study investigated the effect of classic different polysaccharides and Ca2+ concentrations on the membrane fouling during ultrafiltration. Seven different structural and functional features of polysaccharide samples were studied, drawing the same conclusion that the formation of the spatial structure of

Credit author statement

Xianghao Meng: Conceptualization, Methodology, Experiment, Data curation, Investigation, Writing – original draft & revision. Duoji Luosang: Experiment, Data curation, Investigation. Shujuan Meng: Writing – review & editing, Formal analysis, Funding acquisition. Rui Wang, Wenhong Fan, Dawei Liang, Xiaohu Li, Qian Zhao and Linyan Yang: Formal analysis, Visualization,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by grants from the National Natural Science Foundation of China [No. 51808019].

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