Spatially-resolved in-situ quantification of biofouling using optical coherence tomography (OCT) and 3D image analysis in a spacer filled channel

Abstract

The use of optical coherence tomography (OCT) to investigate biomass in membrane systems has increased with time. OCT is able to characterize the biomass in-situ and non-destructively. In this study, a novel approach to process three-dimensional (3D) OCT scans is proposed. The approach allows obtaining spatially-resolved detailed structural biomass information. The 3D biomass reconstruction enables analysis of the biomass only, obtained by subtracting the time zero scan to all images. A 3D time series analysis of biomass development in a spacer filled channel under representative conditions (cross flow velocity) for a spiral wound membrane element was performed. The flow cell was operated for five days with monitoring of ultrafiltration membrane performance: feed channel pressure drop and permeate flux. The biomass development in the flow cell was detected by OCT before a performance decline was observed. Feed channel pressure drop continuously increased with increasing biomass volume, while flux decline was mainly affected in the initial phase of biomass accumulation. The novel OCT imaging approach enabled the assessment of spatial biomass distribution in the flow cell, discriminating the total biomass volume between the membrane, feed spacer and glass window. Biomass accumulation was stronger on the feed spacer during the early stage of biofouling, impacting the feed channel pressure drop stronger than permeate flux.

Early biofouling detection using fluorescence-based extracellular enzyme activity

“…This can be associated with the increase in bacterial enzyme production as bacterial abundance increases. In Figure 8, we observe early biomass deposition on the feed spacer using the OCT, which is in agreement with previous studies [46]. Theoretically, fluorescence-based EEA signal increases are not dependent on where bacteria deposit, demonstrating the practicality of using EEA to monitor biomass accumulation across the membrane module in seawater processes.…”

Optical coherence tomography in biofilm research: A comprehensive review

“…The results clearly confirm that (i) the feed spacer is markedly influencing the fouling behavior as well as that (ii) imaging tools such as OCT are necessary to understand differences among experimental parameters (e.g., feed and feed spacer geometry). A similar approach was recently published by Fortunato et al (2017a). Working with feed spacers is challenging with respect to image analysis.…”

The membrane fouling simulator: development, application, and early-warning of biofouling in RO treatment

“…Early warning using an MFS monitored by sensitive pressure drop measurements can be combined with an autopsy of the spacer and membrane sheets sampled from the MFS to quantify accumulated ATP and total organic carbon (TOC) [54], or with non-destructive imaging methods such as optodes or NMR microscopy. A method that recently gained interest for non-destructive imaging of biofilms is OCT [51,96,97].…”

“…Such device should be representative for conventionally used membrane modules, thus involving the used materials (properties and structure) such as membrane and spacer, the height of the flow channels and hydraulics. The membrane fouling simulator (MFS) was introduced in 2006 [4] and since then many articles have appeared on various research aspects of biofilm characterization [2,3,[27][28][29][30][31][32][33][34][35][36], biofouling control [5,[37][38][39][40][41][42][43][44][45][46][47][48][49], and strategies for early warning of biofouling [50][51][52][53][54][55] applying the developed MFS.…”