Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7q. Managing PFAS at Publicly-Owned Treatment Works (POTWs)

Formatted Title:

Treatment of a 1 MGD Lagoon System POTW Effluent to PFAS Drinking Water Standards Using Foam Fractionation

Background/Objectives:

The Anson-Madison Sanitary District (AMSD) treats a mixture of domestic wastewater, landfill leachate, septage, liquid sludges, stormwater, and other sources, including industrial flow from a nearby wood fiber insulation manufacturing facility. The combined wastes contain elevated levels of per- and polyfluoroalkyl substances (PFAS). Wastes are pretreated through primary clarification and then processed through an aerated lagoon with a settling cell and polishing pond. Polishing pond effluent is disinfected prior to discharge to the Kennebec River. The Kennebec River is a source of drinking water for several downstream communities.

State regulators have advised AMSD to evaluate upgrades to reduce PFAS concentrations in its treated effluent to below the State of Maine’s drinking water PFAS standard: the sum of six PFAS (PFOS + PFOA + PFHxS + PFPeA + PFNA + PFDA) less than 20 parts per trillion (ppt). AMSD began the search for a cost-effective technology or combination of technologies to provide this level of treatment. It also started looking for a more cost-effective way to remove residual total suspended solids (TSS), primarily colloidal solids, from their aerated lagoon effluent. AMSD had been adding coagulant prior to a downstream polish pond, resulting in both high chemical cost and excessive chemical sludge generation. The treatment technology solution needed to be able to handle aerated lagoon effluent with high fouling potential, including elevated suspended and colloidal solids.

Approach/Activities:

Foam fractionation was selected as a candidate treatment technology because of its simplicity, cost effectiveness and ability to effectively treat many waters with high fouling potential. A pilot-scale foam fractionation system was installed onsite in September 2021 and has been operating intermittently for over 24 months. Initial trials were not successful in achieving the stated goals for PFAS and TSS removal. A number of modifications were made to address these challenges, including both physical system changes as well as the addition of foam boost agent(s) or coagulant(s), and were tested over a wide variety of influent water quality and system operating conditions. The testing focused mainly on optimizing PFAS and TSS removal. A substantial data set was collected from this intensive testing exercise.

Results/Lessons Learned:

The pilot foam fractionation system modifications, coupled with the water chemistry alterations, were effective in consistently reducing PFAS to below the Maine drinking water standard and also reducing TSS concentrations to below the permitted levels. A comprehensive data set has been summarized in tabular and graphical form. These figures will be shared and discussed to clearly present the results of the successful pilot study, including the scientific approach used to achieve this success. The sum of the Maine 6 PFAS compounds in the influent ranged from 416 to 690 ppt and averaged 591 ppt. The sum of the Maine 6 PFAS compounds in the effluent ranged from 9 to 16 ppt and averaged 12 ppt. Influent TSS averaged 114 milligrams per liter (mg/L) and effluent TSS averaged 30 mg/L.

Based on the success of the pilot, a full-scale system is being designed and is scheduled to be installed during the first six months of 2024.The full-scale design flow of the system is 640 gallons per minute (nearly 1 million gallons per day). This system is anticipated to be the world’s largest foam fractionation system for PFAS removal, by a substantial margin.

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Chris Hutchins