Development and implementation of a screening method to categorise the greenhouse gas mitigation potential of 91 landfills

Nitrogen in landfills: Sources, environmental impacts and novel treatment approaches

Nitrogen (N) accumulation in landfills is a pressing environmental concern due to its diverse sources and significant environmental impacts. However, there is relatively limited attention and research focus on N in landfills as it is overshadowed by other more prominent pollutants. This study comprehensively examines the sources of N in landfills, including food waste contributing to 390 million tons of N annually, industrial discharges, and sewage treatment plant effluents. The environmental impacts of N in landfills are primarily manifested in N2O emissions and leachate with high N concentrations. To address these challenges, this study presents various mitigation and management strategies, including N2O reduction measures and novel NH4+ removal techniques, such as electrochemical technologies, membrane separation processes, algae-based process, and other advanced oxidation processes. However, a more in-depth understanding of the complexities of N cycling in landfills is required, due to the lack of long-term monitoring data and the presence of intricate interactions and feedback mechanisms. To ultimately achieve optimized N management and minimized adverse environmental impacts in landfill settings, future prospects should emphasize advancements in monitoring and modeling technologies, enhanced understanding of microbial ecology, implementation of circular economy principles, application of innovative treatment technologies, and comprehensive landfill design and planning.

Quantifying the impact of urban road traffic on air quality: activity pre-pandemic and during partial and full lockdowns

The impact of partial and full COVID lockdowns in 2020 on vehicle miles traveled (VMT) in Kuwait was estimated using data extracted from the Directions API of Google Maps and a Python script running as a cronjob. This approach was validated by comparing the predictions based on the app to measuring traffic flows for 1 week across four road segments considered in this study. VMT during lockdown periods were compared to VMT for the same calendar weeks before the pandemic. NOx emissions were estimated based on VMT and were used to simulate the spatial patterns of NOx concentrations using an air quality model (AERMOD). Compared to pre-pandemic periods, VMT was reduced by up to 25.5% and 42.6% during the 2-week partial and full lockdown episodes, respectively. The largest reduction in the traffic flow rate occurred during the middle of these 2-week periods, when the traffic flow rate decreased by 35% and 49% during the partial and full lockdown periods, respectively. The AERMOD simulation results predicted a reduction in the average maximum concentration of emissions directly related to VMT across the region by up to 38%, with the maximum concentration shifting to less populous residential areas as a result of the lockdown.

An integrated framework for exploring the tradeoffs between cost-optimized fuel allocation and regional air quality impacts in a water-energy nexus infrastructure

This paper presents an integrated framework in which an air quality dispersion model is combined with an economic dispatch model to address the environmental tradeoffs of a cost-optimized fuel allocation strategy. A unit commitment dispatch model was developed to re-allocate fuel between power generation and desalination plants. Then, an air quality dispersion model was run for a 1-year period to simulate the spatiotemporal transport of pollutants and the possible formation of air pollution hotspots. The results showed that optimizing fuel allocation can reduce the associated fuel cost by as much as 16.5% of the total cost (1.08 billion USD). The optimized fuel allocation approach resulted in reducing the base case emissions of NOx, SO₂, CO, and PM₁₀ by 25%, 4.6%, 3.1%, and 7.6%, respectively. However, the air quality impact of the optimized fuel allocation scheme was not as favorable. The 1-h-averaged maximum concentration of SO₂ increased, and NOx concentrations were slightly above the allowable limits. Although fewer pollutants were emitted over the study period in the optimized fuel allocation case, the variability in how fuel was allocated between power and desalination plants concentrated emissions near residential areas. As a result of this trend, the maximum 1-h concentrations of all pollutants increased, with increases ranging from 1% for CO to 29% for PM₁₀. In addition, the total number of hourly SO₂ concentration violations increased dramatically, leading to additional hotspot areas. Therefore, the effectiveness of any environmental-economic fuel dispatch strategy should be tested based on additional indicators such as the allowable limits of pollutant concentrations and not exclusively the overall emissions of the system. This approach could promote the selection of the most economic fuel dispatch method while simultaneously considering regional air quality impacts.

Methane emissions from Icelandic landfills - A comparison between measured and modelled emissions

This study compares methane (CH₄) emissions from five Icelandic landfills, quantified using tracer gas dispersion to modelled emission rates using the IPCC FOD model. The average CH₄ emission rates measured from the investigated landfills were 475.4 kg CH₄ h^-1 (Álfsnes landfill), 32.5 kg CH₄ h^-1 (Fíflholt), 40.8 kg CH₄ h^-1 (Gufunes), 9.8 kg CH₄ h^-1 (Kirkjuferjuhjáleiga) and 78.4 kg CH₄ h^-1 (Stekkjarvík). At three of the landfills (Álfsnes, Fíflholt and Kirkjuferjuhjáleiga), the modelled emission was higher than the measured emission by factors ranging from 1.1 to 4.8, neglecting any CH₄ oxidation in the cover soils. Even though CH₄ oxidation might play a role at some of the investigated landfills, and thus reduce the gap between modelled and measured emissions, it is likely that the model overestimated CH₄ generation due to uncertainties in input model parameters. Assuming that the measured emissions at the five landfills are representative of all the waste disposed in Iceland from 2007 to 2016, the measured emission should be extrapolated to 817 kg CH₄ h^-1, which is relatively close to the modelled national emission of 936 kg CH₄ h^-1 in 2017. This study showed that the application of the IPCC FOD model at national level is appropriate for estimating landfill CH₄ emissions in Iceland. CH₄ emissions from landfills in Iceland can be reduced by expanding or implementing gas collection or biocover systems for optimised microbial oxidation.

Quantification and control of gaseous emissions from solid waste landfill surfaces

Landfilling is the most common option for solid waste disposal worldwide. Landfill sites can emit significant quantities of greenhouse gases (GHGs; e.g., methane, carbon dioxide, and nitrous oxide) and release toxic and odorous compounds (e.g., sulfides). Due to the complex composition and characteristics of landfill surface gas emissions, the quantification and control of landfill emissions are challenging. This review attempts to comprehensively understand landfill emission quantification and control options by primarily focusing on GHGs and odor compounds. Landfill emission quantification was highlighted by combining different emissions monitoring approaches to improve the quality of landfill emission data. Also, landfill emission control requires a specific approach that targets emission compounds or a systematic approach that reduces overall emissions by combining different control methods since the diverse factors dominate the emissions of various compounds and their transformation. This integrated knowledge of emission quantification and control options for GHGs and odor compounds is beneficial for establishing field monitoring campaigns and incorporating mitigation strategies to quantify and control multiple landfill emissions.

Transport mechanisms and emission of landfill gas through various cover soil configurations in an MSW landfill using a static flux chamber technique

This study evaluated the transport mechanisms and emission rates of landfill gas (LFG) from 200- (vegetated with short grass), 300- (vegetated with short grass), and 450-mm-thick (non-vegetated) interim cover soils within a municipal solid waste landfill. LFG emission and diffusion mechanisms were evaluated using static flux chambers and laboratory-scale diffusion columns. Overall, the greatest CH₄ and CO₂ emissions were consistently observed from the 200-mm-thick cover soil with an average flux rate of 39.2 mg m^-2 h^-1 and 3.07 × 10³ mg m^-2 h^-1, respectively. In addition to CH₄ and CO₂, H₂S migration through a 450-mm interim cover soil was also evaluated. The H₂S emission rate was relatively more uniform at an average of 2.47 × 10^-5 mg m^-2 h^-1. Long-term LFG emission was predicted using an emission model based on a first-order decomposition rate equation and compared with the static flux chamber method. The field-measured CO₂, CH₄ and H₂S emissions were less than the estimated emissions from the emission model, by 22%, 85%, and 91%, respectively. Further, the diffusion coefficients of CH₄, CO₂, and H₂S for the interim cover soils were determined using a laboratory-scale diffusion column test and compared with a three-parameter diffusion model. The measured and estimated diffusion coefficients for the three landfill gases were within the 10% variation limits. Based on these findings, the LFG emission rate varied depending on the physical-chemical properties of the cover soil (e.g., cover thickness, moisture content, compaction ratio, uneven distribution of soil), organic material content and age of buried refuse, and seasonal environmental conditions (such as temperature). Test results showed that fugitive CH₄ emissions can be reduced one fourth by utilizing an appropriate cover soil (300-mm to 450-mm, CL) compared to cases with a thinner cover soil.

A Near-Field Gaussian Plume Inversion Flux Quantification Method, Applied to Unmanned Aerial Vehicle Sampling

The accurate quantification of methane emissions from point sources is required to better quantify emissions for sector-specific reporting and inventory validation. An unmanned aerial vehicle (UAV) serves as a platform to sample plumes near to source. This paper describes a near-field Gaussian plume inversion (NGI) flux technique, adapted for downwind sampling of turbulent plumes, by fitting a plume model to measured flux density in three spatial dimensions. The method was refined and tested using sample data acquired from eight UAV flights, which measured a controlled release of methane gas. Sampling was conducted to a maximum height of 31 m (i.e. above the maximum height of the emission plumes). The method applies a flux inversion to plumes sampled near point sources. To test the method, a series of random walk sampling simulations were used to derive an NGI upper uncertainty bound by quantifying systematic flux bias due to a limited spatial sampling extent typical for short-duration small UAV flights (less than 30 min). The development of the NGI method enables its future use to quantify methane emissions for point sources, facilitating future assessments of emissions from specific source-types and source areas. This allows for atmospheric measurement-based fluxes to be derived using downwind UAV sampling for relatively rapid flux analysis, without the need for access to difficult-to-reach areas.

Methodologies for measuring fugitive methane emissions from landfills - A review

Fugitive methane (CH₄) emissions from landfills are significant global sources of greenhouse gases emitted into the atmosphere; thus, reducing them would be a beneficial way of overall greenhouse gas emissions mitigation. In Europe, landfill owners have to report their annual CH₄ emissions, so direct measurements are therefore important for (1) evaluating and improving currently applied CH₄ emission models, (2) reporting annual CH₄ emissions and (3) quantifying CH₄ mitigation initiatives. This paper aims at providing an overview of currently available methodologies used to measure fugitive CH₄ emissions escaping from landfills. The measurement methodologies are described briefly, and the advantages and limitations of the different techniques are discussed with reference to published literature on the subject. Examples are given of individual published studies using different methodologies and studies comparing three or more methodologies. This review suggests that accurate, whole-site CH₄ emission quantifications are best done using methods measuring downwind of the landfill, such as tracer gas dispersion and differential absorption LiDAR (DIAL). Combining aerial CH₄ concentration measurements from aircraft or unmanned aerial vehicles with wind field measurements offers a great future potential for improved and cost-efficient integrated landfill CH₄ emission quantification. However, these methods are difficult to apply for longer time periods, so in order to measure temporal CH₄ emission changes, e.g. due to the effect of changes in atmospheric conditions (pressure, wind and precipitation), a measurement method that is able to measure continuously is required. Such a method could be eddy covariance or static mass balance, although these procedures are challenged by topography and inhomogeneous spatial emission patterns, and as such they can underestimate emissions significantly. Surface flux chambers have been used widely, but they are likely to underestimate emission rates, due to the heterogeneous nature of most landfill covers resulting in sporadic and localised CH₄ emission hotspots being the dominant emission routes. Furthermore, emissions from wells, vents, etc. are not captured by surface flux chambers. The significance of any underestimation depends highly on the configuration of individual landfills, their size and emission patterns.

Guidelines for landfill gas emission monitoring using the tracer gas dispersion method

Landfill gas often containing 50-60% methane, is generated on waste disposal sites receiving organic waste. Regulation requires that this gas is managed in order to reduce emissions, but very few suggestions exist as to how management activities are monitored, what should be set up to ensure this management and how criteria should be developed for when monitoring activities are terminated. Methane emission monitoring procedures are suggested, based on a robust method for measuring total leakage from the site; additionally, quantitative measures, to determine the efficiency of the performed emission mitigation, are defined. The tracer gas dispersion measuring technique is suggested as the core emission measurement methodology in monitoring plans for methane emissions from landfills and a guideline for best practice measurement performance is presented. A minimum methane mitigation efficiency of 80% is suggested. Finally, several principles are presented on how criteria can be developed for when a monitoring program can be terminated. Three of the suggested principles result in comparable completion criteria of about 1-3 kg CH₄/h for a small landfill (an area of 4 ha).