Introduction. Ion exchange (IX) technology has been demonstrated to be an effective treatment method for the removal of per- and polyfluoroalkyl substances (PFAS) from groundwater and drinking water. Several studies have demonstrated efficiencies using IX versus granular activated carbon. Full-scale application of both regenerable and non-regenerable IX are now in service. US Department of Defense (DoD) seeks to further develop, refine, demonstrate and validate the technology through projects being conducted currently in the Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP), US DoD’s Environmental Research Program.

Objective. The objective of the research is to develop an effective treatment train for removal of aqueous phase PFAS from water, including both long- and short-chain perfluoroalkyl substances as well as their polyfluorinated precursors, and provides on-site destruction. Such a solution would reduce and potentially eliminate off-site liabilities associated with disposal of partially treated water and would support remote project sites where off-site disposal is not an option or cost-prohibitive. The treatment train includes pre-treatment, separation, regeneration, recovery, and destruction. Pre-treatment enhances precursor transformation and mobilization of PFAS and expedites treatment. Oxygen or chemical oxidants are introduced in-situ to transform less mobile precursors, cations, and zwitterions into more mobile and smaller anions that are generally repelled by the soil matrix, thereby enhancing mobility for pump and treat. Separation occurs ex-situ in ion exchange treatment vessels. This research focuses on regenerable ion exchange media which can be reused indefinitely. Regeneration occurs onsite by back-flushing the ion-exchange media with a regeneration solution, rinsing and placing back in service. Recovery occurs onsite through distillation and reuse of the regeneration solution. Destruction of the concentrated PFAS still bottoms occurs onsite in an enhanced contact, low energy plasma reactor. Throughout the process, PFAS are concentrated over many orders of magnitude from parts per trillion to parts per thousand and then efficiently destroyed onsite.

Methodology. The PFAS treatment train is being investigated through two parallel projects in the SERDP/ESTCP Program by a consortium of academic, technology, and engineering partners working with a DoD sponsor. The SERDP project is a series of laboratory trials to refine and optimize methodologies. Soil and groundwater from a PFAS source zone is treated with various oxidants. The efficacy of transformation and mobility of PFAS constituents is compared. Pre-treated water is extracted and PFAS is separated onto regenerable IX resins in columns and optimized for bed configuration and flow rates. IX media regeneration is optimized on regenerate solution formulation, volumes, and contact time. Regenerate solution is recovered and PFAS residue is concentrated through distillation. The concentrate is destroyed in a plasma reactor that is optimized on configuration and flow through rates. The laboratory trial results feed into the ESTCP project which is a field scale demonstration of the optimized PFAS treatment train.

Conclusions. The outcome will result in a more cost-effective and efficient method for treating PFAS in water that can be considered a “closed-loop” on-site system, thereby reducing future liability. The validated field demonstration will include a cost and performance evaluation that will inform implementing the technology at full scale. Upon completion, the demonstration will be translated into a users’ guide for implementation across the extensive portfolio of sites that will require groundwater remediation for PFAS in the coming years.

Nathan Hagelin, Service Line Program Leader, Wood
Nathan Hagelin is the Service Line Program Leader at Wood working out of Portland, Maine. He is the remediation technology leader in Wood’s Emerging Contaminants Work Group. He is a Certified Geologist, Licensed Environmental Professional, and Board Certified Environmental Scientist working for 29 years on the remediation of contaminated industrial properties and military installations. He has prior experience as a Hydrologist with the U.S. Geological Survey Water Resource Division.

1,4-Dioxane (1,4-D) and 1,2,3-trichloropropane (TCP) are suspected carcinogens and common groundwater and drinking water contaminants. These compounds share stringent regulatory limits, elevated water solubility and produce large dilute plumes with associated remediation challenges. TCP was historically used as a paint remover, cleaning and degreasing agent and was an impurity in soil fumigants. 1,4-D is used in manufacturing, personal care products and was used as a solvent stabilizer. Options for assessing and implementing sustainable bioremediation of these two emerging contaminants is expanding; this presentation will explore recent advances in bioremediation for these contaminants as outlined further below.

Assessment of Biodegradation Processes. Specialized technologies to assess 1,4-D and TCP bioremediation include genetic tests, compound specific isotope analysis (CSIA) and biotreatability studies. These tools are particularly useful for 1,4-D and TCP, as breakdown products can be difficult to detect and site-specific degradation processes are often poorly understood. The ability to quantify key biodegraders using genetic tests or detect biodegradation using isotopic enrichment of the parent compound (CSIA) provides needed evidence for the effectiveness of enhanced bioremediation. These technologies can also be valuable for evaluating natural attenuation processes. Biotreatability studies allow testing of multiple strategies and can confirm remediation options in the laboratory, prior to field implementation.

Bioremediation of 1,4-D. 1,4-D degrades primarily under aerobic conditions and effective delivery of oxygen for in-situ or ex-situ remedial approaches is a key remedial consideration. Nevertheless, field applications of aerobic cometabolic bioventing via oxygen and alkane gas addition to groundwater have been successfully implemented. The discovery of Pseudonocardia dioxanivorans CB1190, a microorganism that uses 1,4-D as an energy source, was a milestone. Where indigenous 1,4-D biodegraders are absent, bioaugmentation with energy yielding 1,4-D degrading cultures is effective in laboratory studies and field pilot studies are pending.

Bioremediation of TCP. TCP is degraded primarily by anaerobic reductive pathways with Dehalogenimonas (Dhgm) identified as a key microorganism in the process. A bioaugmentation culture for TCP bioremediation with a high abundance of Dhgm has been developed. The research has indicated that TCP dechlorination and Dhgm growth occurred over a wide range of TCP concentrations. Furthermore, the culture has performed well in bench-scale studies, while TCP concentrations remained elevated in non-bioaugmented microcosms. Based on these results, the first field test of the culture was performed at a site in California in 2016. Initial field results are promising.

This presentation will discuss a range of monitoring and remediation approaches focusing on TCP and 1,4-D case studies. The tools and methodologies presented should be transferable to other emerging contaminants present at federal sites in Canada.

Jeff Roberts, Senior Manager, SiREM
Jeff Roberts received his M.Sc. Earth Sciences at the University of Waterloo. Jeff is a Senior Manager at SiREM with extensive technical experience in the laboratory assessment and field implementation of soil, sediment and groundwater remediation technologies at sites containing contaminants including chlorinated solvents, petroleum hydrocarbons and other recalcitrant compounds. Over the past fifteen years he has conducted and managed hundreds of bench-scale batch and column treatability studies and also has technical experience in the growth, scale up and field implementation of several anaerobic microbial cultures for bioremediation remedies. Jeff has several years of passive sampling experience and was a lead member in the development and commercialization of the SP3TM sampler.

1,4-Dioxane (dioxane), a solvent stabilizer and likely human carcinogen with federal and provincial/state health risk guidelines in the United States and Canada, is commonly associated with chlorinated solvent contamination of groundwater. The chemical characteristics of dioxane make it difficult to remove or degrade using traditional remediation and water treatment technologies.

The City of New Brighton (City) is a suburb of Minneapolis, Minnesota (United States) with a population of approximately 21,000 people. Volatile organic compounds (VOCs), including trichloroethylene (TCE), were discovered in the City water supply wells in 1981. The source of the contamination was identified as the Twin City Army Ammunition Plant (TCAAP), located approximately four kilometers away from the City wells, where historical munitions manufacturing operations resulted in releases of chlorinated solvents to soil and groundwater. Since 1988, the City’s 27.6 megalitre per day Water Treatment Plant 1 (WTP1) has supplied potable water and has served as a remediation system for the contaminated groundwater plume. WTP1 utilizes a granular activated carbon (GAC) adsorption system to treat TCE. The United States Army reimbursed the City for the construction and operation of WTP1 as part of a litigation settlement agreement that requires the City to pump 12.1 to 26.1 megalitres per day for plume remediation purposes.

Elevated dioxane concentrations were discovered in the City’s groundwater supply wells in 2014. In response, the City determined it wanted to upgrade its existing plant to remove dioxane and protect public health. The United States Army stated it was committed to working cooperatively with the City, and provided funding for evaluating and implementing dioxane treatment technologies.

Advanced oxidation processes (AOPs) are the most effective technology for removing dioxane from water, but at that time had not previously been applied in Minnesota for drinking water treatment. Because treatment efficiency is highly dependent on site-specific water quality, a six-month pilot test was conducted using low-pressure UV/peroxide and ozone/peroxide, two AOP technologies, along with pilot units for greensand filtration and GAC adsorption. This is the most extensive evaluation of dioxane treatment conducted to date in Minnesota. Testing was conducted in several distinct phases to evaluate:

1. Operating conditions and chemical doses required to treat current and elevated dioxane levels to a dioxane removal target;
2. The effect of changes in greensand filter effectiveness on AOP treatment;
3. Estimated GAC breakthrough time for peroxide and chlorinated ethanes for catalytic and non-catalytic carbons; and,
4. Reliability of AOP processes during long-term operation.

Pilot testing indicated that both AOP systems remove dioxane to below 0.1 parts per billion, and that AOP process addition is not expected to affect operation of existing greensand filter or carbon adsorption processes. A low-pressure UV/peroxide for dioxane treatment in this application was recommended, with the system located after greensand filtration, and prior to the existing GAC adsorption system. The ozone/peroxide system was eliminated due to higher operational complexity and elevated bromate concentrations in the system effluent caused by the reaction of naturally occurring bromide and ozone.

Following pilot testing, final design was completed in 2017, and plant start-up occurred in fall 2018.

Katie Wolohan, Environmental Engineer, Barr Engineering Company
Katie Wolohan is a professional environmental engineer with seven years of consulting experience assisting clients with water and wastewater treatment, water reuse, and environmental compliance and permitting. She has worked with both industrial and municipal clients to navigate PFAS and 1,4-dioxane water treatment options and challenges. Katie graduated with a Bachelor of Science degree in Environmental Engineering from Michigan Technological University.