Development of a Comprehensive PFAS Source Tracking and WRRF Monitoring Program

Introduction
Per- and polyfluoroalkyl substances (PFAS) are a group of more than 5,000 synthetic chemicals containing a fluorinated carbon chain that are used in a variety of industrial and consumer applications. Complex mixtures of PFAS have become ubiquitous environmental contaminants in the influents to WRRFs. Due to the persistence of PFAS through conventional WRRF processes, PFAS can be extensively cycled within the WRRF and be present in the effluent and biosolids. Developing a comprehensive strategy for managing PFAS at WRRFs requires an understanding of several factors (Figure 1), including sources of PFAS and behavior of PFAS within conventional WRRFs unit processes. This work will provide insights into the benefits and drawbacks of several PFAS methodologies by presenting a case study of how one WRRF has developed a comprehensive PFAS monitoring plan to identify major PFAS contributors and fate of PFAS through the WRRF.
Insights on PFAS Monitoring at WRRFs
PFAS, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), can be present in WRRF influents due to direct discharge from domestic or industrial sources. WRRF influents can also have perfluoroalkyl acids (PFAA) precursor compounds. These PFAA precursor compounds can ultimately breakdown to PFAAs via biological and chemical processes at WRRFs, e.g., activated sludge, anaerobic digestion, thermal treatment. Current methods using LC-MS/MS for quantifying PFAS in wastewater and biosolids matrices are largely focused on PFAAs. PFAA precursors within WRRFs are largely undetected in LC-MS/MS analysis adopted from EPA methods 533 and 537.1 that are routinely used to analyze PFAS concentrations in drinking and ground water, because these methods only target for 29 PFAS. As a result, performing mass balances using data from these LC-MS/MS methods can lead to the incorrect conclusion that PFAS are being produced within WRRFs. Instead, it is likely that non-quantified precursor compounds that are not being monitored are being transformed to PFAAs, which are then detected (quantified) in the WRRF effluent or biosolids. This phenomenon can explain why effluent or biosolids PFAA concentrations can be higher than influent concentrations. Monitoring for PFAS in WRRFs needs a multi-pronged approach for data generation (Figure 2). Utilizing a combination of non-targeted and targeted LC-MS/MS analyses can allow for identification and quantification of key PFAS compounds unique to the system. Total organo-fluorine (TOF), which can be obtained using 19F-Nuclear Magnetic Resonance (19F-NMR) spectroscopy or combustion ion chromatography, should be used to complete mass balances and demonstrate that WRRFs are not generators of PFAS.
A Case Study on PFAS Fate and Source Tracking
Utility A is a 12 mgd facility that employs primary treatment and biological nutrient removal for liquids treatment. Solids management involves a combination of disposal including stabilization or composting. Targeted PFAS sampling at Utility A has suggested that the effluent concentrations/loads of PFOS and PFOA are substantially higher than raw influent concentrations/loads. In order to address the potential for PFAS at Utility A, a comprehensive evaluation of PFAS sources is being completed. Source tracking of PFAS in collection systems is critical for understanding the major contributors of PFAS to WRRFs. Understanding major sources can help utilities develop pre-treatment strategies to help PFAS load to the WRRF. This work included developing a contribution analysis to identify and rank potential PFAS contributors in the collection system based on potential total load and potential average load to the WRRF. In this evaluation, over 35 potential dischargers were identified in the service area. These potential dischargers were aggregated into sewershed locations for sampling to quantify the masses of PFAS from dischargers to help identify major PFAS contributors. Preliminary TOF results for sewershed monitoring identified three sewershed locations that are major potential major contributors of PFAS to the collection system. Industrial dischargers within the sewersheds include metal coating, electrical, plastic, textile, and paper industries. These preliminary results provide insight into potential source control opportunities to limit PFAS discharge to the WRRF. Further, extensive monitoring at the WRRF was completed to understand the fate of PFAS within the facility. Figure 3 demonstrates the various methodologies that were utilized for monitoring within the WRRF. TOF analyses was used to calculate mass fluxes of organo-fluorine compounds entering and leaving the WRRF and to construct a mass balance around the WRRF. Non-targeted analyses was used to identify the major components of PFAS relevant to the collection system and WRRF. Targeted analyses was performed to quantify specific PFAS at the WRRF.
Preliminary results indicated that landfill leachate and raw influent have the highest 'measurable' PFAS contribution to the WRRF influent. These results suggest that leachate management may significantly reduce the total load of PFAS to the facility. A mass balance of soluble TOF load within the WRRF indicated a higher soluble TOF load in the output of the WRRF compared to the influent, suggesting that organofluorine is desorbing from the particulate fraction into the liquids stream. Further analysis will be completed to determine whether TOF present in the solids fraction is a significant source of PFAS to the WRRF. Additional results will be presented in the final paper. The results of this study provide insight into the practical application of various PFAS methodologies and valuable information gained from employing multiple methods to understand the fate and transformation of PFAS within a WRRF.