At the Procter & Gamble manufacturing plant in Greensboro, N.C., an Aquionics ultraviolet (UV) dechlorination unit was installed before two banks of reverse osmosis (RO) membranes. Before this system was installed, dechlorination was achieved using sodium bisulfite.
Chlorine is widely used for water disinfection in many difference process industries. Because of its properties, however, it can damage delicate process equipment such as RO membranes and deionization (DI) resin units and must be removed once it has performed its disinfection function. To date, the two most commonly used methods of chlorine removal have been granular activated carbon (GAC) filters or the addition of neutralizing chemicals such as sodium bisulfite.
Both of these methods have their advantages, but they also have a number of significant drawbacks. GAC filters have a porous structure and nutrient-rich environment, which become a breeding ground for bacteria. Dechlorination chemicals such as sodium bisulfite, which usually are injected just in front of RO membranes, also can act as incubators for bacteria, causing biofouling of the membranes. In addition, these chemicals are hazardous to handle and there is a danger of over- or under-dosing due to human error.
An increasingly popular dechlorination technology with none of the drawbacks the chemicals may have is UV treatment. High intensity, broad-spectrum UV systems dissociate both free chlorine and chloramine compounds (mono-, di- and tri-) into easily removed byproducts. UV has the added benefit of providing both high levels of microbial disinfection and total organic carbon (TOC) destruction.
Trials that ran soon after the UV system’s installation showed a dramatic reduction in the RO membrane wash frequency—down from an average of eight cleanings per month to only two per month.
“We are very pleased with the UV system,” said Kurt Loughlin, utilities process engineer at Proctor & Gamble. “Not only have we saved money since it was installed, but the disruption caused by plant shutdowns as a result of RO membrane fouling also has been significantly reduced. UV provided a high standard of dechlorination without any of the drawbacks we faced with chemicals of GAC filters.”
With the dramatic reduction of cleanings came savings of approximately $70,000 annually. The number of shutdowns for RO membrane maintenance also was significantly reduced.