Time-resolved monitoring of biofouling development on a flat sheet membrane using optical coherence tomography

Luca Fortunato,Torove Leiknes,Sanghyun Jeong

doi:10.1038/s41598-017-00051-9

Luca Fortunato, Torove Leiknes + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-00051-9

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Abstract

Biofouling on a membrane leads to significant performance decrease in filtration processes. In this study, an optical coherence tomography (OCT) was used to perform a time-resolved analysis of dynamic biofouling development on a submerged membrane under continuous operation. A real-time change in the biofouling morphology was calculated through the image analysis of OCT scans. Three videos were generated through the acquisition of serial static images. This is the first study that displays the dynamic biofouling formation process as a video. The acquisition of OCT cross-sectional scans of the biofouling allowed to evaluate the time-lapsed evolution for three different time periods (early stage, double layers and long-term). Firstly, at the early filtration stage, membrane coverage and average biofouling layer thickness were found to be linearly correlated with the permeate flux pattern. Secondly, after 3 d of operation, an anomalous morphology was observed, constituted by a double-layered biofouling structure: denser on the bottom and looser on the top. In a long-term operation, the biofouling structure underwent a dynamic evolution over time, resulting in a multi-layered structure. The biofouling formation information was closely associated with filtration performance (i.e. flux) indicating the suitability of OCT as real-time and in-situ biofouling monitoring technique.

Highlights

The growth of a fouling layer by deposition of undesirable materials such as suspended solids, colloids and microbial cells onto or into a membrane is a persistent problem in membrane filtration processes
Optical coherence tomography (OCT), an emerging imaging technique mainly used in biomedical applications[12, 13], has recently gained popularity in the study of biofouling in membrane filtration processes
The dynamic formation of the biofouling layer was investigated through two experiments

Summary

Introduction

The growth of a fouling layer by deposition of undesirable materials such as suspended solids, colloids and microbial cells onto or into a membrane is a persistent problem in membrane filtration processes. There are various factors that affect membrane fouling of MBR, such as membrane properties, biomass properties, feedwater characteristics and operating conditions, membrane biofouling via microbial products plays a critical role in determining the MBR performance[6] This causes an increase in transmembrane pressure (TMP) under constant flux operation or a decrease in the permeate flux under constant pressure mode. Ex-situ methods (i.e. membrane autopsies), wherein a fouled membrane is taken out of the system after operation, can provide important insights to the thickness and structure of the biofouling on membrane[8, 9] These approaches can give misleading results as biofilms or biofouling layers could change in nature due the manor in which samples are collected, and only characterize conditions representative of the point of time point at which filtration was terminated. OCT time-lapse measurements have been reported and used in the evaluation the impact of shear stress conditions on biofilm behavior[16]

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