Flux and Water Permeability

Microfiltration flux decreased by approximately 60 % (630 to 385 L m % ) during the initial batch and then stabilised. No flux variation during the filtration cycle due to backflush was measurable. Since the MF served as a pretreatment step, and therefore the flux was not continuously monitored. However, serious flux decline soon became apparent which encouraged further investigations. 

No significant flux decline occurred during normal hatches with concentration factors of up to 100. A small flux decline that was observed can probably be attributed to osmotic effects due to the salt concentration. The osmotic pressure of the salt solution (which is of a higher concentration in the boundary layer) reduces the effective transmembrane pressure. 

However, cleaning solutions (water and KOH solution) contained substantial amounts of organic matter. The RO unit was first flushed with 30 L of clean water (permeate) and then for 1 hour with 20 L of 0.1% KOH (pH 11.7) at low pressure and high flow to avoid permeate production. Unfortunately, it was not possible to distinguish between material adsorbed on the membrane and organics which accumulated in other parts of the equipment, when operating at such a relatively large scale. 

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