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3.4.7 Boundary conditions

Membranes serve as selective barriers between two phases and remain impermeable to specific particles. In fact, membranes are a physical treatment and therefore subject to physical limitations. Media that are filled with particles or organic materials can plug membrane pores.

Surface water and waste water e.g. may need pre-treatment before nanofiltration. Therefore the pre-treatment process produces large volumes of concentrate and consequently large disposals are needed.

Source water, waters with high parts of iron, chlorine and manganese always need pre-treatment so that these particles could limit lifetime of membranes. Even nanofiltration systems under ideal conditions need membrane cleaning and periodic replacement.

Membranes for nanofiltration systems are made of different materials with their inherent positive respectively negative characteristics. To choose the optimal membrane under given conditions can be a great challenge for water treatment^[30].