Advanced Oxidation Process for 1,4-Dioxane Removal

The process itself is different from conventional water treatment processes. Advanced oxidation refers to any process that produces hydroxyl radicals (•OHs). •OHs are powerful oxidants able to destroy 1,4-dioxane and other contaminants. In the AOP system built by SCWA, •OHs are generated by the interaction hydrogen peroxide and UV light. 

Important considerations for AOP photochemistry needed to be addressed in the system design and operational plan. The first was that the reaction between UV and peroxide has low efficiency, resulting in peroxide carryover from the UV reactor. The second was that although •OH radicals are extremely powerful, they may not completely oxidize the target contaminant, and byproduct compounds can be formed. 

Though control of the peroxide dose is critical to contaminant destruction in AOP, U.S. EPA-approved analytical methods do not yet exist. The project included testing of an online analyzer and comparative testing of several commercially available field test kits with various reagent chemistries.

Experiments conducted during full-scale trials were designed to confirm the accuracy and reliability of the methods, and evaluate their ability to be used for process control. Results were submitted, and a full-scale protocol for peroxide control in AOP was developed. 

For the byproducts, NYSDOH and SCDHS developed the sampling plan for the operational AOP system, which included aldehyde, carboxylic acids and assimilable organic carbon (AOC) sampling across the treatment train. SCWA conducted a matrix of experiments designed to look at the effect of process variables on byproduct formation and to look for potential sources of error due to analytical methods. 

It was understood going into the project that the AOP system would not be able to be placed in service without first undergoing extensive challenge testing. Provisions were made so the finished system could be tested at full design flows for extended periods of time without pumping to the system. 

Full-scale start-up trial plans were developed and completed during the summer of 2017. The tests consisted of a three-by-three matrix of full-scale trials, using three UV intensity intensities and three peroxide doses. Sampling across the treatment train confirmed the destruction of 1,4-dioxane and addressed the formation and fate of byproducts, as well as peroxide impacts on granular activated carbon.

The final project submitted to NYSDOH and SCDHS was a standard operating procedure (SOP) for an AOP system. The SOP addressed regulatory concerns related to system operation, process control and SCADA integration, and system alarms. It serves as a framework for future AOP systems in New York.

“SCWA is extremely satisfied with the end result: The project represented a major contribution to drinking water treatment in New York State. It allowed SCWA, NYSDOH and SCDHS to work together to confirm the effectiveness of UV-H2O2 AOP for 1,4-dioxane treatment, design and establish the operational framework for AOP, and work with local mechanical contractors and consultants to build the first system. As the interest in AOP grows, this system will serve as an important source of information for other water providers on Long Island,” Meyerdierks said. 

Meyerdierks’ findings from the project and project experiences have been shared with the drinking water community at conferences, training classes and during onsite tours. It will continue to use the findings to provide even better AOP systems in the future.

“The SCWA is very proud to be taking a lead role in addressing one of the most pressing emerging contaminant threats on Long Island—the synthetic chemical 1,4-dioxane,” said Jeffrey W. Szabo, SCWA CEO. “As always, we will take whatever actions are necessary to continue to provide high-quality drinking water to all of our customers.”