Sewage Sludge Research Articles

Ultrasound assisted bio-acid leaching of sewage sludge ash for phosphorus extraction using lemon juice: optimization and ecological risk assessment

Ultrasound assisted bio-acid leaching of sewage sludge ash for phosphorus extraction using lemon juice: optimization and ecological risk assessment

Elucidating the Molecular Mechanisms and Comprehensive Effects of Sludge-Derived Plant Biostimulants on Crop Growth: Insights from Metabolomic Analysis.

The utilization of urban waste for land management plays a crucial role in reshaping material flows between human activities and the environment. Sewage sludge alkaline thermal hydrolysis (ATH) produces sludge-derived plant biostimulants (SPB), which have garnered attention due to the presence of indole-3-acetic acid. However, there remains a gap in understanding SPB's molecular-level effects and its comprehensive impact on crops throughout their growth cycle. In this study, non-targeted and targeted metabolomic approaches are employed to analyze 51 plant hormones and 1,177 metabolites, revealing novel insights. The findings demonstrate that low concentrations of SPB exerted multiple beneficial effects on rice roots, leaves, and the root-soil system, facilitating rapid cell division and enhancing antioxidant defense mechanisms. These results provide a vital foundation for understanding ATH metabolic pathways and advocating for widespread SPB application, offering significant implications for sustainable land management.

Behavior and flow of microplastics during sludge treatment in Japan.

Microplastic (MP) pollution is a growing public and scientific concern. In urban environments, wastewater treatment plants (WWTPs) are major sources of MPs. This study sampled sludge and separated water from each sludge treatment unit in two WWTPs in Osaka, Japan. Analyzing method for MPs in sewage sludge was optimized, ultrasonic pretreatment and double digestion were introduced into the analyzing method of MPs in sewage sludge, recovering test of standard MPs proved its high efficiency. Then MPs larger than 100 μm were extracted and analyzed, their size and type were recorded, the MP concentration was calculated, and the MP flow in the sludge treatment system was estimated. MPs were detected at every step of the sludge treatment process, and 13 types of MPs were identified. The MP concentration in sludge ranged from 81 ± 48 to 6470 ± 1490 particles/kg dry sludge (DS). In the separated water, MP concentrations were much lower, ranging from 0 to 1740 ± 794 particles/kg DS. During the thickening and dewatering processes, nearly all MPs were transferred into thickened or dewatered sludge; only 5-10 % of MPs returned to the primary sedimentation pond with the separated water. The most common types of MPs were PMMA, PE, and PS. No significant differences in MP type distributions were observed among sampling batches; however, significant differences in a few types of MPs were detected between treatment units, which requires further investigation. All detected MPs were smaller than 1000 μm; larger MPs might have been removed in the grit chamber before reaching the primary or secondary sedimentation ponds. Overall, the particle size distribution did not substantially change during sludge treatment.

Comparative Analysis of Sewage Sludge Characteristics After Natural Deposition, Accelerated Aging, and Composting

This study investigated treatment methods for urban wastewater sludge, specifically examining natural drying over five years, accelerated freeze–thaw–drying cycles, and composting with and without a zeolite additive. The findings reveal that composting effectively stabilized the sludge while retaining essential nutrients crucial for agriculture. Notably, with the addition of 2% zeolite by total mass, approximately 40% of the total nitrogen was preserved. Adequate aeration during composting maintained acceptable levels of phosphorus compounds, with the phosphorus content expressed as P2O5 showing significant retention compared with the natural drying methods. Composting also demonstrated a substantial reduction in petroleum hydrocarbon concentrations, which decreased from 30 mg/kg to 3 mg/kg, thereby showcasing its potential for processing contaminated sludge. The inclusion of zeolite enhanced the nitrogen retention by an additional 10–20% compared with the composting without zeolite, aligning with previous studies on its effectiveness. While composting and thermal treatments, like accelerated freeze–thaw cycles, influenced the physical properties of the sludge—such as reducing the moisture content and altering the volatile substance concentrations—they did not significantly affect the heavy metal levels. Natural drying over five years resulted in reduced metal quantities, which possibly reflected changes in the wastewater characteristics over time. Given that the heavy metal concentrations remained largely unchanged, additional treatment methods are recommended when the initial sludge contains high levels of these contaminants to ensure the safe use of the final product as fertilizer. This study underscored the significant role of biochemical and microbiological processes during composting and natural drying in transforming sludge properties. Future research should focus on establishing upper contamination thresholds and exploring microbiological safety measures to enhance the viability of sludge reuse in agriculture, balancing nutrient preservation with environmental safety.

Policy impact on economic and environmental sustainability of anaerobic digestion: Industrial case study Insights.

This paper thoroughly examines how policy incentives impact the economic and environmental sustainability of anaerobic digestion (AD) systems. It uses techno-economic and life cycle analyses, along with real industry data, to explore the entire AD process-from feedstock acceptance to digestate disposal. It evaluates the effects of various U.S. policy crediting programs on the economic viability of different AD pathways for treating sewage sludge and food waste. Tipping fees are identified as the primary driver of profitability, while policy credits play a crucial role in enhancing economic feasibility, particularly for renewable natural gas production. However, future regulatory changes could reshape this economic landscape. All AD pathways are found to significantly reduce greenhouse gas emissions, though economic outcomes are highly sensitive to digestate disposal costs and feedstock tipping fees. Co-digestion with food waste is proposed as a strategy to reduce dependence on policy credits and improve long-term economic stability.

Reproductive and Metabolic Health Following Exposure to Environmental Chemicals: Mechanistic Insights from Mammalian Models.

The decline in human reproductive and metabolic health over the past 50years is associated with exposure to complex mixtures of anthropogenic environmental chemicals (ECs). Real-life EC exposure has varied over time and differs across geographical locations. Health-related issues include declining sperm quality, advanced puberty onset, premature ovarian insufficiency, cancer, obesity, and metabolic syndrome. Prospective animal studies with individual and limited EC mixtures support these observations and provide a means to investigate underlying physiological and molecular mechanisms. The greatest impacts of EC exposure are through programming of the developing embryo and/or fetus, with additional placental effects reported in eutherian mammals. Single-chemical effects and mechanistic studies, including transgenerational epigenetic inheritance, have been undertaken in rodents. Important translational models of human exposure are provided by companion animals, due to a shared environment, and sheep exposed to anthropogenic chemical mixtures present in pastures treated with sewage sludge (biosolids). Future animal research should prioritize EC mixtures that extend beyond a single developmental stage and/or generation. This would provide a more representative platform to investigate genetic and underlying mechanisms that explain sexually dimorphic and individual effects that could facilitate mitigation strategies.

A Systematic Review and Meta-Analysis of the Sustainable Impact of Sewage Sludge Application on Soil Organic Matter and Nutrient Content

The increasing scarcity of natural resources makes the linear production model unsustainable, highlighting the need for more sustainable practices under the umbrella of circular economic principles. Sewage sludge emerges as a promising solution to provide soil organic matter (SOM) and nutrients. This meta-analysis evaluated the impacts of three levels of sludge application (low, medium, and high) on organic matter (OM), nitrogen (N), phosphorus (P), copper (Cu), and zinc (Zn) contents, considering different areas and experimental conditions worldwide. The analysis included 37 studies and 355 comparisons, after screening 7625 records, following the 2020 PRISMA protocol. The effects of sludge concentrations, continents, and types of experiment (field or greenhouse) were evaluated. Sewage sludge application significantly increased OM, N, Cu, and Zn levels, mainly at medium and high rates. The largest effects were observed in greenhouses, suggesting variation by location and environment. Moderators explained a part of the variation in the results, but the residual heterogeneity test revealed that there is still unexplained variability.

Limitations of soil-applied non-microbial and microbial biostimulants in enhancing soil P turnover and recycled P fertilizer utilization - a study with and without plants

IntroductionPhosphorus recovery from waste streams is a global concern due to open nutrient cycles. However, the reliability and efficiency of recycled P fertilizers are often low. Biostimulants (BS), as a potential enhancer of P availability in soil, could help to overcome current barriers using recycled P fertilizers. For this, a deeper understanding of the influence of BSs on soil P turnover and the interaction of BSs with plants is needed. MethodsWe conducted an incubation and a pot trial with maize in which we testednon-microbial (humic acids and plant extracts) and microbial BSs (microbial consortia) in combination with two recycled fertilizers for their impact on soil P turnover, plant available P, and plant growth.Results and discussionBSs could not stimulate P turnover processes (phosphatase activity, microbial biomass P) and had a minor impact on calcium acetate-lactate extractable P (CAL-P) in the incubation trial. Even though stimulation of microbial P turnover by the microbial consortium and humic acids in combination with the sewage sludge ash could be identified in the plant trial with maize, this was not reflected in the plant performance and soil P turnover processes. Concerning the recycled P fertilizers, the CAL-P content in soil was not a reliable predictor of plant performance with both products resulting in competitive plant growth and P uptake. While this study questions the reliability of BSs, it also highlights the necessity toimprove our understanding and distinguish the mechanisms of P mobilization in soil and the stimulation of plant P acquisition to optimize future usage.

Carbon dioxide capture in large-scale CCGT power plant from flue gases obtained from various fuel mixtures

In this study, the thermodynamic analysis of a combined cycle gas turbine integrated with post-combustion carbon capture and storage using the solvent method is performed. The syngas obtained from the gasification of sewage sludge is mixed with methane and nitrogen-rich natural gas fuels at different proportions, used in the gas turbine, and the properties of fuel and flue gases are analyzed. The flue gas obtained from the fuel mixture is passed through the post-combustion carbon capture and storage at various load conditions to assess the heat and electricity required for the carbon capture process. The solvent used for the carbon capture from flue gases enables CO2 capture with the high efficiency of 90%. With the calculated results, the load conditions of flue gas using fuel mixtures are identified, which reduces the heat and power demand of post-combustion carbon capture and storage and provides the possibility to achieve neutral emission. The impact of selected operating conditions of post-combustion carbon capture and storage on the CO2 emission reduction process and on the power plant performances is investigated. Considering the factors of electricity generation, energy efficiency, heat supply to the consumers, operating load of post-combustion carbon cap-ture and storage and CO2 emission, the 50% mixture of syngas with both fuels performs better. Also, the use of a mixture of 2-amino-2methyl-1-propanol and piperazine with reboiler duty 3.7 MJ/kgCO2 in post-combustion carbon capture and storage slightly enhanced the performance of the power plant compared to the use of monoethanolamine with reboiler duty 3.8 MJ/kgCO2.

Enhancement of the Plant-Accessible Phosphate Fraction in Sewage Sludge Ashes by Na+ or K+ Addition Prior to Combustion.

With the aim of transforming sewage sludge into a P-fertiliser material in a single combustion step, the chemical processes underlying sewage sludge combustion were analysed using powder X-ray diffraction (P-XRD), infrared spectroscopy (IR), thermogravimetric (TGA) as well as elemental analyses (EA). In addition to the combustion of sewage sludge on its own ("mono-combustion"), additions of different additives prior to the combustion step were also carried out. Based on the very positive effects of the additives sodium and potassium carbonate on the obtained ashes concerning their phosphate solubilities in neutral ammonium citrate (NAC) solution, sewage sludge combustions after additions of Na2CO3 or K2CO3 were investigated in detail. We found that these additions altered the main phosphate-containing product found in the ashes from whitlockite (Ca9(Mg,Fe)(PO3OH)(PO4)6), a hardly plant-accessible species, to other phosphate containing compounds such as buchwaldite (CaNaPO4), which is known for a long time as a very good P‑source for plants. Consecutive greenhouse experiments with maize (Zea mays L.) as test plant confirmed the results of the chemical analyses and demonstrated that Na- or K-ashes obtained from a "co-combustion" of sewage sludge mixed with alkali carbonates exhibit relative P-fertilising efficiencies of up to ~80% in comparison to commercial superphosphate.

Inhibition of Polycyclic Aromatic Hydrocarbons Formation During Supercritical Water Gasification of Sewage Sludge by H2O2 Combined with Catalyst

This work evaluated the alterations in the levels and types of polycyclic aromatic hydrocarbons (PAHs) within both liquid and solid products throughout the process of the catalytic supercritical water gasification of dewatered sewage sludge to examine the catalytic effect of various catalysts and the inhibit reaction pathways. The addition of Ni, NaOH, Na2CO3, H2O2, and KMnO4 reduced the concentrations of PAHs, with Ni and H2O2 showing the best performance. The concentrations of PAHs, especially higher-molecular-weight compounds in the residues, decreased sharply as the H2O2 amount increased. At a 10 wt% H2O2 addition, the levels of PAHs in the liquid and solid products were reduced by 91% and 88%, respectively. High-ring PAHs were not detected in the residues as the H2O2 amount increased to an 8 wt%. H2O2 addition evidently inhibits PAH formation by promoting the ring-opening reactions of initial aromatic compounds in raw sludge and inhibiting the polymerization of open-chain intermediate products. The addition of NaOH + H2O2 or Ni + H2O2 as combined catalysts significantly lowered PAH concentrations while increasing the H2 yield. The addition of 5 wt% Ni + H2O2 reduced PAH concentrations in the liquid and solid residues by 70% and 44%, respectively, while the H2 yield escalated from 0.13 mol/kg OM to 3.88 mol/kg OM. Possible mechanisms associated with the reaction pathways of these combined catalysts are proposed.

Measuring Microplastic Concentrations in Water by Electrical Impedance Spectroscopy

Plastics are vital for society, but their usage has grown exponentially and contributes to the growth of pollution worldwide. The World Health Organization, WHO, already reported that microplastics (MPs) are found everywhere, in waste and fresh water, and in the air and soil. Regarding water effluents, waste-water treatment plants only minimize the problem, trapping only larger size particles. In contrast, smaller ones remain in oxidation ponds or sewage sludges, or are even released to aquifers environment. Classic procedures for MPs detection are still quite laborious, and are usually conducted off-line, involving several steps and expensive equipment. Electrical Impedance Spectroscopy, EIS, is a technique that allows the analysis of a system’s electrical response, yielding helpful information about its domain-dependent on physical-chemical properties. Due to the superficial electronegativity of MPs’ particles, EIS may allow to attain the purpose of the present work: to provide a fast and reliable method to detect/estimate MPs’ concentration in water effluents. Among the most common microplastics are Polyethylene, PE, and Polyvinyl Chloride, PVC. Using the developed setup and experimental data collection methodology, the authors could differentiate between MPs’ suspensions containing the same concentration of the different evaluated MPs, PVC and PE, and assess PVC concentration variation, in the interval between 0.03 to 0.5 g (w/w), with an error, estimated based on the obtained impedance modulus, around or below 3% for the entire stimulus signal frequency range (from 100 Hz to 40 MHz) for the PVC particles.

Application of QuEChERS extraction and LC-MS/MS for determination of pharmaceuticals in sewage sludges sampled across the Czech Republic.

The use of pharmaceuticals entails a significant risk of environmental contamination. Wastewater treatment plants (WWTPs) are considered to be the main contributors to contamination as they ineffectively eliminate these compounds from wastewater. Simultaneously, they produce solid waste, sludge, which often contains a variety of retained pollutants, including pharmaceuticals. Since sewage sludge is frequently applied to agricultural soil due to its rich nutrient content, pollutants are introduced into the environment in this way. Only a few studies have been carried out on the topic of the analysis of pharmaceuticals in sludge. Therefore, information on the occurrence of pharmaceuticals in sludge is limited. The present study employed quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis to establish a simple and reliable procedure for determining 16 pharmaceuticals (antibiotics, anticonvulsants, antidepressants and β-blockers) in sewage sludge. The method has been thoroughly validated, and parameters such as linear range, accuracy, precision, matrix effects and detection and quantification limits were assessed. Our method achieved low limits of quantification (0.5-9.0µgkg-1) and satisfactory recoveries (51-101%). Forty sludge samples from different WWTPs across the Czech Republic were analysed. Fourteen compounds were detected and quantified in most samples, with antidepressants having the highest detection frequency and overall content. Sertraline, with a mean concentration of 521.0µgkg-1, was notably prevalent alongside its metabolite norsertraline (mean concentration 204.9µgkg-1). The antibiotic azithromycin was also found at higher levels (mean concentration 185.1µgkg-1).

Evaluation of Organic Waste Long-Term Effects on Cellulose, Hemicellulose and Lignin Content in Energy Grass Species Grown in East-Central Poland

Biomass can be used for electricity generation, especially in developing countries, but also in developed ones, where the utilization of renewable energy sources is being integrated into a sustainable economy. There are considerable differences in the scale of biomass use and in the technology of its processing. One of the most important sources of biofuel is the biomass of grass. This research aimed to determine the long-term effects of organic fertilizers on cellulose, hemicellulose, and lignin content in the biomass of three grass species: giant miscanthus (Miscanthus × giganteus), prairie cordgrass (Spartina pectinata), and switchgrass (Panicum virgatum L.) in the first three years of growth. The experiment was established in four replications on microplots of 2 m2 in April 2018. Before planting grass rhizomes, municipal sewage sludge (SS) and spent mushroom substrate (SMS) were introduced into the soil in various combinations. Biomass is harvested in December every year. The content of structural polysaccharides in the grass species statistically significantly varied in response to organic waste. Compared to other fertilizer combinations, SS application increased the content of cellulose in the biomass of Miscanthus giganteus (43.66% of DM) and Spartina pectinata (37.69% of DM) and hemicellulose in Spartina pectinata (27.80% of DM) and Panicum virgatum (23.64% of DM). Of the three species of grass, the chemical composition of Miscanthus giganteus cell walls was the most favorable for biofuel production, with the most cellulose and hemicellulose and the least lignin compared to other grass species. The content of lignin in the biomass of Miscanthus × giganteus and Spartina pectinata was the greatest on the plot with SMS and amounted to 7.79% of DM and 12.32% of DM, respectively. In the case of Panicum virgatum, the average content of lignin was similar across all fertilized plots, with 15.42% DM.

Ultrasound-Assisted Community Bureau of Reference (BCR) Procedure for Heavy Metal Removal in Sewage Sludge

Sewage sludge (SS) resulting from wastewater treatment plants (WWTP) is commonly applied worldwide as a fertilizer in agriculture. This can be done following a rigorous analysis of the sewage sludge composition. Due to its toxic potential, heavy metal ion content is one of the key parameters to test when evaluating SS sample usage as fertilizer. The distribution of metals present in SS samples produced by five municipal WWTPs in Romania was studied. To obtain information regarding metal distribution in SS, a modified ultrasound-assisted extraction procedure of the Community Bureau of Reference (BCR) was employed for As, Cd, Cr, Cu, Mo, Ni, Pb, Zn, and Co quantitation. Concentrations of these metals were measured using ICP-EOS spectrometry. Method extraction accuracy was verified using CRM-483 certified reference material. Results show that extraction efficiency was lowest for the exchangeable fraction for all studied metals. The detected ion metals were found distributed in fractions (F) 2 and 3, which are unavailable for plants and groundwater under natural environmental conditions. One noteworthy finding was that using ultrapure water for the leachate test resulted in low metal solubility, indicating slight metal desorption in real environmental samples. Furthermore, maize stalk bio-adsorbent was used to minimize metal ion content in WWTP leachate samples produced by the storage of SS in terms of metal ion adsorption.

Co-hydrothermal carbonisation of sewage sludge and kitchen waste: Influence of process parameters

This study assessed the impact of process temperature and time on the co-hydrothermal carbonisation (co-HTC) of kitchen waste and sewage sludge. To address the limitations of using a single feedstock and to circumvent the energy costs associated with pre-drying, the two organic feedstocks were mixed at a 1:1 ratio (wet basis). Co-HTC experimental runs were conducted in the temperature range of 180 °C–260 °C for 1, 3, and 5h durations. Co-HTC for sewage sludge and kitchen waste (1:1 ratio) at 260 °C temperature for 3h duration demonstrated optimal energy enrichment with a maximum energy and carbon densification of 1.50 and 1.47, respectively. The thermogravimetric analysis (TGA) revealed that the hydrochar (HC) produced at 260 °C temperature for 3h duration underwent multistage decomposition with stable intermediates due to the formation of more stable aromatic structures and a heat energy of 21.29 kJ g−1 at 292.87 °C. At the optimal reaction conditions, the process water (PW) exhibited a high volatile fatty acids (VFA) and total kjeldahl nitrogen (TKN) concentration of 1420 mg L−1 and 431.2 mg L−1, indicating its potential for simultaneous energy recovery through anaerobic digestion and nutrient recovery.

Techno-economic feasibility study of ammonia recovery from sewage sludge digestate in wastewater treatment plants

Wastewater treatment plants play a vital role in resource recovery, particularly through biogas production, a key renewable energy source. Beyond biogas, the digestate from anaerobic digestion is rich in nutrients like ammonia. This study explored the feasibility of recovering ammonia from sewage sludge digestate using air stripping. The process was modeled using Aspen Plus® software, utilizing real data from As-Samra WWTP in Jordan. Various operational parameters, such as digestate feed flow, air flow rate, temperature, and pressure, were analyzed to optimize ammonia recovery. The results showed that with a feed flow rate between 10,000 and 30,000 kg/hr, ammonia recovery reached 85%, with production exceeding 100 kg/hr, where the effect of the flow rate appears mostly at elevated feeding temperatures. Increased air flow rates significantly boosted recovery, achieving 90% efficiency at 60 °C with 50,000 kg/h as air flow. Flashing pressure peaked at 1.5 bar, with 85% efficiency at 95 °C, while higher pressures yielded diminishing returns, stabilizing production around 106 kg/hr. The NaOH feed rate also influenced output, rising from 100 kg/hr at a 50 kg/hr feed rate to 107 kg/hr at 750 kg/hr, with recovery efficiency exceeding 85%. The economic analysis showed that the project had a payback period of 6.07 years, reflecting a reasonable recovery of the initial investment. The net present value was 122,924 USD over 15 years, with 8% amortization rate, indicating that the project created value beyond the initial cost. The internal rate of return was 14.23%, surpassing the discount rate and highlighting the project's financial attractiveness.

Investigation of the Morphology, Composition, and Structure of Dehydrated Sewage Sludge of a Pulp and Paper Enterprise

Investigation of the Morphology, Composition, and Structure of Dehydrated Sewage Sludge of a Pulp and Paper Enterprise

Acid-catalyzed co-hydrothermal carbonization of sewage sludge and mixed straws to produce high-quality solid fuel

To improve the hydrochar fuel quality, acid-catalyzed co-hydrothermal carbonization (co-HTC) of sewage sludge with mixed straws were performed at 220 °C. The impacts of mixing ratio (1:0, 1:3, 1:1, 3:1, and 0:1) and solvent (0.5 M HCl or dionized water) on hydrochar quality were assessed. The acid-catalyzed co-HTC increased the higher heating value and fuel ratio of the hydrochar by decreasing the H/C atomic ratio and increasing the O/C atomic ratio. The devolatilization index (Di) and combustibility index (S) of the hydrochar from co-HTC at a sludge-to-straws dry-mass ratio of 1:1 reached 64.6 and 26.8 (10−8 wt%2 min−2 K−3), respectively, which was over three times and 2.5 times that from sludge. Di was affected by the surface functional groups, whereas S was related to the chemical composition and fuel properties. Less energy is required after acid-catalyzed co-HTC for both pyrolysis and combustion processes, because of the increase in O/C atomic ratio. This study not only demonstrates the yields and quality of the hydrochar in response to the variation of mixing ratio and solvent, but also uncovers the relationship between hydrochar quality and pyrolysis/combustion performance, thereby providing valuable information for optimizing the acid-catalyzed co-HTC process.

PFAS, PCBs, PCDD/Fs, PAHs and extractable organic fluorine in bio-based fertilizers, amended soils and plants: Exposure assessment and temporal trends

Bio-based fertilizers (BBFs) produced from organic waste contribute to closed-loop nutrient cycles and circular agriculture. However, persistent organic contaminants, such as per- and poly-fluoroalkyl substances (PFAS), polychlorobiphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), as well as polyaromatic hydrocarbons (PAHs) can be present in organic waste or be formed during valorization processes. Consequently, these hazardous substances may be introduced into agricultural soils and the food chain via BBFs. This study assessed the exposure of 84 target substances and extractable organic fluorine (EOF) in 19 BBFs produced from different types of waste, including agricultural and food industrial waste, sewage sludge, and biowaste, and through various types of valorization methods, including hygienization at low temperatures (<150 °C) as well as pyrolysis and incineration at elevated temperatures (150–900 °C). The concentrations in BBFs (ΣPFOS & PFOA: <30 μg kg−1, Σ6PCBs: <15 μg kg−1, Σ11PAHs: <3 mg kg−1, Σ17PCDD/Fs: <4 ng TEQ kg−1) were found to be below the strictest thresholds used in individual EU countries, with only one exception (pyrolyzed sewage sludge, Σ11PAHs: 5.9 mg kg−1). Five BBFs produced from sewage sludge or chicken manure contained high concentrations of EOF (>140 μg kg−1), so monitoring of more PFAS is recommended. The calculated expected concentrations in soils after one BBF application (e.g. PFOS: <0.05 μg kg−1) fell below background contamination levels (PFOS: 2.7 μg kg−1) elsewhere in the literature. This was confirmed by the analysis of BBF-amended soils from field experiments (Finland and Austria). Studies on target legacy contaminants in sewage sludge were reviewed, indicating a general decreasing trend in concentration with an apparent half-life ranging from 4 (PFOS) to 9 (PCDD/Fs) years. Modelled cumulative concentrations of the target contaminants in agricultural soils indicated low long-term risks. Concentrations estimated and analyzed in edible plant part were low, indicating that exposure by plant consumption is well below tolerable daily intakes.