Utilities face growing regulatory pressure with limited understanding of PFAS behavior
The One Water Perspective illustrates the role played by wastewater treatment plants (WWTPs) in managing water touched by human activities and uses. We know that WWTPs can act as transfer point for per- and polyfluoroalkyl substances (PFAS) to enter the environment from domestic, commercial and industrial sources. After treatment, effluent is often discharged to surface waters and biosolids may be applied to land. Both are potential PFAS redistribution pathways. WWTPs are not the originator of PFAS; instead, they receive these substances from upstream contributors and WWTP owners are grappling with how to manage them.
Regulatory bodies are beginning to consider limits that could significantly affect how utilities treat wastewater, manage sludge, and reuse effluent and biosolids containing PFAS. Utilities face elevated expectations to intercept PFAS but often lack a practical understanding of how PFAS behave through treatment. Data gaps around transformation, transport, and changing compound-specific concentration levels create uncertainty, making compliance planning and risk management difficult.
Complex chemistry and behavior revealed through system-wide analysis
PFAS are a large group of synthetic compounds with varying physical and chemical properties, including different carbon chain lengths and degrees of fluorination. These characteristics affect how PFAS behave during treatment and where they accumulate. Evaluating PFAS fate in WWTPs requires a detailed understanding of both chemistry and process design, and AECOM embarked on a study of PFAS behavior to better understand how PFAS redistribution occurs at this critical nexus.
A structured national study to build a clearer picture of PFAS behavior
To address information gaps, AECOM carried out a self-funded national study of PFAS in wastewater treatment plants across the United States starting in 2020. The study included detailed sampling at WWTPs across the Continental United States and combined these results with hundreds of facilities that had participated in public state-specific programs to create a fuller picture.
Our study integrated data across multiple wastewater treatment stages and media, including influent, treated water effluent, and biosolids. We aligned sampling approaches across different facilities while accounting for site-specific configurations that added complexity. The need to assess both liquid and solids streams introduced additional considerations for sample handling and study design, and each presents different potential risks.
The sampling study followed a two-phase approach. In Phase 1, AECOM sampled influent, effluent, and biosolids to identify variability across 19 client facilities from eight states. These data were combined with comparable publicly available data compiled all across Michigan and California, providing a broad statistical basis for assessment for over 100 WWTPs. This diversity provided a broad view of how PFAS behave under a range of real-world operating conditions.
Phase 2 focused on a subset of the 19 WWTPs and examined PFAS behavior in more detail, including how they move through treatment systems and distribute between liquid and solid streams. The selected plants represented a range of sizes, sewershed characteristics, and treatment processes. This diversity provided a broad view of how PFAS behave under a range of real-world operating conditions. AECOM reviewed process flow diagrams and operational data to develop facility-specific sampling and flow measurement plans. We assessed PFAS mass balance and evaluated precursor transformation and how PFAS recirculation influenced concentrations.
The chart below summarizes the results of the prevalence of PFAS evaluated in Phase 1. Two observations stand out: 1) perfluoroalkyl acids dominate the spectrum and 2) effluent has a higher incidence than influent for every perfluorinated compound.
These results showed that PFAS concentrations were influenced by internal treatment dynamics, such as precursor transformation or recirculation. This required interpreting PFAS chemistry across samples and moving beyond simple concentration measurements to understand system behavior.
One of the interesting outcomes was the change in PFAS chemistry from influent to effluent and biosolids. The following three figures provide a logarithmic plot of PFAS concentrations in tested media for the entire set of WWTPs. In these plots, the AECOM, California, and Michigan study concentration ranges are shown in a separate box and whisker for each PFAS measured. There is a remarkable consistency in concentration for any one PFAS regardless of geography. Two main observations: precursor transformation increased perfluorinated compounds during treatment, and long-chain PFAS preferentially partition to biosolids.
Effluent PFAS Concentrations for All 3 Studies – Box Plot
Final Treated Solids PFAS Concentrations For All 3 Studies – Box Plot
In addition, the study highlighted how PFAS enter treatment systems, pointing to opportunities for upstream source control. Identifying potential contributors can help reduce PFAS loading before reaching the plant. Metal finishers (e.g., chrome platers) were identified as one of the main industrial dischargers that contributed significant mass of PFOS to the WWTPs from Michigan that performed the source reduction. Some WWTPs had only one metal finisher discharging to the WWTP. Consequently, in some instances, installing a single pretreatment system on the discharge from the one metal finisher resulted in meaningful reductions in the PFOS influent concentrations at the WWTP. Using this information, Michigan facilities have achieved PFOS reductions of approximately 88–99% by identifying and addressing key industrial contributors.
Improved understanding supports better risk management and decision-making
The study established consistent national trends across multiple states, showed that facility-specific evaluations can pinpoint major PFAS sources, and generated actionable information to support regulatory planning, biosolids management, beneficial reuse decisions, future treatment upgrades, and protection of receiving waters and public health.
The study provides utilities with a clearer understanding of PFAS presence and behavior within wastewater systems. It offers insight into how PFAS concentrations vary and how they distribute between effluent and biosolids, helping utilities evaluate potential pathways for environmental release.
These findings support more informed decisions around compliance with developing regulations, including surface water criteria and requirements for managing treated solids. They also help utilities assess potential risks and liabilities related to biosolids reuse and disposal practices.
Ongoing relevance as PFAS regulation and expectations continue to evolve
As PFAS regulations continue to develop, utilities will need reliable data and defensible approaches to manage these substances. This study improves understanding of PFAS fate and transport in real-world municipal wastewater treatment environments. By clarifying how PFAS behave within wastewater systems, the work supports more proactive strategies, including source control and adaptive treatment approaches. Over time, this system-level understanding will be important in balancing environmental protection with operational and cost considerations.
Read the entire study here.