Investigating the influence of organic matter composition on biofilm volumes in reverse osmosis using optical coherence tomography

Biofouling, a critical issue in membrane filtration, is influenced by several factors such as membrane characteristics and feed water quality. The organic matter (OM) composition is known to significantly influence biofilm formation, but few studies on this subject have been reported. Optical coherence tomography (OCT) allows direct monitoring of biofilm development on the membrane surface without the need for membrane autopsy. The purposes of the present study are 1) to quantify biofouling formation on a membrane surface using OCT; 2) to monitor the temporal variation of OM composition during membrane formation; and 3) to investigate the variation of OM composition. Substantial variations in thickness was observed from OCT images. It demonstrates that biovolume quantified from a single 2D cross-sectional image could result in inaccurate quantification. Here, we quantified foulants on the membrane surface using 3D images and validated the results using confocal laser scanning microscopy (CLSM). As well, variations in the OM composition driven by bacterial activity were observed by fluorescence excitation–emission matrix analysis and size exclusion chromatography. The biovolume estimated by the OCT system was 103.7 μm³/μm². CLSM demonstrated that 10% of the foulants on the membrane surface was composed of live and dead bacteria.