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.
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