Officials in New York state are working to reduce the contaminant 1,4-dioxane, announcing strict maximum contaminant limits for drinking water. The new rules are part of a growing demand in the U.S. to strengthen regulations on drinking water quality and monitoring requirements to address micropollutants.
Filtration technologies, like activated carbon or reverse osmosis, are less effective against 1,4-dioxane due to its high solubility in water. Dealing with these types of challenging contaminants often requires a more reaction-driven approach to treatment, and the UV advanced oxidation process (UV AOP) can be a key part of the solution.
About The UV Advanced Oxidation Process
Similar equipment is used for both traditional UV disinfection and in the UV advanced oxidation process (UV AOP), but the latter requires significantly more UV intensity to perform the rapid advanced oxidation. Additionally, while traditional UV disinfection is based on achieving a predetermined UV dose, the amount of UV required for successful removal of micropollutants, like 1,4-dioxane, is determined by the controlled and managed balance of UV light delivery and an oxidant.
The oxidant, usually hydrogen peroxide, is injected into the raw water stream and mixed far enough ahead of the UV chamber to provide a uniform reaction when exposed to UV light. Within the UV chamber, the hydrogen peroxide converts to highly reactive hydroxyl radicals which immediately interact with contaminants to oxidize chemical bonds to degrade the molecule. About 70 percent of peroxide survives the process and can be removed (quenched) through an activated carbon filter (which can also simultaneously remove other commonly detected groundwater contaminants such as per- or polyfluoroalkyl substances, or PFAS) or neutralized with free chlorine before entering a distribution system.
Accurately sizing a UV advanced oxidation system based on the raw water characteristics and the desired outcome is the key to successfully implementing a UV AOP project. Bench-scale and pilot-scale testing are often needed before full-scale sizing of systems can take place.
Treating 1,4-dioxane With UV AOP on Long Island
Several groundwater aquifers providing drinking water to the residents of Long Island are contaminated with 1,4-dioxane, which has been able to enter the water supply in many cases because it was not easily treated by the activated carbon filters used to treat other micropollutants like trichloroethylene (TCE) and tetrachloroethylene (PCE). As a result, replacement of the filters’ carbon media was frequent and expensive, causing water operators to investigate an alternative treatment process for 1,4-dioxane removal.
Two water extraction sites on Long Island, one operated by the Suffolk County Water Authority and the other by the Bethpage Water District in Nassau County, installed full-scale TrojanUV advanced oxidation systems after months of pilot-scale testing. TrojanUVPhox™ systems were commissioned in 2017 and 2019 for Suffolk County and Bethpage Water District, respectively. The existing activated carbon filters used at these locations were repurposed to remove excess hydrogen peroxide after the UV chambers.
Three additional sites operated by the Bethpage Water District and four others operated by Hicksville Water, also located in Nassau County, commissioned UV AOP installations using the new TrojanUVFlex™AOP in early 2020.
The groundwater pump houses on Long Island are highly decentralized and often located within neighborhood communities. Therefore, space and power management were critical to ensure successful adoption of high-intensity UV advanced oxidation systems at these sites. The low-pressure TrojanUVFlexAOP is engineered specifically to reduce the size of the systems to accommodate installation in a smaller footprint.
To ensure fast and effective piloting at these decentralized locations, several compact UV AOP pilot stations were developed and deployed. These stations were easily mobilized on trucks for simple transport between well sites. At each well site, the pilot station was quickly connected to water and chemical oxidant supplies. This efficient transportability enabled the facilitation of over 24 separate pilots in six months and ensured that contaminated well sites in Nassau County could rapidly meet their groundwater remediation commitments. H2M Engineers was responsible for leading the pilot studies.
Through an effective pilot strategy and an optimized product, Long Island has effectively established a long-term solution for 1,4-dioxane contamination with UV AOP. Dozens of other TrojanUVFlexAOP installations are expected to be commissioned across Nassau County and Suffolk County over the next two years.