C. Dreszer, A.D. Wexler, S. Drusova, T. Overdijk, A. Zwijnenburg, H.-C. Flemming, J.C. Kruithof, J.S. Vrouwenvelder
Water Research, Volume 67, p. 243254, (2014)
OCT, Membrane biofouling monitor, Sensitive biofilm thickness measurement, Biofilm morphology, Transmembrane pressure drop, Feed-channel pressure drop
Biofouling 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−2 h−1).
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−2 h−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