Environmental Forensic Investigation of PFAS in Wastewater Treatment Systems, Biosolids, and Agricultural Land Application
Project Overview
RoseyFields conducted an environmental forensic investigation evaluating the occurrence, transport, transformation, and ultimate fate of per- and polyfluoroalkyl substances (PFAS) within municipal wastewater treatment systems and the subsequent release of PFAS through treated effluent and biosolids. The project focused on understanding how wastewater treatment processes influence PFAS concentrations, how individual PFAS compounds partition between liquid and solid phases, and how land application of biosolids may contribute to long-term contamination of agricultural soils, groundwater, surface water, and private drinking water supplies. The investigation synthesized peer-reviewed scientific literature, wastewater treatment data, sludge-processing studies, biosolids characterization research, and contaminant mass-balance analyses to evaluate environmental exposure pathways and source attribution.
A primary objective was to evaluate whether conventional wastewater treatment plants function as effective removal systems for PFAS or whether they instead redistribute contaminants between treated effluent and biosolids. The investigation examined multiple wastewater treatment technologies, including activated sludge systems, trickling filters, biological nutrient removal processes, rotating biological contactors, aerobic digestion, anaerobic digestion, composting, alkaline stabilization, pelletization, and dewatering operations. Particular attention was given to the transformation of precursor compounds during treatment and the resulting formation of terminal perfluoroalkyl acids that may persist in environmental media.
The project also evaluated the role of wastewater treatment plants as integrators of PFAS from diverse upstream sources, including industrial facilities, commercial users, residential wastewater, landfill leachate, metal finishing operations, textile manufacturing, food packaging industries, firefighting foam releases, and consumer products. Because wastewater treatment plants receive contributions from numerous sources, the investigation considered both contaminant fate and forensic source reconstruction to determine how PFAS ultimately enter receiving waters and biosolids destined for beneficial reuse.
An additional objective was to evaluate how biosolids recycling practices may serve as an environmental transport mechanism by transferring persistent PFAS from wastewater treatment facilities to agricultural lands where contaminants can remain in soils for decades, migrate into groundwater, accumulate in crops, or expose livestock and rural drinking water supplies. This multidisciplinary evaluation integrated environmental chemistry, contaminant fate and transport, wastewater engineering, hydrogeology, exposure assessment, and environmental forensic analysis to reconstruct the complete pathway from PFAS source to environmental receptor.
Chemicals of Concern
The chemicals of concern consisted of per- and polyfluoroalkyl substances (PFAS), a large family of highly persistent fluorinated organic compounds characterized by exceptional resistance to biological degradation, chemical oxidation, and environmental breakdown. Their strong carbon-fluorine bonds allow many PFAS to persist indefinitely in environmental media, leading to widespread designation as “forever chemicals.” PFAS have historically been used in numerous industrial and commercial applications including firefighting foams, metal plating, stain-resistant textiles, food packaging, paper coatings, surfactants, electronics manufacturing, and numerous consumer products.
The investigation emphasized the PFAS compounds most frequently reported in wastewater treatment systems and biosolids, including: Perfluorooctanoic acid (PFOA), Perfluorooctane sulfonate (PFOS), Perfluorohexane sulfonate (PFHxS), Perfluorononanoic acid (PFNA), Perfluorodecanoic acid (PFDA), Perfluorobutanoic acid (PFBA), Perfluoropentanoic acid (PFPeA), Perfluorohexanoic acid (PFHxA), Fluorotelomer sulfonates (FTS), Fluorotelomer phosphate esters (diPAPs), Sulfonamide precursor compounds.
The project also recognized that many precursor PFAS are not routinely measured but can transform during wastewater treatment into more stable perfluoroalkyl acids. Consequently, measured concentrations of terminal PFAS alone may underestimate the overall PFAS burden entering wastewater treatment facilities.
Environmental media evaluated included municipal wastewater influent, treated effluent, primary sludge, waste activated sludge, anaerobically digested biosolids, composted biosolids, pelletized biosolids, agricultural soils, groundwater, surface water, landfill leachate, and private drinking water supplies.
Methods
RoseyFields conducted a comprehensive environmental forensic evaluation integrating wastewater engineering, contaminant mass-balance analysis, biosolids characterization, environmental chemistry, and contaminant fate and transport modeling.
The investigation first evaluated PFAS occurrence throughout wastewater treatment trains by reviewing studies that quantified contaminant concentrations in influent, intermediate treatment stages, final effluent, sludge, and biosolids. Mass-flow analyses were reviewed to determine whether individual PFAS compounds were removed, transformed, or concentrated during treatment. Particular attention was given to studies documenting apparent increases in PFAS concentrations attributable to transformation of precursor compounds rather than new contaminant inputs.
The investigation then examined PFAS partitioning behavior between aqueous and solid phases. Factors evaluated included organic matter content, protein content, lipid content, sludge stabilization method, ionic strength, pH, and wastewater chemistry. Comparative evaluations of activated sludge, biological nutrient removal systems, trickling filters, rotating biological contactors, aerobic digestion, anaerobic digestion, composting, and pelletization were reviewed to determine how treatment technologies influence PFAS retention in biosolids.
RoseyFields also reviewed investigations from numerous wastewater treatment facilities across North America, including large statewide biosolids monitoring programs, municipal treatment plant evaluations, interstage sludge-handling mass balance studies, and national wastewater occurrence surveys. These datasets provided insight into PFAS variability among wastewater treatment plants, treatment processes, industrial source contributions, and biosolids management practices.
The project further evaluated long-term environmental behavior following biosolids land application. Studies addressing microbial weathering, degradation of biosolid organic matter, changes in PFAS partition coefficients, contaminant mobility, and groundwater migration were synthesized to evaluate how biosolids continue releasing PFAS after application to agricultural lands.
Finally, RoseyFields integrated the available information into a source-to-receptor conceptual site model describing contaminant migration from industrial and municipal sources through wastewater treatment systems, biosolids production, land application, soil contamination, groundwater transport, and eventual human exposure pathways.
Results
The investigation demonstrated that conventional municipal wastewater treatment plants generally do not destroy PFAS. Instead, wastewater treatment redistributes contaminants between treated effluent and biosolids, with treatment processes frequently transforming precursor compounds into persistent terminal PFAS that remain environmentally mobile. Multiple studies documented little overall reduction in PFAS mass and, in some cases, observed apparent increases in measured PFAS concentrations resulting from precursor degradation during biological treatment.
The evaluation also demonstrated that compound-specific behavior varies substantially according to molecular structure. Long-chain PFAS generally exhibited greater affinity for wastewater solids and biosolids, whereas shorter-chain PFAS remained more mobile within treated effluent and receiving waters. Sludge stabilization methods significantly influenced PFAS partitioning, with anaerobically digested biosolids generally exhibiting stronger PFAS sorption than aerobically digested or composted materials. Protein content, organic matter composition, pH, and dissolved cation concentrations were identified as major controls on PFAS partitioning behavior.
The review further found that wastewater treatment facilities receiving industrial wastewater or landfill leachate often exhibited elevated PFAS concentrations relative to facilities receiving predominantly residential wastewater. Industrial contributors including metal finishing operations, landfills, firefighting foam sources, manufacturing facilities, and commercial users may significantly influence wastewater PFAS signatures and biosolids contamination.
Studies evaluating biosolids consistently demonstrated that treated solids represent a significant reservoir of PFAS. Large-scale monitoring programs documented widespread detection of numerous PFAS compounds in final biosolids, including substantial concentrations of precursor compounds capable of transforming after land application. Biosolids therefore represent both an immediate source of PFAS and a continuing long-term source as precursor compounds degrade within soils.
The investigation also found that microbial weathering and natural decomposition of biosolids can alter PFAS partitioning over time, increasing contaminant mobility and potentially enhancing migration toward groundwater. These findings indicate that PFAS release from land-applied biosolids continues long after the initial application event and may contribute to persistent contamination of agricultural soils, groundwater, and surface water.
Conclusions
This environmental forensic investigation demonstrates that wastewater treatment facilities function as redistribution systems rather than destruction systems for PFAS. Conventional treatment technologies may alter PFAS speciation, transform precursor compounds, and partition contaminants between liquid and solid phases, but they generally do not eliminate PFAS from the waste stream. Consequently, treated effluent and biosolids remain important pathways by which PFAS enter aquatic and terrestrial environments.
The project further demonstrates that biosolids constitute a significant environmental transport mechanism capable of transferring PFAS from industrial and municipal wastewater sources to agricultural soils where contaminants may persist, migrate to groundwater, enter surface waters, accumulate in crops, or expose livestock and nearby residents through multiple environmental pathways.
The investigation also highlights the importance of understanding PFAS partitioning behavior, sludge stabilization processes, wastewater treatment chemistry, and precursor transformation when reconstructing contaminant migration and assigning environmental responsibility. Effective environmental forensic investigations require integration of wastewater treatment operations, contaminant mass-balance analyses, source tracing, hydrogeology, biosolids management practices, and long-term contaminant fate and transport rather than reliance on individual sampling events alone.
This investigation was conducted under the direction of Dr. Paul Rosenfeld, an environmental scientist and environmental forensic expert with experience in PFAS contamination assessment, wastewater treatment systems, biosolids management, contaminant fate and transport, groundwater and soil contamination, exposure assessment, and environmental chemistry. Through RoseyFields LLC, Dr. Rosenfeld provides environmental forensic investigations, PFAS source identification, wastewater and biosolids evaluations, contaminant migration analyses, groundwater and agricultural exposure assessments, regulatory review, and expert witness services involving emerging contaminants, industrial discharges, land application of biosolids, and complex environmental litigation.
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