Biofouling in reverse and forward osmosis membrane systems

Abstract

Global freshwater demand has significantly increased over the past century and continued growth is expected in the coming century. Since more than 97 percent of the water in the world is seawater, desalination technologies have the potential to solve the fresh water crisis. Currently, the most used desalination technology is reverse osmosis, where a semipermeable membrane is used to separate the salt from the water. The driving force of reverse osmosis desalination is hydraulic pressure, which has to be greater than the osmotic pressure of the seawater. Due to the high hydraulic pressure reverse osmosis has a high energy demand. Lately, hybrid desalination systems, e.g. indirect desalination with forward osmosis combined with low pressure reverse osmosis are getting more importance. Forward osmosis is also a membrane based process that uses the osmotic pressure difference as driving force. One of the main advantages of forward osmosis is the limited amount of external energy requirement compared to reverse osmosis. The major problem of membrane desalination process is fouling, the accumulation of unwanted material on the membrane surface, causing performance decline and increase of costs. Several types of fouling can occur in membrane processes, biofouling (microbial biofilm formation), scaling (mineral salt precipitation), organic fouling (deposition of organic macromolecules) and colloidal fouling (deposition of particulate matter). In practice biofouling is considered as the major problem in membrane systems.