A comparison between laboratory and industrial fouling of reverse osmosis membranes used to concentrate milk

Reverse osmosis with polyamide spiral wound membranes is used to concentrate milk to reduce its volume before transport to processing facilities. The main aim of this work was to identify the cause of unusually low flux through a membrane that had been used in an industrial facility. The fluxes of new and used industrial membranes were measured using a flat-sheet cross-flow laboratory system. It was found that the fouling characteristics of laboratory fouled membranes were entirely different from the industrial membrane. The laboratory membranes could be restored to a high flux with a regime of water flushing, caustic and acid. FTIR showed no significant build-up on the membrane. In contrast the industrial membrane could not be cleaned in this manner. FTIR and FT-Raman showed species associated with milk lipids. Cleaning by solvent extraction using a two-phase mixture of water, isopropanol and cyclohexane increased the flux from 1% to almost 50% of the value of a new membrane. Analysis of the solvent-extracted material indicated the presence of phospholipids with a relatively high concentration of sphingomyelin. It was concluded that the laboratory experiments did not mimic industrial processes and an effective industrial cleaning system was not found.