In-situ biofilm characterization in membrane systems using Optical Coherence Tomography: Formation, structure, detachment and impact of flux change
Wexler, Adam D.
Flemming, Hans Curt
Kruithof, Joop C.
Vrouwenvelder, Johannes S.
KAUST DepartmentWater Desalination and Reuse Research Center (WDRC)
Environmental Science and Engineering Program
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AbstractBiofouling causes performance loss in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane operation for process and drinking water production. The development of biofilm formation, structure and detachment was studied in-situ, non-destructively with Optical Coherence Tomography (OCT) in direct relation with the hydraulic biofilm resistance and membrane performance parameters: transmembrane pressure drop (TMP) and feed-channel pressure drop (FCP). The objective was to evaluate the suitability of OCT for biofouling studies, applying a membrane biofouling test cell operated at constant crossflow velocity (0.1 m s-1) and permeate flux (20 L m-2h-1).In time, the biofilm thickness on the membrane increased continuously causing a decline in membrane performance. Local biofilm detachment was observed at the biofilm-membrane interface. A mature biofilm was subjected to permeate flux variation (20 to 60 to 20 L m-2h-1). An increase in permeate flux caused a decrease in biofilm thickness and an increase in biofilm resistance, indicating biofilm compaction. Restoring the original permeate flux did not completely restore the original biofilm parameters: After elevated flux operation the biofilm thickness was reduced to 75% and the hydraulic resistance increased to 116% of the original values. Therefore, after a temporarily permeate flux increase the impact of the biofilm on membrane performance was stronger. OCT imaging of the biofilm with increased permeate flux revealed that the biofilm became compacted, lost internal voids, and became more dense. Therefore, membrane performance losses were not only related to biofilm thickness but also to the internal biofilm structure, e.g. caused by changes in pressure.Optical Coherence Tomography proved to be a suitable tool for quantitative in-situ biofilm thickness and morphology studies which can be carried out non-destructively and in real-time in transparent membrane biofouling monitors.
SponsorsThis work was performed at Wetsus, Centre of Excellence for Sustainable Water Technology (www.wetsus.nl). Wetsus is funded by the Dutch Ministry of Economic Affairs, the European Union European Regional Development Fund, the Province of Fryslan, the city of Leeuwarden and by the EZ-KOMPAS Program of the "Samenwerkingsverband Noord-Nederland". The work was funded by Wetsus, the King Abdullah University of Science and Technology (KAUST) and Evides waterbedrijf. The authors like to thank the participants of the Wetsus research theme "Biofouling", KAUST and Evides waterbedrijf for the fruitful discussions and their financial support. In addition the authors would especially like to thank the student Melvin Boelens for his support with the experimental work in the laboratory.
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