Multiple campaigns to measure methane emissions from municipal solid waste (MSW) landfills across North America using a constellation of nine high-resolution (30 m pixels) satellites equipped with short-wave infrared sensors (SWIRS) were conducted. The purpose of the survey was to evaluate emission estimates using the integrated mass enhancement (IME) method for a range of landfills equipped with gas collection systems. We report a geometric average emission estimate of 481 kg CH4 h-1 across 60 active MSW landfills from 697 site observations with 457 discrete plumes and 247 nondetect observations from 2021 to 2024. Minimum and maximum observations were 116 and 6422 kg h-1, reflecting considerable variability, likely due to method uncertainty, environmental conditions, and management practices. Gas collection efficiency (CE) was assessed for a subset of 25 landfills that were routinely measured for one calendar year. When these instantaneous emission estimates were compared to gas collection data at the time of the observation, 15 of 25 sites were found to have greater CEs than were assumed in modeling data that informed the 2023 U.S. greenhouse gas inventory. Measured (38-96%) and modeled CEs (65-90%) were poorly correlated (r2 = 0.18), which suggests that limitations exist for reconciling the data with values used to assemble inventories.

As part of its commitment to the United Nations Framework Convention on Climate Change, the U.S. annually develops a national estimate of methane emissions from municipal solid waste (MSW) landfills by aggregating activity data from each facility. Since 2010, the U.S. has reported a 20 % decrease in MSW landfill emissions despite a 21 % increase in tons disposed. Operator-submitted data were investigated to understand the causes of this decline. In the U.S., operators of landfills with a gas collection and control system (GCCS) calculate their facility's emissions via two separate approaches - (1) first-order decay (FOD) and (2) collection efficiency assumption (CEA) - and select either result to feed into the annual inventory. The FOD model predicts methane generation proportional to waste disposal and that approach calculated a 19 % increase in total methane generated from 2010 to 2022, whereas generation via the CEA approach decreased by 8.9 %. The amount of measured methane collected has increased 7.5 % for the same years. Discrepancies between the two models' generated methane, assumed gas collection efficiencies, and oxidized methane compound into substantive differences in national estimates. Operators more frequently select the CEA method, which results in decreased national estimates. If only the FOD method was used, U.S. MSW landfill emissions would be 1.3-1.7 times greater than current estimates which is similar to recent extrapolations from remote sensing campaigns in the U.S. Both models contain parameters with large inherent uncertainty. Without measurement methods that continuously quantify both point-source and diffuse emissions, an assessment of either equation's accuracy cannot be made.

Methane emissions from solid waste may represent a substantial fraction of the global anthropogenic budget, but few comprehensive studies exist to assess inventory assumptions. We quantified emissions at hundreds of large landfills across 18 states in the United States between 2016 and 2022 using airborne imaging spectrometers. Spanning 20% of open United States landfills, this represents the most systematic measurement-based study of methane point sources of the waste sector. We detected significant point source emissions at a majority (52%) of these sites, many with emissions persisting over multiple revisits (weeks to years). We compared these against independent contemporaneous in situ airborne observations at 15 landfills and established good agreement. Our findings indicate a need for long-term, synoptic-scale monitoring of landfill emissions in the context of climate change mitigation policy.

In the United States (U.S.), the management of sludges generated from drinking water and wastewater treatment are overseen by the state agencies and much of that information, especially quantities incinerated or landfilled, are not communicated to the U.S. Environmental Protection Agency (U.S. EPA). Instead, estimates of beneficial use or disposal of sludges have been periodically quantified through time- and resource-intensive surveys of facility operators. Simple methods to estimate annual sludge generation and disposal, informed by publicly available state-level data, were developed. The generation of drinking water treatment plant (DWTP) sludge was estimated using water supply data and a sludge generation factor (SGF) based on existing literature. A processaveraged SGF, 1.3% as wet-weight per gallons treated, resulted in 35-40 mmt dw sludge/year from 2000 to 2015, yielding 150 kg DWTP sludge dw/person-year. Based on publicly available data from 15 states, WWTP sludge was approximately 1-2% of landfilled waste composition. State-level data regarding the (1) generation or (2) disposal of municipal wastewater treatment plant (WWTP) sludges were used to extrapolate national estimates. From 2010 to 2020, the US generated (1) 7.5-6.8 or (2) 7.9-7.1 mmt dw WWTP sludge/year. National figures for WWTP sludge incineration could not be estimated based on limited data. The development of transparent and simple estimation methods that utilize publicly-available data will help improve generation, disposal, and recycling estimates at the national level.

Airborne remote sensing observations were collected at 217 landfills across 17 states in the US in 2023. We used these observations to attribute emissions to major sources, including the landfill work face, where new waste is placed at the landfill and gas-control infrastructure. Methane emissions from the work face appeared to be more prevalent than gas-control infrastructure emissions, with 52 landfills exhibiting work face emissions out of the 115 observed landfills shown to be emitting in 2023. Landfills with work face emissions were often the highest emitters, especially sites with associated renewable natural gas facilities, and the total average site emissions from these landfills accounted for 79% of the observed emissions, indicating inefficient gas capture at these sites. Landfills with work face emissions also displayed the greatest disparity between observed emission rates and hourly emission rates that we estimated using annual emissions reported to the US EPA's Greenhouse Gas Reporting Program. Work face emissions present a major opportunity for methane mitigation: Observed emissions from work face emitting-landfills in this study were equivalent to 15% of US methane emissions from municipal solid waste landfills in 2022, as reported in the 2024 Greenhouse Gas Inventory, though these landfills accounted for only 4% of open sites in the US. As the 217 landfills in this study cover only 17% of open landfills in the US, the total mitigation potential is likely greater. Using remote sensing, we find that the largest contributor to observed methane emissions at US landfills is the landfill work face, an area of the landfill often left out of the required monitoring and traditional emissions accounting methods.

Precipitation, evapotranspiration (ET), waste tonnage, landfill gas (LFG), and leachate data were aggregated from public sources to perform a 5-10 year water balance and estimate the contributions of three water sources (precipitation, incoming waste, and leachate recycling) for 36 active municipal solid waste (MSW) landfills in Ohio, USA. Uniquely, the water balance incorporated waste decomposition, using gas collection data to inform mass loss from biodegradation. Moisture contents of 20-30% for incoming waste indicate that entrained water is the largest source of landfill moisture. Infiltration of precipitation into the landfill after ET was the second largest source. Even at facilities where a majority of the leachate generated was recirculated, it did not significantly affect the moisture content in that year. Using the water balance approach, it appears leachate recirculation is unlikely to increase moisture content above 40% by mass, a regulatory threshold in the US, which would impose stricter air pollution control requirements. However, poor stormwater management could easily allow for "bioreactor" conditions to develop. The calculated landfill moisture content was significantly affected by the assumed runoff coefficient (CRO) parameter. CRO values below 20% and above 50% produced unrealistically high or low moisture contents, respectively. This approach can assist operators and regulators in understanding the contribution of different sources to a landfill's moisture profile and avoid future operational problems.

Landfill gas (LFG) wellhead data were compared to understand the range of observations due to unique con-ditions at five elevated temperature landfills (ETLFs) in the U.S. Correlations of the primary gas ratio, CH4:CO2, show distinct compositional indicators for (1) typical operation, (2) subsurface exothermic reactions (SERs), (3) high moisture content, and (4) air intrusion that can help operators and regulators diagnose conditions across gas extraction wells. ETLFs A, B, D, and E showed similar trends, such as decreasing CH4 and increasing CO2, CO, and H2 that have been previously described. ETLF C uniquely exhibited elevated CH4 and temperatures simulta-neously due to carbonation (i.e., CO2 consumption) of a steel slag which was used as alternative daily cover (ADC). At the maximum gas well temperature, T = 82 degrees C/180 degrees F, CH4 and CO2 concentrations were 47% and 28%, respectively. At ETLFs A, B, and E, H2 > 50% were regularly observed in affected gas wells for several years. At the five ETLFs, maximum CO concentrations ranged from 1400-16,000 ppmv. Like the analysis of CH4:CO2, it is hypothesized here that H2 (%):CO (ppmv) may infer the types of waste that are thermally degrading. Co-disposal of industrial wastes and MSW and the use of potentially reactive ADCs should remain an important consideration for landfill operators and regulators because of their potential long-term impacts to LFG quality.

Landfills manage materials containing per-and polyfluoroalkyl substances (PFAS) from municipal solid waste (MSW) and other waste streams. This manuscript summarizes state and federal initiatives and critically reviews peer-reviewed literature to define best practices for managing these wastes and identify data gaps to guide future research. The objective is to inform stakeholders about waste-derived PFAS disposed of in landfills, PFAS emissions, and the potential for related environmental impacts. Furthermore, this document highlights data gaps and uncertainties concerning the fate of PFAS during landfill disposal. Most studies on this topic measured PFAS in liquid landfill effluent (leachate); comparatively fewer have attempted to estimate PFAS loading in landfills or other effluent streams such as landfill gas (LFG). In all media, the reported total PFAS heavily depends on waste types and the number of PFAS included in the analytical method. Early studies which only measured a small number of PFAS, predominantly perfluoroalkyl acids (PFAAs), likely report a significant underestimation of total PFAS. Major findings include relationships between PFAS effluent and landfill conditions - biodegradable waste increases PFAS transformation and leaching. Based on the results of multiple studies, it is estimated that 84% of PFAS loading to MSW landfills (7.2 T total) remains in the waste mass, while 5% leaves via LFG and 11% via leachate on an annual basis. The environmental impact of landfill-derived PFAS has been well-documented. Additional research is needed on PFAS in landfilled construction and demolition debris, hazardous, and indus-trial waste in the US.

The early stages of municipal solid waste degradation in landfills are complex harmonies of physical, biological, and chemical interactions that all work in concert to degrade trash into smaller and more stable materials. While many approaches have been taken to understand parts of this process, this new work attempted to simulate the early stages of landfills in controlled laboratory environments while observing the impacts of food waste content at different concentrations. This was completed by operating landfill lysimeters in a laboratory for approximately 1000 days, simulating landfill interior conditions while measuring the gas and liquid byproducts to study the impact of food waste presence in these environments. Metagenomic analysis after the experiment identified over 18,000 individual species and allowed comparison with past studies while also surveying microorganisms present in landfills. Similar populations found in past studies suggested the current experiments successfully replicated landfill conditions. While food waste diversion had a discernable impact on gas production, it did not show a clear and consistent impact on the microbiomes identified in this study.

This data brief presents leachate disposal and management data for 43 active or closed municipal solid waste (MSW) landfills and planar surface areas for 40 of those landfills in Ohio, USA. Data were extracted from publicly available Annual Operational Reports from the Ohio Environmental Protection Agency (Ohio EPA) and consolidated into a digital dataset of two delimited text files. A total of 9,985 data points represent monthly leachate disposal totals, arranged by management type and by landfill. Leachate management data for some landfills extend from 1988-2020 but are mostly limited to 2010-2020. Annual planar surface areas were identified from topographic maps in the annual reports. A total of 610 data points were created for the annual surface area dataset. This dataset aggregates and organizes the information, allowing for accessibility and increased application to engineering analysis and research projects.

Liquid addition to landfilled municipal solid waste (MSW) is a practice employed to accelerate the biodegradation of the organic fraction of MSW and ensuing gas generation. Pore landfill gas (LFG) and leachate pressure from the added moisture and enhanced gas generation are expected to impact the geotechnical stability of landfill slopes. The impact of moisture addition and gas collection on the stability of landfills was numerically modeled using transient isothermal dual-phase flow and slope stability modeling. The temporal variation in the factor of safety (FS) for slope stability analysis was estimated for the simultaneous flow of LFG and leachate with and without gas collection and leachate recirculation for varying LFG generation rates and waste moisture contents. A significant decline in the FS for landfill slope stability was observed when recirculating leachate without active gas collection. Even without pressurized leachate recirculation, a significant decline in the FS value was observed for landfills with relatively high in situ moisture content without active gas collection. In some modeled scenarios without LFG collection, the FS value was lower than 1. The analysis suggests that the landfill side slope stability analysis should incorporate LFG generation and the resultant pressure for landfills containing high-moisture-content waste and for the landfill with pressurized leachate recirculation. The analysis suggests that an efficient gas collection system plays a critical role in the geotechnical stability of the slope of wet landfills and the performance of leachate recirculation trenches.

Elevated temperature landfills (ETLFs) are municipal solid waste (MSW) landfills that have been impacted by subsurface exothermic reactions (SERs) and display unusual gas and leachate composition. Leachate quantity and quality data were analyzed to identify indicators of a SER at an ETLF in Ohio, USA. ETLF leachate generation increased from 2.04 to 14.4 m3/hectare-day (218 to 1,539 gallons/acre-day), peaking 16 months after the reaction was first noticed. The leachate generation rate for this ETLF remains about two times greater than the average Ohio MSW landfill. Several general parameters such as pH, electrical conductivity (EC), and total dissolved solids (TDS) remain impacted 5 years later. Similarly, metals such as arsenic, iron, calcium, potassium, and magnesium have increased in concentration. Volatile organic compounds (VOCs) behavior was less consistent as a group of chemicals. Increases of VOCs such as acetone, benzene, and methyl ethyl ketone (MEK) also increased. Importantly, in one year, benzene exceeded its toxicity characteristic threshold meaning the leachate was a hazardous waste, substantially increasing treatment and disposal costs. It is not clear if the VOCs are produced directly by the SER or if they are an indicator that microbial processes-which would otherwise consume them-have been disrupted. ETLFs likely do not all undergo the same exothermic reaction(s) and, unlike the analysis of landfill gas composition, temporal changes in leachate constituents' concentrations may be more important than comparing to absolute values.

The leachate collection system (LCS) and leak detection system (LDS) flow rate data from 240 cells (or a combination of cells) at 54 municipal solid-waste landfills (located in seven US states) with double-liner systems were analyzed to assess the performance of the primary liner system. The average LCS leachate collection rates for the study sites ranged from 380 L ha-1 day-1 (40.7 gal. acre-1 day-1) to 22,400 L ha-1 day-1 (2,390 gal. acre-1 day-1) on a sitewide basis, and the average LDS leachate collection rates ranged from 1.8 L ha-1 day-1 (0.2 gal. acre-1 day-1) to 577 L ha-1 day-1 (61.7 gal. acre-1 day-1) on a sitewide basis. Assuming all leachate generated is collected either by the LCS or LDS, the data suggest that the primary liner systems' aggregated efficiency is over 98%. The collection efficiency at sites that used a composite liner (geomembrane underlain by a geosynthetic clay liner or a compacted clay liner) system was not statistically different from the sites that used only a geomembrane as the primary liner (geomembrane underlain by a permeable layer) (median of 99% for both types). Leakage rates were compared with those estimated from the equations used by the hydrologic evaluation of landfill performance (HELP) model. The comparison suggests that the equations used by the HELP model to estimate leakage through the liner overestimate the leakage rate through geomembrane primary liners but underestimate the leakage rate through composite primary liners based on the HELP-model-default defect size and suggested defect frequency. It is also possible that groundwater intrusion could contribute to a portion of the leachate collected from the LDS because leachate quality data collected from a few sites indicated the LCS leachate had a higher concentration of most constituents than the leachate collected from LDS.

The release of persistent per- and polyfluoroalkyl substances (PFAS) into the environment is a major concern for the United States Environmental Protection Agency (U.S. EPA). To complement its ongoing research efforts addressing PFAS contamination, the U.S. EPA's Office of Research and Development (ORD) commissioned the PFAS Innovative Treatment Team (PITT) to provide new perspectives on treatment and disposal of high priority PFAS-containing wastes. During its six-month tenure, the team was charged with identifying and developing promising solutions to destroy PFAS. The PITT examined emerging technologies for PFAS waste treatment and selected four technologies for further investigation. These technologies included mechanochemical treatment, electrochemical oxidation, gasification and pyrolysis, and supercritical water oxidation. This paper highlights these four technologies and discusses their prospects and the development needed before potentially becoming available solutions to address PFAS-contaminated waste.Implications: This paper examines four novel, non-combustion technologies or applications for the treatment of persistent per- and polyfluoroalkyl substances (PFAS) wastes. These technologies are introduced to the reader along with their current state of development and areas for further development. This information will be useful for developers, policy makers, and facility managers that are facing increasing issues with disposal of PFAS wastes.

Managing municipal solid waste (MSW) presents many challenges, including the production of methane when MSW biodegrades in landfills. The search for methods to predict methane generation easily and accurately has been ongoing as MSW management improves and the damage presented by greenhouse gases is realized. To study MSW biodegradability, samples of solid waste were collected by sorting trash at four landfills and transfer stations in the southeast United States and transported to laboratories where the MSW was processed and analyzed for methane potential using biochemical methane potential assay, fiber content (lignin, cellulose, and hemicellulose), total carbon analysis, and elemental analysis. Searches for correlation between these data and methane generation revealed that average cellulose content correlated with methane generation potential (R2 = 0.90). A formula for predicting the methane potential of MSW samples using elemental analysis and 1 of 14 different correction factors, assigned by waste category type, is also presented. The methods presented in this work can help researchers and landfill operators better evaluate the methane potential of the MSW they work with.

Concentrations of per- and poly-fluoroalkyl substances (PFAS) present in wastewater treatment biosolids are a growing concern. Pyrolysis is a thermal treatment technology for biosolids that can produce a useful biochar product with reduced levels of PFAS and other contaminants. In August 2020, a limited-scope study investigated target PFAS removal of a commercial pyrolysis system processing biosolid with the analysis of 41 target PFAS compounds in biosolids and biochar performed by two independent laboratories. The concentrations of 21 detected target compounds in the input biosolids ranged between approximately 2 µg/kg and 85 µg/kg. No PFAS compounds were detected in the biochar. The PFAS concentrations in the biochar were assumed to equal the compounds' minimum detection limits (MDLs). The pyrolysis system's target PFAS removal efficiencies (REs) were estimated to range between >81.3% and >99.9% (mean >97.4%) with the lowest REs being associated with the lowest detected PFAS concentrations and the highest MDLs. No information on non-target PFAS compounds in influent or effluent media or products of incomplete combustion was considered. Selected gaseous emissions were measured by Fourier transform infrared spectroscopy and gas chromatography time-of-flight mass spectrometry to provide additional information on air emissions after process controls. This limited-scope study indicated that additional research to further understand this process is warranted.Implications: Development of alternative approaches to manage PFAS-impacted biosolids is of emerging international importance. A commercially operating biosolid pyrolysis process was shown to lower target PFAS levels in produced biochar. Additional research is warranted to understand all potential PFAS transformation emission routes and optimal air pollution emissions control strategies for this technology class.

Remote locations, small communities, and weather prohibit the operation of piped sanitary sewers in many Alaska Native Villages (ANVs). Research was conducted to understand the technical feasibility of installing anaerobic digesters (ADs) in remote ANVs which would be heated by solar thermal collectors. Biochemical methane potential (BMP) assays were conducted to understand the effect of freezing and thawing on methanogenic activity of synthetic human feces. BMPs were frozen at -20 or -80 °C for 7 days and then incubated at psychrophilic (20 °C) or mesophilic (37 °C) conditions. Psychrophilic BMPs frozen at -20 or -80 °C yielded 453 ± 119 and 662 ± 77 mL CH4/g VS, respectively. Mesophilic BMPs frozen at -20 or -80 °C yielded 337 ± 59 and 495 ± 63 mL CH4/g VS, respectively. Freezing caused a lag period, but ultimately many of the assays reached yields similar to or even greater than the baseline, unfrozen assays. Monthly solar radiation and air temperature data were used to identify the number of solar thermal collectors that would be required to supplement heat energy to operate the ADs in several locations. Alaskan subarctic locations receive enough solar thermal energy in summer months to support seasonally operated, psychrophilic ADs.

Water above 374 °C and 22.1 MPa, becomes supercritical, a special state where organic solubility increases and oxidation processes are accelerated. Supercritical water oxidation (SCWO) has been previously shown to destroy hazardous substances such as halogenated compounds. Three separate providers of SCWO technology were contracted to test the efficacy of SCWO systems to reduce per- and poly-fluoroalkyl substances (PFAS) concentrations from solutions of dilute aqueous film-forming foam (AFFF). The findings of all three demonstration studies, showed greater than 99% reduction of the total PFAS identified in a targeted-compound analysis, including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). PFOS was reduced from 26.2 mg/L to 240 μg/L, 30.4 mg/L to 0.310 μg/L, and 190 mg/L to 8.57 μg/L, from the Aquarden, Battelle, and 374Water demonstrations, respectively. Similarly, PFOA was reduced from 930 to 0.14 μg/L, 883 to 0.102 μg/L, and 3,100 μg/L to non-detect in the three evaluations. Additionally, chemical oxygen demand of the dilute AFFF was shown to reduce from 4,750 to 5.17 mg/L after treatment, indicating significant organic compound destruction. In one demonstration, a mass balance of the influent and effluent found that the targeted compounds accounted for only 27% of the generated fluoride, suggesting that more PFAS were destroyed than measured and emphasizing the limitations of targeted analysis alone. As a destructive technology, SCWO may be an alternative to incineration and could be a permanent solution for PFAS-laden wastewaters rather than disposal by injection into a deep-well or landfilling. Additional investigation of reaction by-products remains to be conducted for a complete assessment of SCWO's potential as a safe and effective PFAS treatment technology.

A critical examination of the US Environmental Protection Agency's (US EPA's) Greenhouse Gas Reporting Program (GHGRP) database provided an opportunity for the largest evaluation to date of landfilled waste decomposition kinetics with respect to different US climate regimes. In this paper, 5-8 years of annual methane collection data from 114 closed landfills located in 29 states were used to estimate site-specific waste decay rates (k) and methane collection potentials (Lc). These sites account for approximately 9% of all landfills required to report GHG emissions to the US EPA annually. The mean methane collection potential (Lc) for the sites located in regions with less than 635 mm (25 in) annual rainfall was significantly (p<0.002) lower than the mean methane collection potential of the sites located in regions with more than 635 mm (25 in) annual precipitation (49 and 73 m3 methane Mg-1 waste, respectively). This finding suggests that a fraction of the in-place biodegradable waste may not be decomposing, potentially due to a lack of adequate moisture content of landfills located in arid regions. The results of this evaluation offer insight that challenges assumptions of the traditional landfill methane estimation approach, especially in arid climates, that all methane corresponding to the total methane generation potential of the buried solid waste will be produced. Decay rates showed a significant correlation with annual precipitation, with an average k of 0.043 year-1 for arid regions (< 508 mm (20 in) year-1), 0.074 year-1 for regions with 508-1,016 mm (20-40 in) annual precipitation, and 0.09 year-1 in wet regions (> 1,016 mm (40 in) year-1). The data suggest that waste is decaying faster than the model default values, which in turn suggests that a larger fraction of methane is produced during a landfill's operating life (relative to post-closure).

Municipal solid waste landfills utilize drainage material (oftentimes a sand with high-hydraulic conductivity) to prevent the accumulation of leachate on the bottom liner. The drainage media must meet specification criteria to ensure adequate performance. At a Florida landfill site, the mine tailings meeting all specification criteria were used as drainage media, and after heavy rainfall prior to waste placement, humic substances washed from the media into unlined stormwater collection ponds, causing elevated turbidity levels. Effluent turbidity of landfill drainage sand can have negative impacts on leachate collection and stormwater systems, but may not be adequately addressed by typical material specifications. Tests were performed on impacted stormwater and the mine tailings, as well as several control materials, and while all met the standard material specification requirements, differences in organic material content and effluent turbidity were noted. Stricter organic content specifications and/or additional test specifications for effluent turbidity are recommended to prevent turbidity impacts caused by organic material in drainage sand.