Mini-review: novel non-destructivein situbiofilm characterization techniques in membrane systems

Abstract

A B S T R A C TMembrane systems are commonly used in the water industry to produce potable water and for advanced wastewater treatment. One of the major drawbacks of membrane systems is biofilm formation (biofouling), which results in an unacceptable decline in membrane performance. Three novel in situ biofouling characterization techniques were assessed: (i) optical coherence tomography (OCT), (ii) planar optodes, and (iii) nuclear magnetic resonance (NMR). The first two techniques were assessed using a biofilm grown on the surface of nanofiltration (NF) membranes using a transparent membrane fouling simulator that accurately simulates spiral wound modules, modified for in situ biofilm imaging. For the NMR study, a spiral wound reverse osmosis membrane module was used. Results show that these techniques can provide information to reconstruct the biofilm accurately, either with 2-D (OCT, planar optodes and NMR), or 3-D (OCT and NMR) scans. These non-destructive tools can elucidate the interaction of hydrodynamics and mass transport on biofilm accumulation in membrane systems. Oxygen distribution in the biofilm can be mapped and linked to water flow and substrate characteristics; insights on the effect of crossflow velocity, flow stagnation, and feed spacer presence can be obtained, and in situ information on biofilm structure, thickness, and spatial distribution can be quantitatively assessed. The combination of these novel non-destructive in situ biofilm characterization techniques can provide realtime observation of biofilm formation at the mesoscale. The information obtained with these tools could potentially be used for further improvement in the design of membrane systems and operational parameters to reduce impact of biofouling on membrane performance.

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

“…To better understand the biomass development in membrane systems, in-situ qualitative and quantitative analyses of the biomass under operational conditions are needed). Several techniques are currently available to study the biomass formation under membrane operational conditions, such as nuclear magnetic resonance spectroscopy (NMR), planar optodes and optical coherence tomography (OCT) (Valladares Linares et al, 2016).…”

Fouling Monitoring in Membrane Filtration Systems

“…The structural analysis of the fouling layer deposited on a membrane coupon consists of using imaging techniques. Most of the imaging approaches and practices to characterize the fouling morphology reported in the literature include require destructive procedures and are performed after membrane autopsy (Figure 4) [11,12]. Scanning electron microscopy (SEM) has been for many years the most employed technique to characterize membrane coupons.…”

A review of efforts to reduce membrane fouling by control of feed spacer characteristics

“…Alternative imaging methods, such as scanning electron microscope, can offer a high image resolution. However, it is a destructive technique, the visual area is small and comprises only a small part of the feed spacer or the membrane, and in addition it cannot be used to measure fouling processes directly in-situ [102][103][104]. Fouling characterization has also been carried out using electrical impedance spectroscopy [105,106] and ultrasonic time domain reflectometry [107,108] , but again it is difficult for these sensor-based methods to produce high resolution images of the fouling process directly.…”