Regulatory Landscape
Federal oversight is evolving, with the EPA taking steps to establish PFAS risk assessments and pollutant limits for biosolids. However, states like Maine, Connecticut, and Michigan have implemented stricter controls, emphasizing the need for a unified approach. Legal actions are also increasing, with citizen suits targeting municipalities, industries, and landowners linked to biosolid-related PFAS contamination.
Management Strategies
Biosolid management options include land application, landfilling, and incineration, each with associated risks and challenges. Emerging technologies focusing on PFAS stabilization and transformation show promise but face scalability and cost barriers. Upstream controls, such as pretreatment of industrial discharges and monitoring requirements, are critical to reducing PFAS loads entering WWTPs.
This first article in a three-part series addresses the growing regulations surrounding PFAS as they relate to biosolids, also known as sewage sludge.
PFAS are very useful, making stain-resistant fabrics, firefighting foams, food packaging, medical devices and as a surfactant in industrial processes. PFAS have been in use since the 1940s but only recently gained scrutiny as the potential toxicity of certain PFAS at low levels has come to light.
PFAS are a man-made family of chemicals that have a chain of carbon atoms bonded to fluorine atoms with an end or side carbon attached to a different functional group, for example here is the structure of perfluorooctanoic acid (PFOA).
The EPA recently added two PFAS chemicals—perfluorooctanic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)—as hazardous substances under CERCLA. It introduced drinking water regulations with stringent limits for six different PFAS compounds. Additionally, PFAS are regulated by at least 23 states, and the EPA has added 205 PFAS to the Toxics Release Inventory under the Emergency Planning and Community Right-to-Know Act. While PFAS in biosolids have not received the same level of attention as PFAS in drinking water, they do impact drinking water, groundwater, surface water, crops, reclaimed land, and agricultural products.
Background and Use of PFAS
The term "PFAS" encompasses a family of over 15,000 compounds that have been in use for over 70 years. While PFAS are often discussed collectively, each PFAS compound is unique. Both scientists and regulators have thus generally sought to address and regulate PFAS using compound-specific data where feasible, as compound-specific toxicity values vary widely among PFAS species and isomers. The two most studied, understood, and regulated PFAS are PFOA and PFOS, early 8-carbon chain (C-8) PFAS that manufacturers had voluntarily moved away from by 2015 in favor of shorter chain C-6 chemicals like GenX (hexafluoropropylene oxide dimer acid) and ADONA (ammonium 4,8-dioxa-3H-perfluorononanoate) While these replacements were thought likely to have lower toxicity, current studies are casting doubt on their toxicity and treatability. Further, they also tend to be “precursors” (larger, newer, unknown and even undetectable PFAS) that break down into more toxic and persistent building block chemicals like PFOS and PFOA. These “building blocks” are very stable PFAS called “terminal PFAS” or “terminal degradation products.” Terminal PFAS will not degrade to other PFAS under normal environmental conditions.
Use of Biosolids
Biosolids are a nutrient-rich product derived from the wastewater (sewer) treatment process, where solids are separated and treated. These biosolids can be beneficially used in agriculture and land reclamation, offering advantages like nutrient addition, improved soil structure, and reduced reliance on synthetic fertilizers. They may also be disposed of through incineration, underground injection, landfilling, or other technologies.
Biosolids are classified into "Class A" and "Class B" based on treatment levels. Class A is free of pathogens, whereas Class B contains manageable levels of pathogens, necessitating certain restrictions. Both classes must meet federal and state regulations under 40 C.F.R. Part 503, with additional state-specific requirements possibly in place. These requirements are discussed in detail in the second article of this three-part series.
PFAS Transformation in Biosolids Treatment
The treatments used to convert raw sewage sludge into Class A biosolids for land application involve transformative processes, such as anaerobic digestion, composting, heat drying, or other pathogen reduction methods. These treatments are transformative enough to significantly break down PFAS precursors into intermediate or even terminal PFAS compounds like PFOS and PFOA. This results in an increase of total detectable PFAS after biosolids Class A treatment.
Understanding the Sources of PFAS in Wastewater and Biosolids
PFAS can be found in virtually every municipal WWTP influent, effluent, and sewage sludge (biosolids) in the United States. In fact, many WWTPs have been sued over PFAS in their effluent, which is returned to surface water and, consequently, into drinking water. While PFAS may be transformed by the wastewater process, the source of PFAS is not the WWTP. PFAS is already in the wastewater (sanitary, industrial, and stormwater sewer streams) influent to the plants. How does PFAS end up in sewage and stormwater? Here are the main culprits:
- Industrial discharges. One of the primary sources of PFAS in wastewater is industrial discharge. Industries such as chemical manufacturing, textiles, electronics, electroplating, and firefighting foam production or use have historically used PFAS in their processes. Wastewater from these industries often contains high concentrations of PFAS, which can subsequently enter municipal wastewater treatment plants. Unfortunately, most conventional treatment processes are not equipped to remove PFAS, leading to their accumulation in treated effluents.
- Municipal wastewater. PFAS are also present in municipal wastewater due to their prevalence in everyday consumer products. Items such as nonstick cookware, water-repellent clothing, stain-resistant fabrics, and food packaging often contain PFAS. When these products are washed or disposed of, PFAS can enter the wastewater system. Personal care products like shampoos and cosmetics can also contribute to PFAS in wastewater.
- Landfill leachate. Landfills serve as another significant source of PFAS in wastewater. As PFAS-containing products break down in landfills, the resulting leachate (liquid that has percolated through waste) can carry PFAS into nearby water systems or be directed to wastewater treatment facilities. This leachate often contains a complex mix of contaminants, including PFAS, which poses a challenge for wastewater treatment.
- Aqueous film-forming foams (AFFFs). Firefighting activities, especially those involving AFFFs, are a well-known source of PFAS contamination. These foams have been widely used to combat flammable liquid fires and are known to contain high levels of PFAS. Runoff from firefighting activities or spills can lead to significant PFAS contamination in wastewater.
End Use and Impact
Biosolids are applied to approximately one-fifth of agricultural land in the United States. This equals about 109,000 square miles, which is about the size of Arizona. Their use in agriculture is critical to managing the volume of sewage sludge created in the United States annually and increasing crop yields. In 2020, 20,750 facilities (wastewater treatment plants) generated biosolids, creating over 15 million tons of sludge. If land application or incineration of biosolids were paused or banned, storage of used biosolids would create an issue, especially in the northeastern U.S.
