Membrane Process - Nanofiltration

The two most common membrane processes used to treat potable water in the United States are reverse osmosis (RO) and nanofiltration (NF). Nanofiltration systems can eliminate contaminants and particles that have diameters as small as 0.001 micrometers, while RO systems filter out particles with diameters as small as 0.0001 micrometers. NF and RO systems are also increasingly being used in developing countries since they are considered inexpensive compared with other filtrations methods.

The membranes used in RO or NF systems are constructed either in spiral-wound or hollow fine-fiber (HFF) configurations and the membranes can be made of organic polymers, polymides as well as their respective derivatives. NF systems can be used to filter out salts, hardness, pathogens, turbidity and disinfection by-products (DBPs) from water, along with synthetic organic compounds (SOCs) and pesticides.

NF and RO are used for a variety of applications including converting seawater into drinking water. These systems are also recommended for filtering out DBPs from drinking water from water supplies with high amounts of natural organic materials (NOM), which react with additives such as chlorine or other chemical oxidizing agents, meant to disinfect water.

While membrane systems are effective against preventing viruses, pathogens and cysts, occasionally bacteria can make it through the membranes used in nanofiltration. Pesticides with a molecular weight less than 190, such as ethylene dibromide (EDB), have also been able to pass through.

References:

American Water Works Association Research Foundation, Lyonnaise des eaux-Dumez (Firm), South Africa. Water Research Commission

Author: Joel Gershon