Translating landfill methane generation parameters among first-order decay models

Turbine system vs engine generator in the production of energy by methane in the pacific of Mexico: a technical, economic, and environmental analysis

This paper aims to analyze the potential of energy production using methane from organic waste as a sustainable alternative to mitigate the environmental impact of energy generation from fossil fuels and the generation of Municipal Solid Waste (MSW). To carry out the analysis, two technologies were evaluated from technical, economic, and environmental perspectives. The LandGEM model was used to estimate the methane generation potential. The amount of energy produced, along with the respective financial indicators, was also calculated. The results showed that for an average feed of 671,892 tons per year of waste, 6160 ft3/min of CH4 would be generated at a maximum peak in the tenth year, with an annual average of 4735 ft3/min. Additionally, 0.831 million metric tons of CO2 equivalent would be avoided. In terms of power generation, a combined cycle micro-turbine system with an installed capacity of 11.35 MW would be feasible and would yield an Internal Rate of Return (IRR) of 35% and a Net Present Value (NPV) of $11,608,006 USD. For an engine-generator system, it was not possible to verify profitability due to a significant increase in capital and O&M costs. These results are intended to provide reference information to assist in the decision-making process related to the implementation of projects aligned with the Sustainable Development Goals within the framework of the 2030 Agenda.

Greenhouse gas reporting data improves understanding of regional climate impact on landfill methane production and collection

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 (L_c). These sites account for approximately 9% of all landfills required to report GHG emissions to the US EPA annually. The mean methane collection potential (L_c) 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).

Temporally-differentiated biogenic carbon accounting of wood building product life cycles

Although standards have identified temporary carbon storage as an important element to consider in wood product LCAs, there has been no consensus on a methodology for its accounting. This work aims to improve the accounting of carbon storage and fluxes in long-life wood products in LCA. Biogenic carbon from harvested roundwood logs were tracked using the Carbon Budget Model Framework for Harvested Wood Products (CBMF-HWP). Carbon flows through wood product manufacturing, building life and end-of-life phases, and carbon stocks and fluxes from harvest to the atmosphere were estimated. To cover the products commonly used in the Canadian building industry, a range of softwood products types, provinces and territories and building lifetimes were considered. In addition, policy scenarios were considered in order to model the effects of dynamic parameters through time as a policy target is reached. Most wood products have similar emissions profiles, though cross-laminated timber has higher sawmill emissions and oriented-strand board has higher initial post-demolition emissions. The region of construction is also predictive of the initial post-demolition emissions. Higher recycling rates shift materials from landfills into subsequent product systems, thus avoiding landfill emissions. Landfill decay rates are affected by climate and results in a large range of landfill emissions. The degree of postponement of end-of-life emissions is highly dependent upon the wood product type, region and building lifespan parameters. This work develops biogenic carbon profiles that allows for modelling dynamic cradle-to-grave LCAs of Canadian wood products.

Low fraction of methane in landfill gas emissions in an industrial waste landfill containing incineration ash and gypsum board waste under anaerobic conditions

The behaviour of carbon dioxide (CO₂) and methane (CH₄) emissions at the surface and below the soil cover in an industrial waste landfill under anaerobic operating conditions was evaluated for six years. This landfill contained gypsum board waste and incineration ash - a practice currently allowed because of a change in Japanese regulations. The CO₂ and CH₄ fluxes decreased throughout the six years of the survey. Almost all of the survey points exhibited fractions of CH₄ in landfill gas emissions of <0.5 (mean values: 0.0-0.1 [surface], 0.0-0.3 [subsurface]) under anaerobic conditions. In addition, a relatively high first-order reaction rate constant for the landfill gas emissions (0.3 year^-1) was observed. The landfill leachate showed a relatively high sulphate ion (SO₄ ^2-) concentration, although other environmental conditions, such as the pH, oxidation-reduction potential and ammonium concentration, were not at levels that could have inhibited CH₄ production. These findings suggest that the low fractions could have been related to the lower amounts of CH₄ generation caused by competition between methanogens and sulphate-reducing bacteria (SRB). Therefore, SRB could play a major role in the degradation of organic carbon in the landfill.

Scaling up laboratory column testing results to predict coupled methane generation and biological settlement in full-scale municipal solid waste landfills

Prediction of methane (CH₄) generation and settlement of biodegrading municipal solid waste (MSW) is of primary interest to landfills aiming at biogas recovery for energy generation and MSW stabilization. We investigate these two concurring processes using datasets from 35 laboratory column tests and 8 pilot- and full-scale landfill cells available in the literature. We fit the datasets using three CH₄ generation models, i.e., conventional first-order decay (FOD) model, coupled FOD model, and coupled Gompertz model. The latter two models are proposed in this study which couple CH₄ generation with biological settlement strain (ε_B) instead of elapsed time. Each model requires only four to five input parameters which can be reasonably estimated a priori based on the initial conditions of the MSW and landfills. The performances of the models are compared using jackknife resampling approach and normalized root-mean-square error (NRMSE) values. The coupled Gompertz model results in on average 50% lower NRMSE when predicting the time-dependent CH₄ generation in all the datasets compared to the other two models. Thus, we demonstrate that CH₄ generation from biodegrading MSW in landfills can be better predicted using the corresponding ε_B than the elapsed time.

Modeling landfill gas potential and potential energy recovery from Thohoyandou landfill site, South Africa

The increase in solid waste generation has been a major contributor to the amount of Greenhouse gases (GHGs) present in the atmosphere. To some extent, a great chunk of these GHGs in the atmosphere is from landfill. This study assesses two theoretical models (LandGEM and Afvalzorg models) to estimate the amount of landfill gas (LFG) emitted from Thohoyandou landfill site. Also, the LFGcost Web model was used to estimate the cost and benefits of the implementation of an LFG utilization technology. The Thohoyandou landfill started operations in the year 2005 and it is proposed to reach its peak at approximately in the year 2026. The LandGEM calculates the mass of landfill gas emission using methane generation capacity, mass of deposited waste, methane generation constant and methane generation rate. Meanwhile, the Afvalzorg model determines the LFG emissions using the Methane correction factor, yearly waste mass disposal, waste composition, Degradation Organic Carbon, methane generation rate constant, LFG recovery efficiency. The study findings indicate that the methane (CH₄) and carbon dioxide (CO₂) emitted from the landfill estimated from LandGEM will peak in the year 2026 with values of 3517 Mg/year and 9649 Mg/year, respectively. Results from the Afvalzorg model show that CH₄ emission will peak in the year 2026 (3336 Mg/year). The LandGEM model showed that the total LFG, CH₄ and CO₂ emitted from the landfill between 2005 and 2040 are 293239.3 Mg/year, 78325.7 Mg/year and 214908.6 Mg/year, respectively. The simulation from the Afvalzorg model found that the CH₄ emitted from the years 2005- 2040 is 74302 Mg/year. The implementation of an LFG utilization technology was economically feasible from consideration of the sales of electricity generated and Certified Emission Reductions (CER) (carbon credits).

IMPLICATIONS

The methane (CH₄) and carbon dioxide (CO₂) emitted from the Thohoyandou landfill estimated from LandGEM will peak in the year 2026 at 3517 Mg/year and 9649 Mg/year, respectively. The Afvalzorg model shows that CH₄ emission will peak in the year 2026 (3336 Mg/year). The LandGEM model showed that total LFG, CH₄ and CO₂ emitted from the landfill between 2005 and 2040 (Mg/year) are 293,239, 78,325 and 214,908, respectively. The simulation from the Afvalzorg model found that CH₄ emitted from years 2005- 2040 is 74,302 Mg/year. Therefore, implementation of LFG utilization is economically feasible from sales of electricity generated and Certified Emission Reductions.

The environmental impacts of municipal solid waste landfills in Europe: A life cycle assessment of proper reference cases to support decision making

In Europe, 23% of the generated municipal solid waste (MSW) was landfilled in 2017. Despite the landfill targets which define waste and landfill requirements, there is still high variability in the waste management performance between EU Member States. Aim of the study was to give an overview of the variability of environmental impacts of MSW sanitary landfills in Europe in relation to the different levels of implementation of the requirements. Life cycle assessment (LCA) was adopted as tool to define the impacts of the different landfill conditions over a 100-year period. Based on previous studies, consistent methodological choices were made to allow comparability of the results. Four reference cases were defined based on average bulk MSW compositions to represent the European conditions, with L₀ values of 18, 61, 90 and 138 [m³ CH₄/t waste]. Furthermore, multiple scenario analysis was used to increase the relevance of the assessment and address the variability of site-specific factors, such as waste composition, climatic conditions and landfill management, which influence the impacts of landfills. Results of the study showed the range of potential impacts in Europe in relation to the variation of influencing factors, with values for climate change ranging from 124 to 841 kg CO2 eq., and with environmental savings obtained for categories such as ecotoxicity and human toxicity for scenarios with landfill gas - to - energy (LFGTE) solutions. The results emphasized the dependence of landfill impacts on waste composition, but also on the LFG treatment and climatic conditions. The outcome of the study also highlight how low amounts of biodegradable fractions reduce the impacts of landfills, as well as their variability in relation to leachate production rates or LFG treatment solutions. Therefore the overall results support the current targets and requirements reported in the Waste Directive 2008/98/EC, Circular Economy package and Landfill Directive 1999/31/EC.

Assessment of Power Generation Using Biogas from Landfills in an Equatorial Tropical Context

This work evaluates the biogas production potential of the Ceibales landfill for feeding a power plant in the southern region of Ecuador. Biogas production is estimated through mathematical models that consider energy generation and technologies available to supply electricity plants. Characteristic landfill data are accounted for to analyze and develop these mathematical models. Once the generation capability of each source is identified, a decision can be made on the most suitable electricity generation technology. A local model (Ecuadorian model) is applied to calculate the potential of biogas and is compared with other models commonly used for evaluating this type of project. This type of renewable energy is attractive because it produces electricity from waste; however, it is not an attractive option unless its application is encouraged, as hydro has been encouraged through the investment of taxpayer resources. Technologies require a boost to become profitable, and even more so if they compete with traditional technologies.

Landfill reactions to society actions: The case of local and global air pollutants of Cerro Patacón in Panama

This paper studies landfill emissions and the related environmental and health risks in Panama City, with the aim to sensitize the population about the harmful effects of irresponsible resource consumption and non-deliberate solid waste generation that it is disposed of in an uncontrolled manner in landfills. Empirical data on Cerro Patacón, Panama City's landfill was obtained to describe the status of municipal waste disposal. Ten known methane generation models were used to estimate the yearly emission rate of methane from the landfill for a 100-year period starting from its inception in 1986. From the models used, the GasSIM model was chosen to estimate emission rates of six long-term hazardous air pollutants. The AERMOD source dispersion model was used to simulate their atmospheric downwind dispersion by levels of concentration over nearby affected communities; results were mapped in Google Earth. The relative contributions by population of the 32 towns making up Panama City to the forecasted waste generation in 2022 and related hazardous air pollutants emission rates from the landfill were assessed. It was found that Cerro Patacón will generate 45% of the countrywide methane generation by 2022; an average of 47 Gg. The solid waste generated by the 1.5 million inhabitants of Panama City impacts the health of ~73,600 inhabitants in nearby communities through the dispersion of hazardous atmospheric pollutants derived from the landfill. The highest emission rates were from hydrogen sulfide and dichloromethane, which can be largely attributed to the waste generated by the communities of Juan Diaz and Tocúmen. The concentration of hydrogen sulfide and benzene was over the reference concentration (uncertainty factor spanning three orders of magnitude) for all communities and years simulated. The concentration of vinyl chloride was over the RfC for all communities and years simulated, except in 2018 for 12 communities.

Intergovernmental panel on climate change's landfill methane protocol: Reviewing 20 years of application

The Intergovernmental Panel on Climate Change (IPCC) protocol for predicting national methane emission inventories from landfills was published 22 years ago in the 1996 Revised Guidelines. There currently exists a broad dataset to review landfill parameters and reported values and their appropriateness in use and application in a range of site-specific, regional, and national estimates. Degradable organic carbon (DOC) content was found to range from 0.0105 to 0.65 g C/g waste, with an average of 0.166 g C/g waste. The fraction of DOC that would anaerobically degrade (DOC _f) was reported to range from 50-83%, whereas higher and lower values have been experimentally determined for a variety of waste components, such as wood (0-50%) and food waste (50-75%). Where field validation occurred for the methane correction factor, values were substantially lower than defaults. The fraction of methane in anaerobic landfill gas ( F) default of 50% is almost universally applied and is appropriate for cellulosic wastes. The methane generation rate constant ( k) varied widely from 0.01 to 0.51 y^-1, representing half-lives from 1 to 69 years. Methane oxidation (OX) default values of 0 and 10% may be valid, but values greater than 30% have been reported for porous covers at managed sites. The IPCC protocol is a practical tool with uncertainties and limitations that must be addressed when used for purposes other than developing inventories.

Methods for determining the methane generation potential and methane generation rate constant for the FOD model: a review

In the first order decay (FOD) model of landfill methane generation, the methane generation potential ( L₀) and methane generation rate constant ( k) for both bulk municipal solid waste (MSW) and individual waste components have been determined by a variety of approaches throughout various literature. Differences in the determination methods for L₀ and k are related to differences in our understanding of the waste decomposition dynamics. A thorough understanding of the various available methods for determining L₀ and k values is critical for comparative study and the drawing of valid conclusions. The aim of this paper is to review the literature on the available determining methods and the ranges for L₀ and k values of both bulk MSW and individual waste components, while focusing on understanding the decomposition of waste, including the role of lignin. L₀ estimates in the literature are highly variable and have been derived from theoretical stoichiometric calculations, laboratory experiments, or actual field measurements. The lignin concentration in waste is correlated with the fraction of total degradable organic carbon (DOC_f) that will actually anaerobically degrade in the landfill. The k value has been determined by precipitation rates, laboratory simulations, aged-defined waste sample, and model fitting or regression analysis using actual gas data. However, the lignin concentration does not correlate well with the k value, presumably due to the impact of lignin arrangement and structure on cellulose bioavailability and degradation rate. In sum, this review summarizes the literature on the measurement of L₀ and k values, including the dynamics and decomposition of bulk MSW and individual waste components within landfills.

Optimization of first order decay gas generation model parameters for landfills located in cold semi-arid climates

Canada has one of the highest waste generation rates in the world. Because of high land availability, land disposal rates in the province of Saskatchewan are high compared to the rest of the country. In this study, landfill gas data was collected at semi-arid landfills in Regina and Saskatoon, Saskatchewan, and curve fitting was carried out to find optimal k and L_o or DOC values using LandGEM, Afvalzorg Simple, and IPCC first order decay models. Model parameters at each landfill were estimated and compared using default k and L_o or DOC values. Methane generation rates were substantially overestimated using default values (with percentage errors from 55 to 135%). The mean percentage errors for the optimized k and L_o or DOC values ranged from 11.60% to 19.93% at the Regina landfill, and 1.65% to 10.83% at the Saskatoon landfill. Finally, the effect of different iterative methods on the curve fitting process was examined. The residual sum of squares for each model and iterative approaches were similar, with the exception of iterative method 1 for the IPCC model. The default values in these models fail to represent landfills located in cold semi-arid climates. The use of site specific data, provided enough information is available regarding waste mass and composition, can greatly help to improve the accuracy of these first order decay models.