St. Anthony Village, MN- Advanced Oxidation Project (2017)
As early as the 1940’s, chemicals and other wastes were being disposed of in the region by the Twin Cities Army Ammunition Plant (TCAAP). In 1987, TCAAP was positively identified as the source of Volatile Organic Compunds (VOC) contamination in several community water supplies. The contamination at the time consisted of Trichloroethylene (TCE). Trace amounts of 1,4 Dioxane were discovered in 2015 by the City of St Anthony Village and neighboring communities. 1,4 Dioxane is a chemical stabilizer added to chlorinated solvents to prevent their acidification and breakdown.
St Anthony Village is the 35th public water system in North America to specifically treat 1,4 Dioxane using Advanced Oxidation with UV-Peroxide.The six (6) Trojan UVPhox Reactors each contain 144 low-pressure high-output UV lamps. The overall system can remove more than 99% of 1,4 Dioxane at Peak Flow Conditions of 3,000 GPM. Due to its high solubility and limited sorption to soils, natural degredation of 1,4 dioxane in water is limited. Further, it’s low Henry’s Law Constant makes 1,4 dioxane resistant to traditional treatment methods used for removal of VOC’s.
Superior, WI – Low UVT Wastewater is still no match for the Trojan 3000PLUS
The Environmental Services Division of Public Works (ESDPW) for Superior WI is comprised of ten (10 Sanitary Sewer Districts and carries four discharge permits. The main WWTF treats an average of 3-4 million gallons per day with peak flows hitting 11 million gallons per day during storm events. Several years ago, the City was faced with a decision to rehabilitate the existing Chlorine disinfection facility or convert to another form of disinfection. After evaluating all of the alternatives, Superior chose UV disinfection over chemical disinfection for several reasons:
• Location of the WWTF was close to several high population density areas
• The City could eliminate the need for additional Risk Assessment Reports and Emergency Action Plans typically associated with feed chlorine gas
• The City was required to dechlorinate with sulfur dioxide and the existing S02 system was also at the end of it’s useful life
The City evaluated several different types of UV systems and manufacturers and ultimately chose the Trojan3000PLUS with the Automatic Chemical and Mechanical Cleaning System. The WWTF has at times a ( generally about 50 and at high flows down to 30’s) relatively low Ultra-Violet Transmittance (UVT) combined with using Ferric Chloride as a Coagulant for Phosphorus Removal. For these reasons, the chemical and mechanical cleaning system is vital to the performance of the UV System. According to Mark Simmonds the Operations and Maintenance Supervisor, “when having a UVT of less than 40%, we are typically seeing non-detect or single digit E-Coli counts in our sample. We are very happy with our switch to UV Disinfection.” The Operations staff removes the modules twice per year to recharge the chemical cleaning solution since they have a year-round disinfection permit.