Landfills are considered the third largest source of anthropogenic methane emissions in the U.S. and there is considerable interest in estimating emissions from individual landfills. Collection efficiency (CE) or methane collection index (MCI) is used in models to estimate emissions. The objective of this review is to critically analyze literature describing measured CEs and MCIs. Reported values ranged from 14 to 95% for intermediate covers and 53-100% for final covers. Many factors contribute to the ranges including: covers were classified as intermediate or final which is overly simplistic; variability in operational factors (e.g., well coverage, maintenance quality); waste characteristics such as age, composition, and mass in place which influence methane generation and likely collection; and uncertainty in emissions measurements and sometimes collected methane. A desired outcome of this review was to recommend values or ranges for intermediate and final covers that could be used in methane emissions models as applied to U.S. landfills. Such a recommendation is difficult considering the ranges reported in the literature and numerous site-specific factors that influence methane collection. Ultimately, each reported measurement is valid for a specific landfill at a specific time. Models that relate cover type and operational variables to MCI would best support estimation of a site-specific MCI, but such models are not available. Based on this review, the authors do not recommend a specific value for the MCI for an intermediate or final cover but rather expect the operator to select a value considering factors applicable to their landfill and the information presented here.

Lithium-ion batteries (LiBs) are widely used in electronic devices and renewable energy systems. Fluorochemicals are essential components of LiBs, as a component of electrolytes, electrodes, and coatings. However, there are concerns about the environmental release of fluorochemicals, especially within landfills after disposal, due to the fact that landfill leachate is typically treated in facilities not designed to attenuate fluorochemicals. We have evaluated the occurrence of fluorochemical compounds in commercial LiBs and fluoropolymer binders and the release of LiB-derived fluorochemicals in simulated municipal solid waste (MSW) leaching experiments. Our survey of 19 LiBs found per- and polyfluoroalkyl substances (PFAS) including bis(perfluoroalkyl)sulfonimide (bis-FASI, up to 36 mg) and inorganic fluorochemicals such as hexafluorophosphate (PF6-, up to 1.4 g) and bis(fluorosulfinyl)imide (bis-FSI, up to 250 mg). PFAS were also measured in fluoropolymer binders in the range of 2-2000 ng/g. Nontargeted analysis resulted in detection of diverse fluorinated sulfonimides and organic phosphofluoridates in batteries as well as 6 novel PFAS in fluoropolymer binders. Analysis of MSW landfill leachates indicated the presence of LiB-derived fluorochemicals up to 76 μg/L. Simulated MSW leaching experiments showed that LiBs released PFAS (up to 100 mg/L) and inorganic fluorochemicals (up to 1.4 g/L) into the landfill leachate over a period of 220 days. Furthermore, PF6- and bis-FSI transformed in landfill leachate to form organic phosphofluoridates and novel amino sulfonyl fluorosulfanomides. This is the first report of PFAS and fluorochemical release from LiBs and transformation under landfill leaching conditions.

Estimates of annual per- and polyfluoroalkyl substances (PFAS) emissions from landfill gas (LFG) using data from a nationwide sampling campaign have not been reported. The objective of this study was to characterize volatile PFAS in LFG and to estimate the annual mass of volatile PFAS released from US landfills. LFG samples were collected from 30 landfills in 17 states represented by different annual precipitation regions. PFAS concentrations varied by orders of magnitude, with a median concentration of 19,000 ng/m3. Fluorotelomer alcohols, 6:2 and 8:2 FTOH, are the dominant PFAS in LFG, accounting for more than 95% of the total PFAS concentration. Minor components such as fluorotelomer olefins (FTOs) are also present, with concentrations ranging from 0-28,000 ng/m3 and a median of 316 ng/m3. The variability in PFAS concentrations was influenced by precipitation, as well as temporal and site-specific factors. By coupling the median concentration of PFAS with an estimate of US LFG emissions, it is estimated that 836 kg/yr of volatile PFAS are emitted from US landfills in uncollected gas with a 95% confidence interval (2.5% to 97.5% of the distribution) of 15-5,590 kg/yr. This estimate is comparable to ∼600 kg of PFAS released annually into landfill leachate.

The presence of per- and polyfluoroalkyl substances (PFAS) in both municipal solid waste (MSW) landfill leachate and in domestic wastewater is well documented. Landfill leachate is commonly treated at wastewater treatment plants (WWTPs), but most WWTPs do not effectively remove PFAS prior to discharge. The objectives of this research were to (1) evaluate the significance of landfill leachate as a source of PFAS to WWTPs and ultimately surface water in North Carolina (NC) and (2) estimate leachate generation and PFAS release from construction and demolition (C&D) waste landfills in NC. Leachate from 15 MSW and 5 C&D waste landfills as well as influents and effluents from 31 WWTPs were sampled. PFAS mass flows from NC MSW landfills, C&D landfills, and WWTP effluents are estimated at 2.3, 5.1, and 320 kg PFAS/year, respectively. Leachate is generally a small contributor to PFAS mass flows to WWTPs. However, for the case of a large landfill (1 standard deviation above the mean) in a region of the U.S. with >51 cm of annual rain, sending leachate to a small WWTP (3800 m(3)/d), the summed PFAS loading from leachate and domestic wastewater are comparable. As every WWTP influent is unique, scrutiny of PFAS-containing streams other than domestic wastewater (e.g., industrial wastewater, landfill leachate) is warranted.

The accumulation of municipal solid waste (MSW) continues to rise due to burgeoning population, rapid global urbanization and economic growth, intensifying ecological concerns associated with landfills and greenhouse gas (GHG) emissions. Over the past 2 decades, global waste generation has surged by 50%, with one-third remaining uncollected and about 70% sent to landfills. This review examines the critical role of integrating emerging technologies, such as advanced sensors and artificial intelligence (AI), into end-to-end MSW management to alleviate landfill burdens. The suitability of various AI tools for different stages of MSW management is assessed, alongside the deployment of advanced sensors including hyperspectral cameras, computer vision systems, and internet of things (IoT) devices for material identification. Applications of genetic algorithms and reinforcement learning for optimizing collection routes, reducing costs, and lowering emissions are highlighted. Life cycle assessment (LCA) across all stages of MSW management is also reviewed, along with future trends in leveraging generative AI, natural language processing (NLP), and agent-based AI systems to analyze waste generation patterns and public sentiment. Efficient collection and handling can be enhanced through route optimization with geographic information systems and real-time bin-level monitoring. Furthermore, sensor-embedded, real-time object detection systems paired with robotics enable material characterization and automated sorting, thereby lowering costs and diverting waste from landfills into value-added products for diverse industrial sectors including packaging, chemicals, textiles, metals and glass, transportation, and electronics industries. Without intervention, global waste is projected to reach 4.54 billion tons by 2050, contributing direct economic costs of $400 billion and roughly 2.38 billion tons of CO2-equivalent emissions annually. This review demonstrates how AI-driven, end-to-end solutions for MSW management can mitigate economic and environmental challenges, while directly supporting the United Nations Sustainable Development (UNDP) goals related to innovation and infrastructure (SDG 9), sustainable cities (SDG 11), responsible consumption and production (SDG 12), and climate action (SDG 13).

Cellulose fibers are an abundant material that is well known for its biodegradability. Various forms of cellulose, such as cotton, paper pulp fibers, and microcrystalline cellulose can be regarded as benchmarks for biodegradability, when comparing other materials. However, as revealed by the literature, broad ranges of time and extent of biodegradation have been reported for cellulose. These large ranges can be attributed not only to environmental factors but also to the presence of lignin, the degree and perfection of crystallinity, the size and density of the physical specimens, and chemical modifications to the cellulose, if any. Studies also have shown differences in biodegradability associated with the selection of test methods. Although cellulose is subject to well-known enzyme-promoted mechanisms of biodegradation, the evolution of plant materials has favored development of some resistance to decay, i.e. recalcitrance. Cellulosic materials are clearly less biodegradable than starch. However, they are more biodegradable than various synthetic or bio-based plastics, as well as some cellulose derivatives, which persist in ocean water or soils for very long periods. This review indicates that cellulose biodegradability, while generally rapid and natural, has a rate and extent that depends on a complex and sometimes subtle set of environmental and chemical factors.

Sustainable aviation fuels (SAF) production from cellulosic paper fractions of municipal solid waste (MSW) destined for landfills has strong potential to advance environmental, social, and economic sustainability across the aviation and waste sectors. This study proposes an artificial intelligence-enabled material recovery facility (AI-MRF) design to efficiently characterize, separate, process, and convert recovered paper waste from MSW into intermediate chemicals and SAF. The AI-MRF, designed to process 233,091 metric tons of MSW annually, integrates smart manufacturing technologies including AI, visual and hyperspectral imaging, multi-sensor data, and traditional sorting systems. Well-characterized and sorted cellulosic paper waste was utilized for chemical and fuel production scenarios, while clean plastics, metals, and glass were considered for recycling. Conversion of paper waste into intermediate sugars achieved a net present value (NPV) of up to $67 million. For sugar-toSAF production scenarios, the minimum fuel selling price (MFSP) was calculated at $6.11 per gasoline gallon equivalent (GGE) when excluding recyclable revenue, and $4.03 per GGE when halving recyclable revenue. The MFSP was further reduced to $1.96 per GGE when accounting for SAF sales and recyclables. Nationally, this approach could yield about 2 billion GGE of hydrocarbon fuel annually from available MSW in the United States.

Biodegradable plastics are often considered to exhibit superior environmental performance compared to conventional recalcitrant plastics. Here, we assess the greenhouse gas (GHG) emissions of selected biodegradable and recalcitrant plastics made from both fossil and biogenic carbon (C) as disposed in a national average U.S. landfill. This average landfill incorporates consideration of size, precipitation, landfill gas management, and gas collection installation schedule. The GHG emissions of an 80% biodegradable polycaprolactone (PCL _f ) made from fossil C and a 2% biodegradable poly(butylene succinate) (PBS _b ) made from biogenic C were evaluated to represent the range of anaerobic biodegradabilities. The 2% biodegradable PBS _b has lower GHG emissions than the 80% biodegradable PCL _f in the national average landfill. In the best case, which includes aggressive gas collection, conversion of gas to energy, and disposal in a large landfill, the PCL _f results in 2423 kg CO _2 e/mt, which is well above PBS _b (−1956 kg CO _2 e/mt), a hypothetical biogenic and 80% biodegradable PCL _b (4739 kg CO _2 e/mt), and recalcitrant fossil plastic (0 kg CO _2 e/mt). From a disposal perspective, a recalcitrant biogenic plastic is optimal given the long-term storage of carbon. This study informs the direction of materials research to develop materials that minimize their overall environmental footprint at end-of-life.

A key question in anaerobic microbial ecology is how microbial communities develop over different stages of waste decomposition and whether these changes are specific to waste types. We destructively sampled over time 26 replicate bioreactors cultivated on fruit/vegetable waste (FVW) and meat waste (MW) based on pre-defined waste components and composition. To characterize community shifts, we examined 16S rRNA genes from both the leachate and solid fractions of the waste. Waste decomposition occurred faster in FVW than MW, as accumulation of ammonia in MW reactors led to inhibition of methanogenesis. We identified population succession during different stages of waste decomposition and linked specific populations to different waste types. Community analyses revealed underrepresentation of methanogens in the leachate fractions, emphasizing the importance of consistent and representative sampling when characterizing microbial communities in solid waste.

Recovery of plastics may need to move beyond traditional mechanical methods and adopt emerging recycling processes including dissolution/precipitation, solvolysis, and pyrolysis. We investigate the costs and climate impacts of optimal solid waste management (SWM) strategies when deploying emerging recycling processes. Introducing a mix of emerging recycling technologies can reduce SWM system costs, increase plastic recycling rates, and potentially help SWM systems achieve net reductions in life cycle emissions. Recycling programs that rely solely on traditional mechanical recycling incur higher system costs, but can achieve the lowest life cycle emissions, regardless of whether the rejected plastic streams are landfilled or treated in waste-to-energy. In a future with increased recycling, SWM systems that utilize fully commercialized dissolution/precipitation and chemical recycling can further improve the cost advantage and the emission reduction potential. The sensitivity analysis demonstrates that enhancing waste collection and refining emerging recycling technologies can considerably increase the economic and environmental performance of SWM.

Per- and polyfluoroalkyl substances (PFAS) have been detected in plant fiber-based food packaging and most such packaging is disposed in landfills. The objective of this research was to evaluate the release of volatile PFAS to the gas-phase from PFAS-containing, single-use food packaging materials and from municipal solid waste (MSW) during anaerobic decomposition under simulated landfill conditions. After screening 46 materials for total F and 6:2 fluorotelomer alcohol (FTOH), packaging materials were classified as high or low F. High F materials included microwavable popcorn bags, natural plates, compostable bowls, biodegradable boxes, bagasse containers and eco-friendly plates, while the low F materials tested were paper plates, eco-friendly food trays and poly coated freezer paper. Summed PFAS release from the high F materials was 62-800 ng PFAS/g sample and 6:2 FTOH comprised 96.8-99.9% of the summed PFAS. The low F materials and MSW released 0.1-0.4 ng summed PFAS/g sample and 7:2-secondary (s) FTOH was the dominant volatile PFAS. PFAS were generally released early in the 123-285-day decomposition cycle, suggesting that some PFAS will be released prior to the installation of landfill gas collection systems. Nonetheless, PFAS have been reported in collected landfill gas, indicating that release occurs over many years.

Models that describe heat accumulation in landfills show that ash hydration and carbonation can be a significant source of heat. Ash contains CaO and Ca(OH)(2) as well as other oxides and hydroxides that undergo hydration and carbonation reactions. However, there is no data on heat evolution from ash under landfill conditions to parametrize heat accumulation models. The objective of this study was to develop and demonstrate a quasi-adiabatic reactor to measure heat generation from ash under landfill conditions. The reactor method was validated with CaO and Ca(OH)(2) and then demonstrated for 6 coal ash and 6 municipal solid waste (MSW) ash samples. Heat recovery in the reactors was similar to 104.5% and 106% of theoretical for CaO hydration and Ca(OH)(2) carbonation, respectively. The heat generation potential of the ashes varied from 11 to 583 and 78 to 297 J g(-1) for coal and MSW, respectively. The wide range demonstrated the uniqueness of each ash. Using the measured rate and extent of heat generation, model simulations showed an insignificant effect on landfill temperatures at 10% ash for most samples, while at 20% ash, two of the coal ashes resulted in predicted temperature increases of 51 and 71 degrees C relative to the burial of MSW only.

This study elucidates per- and polyfluoroalkyl substance (PFAS) fingerprints for specific PFAS source types. Ninety-two samples were collected from aqueous film-forming foam impacted groundwater (AFFF-GW), landfill leachate, biosolids leachate, municipal wastewater treatment plant effluent (WWTP), and wastewater effluent from the pulp and paper and power generation industries. High-resolution mass spectrometry operated with electrospray ionization in negative mode was used to quantify up to 50 target PFASs and screen and semi-quantify up to 2,266 suspect PFASs in each sample. Machine learning classifiers were used to identify PFASs that were diagnostic of each source type. Four C5-C7 perfluoroalkyl acids and one suspect PFAS (trihydrogen-substituted fluoroethernonanoic acid) were diagnostic of AFFF-GW. Two target PFASs (5:3 and 6:2 fluorotelomer carboxylic acids) and two suspect PFASs (4:2 fluorotelomer-thia-acetic acid and N-methylperfluoropropane sulfonamido acetic acid) were diagnostic of landfill leachate. Biosolids leachates were best classified along with landfill leachates and N-methyl and N-ethyl perfluorooctane sulfonamido acetic acid assisted in that classification. WWTP, pulp and paper, and power generation samples contained few target PFASs, but fipronil (a fluorinated insecticide) was diagnostic of WWTP samples. Our results provide PFAS fingerprints for known sources and identify target and suspect PFASs that can be used for source allocation.

Historically, ash from coal combustion has been disposed of in ponds that were not designed with engineered containment systems. As a result of regulatory changes, it is estimated that coal combustion residuals (CCRs) from hundreds of unlined ponds will have to be excavated and disposed of in new lined landfills or the existing CCR ponds will have to been closed in-place with an engineered final cover system. The excavated or in-place CCR may contain vegetative matter that has the potential to decompose to CH4 and CO2. The objective of this study was to demonstrate a framework to assess the need for a gas collection system to accommodate the disposal of a mixture of CCR and vegetation in a lined landfill. Methane generation rates and yields for vegetative matter mixed with CCR were measured in biochemical methane potential and specific methane activity tests at 15, 20, and 37 degrees C. The data were then used to parameterize a methane generation model to estimate the gas flux at the landfill surface for a series of hypothetical disposal scenarios. Results showed that the specific decay rate constant (k) ranged from 0.00037 to 0.00872 yr-1, while the methane yield (L0) ranged from 84 to 120 mL CH4/dry g. Temperature was the most important determinant of the decomposition behavior. Simulations of gas flux for several disposal scenarios showed that the modeled flux from the decomposition of vegetation was below the CH4 and CO2 transmission rates reported for a geomembrane liner final cover system, suggesting that an active gas collection will not be necessary under the modeled disposal conditions.

There have been reports of North American municipal solid waste landfills exhibiting temperatures in excess of 80 degree celsius. Although mathematical models have been developed to predict heat generation and accumulation in landfills, predictions have not been compared to temperature data from a full-scale landfill that receives heat generating ash. The objectives of this study were to apply a three-dimensional finite element model to a southeastern U.S. landfill and to compare model predictions with field data. The model incorporates gas-liquid-heat reactive transfer with exothermic biological reactions and hydration and carbonation of ash. An 8-step reconstruction approach digitalized the landfill geometry for the incorporation of a site-specific waste disposal strategy and initial and boundary conditions. The model was calibrated to adjust laboratory-measured rates of ash hydration and carbonation to the field rates. Once calibrated, the results showed a total root-mean-square error of 11 degree celsius across 40 measurements in five temperature probes. The model predicted an elevated temperature zone in a region of the landfill between two temperature probes, and the predicted temperatures were consistent with the temperature trends in gas collection wells. The model is sensitive to the CaO content of ash, highlighting the importance of understanding the ash composition prior to disposal.

Landfills receive over half of the municipal solid waste generated in the U.S. Wastes in landfills include consumer products, some of which are known to contain of per-and polyfluoroalkyl substances (PFAS). Although the occurrence of nonvolatile (ionic) PFAS in landfill leachate is established and volatile (neutral) PFAS are found in ambient air near landfills, the neutral PFAS composition of landfill gas (LFG) collected in situ from landfills is unknown. A thermal desorption-gas chromatog-raphy-mass spectrometry (TD-GC-MS) sampling and analysis approach was optimized for the quantification of 25 target neutral PFAS, including fluorotelomer alcohols (FTOHs) and five other PFAS classes, in landfill from a gas well or header pipe. Optimized LFG sampling parameters included the use of an explosion-proof pump, a 100 mL/min flow rate through a sorbent tube, and a LFG volume of 350 mL. The method was applied to LFG samples collected from southeastern U.S. landfills for method demonstration. Fluorotelomer alcohols were found at the highest levels, ranging from 830,000-4,900,000 pg/m3, which is approximately 2 orders of magnitude greater than FTOH levels reported in ambient air collected near landfills.

The anaerobic digestion of food waste can yield valuable volatile fatty acids (VFAs), especially when methane (CH4) production is inhibited. Selecting an inoculum with lower methanogenic populations may help reduce CH4 production and improve VFA accumulation. In this study, we investigated VFA and CH4 production in short-term anaerobic batch bioreactors as a function of three inocula compositions derived from a full-scale wastewater treatment facility: (1) anaerobic sludge (AnS), (2) thickened waste activated sludge (TWAS), and (3) TWAS with AnS. The highest VFA concentration (6.62 +/- 0.08 g/L) and the lowest total CH4 volume (296 mL) were measured with TWAS only. In contrast, the highest CH4 volume (625 +/- 3 mL) was measured in the TWAS + AnS, likely because the AnS was well adapted to digesting TWAS. 16S rDNA sequencing showed that TWAS alone had the lowest relative abundance of methanogens at the start and end of the incubations. The addition of TWAS significantly changed the initial community diversity. These insights suggest that TWAS improves VFA accumulation by providing a microbial community that is more diverse and lower in methanogen abundance relative to AnS. These findings will help guide the selection of inoculation strategies that promote VFA accumulation in anaerobic digesters.

Facemasks are important tools for fighting against disease spread, including Covid-19 and its variants, and some may be treated with per- and polyfluoroalkyl substances (PFAS). Nine facemasks over a range of prices were analyzed for total fluorine and PFAS. The PFAS compositions of the masks were then used to estimate exposure and the mass of PFAS discharged to landfill leachate. Fluorine from PFAS accounted only for a small fraction of total fluorine. Homologous series of linear perfluoroalkyl carboxylates and the 6:2 fluorotelomer alcohol indicated a fluorotelomer origin. Inhalation was estimated to be the dominant exposure route (40%-50%), followed by incidental ingestion (15%-40%) and dermal (11%-20%). Exposure and risk estimates were higher for children than adults, and high physical activity substantially increased inhalation exposure. These preliminary findings indicate that wearing masks treated with high levels of PFAS for extended periods of time can be a notable source of exposure and have the potential to pose a health risk. Despite modeled annual disposal of ~29-91 billion masks, and an assuming 100% leaching of individual PFAS into landfill leachate, mask disposal would contribute only an additional 6% of annual PFAS mass loads and less than 11 kg of PFAS discharged to U.S. wastewater.

There have been several reports of landfills exhibiting temperatures as high as 80 to 100 ?C. This observation has motivated researchers to understand the causes of the elevated temperatures and to develop predictive models of landfill temperature. The objective of this research was to characterize the methanogenic activity of microbial communities that were derived from landfill samples excavated from a section of a landfill exhibiting gas well temperatures above 55 ?C. Specific objectives were to: (1) determine the upper temperature limit for methane production; (2) evaluate the kinetics of methane generation when landfill-derived microcosms are incubated above and below their excavation temperature and derive a temperature inhibition function; and (3) evaluate microbial community shifts in response to temperature perturbations. Landfill microcosms were derived from 57 excavated landfill samples and incubated within ?2.5 ?C of their excavation temperature between 42.5 ?C and 87.5 ?C. Results showed an optimum temperature for methane generation of-57 ?C and a 95% reduction in methane yield at-72 ?C. When select cultures were perturbed between 5 ?C below and 15 ?C above their in-situ temperature, both the rate and maximum methane production decreased as incubation temperature increased. Microbial community characterization using 16S rRNA amplicon sequencing suggests that thermophilic methanogenic activity can be attributed to methanogens of the genus Methanothermobacter. This study demonstrated that from a microbiological standpoint, landfills may maintain active methanogenic processes while experiencing temperatures in the thermophilic regime (<72 ?C). ? 2021 Elsevier Ltd. All rights reserved.