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Abstract
A modified version of the membrane fouling simulator (MFS) was developed for assessment of (i) hydraulic biofilm resistance, (ii) performance parameters feed-channel pressure drop and transmembrane pressure drop, and (iii) in situ spatial visual and optical observations of the biofilm in the transparent monitor, e.g. using optical coherence tomography. The flow channel height equals the feed spacer thickness enabling operation with and without feed spacer. The effective membrane surface area was enlarged from 80 to 200 cm2 by increasing the monitor width compared to the standard MFS, resulting in larger biomass amounts for analysis. By use of a microfiltration membrane (pore size 0.05 μm) in the monitor salt concentration polarization is avoided, allowing operation at low pressures enabling accurate measurement of the intrinsic hydraulic biofilm resistance. Validation tests on e.g. hydrodynamic behavior, flow field distribution, and reproducibility showed that the small-sized monitor was a representative tool for membranes used in practice under the same operating conditions, such as spiral-wound nanofiltration and reverse osmosis membranes. Monitor studies with and without feed spacer use at a flux of 20 L m−2 h−1 and a cross-flow velocity of 0.1 m s−1 clearly showed the suitability of the monitor to determine hydraulic biofilm resistance and for controlled biofouling studies.
Acknowledgments
This 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 Fryslân, the city of Leeuwarden, and by the EZ-KOMPAS Program of the “Samenwerkingsverband Noord-Nederland.” The authors like to thank the participants of the research theme “Biofouling” and Evides waterbedrijf for the fruitful discussions and their financial support. In addition, the authors would especially like to thank the students Malgorzata Nowak, Stanislaw Wojciechowski, Judita Laurinonyte, Nathalie Juranek, and Zhen Xiang for their great support with the experimental work in the laboratory. The photographs of the tMBM were taken by Christina Kappel and her work is herewith gratefully acknowledged.