RO with minimal pre-treatment offers financial scope for optimisation

Using reverse osmosis (RO) on (drinking) water sources can produce high quality water directly. In practice, however, RO is never used directly on raw water because without (often costly) pre-treatment the membranes quickly foul. The results of recent TKI research show that fouling of the membranes remains can be controlled even without extensive pretreatment by working at a lower flux, higher cross-flow velocities and improved (periodic) hydraulic cleaning. For this study, a comparison was made between RO on surface water after minimal pre-treatment (screens) or after state-of-the-art ultra-filtration (UF).  This showed that both systems do not operate stably in the long term, but both do produce high-quality product water. Because the process with minimal pre-treatment is much cheaper than the process with UF, there is financial scope to make the operation stable after pre-treatment with screens and to optimise it with the aforementioned adjustments in flux, cross-flow speeds and hydraulic cleaning.

Reducing the membrane flux from 25 L/m2.h to 10 L/m2.h slowed down the membrane fouling by about a factor of 10. Periodical air water cleaning in minimal pre-treated RO resulted in an approximately 4-fold reduction of the spacer clogging rate, while not affecting the membrane fouling rate. The total cost of a minimal pre-treated low flux (10 L/m2.h) operated RO was significantly lower (0.46 €/m3) compared to state-of-the-art UF pre-treated RO at normal flux (25 L/m2.h) (1.21 €/m3). The cost difference in financial space provides an opportunity to develop minimal pre-treated RO systems with improved control of membrane fouling and spacer clogging.

Read more in: Effect of minimal pre-treatment on reverse osmosis using surface water as a source, E.R. Cornelissen, D.J.H. Harmsen, B. Blankert, L.P. Wessels and W.G.J. van der Meer, Desalination, Volume 509, 1 August 2021, 115056.

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