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.

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 a 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 $26.2\mathrm{mg}/\mathrm{L}$ to $240\mathrm{\mu g}/\mathrm{L}$ , $30.4\mathrm{mg}/\mathrm{L}$ to $0.310\mathrm{\mu g}/\mathrm{L}$ , and $190\mathrm{mg}/\mathrm{L}$ to $8.57\mathrm{\mu g}/\mathrm{L}$ , from the Aquarden, Battelle, and 374Water demonstrations, respectively. Similarly, PFOA was reduced from 930 to $0.14\mathrm{\mu g}/\mathrm{L}$ , 883 to $0.102\mathrm{\mu g}/\mathrm{L}$ , and $\mathrm{3,100}\mathrm{\mu g}/\mathrm{L}$ to nondetect in the three evaluations. Additionally, the chemical oxygen demand of the dilute AFFF was shown to reduce from 4,750 to $5.17\mathrm{mg}/\mathrm{L}$ 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 byproducts remains to be conducted for a complete assessment of SCWO’s potential as a safe and effective PFAS treatment technology.

Concentrations of per- and poly-fluoroalkyl substances (PFAS) present in wastewater treatment biosolids is 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 biosolids with 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 were considered. Select 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.

Emissions of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) from oil and natural gas production were investigated using direct measurements of component-level emissions on pads in the Denver-Julesburg (DJ) Basin and remote measurements of production pad-level emissions in the Barnett, DJ, and Pinedale basins. Results from the 2011 DJ on-site study indicate that emissions from condensate storage tanks are highly variable and can be an important source of VOCs and HAPs, even when control measures are present. Comparison of the measured condensate tank emissions with potentially emitted concentrations modeled using E&P TANKS (American Petroleum Institute [API] Publication 4697) suggested that some of the tanks were likely effectively controlled (emissions less than 95% of potential), whereas others were not. Results also indicate that the use of a commercial high-volume sampler (HVS) without corresponding canister measurements may result in severe underestimates of emissions from condensate tanks. Instantaneous VOC and HAP emissions measured on-site on controlled systems in the DJ Basin were significantly higher than VOC and HAP emission results from the study conducted by Eastern Research Group (ERG) for the City of Fort Worth (2011) using the same method in the Barnett on pads with low or no condensate production. The measured VOC emissions were either lower or not significantly different from the results of studies of uncontrolled emissions from condensate tanks measured by routing all emissions through a single port monitored by a flow measurement device for 24 hr. VOC and HAP concentrations measured remotely using the U.S. Environmental Protection Agency (EPA) Other Test Method (OTM) 33A in the DJ Basin were not significantly different from the on-site measurements, although significant differences between basins were observed. Implications: VOC and HAP emissions from upstream production operations are important due to their potential impact on regional ozone levels and proximate populations. This study provides information on the sources and variability of VOC and HAP emissions from production pads as well as a comparison between different measurement techniques and laboratory analysis protocols. On-site and remote measurements of VOC and HAP emissions from oil and gas production pads indicate that measurable emissions can occur despite the presence of control measures, often as a result of leaking thief hatch seals on condensate tanks. Furthermore, results from the remote measurement method OTM 33A indicate that it can be used effectively as an inspection technique for identifying oil and gas well pads with large fugitive emissions.

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.

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.