Contribution of Fe3O4 nanoparticles to the fouling of ultrafiltration with coagulation pre-treatment.

Wenzheng Yu,Lei Xu,Nigel Graham,Jiuhui Qu

doi:10.1038/srep13067

Abstract

A coagulation (FeCl3)-ultrafiltration process was used to treat two different raw waters with/without the presence of Fe3O4 nanoparticle contaminants. The existence of Fe3O4 nanoparticles in the raw water was found to increase both irreversible and reversible membrane fouling. The trans-membrane pressure (TMP) increase was similar in the early stages of the membrane runs for both raw waters, while it increased rapidly after about 15 days in the raw water with Fe3O4 nanoparticles, suggesting the involvement of biological effects. Enhanced microbial activity with the presence of Fe3O4 nanoparticles was evident from the measured concentrations of extracellular polymeric substances (EPS) and deoxyribonucleic acid (DNA), and fluorescence intensities. It is speculated that Fe3O4 nanoparticles accumulated in the cake layer and increased bacterial growth. Associated with the bacterial growth is the production of EPS which enhances the bonding with, and between, the coagulant flocs; EPS together with smaller sizes of the nano-scale primary particles of the Fe3O4-CUF cake layer, led to the formation of a lower porosity, more resilient cake layer and membrane pore blockage.

Highlights

Membrane filtration, as a particle separation process, is in principle an effective method
In this paper we describe the results of mini-pilot-scale tests that were undertaken to explore the contribution of Fe3O4 nanoparticles in polluted raw water to the fouling of a UF membrane with Fe(III) pre-coagulation; the study involved the quantification of changes in the nature of the organic constituents (e.g. extracellular polymeric substances (EPS), natural organic matter (NOM)), the properties of the cake layer, and other relevant parameters
The cake layer of FeNP-CUF membrane still contained Fe3O4 nanoparticles, which accumulated during the membrane operation, and it was able to influence the presence and activity of bacteria, as discussed subsequently

Summary

Introduction

Membrane filtration, as a particle separation process, is in principle an effective method. “In-line” chemical coagulation or coagulation–hydraulic flocculation, has been shown to be an effective way of improving general water quality, but of controlling membrane fouling[11,12,13]. It can be concluded that the existence of Fe(II)-Fe(III) nanoparticles in coagulated surface water, polluted by Fe3O4 nanoparticles, may influence/enhance microorganism growth and thereby affect membrane performance. In this paper we describe the results of mini-pilot-scale tests that were undertaken to explore the contribution of Fe3O4 nanoparticles in polluted raw water to the fouling of a UF membrane with Fe(III) pre-coagulation; the study involved the quantification of changes in the nature of the organic constituents (e.g. EPS, NOM), the properties of the cake layer, and other relevant parameters

Methods

Results

Conclusion