Quantitative Analysis of Membrane Fouling Mechanisms Involved in Microfiltration of Humic Acid–Protein Mixtures at Different Solution Conditions

Chunyi Sun,Shuang Liang,Xiaoqian Liu,Guoyi Ke,Lianfa Song,Fazhan Li,Na Zhang

doi:10.3390/w10101306

Abstract

A systematical quantitative understanding of different mechanisms, though of fundamental importance for better fouling control, is still unavailable for the microfiltration (MF) of humic acid (HA) and protein mixtures. Based on extended Derjaguin–Landau–Verwey–Overbeek (xDLVO) theory, the major fouling mechanisms, i.e., Lifshitz–van der Waals (LW), electrostatic (EL), and acid–base (AB) interactions, were for the first time quantitatively analyzed for model HA–bovine serum albumin (BSA) mixtures at different solution conditions. Results indicated that the pH, ionic strength, and calcium ion concentration of the solution significantly affected the physicochemical properties and the interaction energy between the polyethersulfone (PES) membrane and HA–BSA mixtures. The free energy of cohesion of the HA–BSA mixtures was minimum at pH = 3.0, ionic strength = 100 mM, and c(Ca2+) = 1.0 mM. The AB interaction energy was a key contributor to the total interaction energy when the separation distance between the membrane surface and HA–BSA mixtures was less than 3 nm, while the influence of EL interaction energy was of less importance to the total interaction energy. The attractive interaction energies of membrane–foulant and foulant–foulant increased at low pH, high ionic strength, and calcium ion concentration, thus aggravating membrane fouling, which was supported by the fouling experimental results. The obtained findings would provide valuable insights for the quantitative understanding of membrane fouling mechanisms of mixed organics during MF.

Highlights

Microfiltration (MF) is increasingly applied in water treatment due to the continuously decreasing cost and progressively more efficient performance of MF membranes [1,2]
It was found that the water contact angles (θ W ) of the PES membrane decreased with increasing pH, suggesting that water molecules are energetically favorable for contacting with the membrane
To further elucidate the role of different mechanisms in membrane fouling, the variation in interaction energy components with separation distance under baseline solution conditions is shown in. These results clearly showed that the AB interaction energy was a main contributor to the total interaction energy when the separation distance between the membrane surface and humic acid (HA)–bovine serum albumin (BSA) mixtures was less than 3 nm

Summary

Introduction

Microfiltration (MF) is increasingly applied in water treatment due to the continuously decreasing cost and progressively more efficient performance of MF membranes [1,2]. Membrane fouling, mainly caused by natural organic matter (NOM), still remains the primary impediment for the widespread application of MF technology [3]. Water 2018, 10, 1306 component of NOM [4], and is considered to be one of the main culprits causing membrane fouling [5]. Protein is ubiquitous in natural water and more hydrophilic than. Some investigations found that hydrophilic matter could result in more serious membrane fouling than hydrophobic matter [6,7]. Protein can contribute to membrane fouling in spite of its lower content in natural water [8].

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Results

Conclusion