Biosolids, an important route for transporting poly- and perfluoroalkyl substances from wastewater treatment plants into the environment: A systematic review

PFAS removal through foam harvesting during wastewater aeration

Aeration in wastewater treatment plants (WWTPs) is used for removal of organic matter and nutrients. Here we show that aeration can also lead to removal of per- and polyfluoroalkyl substances (PFAS), by foam fractionation. Rising air bubbles facilitate air-liquid interfacial adsorption of PFAS and spontaneous foaming occurrence. This suggests that some modifications to conventional treatment processes that enable foam removal may be sufficient to achieve PFAS removal at WWTPs. However, high suspended solids concentrations in the mixed liquor suspension within the aerated bioreactors may complicate PFAS removal in foam fractionation, as both air bubbles and suspended biomass retain PFAS. This study explored the feasibility of foam fractionation for PFAS removal and enrichment using actual mixed liquor suspensions with typical total suspended solids concentrations and WWTP-relevant PFAS concentrations. The mechanisms involved in PFAS removal and enrichment in both aqueous and solid phases were suggested, and a mass balance analysis was performed to show PFAS distribution between the two phases. Overall, PFAS removal from the aqueous phase ranged from 70 % to 100 % for PFAS with perfluorinated carbon numbers ≥ 6, while PFAS with perfluorinated carbon numbers < 6 showed low removal of < 20 %. PFAS removal from the solid phase ranged from 20 % to 60 %, depending on the PFAS species. This study represents an ongoing effort to advance the potential implementation of foam fractionation in aerated bioreactors at WWTPs.

Spatially informed multi-objective decision-making tool for retrofitting municipal wastewater treatment plants

The resources embedded in wastewater effluents and residual biosolids have motivated the conversion of traditional energy-intensive wastewater treatment plants (WWTPs) into net energy-positive water resource recovery facilities. Recent food waste regulations, including the New York State (NYS) Food Donation and Food Scraps Recycling Law, created new opportunities to integrate food waste (FW) co-digestion with innovative waste energy and resource recovery technologies at WWTPs. This study develops a spatially informed decision-making tool to facilitate the selection of retrofit design for WWTPs, using NYS as an example. Retrofit configurations for each WWTP was optimized based on both economic and environmental objectives. FW co-digestion is consistently included in the optimal strategy when considering both economic and environmental objectives. For Effluent Thermal Energy Recovery (ETER), local heating/cooling yields a higher net present value (NPV) than biosolid drying but is only cost-effective for WWTPs with a flow above 2.2 MGD. For biosolids upcycling, hydrothermal liquefaction (HTL) generates a higher NPV than hydrothermal carbonization (HTC) but is only cost-effective for WWTPs with a flow above 60 MGD. Co-digestion, ETER for heating/cooling, and Power-to-Gas (P2G) are the most effective strategies for greenhouse gas reduction. If the allocated FW has a high undigested solids content, adding HTC to the process can further reduce GHG emissions. When considering life-cycle environmental impact, co-digestion, ETER for heating/cooling, and hydrothermal processes are the most effective options. HTL can produce greater overall environmental benefits than HTC due to its lower non-GHG-related impact. Finally, four WWTPs were identified as high-priority candidates for retrofitting based on favorable economic and environmental performance, and environmental justice considerations. To our knowledge, this is the first spatially informed decision-making model for WWTP retrofitting that not only recommends optimal strategies for energy and resource recovery at individual WWTPs, but also identifies statewide priority for retrofitting based on economic, environmental, and social considerations. This study demonstrates a holistic approach to support decision-making processes at WWTPs, and offers potential applicability to any municipality exploring food waste management and other resource recovery opportunities.

Suspect and Nontarget Screening of Organic Micropollutants in Swiss Sewage Sludge: A Nationwide Survey

The increasing amount of sewage sludge generated during wastewater treatment poses both growing management challenge and environmental issues. Sludge with many co-occurring contaminants is often destined to land application which raises concern regarding human and environmental health. It is also a good integrator in time and space and can provide valuable information on consumption pattern and change over time. Here, we have conducted suspect and nontarget screening (SNTS) in sludge from 29 wastewater treatment plants (WWTPs) covering 30% of the Swiss population. Over 500 contaminants were identified and up to 382 quantified, with concentrations ranging from a few ng/g to several thousand ng/g, which translated into total annual loads of approximately 5 g of micropollutants per Swiss citizen. The distribution of detected substances was dominated by pharmaceuticals in terms of number of compounds (>250) and personal care products in terms of concentration (e.g., 75 μg/g for linoleic acid). Homologous series analysis revealed the presence of multiple classes of surfactants among those compounds with the highest signal intensities in sludge. Principal component analysis and hierarchical clustering showed that spatial distribution of contaminants across Switzerland was not homogeneous, while Pearson correlation indicated that changes can be attributed to different anaerobic digestion times in WWTPs.

Per- and polyfluoroalkyl substances in environment and potential health impacts: Sources, remediation treatment and management, policy guidelines, destructive technologies, and techno-economic analysis

Per- and polyfluoroalkyl Substances (PFAS), also known as forever chemicals and ubiquitous persistence, pose significant public health challenges due to their potential toxicity, particularly in drinking water and soil contamination. However, PFAS occurrence and their concentrations in different environmental matrices vary globally, but factors influencing trends, transport, fate, toxicity, and interactions with co-contaminants remain largely unexplored. Therefore, this review critically examines the state-of-the-art worldwide PFAS sources, distribution, and pathways, and evaluates how PFASs are processed in wastewater treatment, generally, which causes severe problems with the quality and safety of drinking water. Importantly, the review also underscores health issues due to PFAS consumption and recent research trends on developing effective treatment strategies to manage PFAS contamination. Potential effects of PFAS were linked to urban land use and the proportion of wastewater effluent in streamflow. Besides, major emphasis was provided on challenges for conventional treatment, destructive technologies, environmental accumulation, precursor transformation, and cost-investment related to PFAS removal technologies. To combat PFAS contamination, this review proposes a framework that promotes the comprehensive identification of prevalent compounds, with a focus on their eradication through knowledge-based and targeted analysis. Additionally, it explores the ongoing debate surrounding PFAS laws and legal frameworks, offering ideas for enhancing contamination management. Lastly, this review provides a strategic plan for improving response and preparedness, serving as a foundation for addressing future environmental challenges and informing health risk assessments.

Leaching profile of per- and polyfluoroalkyl substances (PFAS) from biosolids after thickening, anaerobic digestion, and dewatering processes, and significance of protein, phosphorus, and selected ions

Batch leaching experiments were conducted to evaluate the release of forty per- and polyfluoroalkyl substances (PFAS) from sludge samples collected after thickening, anaerobic digestion, and dewatering processes at two wastewater treatment plants. The South District wastewater treatment plant (SDWWTP), which receives domestic wastewater and landfill leachate from a nearby landfill, and the Central District wastewater treatment plant (CDWWTP), which receives only domestic wastewater, were selected for this study. PFAS released into the aqueous phase were analyzed by sacrificial sampling after 1, 3, 7, 14, and 30 days. Results demonstrated rapid PFAS leaching, with the highest levels detected in biosolid leachates after just one day. Distinct differences were observed in PFAS composition and concentrations between the two treatment plants. Of the forty PFAS measured, nineteen were detected, with higher concentrations identified at SDWWTP. The input of landfill leachate to SDWWTP appears to have significantly contributed to the elevated levels of specific PFAS, particularly long-chain compounds, compared to the emerging short-chain PFAS found in biosolids. In addition to PFAS analysis, the compositions of the sludge samples, including total and volatile solids, protein, phosphorus (P), iron, aluminum, calcium, and magnesium, were also assessed. Spearman correlation analyses revealed moderate to strong relationships between PFAS levels in leachate and certain sludge components. For instance, correlations between P content and PFCAs and FTCAs were moderate (R2 = 0.45-0.76). In thickener sludge leachate, strong correlations were observed for FPrPA (3:3 FTCA), PFDA, and PFTrDA with P, with R2 values of 0.60, 0.53, and 0.54, respectively. In the digested sludge, correlations were found for PFHpA, PFDA, and PFNA (R2 = 0.45-0.76). Also, for digested sludge leachate, strong correlations were found between the individual compounds PFHpA, PFHxA, PFNA, PFOA, and PFPeA (R2 = 0.60-0.88). Predominant PFAS in leachate from biosolids were identified, including PFOS, FPePA (5:3 FTCA), PFPeA, PFBA, PFHxA, N-EtFOSAA, and 6-2 FTS.

Comparing occurrence of per- and polyfluoroalkyl substances (PFAS) in municipal biosolids and industrial wastewater sludge: A City of Los Angeles study

Biosolids and sludge are what remain after the liquid fraction of wastewater is separated during wastewater treatment. These high organic content matrices are known to contain organic contaminants, a few of which are the hazardous and environmentally persistent per- and polyfluoroalkyl substances (PFAS). The current study investigates whether sludge from a treatment facility serving mostly industrial establishments and biosolids from a facility serving mostly domestic dwellings retain these 'forever chemicals' similarly. Using 31 markers covering different classes of PFAS, the sludge was found to contain higher levels of PFAS (869 ± 791 ng/g; 21 of 31) than biosolids (31 ± 7 ng/g, 11 of 31). The most abundant overall was perfluorooctane sulfonic acid (PFOS), mostly in sludge (range: 71-1300 ng/g versus 0-18 ng/g in biosolids). The large PFAS concentration variability in sludge was seasonal and sinusoidal. Sludge, additionally, contained all long chain PFAS, precursors (mostly surfactant ingredients and their transformation byproducts) and short chain PFAS (perhaps because of higher moisture content). By regression, the sludge is shown to consistently contain twice as much PFAS as biosolids when the same amounts are exposed to increasing levels of PFAS. Factors observed to cause differential PFAS retention between sludge and biosolids were moisture (98.6 % and 72.1 %, respectively), chain length, input quality (industrial versus residential) and functional group. Sulfonic acids for instance are one C atom shorter than carboxylates with similar occurrence in sludge and biosolids. More studies are needed to define the roles that organic carbon of sludge/biosolids, water chemistry, temperature and factors not considered here play in partitioning PFAS between the two matrices with respect to inputs. Existing Koc values could not help in explaining observed trends, but the ratio of biosolids-to-influent concentrations was found to correlate positively with PFAS size. Using influent in the ratio, and not effluent, is novel. SYNOPSIS: Sludge and biosolids are soil amendments; they contain hazardous and persistent PFAS. Methods of decoupling PFAS from these matrices start with understanding matrix-driven PFAS partitioning as shown here.

Driving factor, source identification, and health risk of PFAS contamination in groundwater based on the self-organizing map

The complex interactions between groundwater chemical environments and PFAS present challenges for data analysis and factor assessment of the spatial distribution and source attribution of PFAS in groundwater. This study employed spatial response analysis combining self-organizing maps (SOM), K-means clustering, Spearman correlation, positive matrix factorization (PMF) and risk quotient (RQ), to uncover the spatial characteristics, driving factors, sources, and human health risks of groundwater PFAS in the Pearl River Basin. The results indicated that the characteristics of PFAS in groundwater were classified into 16 neurons, which were further divided into 6 clusters (I-VI). This division was due to the contribution of industrial pollution (33.2 %) and domestic pollution (31.5 %) to the composition of PFAS in groundwater. In addition, the hydrochemical indicators such as pH, dissolved organic carbon (DOC), chloride (Cl-), and calcium ions (Ca2+) might also affect the distribution pattern of PFAS. The potential human health risk in the area was minimal, with cluster Ⅱ presenting the highest risk (RQ value 0.25) which is closely related to PFOA emissions from fluoropolymer industry. This study provides a theoretical basis and data support for applying of SOM to the visualization and control of PFAS contamination in groundwater.

Evaluation of the impact of L-Tryptophan on the toxicology of Perfluorooctanoic acid in Daphnia magna: Characterization and perspectives

Perfluorooctanoic acid (PFOA) is a pervasive environmental contaminant with well-documented toxic effects on both humans and animals, attracting significant scientific concern. Due to its affinity for proteins, research has predominantly focused on PFOA's interactions with biological macromolecules. However, the specific role of smaller molecules, such as amino acids, remains underexplored. This study uniquely evaluates the potential of l-tryptophan (L-Trp) to mitigate PFOA toxicity and investigates the interaction mechanisms involved. Results indicate that the presence of L-Trp in PFOA-contaminated water reduces acute toxicity in Daphnia magna, with an optimal molar ratio of approximately 1:2 (Trp:PFOA). The findings reveal that non-covalent interactions, particularly van der Waals forces and hydrogen bonds, are central to the Trp-PFOA complex formation. Additional contributions from hydrophobic interactions at the indole group and electrostatic forces between carbonyl and amine groups further stabilize the complex. These interactions likely reduce PFOA's toxicity by altering its bioavailability and distribution. While this study offers valuable insights into the binding mechanisms between L-Trp and PFOA, it raises important questions about the reversibility of this interaction and its applicability to other per- and polyfluoroalkyl substances (PFASs).

Fate of biosolids-bound PFAS through pyrolysis coupled with thermal oxidation for air emissions control

Pyrolysis has been identified as a possible thermal treatment process for reducing perfluoroalkyl and polyfluoroalkyl substances (PFAS) from wastewater solids, though off-gas from the pyrolysis unit can still be a source of PFAS emissions. In this work, the fate of PFAS through a laboratory-scale pyrolysis unit coupled with a thermal oxidizer for treatment of off-gasses is documented. Between 91.5% and >99.9% reduction was observed through the entire system for specific compounds based on targeted analyses. Overall, the pyrolysis and thermal oxidizer system removed 99.4% of the PFAS moles introduced. Furthermore, shorter chain variants comprised the majority of reportable PFAS in the thermal oxidizer flue gas, indicating the longer chain compounds present in the dried biosolids fed to pyrolyzer decompose through the system. PRACTITIONER POINTS: Thermal oxidation is a promising treatment technology for exhaust systems associated with thermal biosolids treatments. Thermal oxidation demonstrated significant degradation capabilities, with gas phase emissions comprising only 0.200% of initial PFAS concentrations to the system. Short-chain PFAS made up a higher percent of thermal oxidizer emissions, ranging between 54.4% and 79.5% of PFAS in the exhaust on a molar basis. The possibility of recombinant PFAS formation and partial thermal decomposition of PFAS in thermal oxidation is a needed area of research.

Evaluation of per- and polyfluoroalkyl substances (PFAS) toxic effects on the acute inflammatory response in the medicinal leech Hirudoverbana

Per- and polyfluoroalkyl (PFAS) substances are a large group of chemicals with elevated water and oil-resistance properties, widely implicated in various applicative fields. Due to the extensive use and high resistance to degradative factors, these compounds pose a significant risk of environmental spreading, bioaccumulating also in living organisms. In this context, despite many researches have been performed to demonstrate "legacy" PFAS harmfulness, only few data are still available about all the emerging fluorinated molecules, industrially introduced to replace the previous ones. For this reason, we proposed the medicinal leech Hirudo verbana as consolidated invertebrate model to assess the effects of four different PFAS (HFPO-DA, PFMoBa, PFOA and PFMOPrA) following freshwater dispersion. Morphological, immunohistochemical and molecular analyses demonstrate that, despite all the compounds basically induce an acute inflammatory and oxidative stress response, a different cellular and molecular response has been observed. Whereas for PFOA and PFMOPrA an increase in the tested concentration leads to a corresponding rise in the immune response, HFPO-DA and PFMoBa trigger an entirely opposite effect. Indeed, the significant recruitment of both granulocytes and macrophage like cells, typically involved in the removal of non-self, is inhibited with increasing concentrations of these compounds. The data collected revealed a different sensitivity of the leech immune system following PFAS exposure, requiring to deepen the current knowledge on the potential toxicity of these compounds.

Non-extractable residues of perfluorooctanoic acid (PFOA) in soil

PER: and polyfluoroalkyl substances have gained increased attention due to their persistence, ubiquitous presence in the environment, and toxicity. We hypothesised that the formation of non-extractable residues [NER] occurs in soils and contributes to the overall persistence of these priority pollutants, and that NER formation is controlled by temperature. To test these hypotheses, we used 14C-labelled perfluorooctanoic acid [PFOA] as target compound, added it to two arable soils (Cambisol, Luvisol), and incubated them at 10 °C and 20 °C in the dark. To support potential co-metabolic decomposition, some samples were additionally fed with glucose to enhance microbial activity. The PFOA residues were then sequentially extracted using 0.01 M CaCl2, followed by accelerated solvent extraction (ASE) with methanol or methanol/acetic acid after 0, 1, 3, 9, 30, 62, and 90 days of incubation. In addition, we monitored the release of 14C into the gas phase as well as [14C]-PFOA-NER after dry combustion and liquid scintillation counting. After 90 days, we found that the [14C]-PFOA content declined in the extraction order of CaCl2 ((bio)available fraction) > ASE (residual fraction) > NER > gas fraction), with most rapid changes occurring in the first 9 days of incubation. NER formation was different in the two soils and reached 5-9% of the applied amount in the Cambisol and Luvisol, respectively. Noteworthy the proportion of 14C-PFOA in the (bio)available fraction remained relatively stable over time at 56-62% of the applied amount, indicating the reversible transfer into this fraction from a bi-exponentially declining residual (ASE) pool. These dissipation patterns were neither influenced by temperature nor by the addition of glucose. We conclude that NER exist for PFOA, but that the majority of PFOA remains in (bio)available form, thus maintaining toxicity and mobility in soil for prolonged periods of time.

Per- and polyfluoroalkyl substances (PFAS) as contaminants in groundwater resources - A comprehensive review of subsurface transport processes

Per- and polyfluorinated alkyl substances (PFAS) are persistent contaminants in the environment. An increased awareness of adverse health effects related to PFAS has further led to stricter regulations for several of these substances in e.g. drinking water in many countries. Groundwater constitutes an important source of raw water for drinking water production. A thorough understanding of PFAS subsurface fate and transport mechanisms leading to contamination of groundwater resources is therefore essential for management of raw water resources. A review of scientific literature on the subject of processes affecting subsurface PFAS fate and transport was carried out. This article compiles the current knowledge of such processes, mainly focusing on perfluoroalkyl acids (PFAA), in soil- and groundwater systems. Further, a compilation of data on transport parameters such as solubility and distribution coefficients, as well as, insight gained and conclusions drawn from the reviewed material are presented. As the use of certain fire-fighting foams has been identified as the major source of groundwater contamination in many countries, research related to this type of pollution source has been given extra focus. Uptake of PFAS in biota is outside the scope of this review. The review showed a large spread in the magnitude of distribution coefficients and solubility for individual PFAS. Also, it is clear that the influence of multiple factors makes site-specific evaluation of distribution coefficients valuable. This article aims at giving the reader a comprehensive overview of the subject, and providing a base for further work.

Treatment of aqueous per- and poly-fluoroalkyl substances: A review of biochar adsorbent preparation methods

Per- and poly-fluoroalkyl substances (PFAS) are synthetic chemicals widely used in everyday products, causing elevated concentrations in drinking water and posing a global challenge. While adsorption methods are commonly employed for PFAS removal, the substantial cost and environmental footprint of commercial adsorbents highlight the need for more cost-effective alternatives. Additionally, existing adsorbents exhibit limited effectiveness, particularly against diverse PFAS types, such as short-chain PFAS, necessitating modifications to enhance adsorption capacity. Biochar can be considered a cost-effective and eco-friendly alternative to conventional adsorbents. With abundant feedstocks and favorable physicochemical properties, biochar shows significant potential to be applied as an adsorbent for removing contaminants from water. Despite its effectiveness in adsorbing different inorganic and organic contaminants from water environments, some factors restrict its effective application for PFAS adsorption. These factors are related to the biochar properties, and characteristics of PFAS, as well as water chemistry. Therefore, some modifications have been introduced to overcome these limitations and improve biochar's adsorption capacity. This review explores the preparation conditions, including the pyrolysis process, activation, and modification techniques applied to biochar to enhance its adsorption capacity for different types of PFAS. It addresses critical questions about the adsorption performance of biochar and its composites, mechanisms governing PFAS adsorption, challenges, and future perspectives in this field. The surge in research on biochar for PFAS adsorption indicates a growing interest, making this timely review a valuable resource for future research and an in-depth exploration of biochar's potential in PFAS remediation.