Addressing the Impacts of PFAS in Biosolids

PFAS Regulations & Impacts on Biosolids

In 2016, the EPA published Drinking Water Health Advisories for PFOA and PFOS at a combined level of 70 parts per trillion (ppt). In February 2019, EPA issued its PFAS Action Plan that included a goal to move forward with a regulatory determination for PFOA and PFOS limits in drinking water. Many states adopted their own regulations, typically at levels below the 70 ppt health advisory level. Implementation of drinking water limits have impacted biosolids beneficial use programs at WRRFs.

At the federal level, regulations have not been promulgated for PFAS in biosolids. The state-specific regulations and guidelines involve concentration limits of different PFAS compounds in drinking water, groundwater, and, in a few cases, surface water. Only Maine has imposed a limit on three PFAS compounds in biosolids.

As of July 2021, there is no EPA approved method for sampling PFAS in biosolids. Meanwhile, drinking water limits have been imposed on biosolids due to the fear that PFAS may migrate to groundwater. Despite the lack of clear guidance, active investigation of biosolids treatment technologies for PFAS removal is underway.

Treatment Alternatives for PFAS in Biosolids

Several treatment and mitigation options can be considered when addressing PFAS in biosolids. While source reduction is the most cost effective and efficient solution, existing and emerging technologies are available. It is anticipated that future regulatory action will streamline research and development of technologies to reduce PFAS from biosolids. Treatment alternatives include the following.

Source Reduction. The strength of the C-F bond increases the ability to bioaccumulate and not readily degrade. Therefore, the easiest and most cost-effective method to reduce PFAS in biosolids is to mitigate discharges to the WRRF. This could be achieved via 1) reduction of point source discharges from industry; and 2) reduction in background concentrations via drinking water treatment. Both can be achieved through regulatory action, such as setting a PFAS limit via Industrial Pretreatment Programs (IPP), or setting drinking water limits.

Incineration. As of July 2021, thermal destruction is the preferred treatment technology to remove PFAS from biosolids, since high temperatures are needed to break the C-F bond. Incineration is the combustion of residual solids to ash and combustion gas and is commonly used for the destruction of persistent organics from hazardous waste. The EPA is actively investigating the time temperature regimes needed to remove PFAS via biosolids incineration. Packaged dryer-incinerators are also available for on-site biosolids destruction and waste heat recovery at WRRFs. A combined dryer-incinerator could be an energy efficient method to destroy PFAS while generating an end product (ash) that has lower mass and volume. However, incinerator systems are expensive and must meet stringent air permitting requirements. A photograph of a biosolids incinerator stack is shown in Figure 3.

Several emerging sludge treatment technologies exist that could meet the goal of reducing biosolids disposal costs and PFAS mitigation. Emerging technologies include pyrolysis, gasification, and supercritical water oxidation and are described in more detail below.

Pyrolysis/Gasification. Pyrolysis is the thermal decomposition of materials at high temperatures (greater than 450 to 500°C) in the absence of oxygen. The process involves treating dried sewage sludge in a closed pressurized high-temperature reactor vessel. The final products include pyrolysis gas (H2+CO+CO2+others), bio-oil and biochar. The benefit of pyrolysis is that it further reduces the mass of feedstock and products can be used for energy production (gas, oil) or agricultural land application (biochar). The disadvantages of the technology are that it is relatively unproven with sludge in the U.S., that it is has a higher cost than other thermal technologies, and that the operating temperatures (450 to 600°C) are lower than the combustion temperatures of most PFAS compounds (greater than 1,000°C). There are ongoing studies however, that are evaluating pyrolysis for its PFAS destruction potential.

Gasification is the thermal decomposition of materials at high temperatures in the presence of low oxygen levels. Process temperatures are typically higher than pyrolysis, and the products are limited to syngas and biochar/ash. Pyrolysis and gasification have been claimed as methods to reduce PFAS from biosolids. However, further research on fluorine mass balance is needed to understand how PFAS degradation products partition to products.

Supercritical Water Oxidation. Supercritical water oxidation (SCWO) refers to the process that leverages supercritical water for complete oxidation of organic compounds in sludge. In the presence of oxygen, organics can be converted to clean water, inert gases, mineral salts and reusable heat.

There are several benefits to SCWO. First, nearly 99% of the incoming solids are reduced in seconds. Second, the process can be fed with sludge at 10 to 15% solids. Third, the carbonaceous end product is carbon dioxide, the nitrogenous end product is N2 (temperature is too low for NOx), and the sulfurous end product is CaSO4 (temperature is too low for SOx), so air permitting concerns are minimal. Finally, the system has been shown to break the C-F bond in PFAS.

The drawback of the system is that there are no known commercial installations at WRRFs. Additionally, there are likely high energy demands to start the system (though the reaction is self-sustaining after startup).

Biosolids Cost Impacts of PFAS

A collaborative team, including CDM Smith, NEBBRA, WEF and NACWA, completed the Cost Analysis of the Impacts on Municipal Utilities and Biosolids Management to Address PFAS Contamination. The research team surveyed WRRFs, biosolids management companies, and end use facilities (incineration, composting, landfills, farms) to estimate the cost and operational impacts from pending or active PFAS regulations.

When the study was published in 2020, the results showed that in areas where PFAS regulations have been implemented, biosolids management costs have increased by an average of 37%. As more data from those same surveyed facilities has been collected in 2021, the management costs at WRRFs with PFAS regulations have increased to an average of 72%. Some of the states which have seen the greatest impact include Arizona, Michigan, Maine and New Hampshire.

The rapid cost increases have been attributed to reduced land application availability due to PFAS and to the use alternative high-cost disposal sites such as landfills.

Meanwhile, cost impacts have been minimal at WRRFs that manage their own biosolids, do not rely on beneficial reuse, and/or at WRRFs located in areas without PFAS regulation. These results clearly show that local, state, or federal PFAS regulations have a significant impact on the costs of biosolids management.

Summary

Many WWRFs in the U.S. are proactively evaluating solutions to mitigate PFAS. Source reduction is the most cost effective and efficient solution, and several WRRFs in New England are working are considering PFAS limits on industry. Additionally, it is anticipated that drinking water limits will reduce the background concentration of PFAS that enters WRRFs.

In areas with already limited land application or landfill capacity, such as New England, WRRFs are currently evaluating incineration as a viable disposal option. However, in these areas, incineration capacity is lacking, which drives up costs. As a result, WRRFs are evaluating methods to reduce the total mass of biosolids that must be managed, such as sludge drying. Implementation of sludge drying offers the potential to produce a low volume, Class A biosolids product that could be cost-effectively transported to states with less strict land application requirements. Several WRRFs in the Midwest are also considering sludge drying to regain control and flexibility in their biosolids management programs.

To date, there are few known installations of emerging technologies such as pyrolysis, gasification and SCWO. It is anticipated that future regulatory action will streamline research and development of technologies to reduce PFAS from biosolids.

About the author:

Johnathon Sheets, PE, PhD, is an environmental engineer for CDM Smith. Sheets can be reached at [email protected]. Maddison Ledoux, EIT is an environmental engineer for CDM Smith. Ledoux can be reached at [email protected].