Impact of Several Biosolids Stabilization Technologies on PFAS

Abstract Summary It is well understood that conventional treatment approaches do not effectively remove PFAS from liquids or solids streams at wastewater treatment plants. Future regulatory enforcement of PFAS has varied state-to-state providing uncertainty for utilities as they plan for future process upgrades. To assist utilities and biosolids producers, several biosolids products were tested including dried biosolids, pyrolyzed dried biosolids and composts, all produced with non-industrially impacted biosolids to assess the concentration of PFAS compounds in the finished products and the ability of these processes to reduce and or remove PFAS compounds. The full paper will summarize findings from this study. Introduction Per- and Poly-Fluoroalkyl Substances (PFAS) are a large family of organic compounds, including more than 4,500 synthetic fluorinated organic chemicals used in commercial, consumer and industrial products since the 1940s. Conventional treatment methods do not efficiently remove PFAS which are resilient to degradation and tend to sequester to the treated solids produced and the resultant biosolids. In its most recent (2021) review of pollutants in biosolids, the US EPA identified eight PFAS in biosolids, and is undergoing a problem formulation process which will serve as the basis for determining whether regulation of PFOA and PFOS in biosolids is appropriate. If EPA determines that a regulation is appropriate (currently expected in 2024), biosolids producers will be required to meet certain standards. This potential outcome of EPA's review underscores the importance of understanding technical solutions available to treat PFAS in biosolids if required based on EPA's review process. Technical Content To assist utilities and biosolids producers to understand options available to them to mitigate potential PFAS contamination in biosolids, several biosolids products were tested including dried biosolids, pyrolyzed dried biosolids and composts, all produced with non-industrially impacted biosolids to assess the concentration of PFAS compounds in the finished products and the ability of these processes to reduce and or remove PFAS compounds. Samples of input and output solids, bulking agents and finished products were analyzed for 24 PFAS compounds utilizing Liquid Chromatography Tandem Mass Spectrometry (LC/MS/MS). The facilities tested include: three dried biosolids facilities, two pyrolyzed dried products including output solids, gas and oil, and six compost products. Figure 1 provides an overview of PFAS (PFOA, PFOS, and total PFAS) concentrations by sludge type and the impact of composting operations. This figure demonstrates the progression (and conversion) of the PFAS concentration from the various raw sludge types. In some cases, the type of bulking agent used (fresh yard waste, wood chips, or the amount of recycled bulking agent used) can impact the concentrations of various PFAS compounds in the final compost products. Depending on the sludge type, the composting process has shown to increase or decrease measured PFAS. The variability in the results suggest the presence of precursors in the raw sludge. Additional detail regarding these impacts will be provided in the full paper. Figure 2 summarizes reduction of PFAS compounds through thermal drying using a rotary kiln dryer, where a range of 25-75% reduction was observed (45% average reduction) through drying. Figures 3 and 4 summarize the impact of pyrolysis on PFAS degradation in undigested digested and digested sludges, respectively. In both cases, a significant reduction in PFAS compounds was observed through pyrolysis, with near non-detect PFAS concentrations in the biochar and between 85% and over 99% reduction of measurable PFAS was achieved on a mass basis of all outputs including biochar, biooil and pyrogas. This will be one of the first published results on the entire outputs from the pyrolysis of wastewater sludges. Paper and Presentation This paper and presentation will provide information regarding the measured concentrations of PFAS in wastewater solids, dried biosolids, pyrolyzed biosolids (including the resultant pygas) and biosolids based compost products. PFAS precursor analyte presence and concentrations in the input solids as well as the wastewater treatment process used to generate these products will also be presented. This information will be useful for those considering methods to reduce or eliminate PFAS in their own wastewater solids or other input wastewater solids at existing or planned biosolids management operations to ensure the lowest feasible PFAS concentrations in end products can be achieved. This presentation will help utility planners, operators, engineers, and administrators understand the nature of the PFAS issue in biosolids, how these compounds are introduced into biosolids, the rapidly changing regulatory landscape, and what technologies are being used to reduce or eliminate these compounds from wastewater biosolids products.