Nanofiltration and Reverse Osmosis

While microfiltration and ultrafiltration membrane technologies are based on processes that use microporous membranes operating under pressure to remove particles via a size exclusion mechanism, nanofiltration (NF) and reverse osmosis (RO) membrane technologies are based on the use of semipermeable membranes that also operate under pressure in order to mainly target the removal of dissolved contaminants via a controlled diffusion separation process. NF membranes were industrialized in the early 1980s as an alternative to RO membranes. The two main materials used to manufacture RO and NF membranes are cellulose acetate and various polyamides (PAs), especially aromatic PAs. A treatment process that includes NF or RO membranes consists of three distinct stages: pre-treatment, membrane treatment and post-treatment. This chapter illustrates a typical surface water treatment process with NF or RO. In all cases, three water flows must be considered: the raw water flow, the produced water flow and the concentrate flow.