Emerging Separation and Destruction Technologies to Mitigate PFAS in Leachate Destined for a Municipal Water Resource Recovery Facility

Per- and polyfluoroalkyl substances (PFAS) have substantially altered our water and wastewater management landscape. It is now critical to understand sources of PFAS into municipal water resource recovery facilities (WRRFs) so that technologies can be assessed for PFAS reduction when needed. Landfills often have high levels of PFAS from the breakdown of consumer products that are composed of PFAS. Leachate is often sent to WRRFs and can be a notable source of PFAS to the WRRF. Reduction of PFAS in the leachate can be beneficial in light of limitations on biosolids land application due to PFAS, effluent surface water limit guidelines, and drinking water concerns when source water is heavily influenced by wastewater effluent. Leachate is a complicated matrix though, and assessment of technologies requires testing on actual leachate samples. Technologies can be categorized into two classes. Separation Technologies can remove PFAS from one phase (such as water) and concentrate the PFAS into another phase. These technologies remove PFAS, but they do not destroy PFAS. Destructive Technologies can actually break the carbon-fluorine bond and thereby destroy PFAS.

Objectives
The objective of this research study was to assess the suitability of both separation and destruction technologies on PFAS removal. Specifically, four emerging technologies were evaluated. Foam Fractionation can concentrate PFAS into a foam phase and remove PFAS from water by addition of air and/or surfactants. Electrochemical Oxidation generates radicals in-situ that can breakdown chemical bonds in PFAS. Supercritical Water Oxidation applies high temperature and pressure to breakdown chemical bonds. Lastly, thermal plasma employs a plasma torch to generate reactive oxidants and reductants to oxidize PFAS. These four technologies were assessed for PFAS removal, and their advantages and disadvantages were evaluated.

Status
Bench-scale studies on all four of these technologies have been completed for assessment of leachate treatment. PFAS analysis in the influent and effluent samples is complete.

Methodology
A municipal landfill's leachate-receiving facility provided samples from their equalization basin for shipment to each of the treatment vendors. Each technology treated 55 liters of leachate samples. Samples were analyzed for influent, effluent and intermediate (both foamate and liquid samples). Forty PFAS were analyzed using EPA 1633 method. Conventional water quality parameters in leachate were analyzed, including hardness, metals, pH, ammonia, nitrate, nitrite, total organic carbon, volatile organic compounds, and solids.

Findings
Foam Fractionation was tested as a technology that could concentrate PFAS in leachate and remove it from the water phase. In general, this technology was good at removing long-chain PFAS (Figure 1). PFBS, a short-chain PFAS, had negligible removal (Figure 1). Foam fractionation has low operational cost and is easy to operate, but it does not effectively remove all PFAS, and the foam fraction requires further processes because of its higher PFAS concentrations.

Two different SCWO technologies were assessed, and both technologies removed PFAS to below detection limit (Table 1). These results are not surprising because SCWO is a high temperature high pressure system. Advantages of SCWO are that it proves non-selective removal of PFAS, i.e., it removes both short and long-chain PFAS. Disadvantages include possibilities for corrosion and fouling as well as salt precipitation.

The results from the electrochemical oxidation tests were interesting as they showed that long-chain PFAS were effectively removed over time, while shorter chain PFAS, specifically PFBS, showed variable concentrations (as depicted in Figure 2). It is plausible that these short-chain PFAS were accumulated from the breakdown of longer-chain PFAS. One advantage of electrochemical oxidation is that it operates at ambient conditions and does not require substantial external additives. However, it does necessitate the use of electrodes, which can be costly, and it can generate short-chain PFAS.

Significance
These findings are important because they illuminate that there are viable technologies for removal of PFAS from landfill leachate, in particular long-chain PFAS including PFOS and PFOA. These two chemicals are of particular interest for land application of biosolids because several states use them for their interim guidelines on land application. Reducing PFAS in leachate that is destined for a WRRF would ultimately reduce PFAS levels in biosolids as well as wastewater effluent. Treatment of landfill leachate could be one targeted area to reduce the perpetual cycling of PFAS through the urban water cycle.