An alternative to sodium bisulfate that doesn't damage delicate RO membranes

Dec. 15, 2002
In this installment of What Works, a company uses ultraviolet dechloriation for non-chemical disinfection.

To dechlorinate water at its Greensboro, N.C. plant, Procter & Gamble (P&G) was using sodium bisulfite as a neutralizing chemical. Unfortunately, it was increasing the costs of maintaining the plant's reverse osmosis (RO) membranes.

Chlorine is used widely as a water disinfection in process industries. However, its properties can damage delicate RO membranes and deionization resins, and it must be removed after disinfecting. The most common chlorine removal methods are granular carbon (GAC) filters or the adding of neutralizing chemicals such as sodium bisulfite. Both methods have drawbacks.

For example, the porous structure of GAC filters makes it a potential breeding ground for bacteria in a nutrient-rich environment. Dechlorination chemicals such as sodium bisulfite also act as bacteria incubators, causing biofouling of RO membranes. In addition, chemicals are hazardous to handle and there is the danger of over- or under-dosing because of human error.

Ultraviolet (UV) dechloriation has none of these drawbacks, according to Aquionics, a Erlanger, Ky.-based provider of non-chemical disinfection and contamination control technologies. Its high-intensity, broad-spectrum system disassociates free chlorine and chloramine into easily removed byproducts. It also provides high levels of microbial disinfection and total organic destruction. "UV is well-suited for disinfection, ozone destruction, TOC destruction and dechlorination," says Brad Shipe, a spokesperson for Aquinoics. "It has been used in the United States for wastewater treatment, but it's now receiving attention because of its ability to address issues such as Giardia and Chryptosporidium." Applications range from the beverage and food industries to the semiconductor and electronics industries.

So far, the Aquionics UV system is helping P&G reduce its maintenance costs. "We are very pleased with the UV system," says Kurt Loughlin, utilities process engineer for P&G. "Not only have we saved money since its installation, but the disruption caused by plant shutdowns as the result of RO membrane fouling has also been significantly reduced." P&G estimates that the UV system has saved it $70,000 annually in maintenance costs and reduced the frequency of monthly RO membrane washings from eight to two.

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