Influence of permeation on air/water cleaning of spiral wound membrane NF/RO elements

摘要

To improve hydraulic conditions, periodic air/water cleaning (AWC) is applied to a nanofiltrationn(NF) spiral wound membrane (SWM) element under permeation conditions to control biofoulingnand particulate fouling. A pilot study was carried out for 212 days with a vertically positionednSWM element fed by tap water enriched with a biodegradable compound (60 mg acetate-C l21).nOperational parameters were daily recorded, rinse water was collected and analysed andna membrane autopsy was performed at the end of the experimental run. Normalized pressurendrop (NPD) increased as a result of biofouling and particulate fouling, and could be controllednby periodic AWC, while the membrane transport coefficient (MTC) and retention based on thenconductivity remained constant. Rinsing water from AWC contained biomass and particulatenmatter (iron), predominantly during the first few minutes of AWC. Membrane autopsy revealednactive biomass and inorganic deposits (mainly iron and copper) at the inlet and outlet of thenmembrane element. The use of AWC in (vertically positioned) NF/RO SWM elements undernpermeation conditions improved the control of membrane fouling (especially biofouling andnparticulate fouling) and did not compromise the integrity of the membrane element (until day 60).