By switching to a UV dechlorination system from Aquionics Inc, Procter & Gamble has not only saved $70,000 per year on reverse osmosis (RO) membrane maintenance at its Greensboro, NC manufacturing plant, but has also significantly reduced the number of maintenance shutdowns required.

Widely used for water disinfection in many different process industries, chlorine must be removed once it has performed its disinfection function in order to avoid damaging delicate process equipment such as RO membranes and deionization (DI) resin units. Traditionally, 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.

While both methods have advantages, they also have a number of significant drawbacks. GAC filters, because of their porous structure and nutrient-rich environment, can become breeding grounds for bacteria. Dechlorination chemicals such as sodium bisulfite, which are usually injected just in front of RO membranes, can also 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 through human error.

UV treatment, with none of these drawbacks, is becoming an increasingly popular dechlorination technology. 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.

At the Procter & Gamble facility, sodium bisulfite was replaced with an Aquionics UV dechlorination unit, which was installed before two banks of RO membranes. Trials run soon after installation showed a dramatic reduction in the RO membrane wash frequency -- down to only two cleanings per month from a previous average of eight -- yielding annual savings of $70, 000.

"We are very pleased with the UV system," says utilities process engineer Kurt Loughlin. "Not only have we saved money since it was installed, but the disruption caused by plant shutdowns as a result of RO membrane fouling has also been significantly reduced. UV provides a high standard of dechlorination without any of the drawbacks of using chemicals or granular activated carbon (GAC) filters."