Gas Collection Efficiency Research Articles

Dynamic Oxygen Collection Efficiency: Unraveling the Effects of Perovskites on Carbon Corrosion As Composite Catalysts for Oxygen Electrode

Introduction The composite catalyst comprising perovskite and carbon has been extensively studied as a catalyst for the oxygen evolution reaction (OER) at the oxygen electrode in alkaline media. However, the competitive corrosion of carbon under harsh OER potential necessitates additional caution when determining OER activity from the overall oxidation current. The use of a rotating ring-disk electrode (RRDE) is acknowledged for its ability to quantitatively determine the faradaic efficiency of the OER. [1] However, for practical applications, the generation of oxygen bubbles can cause unpredictable disturbance, leading to the erroneous collection efficiency. In this study, we aim to establish a dynamic current-response collection efficiency during the generation of oxygen bubbles. This was achieved by modelling with an Au/Au RRDE, well-known for its electrochemical stability under harsh conditions. In addition, using this calibrated collection efficiency, we investigate the influence of perovskite catalysts on the degradation behaviors of carbon materials at OER potentials in alkaline media. Materials and electrochemical measurements Measurements of oxygen gas collection efficiency were conducted using a modeled RRDE comprising an Au disk electrode and an Au ring electrode. The RRDE served as the working electrode, with a Pt wire as the counter electrode, a reversible hydrogen electrode (RHE) as the reference electrode, and a solution of Ar-saturated 1 mol dm-3 KOH as the electrolyte. The disk electrode underwent a 5-minute chronopotentiometry with varied oxidation currents, while the ring electrode underwent chronoamperometry at 0.3 V (vs. RHE). The collection efficiency was calculated from the ring current attributed to the oxygen 2-electron reduction reaction.Two kinds of perovskite catalysts, namely Sr2Co0.8Fe0.2O3Cl[2] (hereafter SCFOC) and LaCoO3 (hereafter LCO), and two carbonaceous materials, namely graphitized carbon black (TOKABLACK#3845, hereafter TB) and ketjen black (EC-600JD, hereafter KB), were used to evaluate the influence of perovskite on the carbon degradation behavior. Four composite catalysts, each comprising perovskite and carbon with a weight ratio of 5:1, were loaded on a disk electrode of the glassy carbon disk/Au ring RRDE. A cell analogous to the aforementioned design was assembled. Electrochemical measurements were conducted through chronoamperometry, employing various potentials at the disk electrode, and maintaining a potential of 0.3 V vs. RHE at the ring electrode, for a duration of 5 minutes. Results and discussion Figure 1 illustrates a three-dimensional representation of the oxygen gas collection efficiency of the Au/Au RRDE as two functions of disk current density and measurement time. It was evident that the oxygen gas collection efficiency varied significantly from the theoretical value (25.6 %) and was dependent on the disk current density and measurement time. The constrained solubility of oxygen in aqueous solution and the hydrophobic nature of the PTFE between the ring and the disk might cause a decrease in the collection efficiency due to the partial retention of oxygen bubbles on the electrode as the oxygen generation current increased and the measurement time elapsed. This suggests that, unlike typical solution reactions, the dynamic determination of the oxygen gas collection efficiency is essential, considering current density and measurement time.Figure 2 illustrates the computation of faradaic oxygen efficiency, utilizing dynamic oxygen collection efficiency. The composite catalyst composed of TB and SCFOC was taken as an illustrative example. The variation in collection efficiency, synchronized with the shape of disk current density, was employed in determining the faradaic oxygen efficiency. This dynamic collection efficiency yielded a comparatively smooth faradaic oxygen efficiency.Utilizing the calibrated faradaic oxygen efficiency, we proceeded to assess the capacity of carbon degradation by integrating the current density of the carbon oxidation reaction (COR) calculated by subtracting the OER current from the overall current. As depicted in Figure 3, the COR capacity as a function of the potential suggested that the components of the composite catalysts had distinct impacts on carbon degradation. Specifically, SCFOC appears to enhance degradation, whereas LCO exhibits a comparatively less pronounced effect.A more comprehensive discussion of these findings will be presented at the upcoming meeting.[1] I.S. Filimonenkov et al., Electrochim. Acta 321, 134657 (2019).[2] Y. Miyahara et al., Chem. Mater. 32, 8195 (2020). Figure 1

Numerical investigation and optimal design of capillary barrier cover with passive gas collection pipes on the performance at limiting landfill gas emissions

Relying solely on soil properties may not fully ensure the performance of capillary barrier covers at limiting landfill gas (LFG) emissions. This study proposed to install passive gas collection pipes in the coarse-grained soil layers of capillary barrier covers to enhance their performance at limiting LFG emissions. First, the LFG generation rate of municipal solid waste and its influencing factors were analyzed based on empirical formulas. This information provided necessary bottom boundary conditions for the analyses of LFG transport through capillary barrier covers with passive gas collection pipes (CBCPPs). Then, numerical simulations were conducted to investigate the LFG transport properties through CBCPPs and reveal relevant influencing factors. Finally, practical suggestions were proposed to optimize the design of CBCPPs. The results indicated that the maximum whole-site LFG generation rate occurred at the end of landfilling operation. The gas collection efficiency (E) of CBCPPs was mainly controlled by the ratio of the intrinsic permeability between the coarse- and fine-grained soil (K2/K1) and the laying spacing between gas collection pipes (D). E increased as K2/K1 increased but decreased as D increased. An empirical expression for estimating E based on K2/K1 and D was proposed. In practice, CBCPPs were supposed to be constructed once the landfilling operation finished. It is best to select the fine- and coarse-grained soils with K2/K1 exceeding 10,000 to construct CBCPPs.

Landfill gas collection efficiency: Categorization of data from existing in-situ measurements

Landfill methane emissions are commonly estimated using cover-type dependent default collection efficiency values, with a first-order decay model or measured gas collection. Current default collection efficiencies used in the United States were predominately derived from 4 studies conducted during or prior to 2007 that relied on flux chambers. Flux chambers are limited by small sample sizes, placement restrictions, and the inability to measure emissions from gas or leachate collection systems. Since 2007, over 14 new studies have been completed using more advanced technologies that allow for direct measurement of methane plumes from most or all of a landfill’s surface. On average, these measurements are 2–3 times greater than emissions predicted by current models and collection efficiency defaults. In lieu of measuring emissions from all landfills, updating collection efficiency defaults can bring modeled emissions into better alignment with measurements. To this end, collection efficiency estimates derived from measured data were categorized into cover types and then adjusted to account for cases where whole plume measurement was an amalgamation of multiple cover types. The resultant adjusted default values were 41% for daily cover, 69% for intermediate cover, and 71% for final cover. Direct measurement of landfill methane emissions is preferrable to account for the full range of variables driving landfill emissions, including collection system design and operation. However, applying these updated defaults back into the landfill emission models eliminates underprediction of landfill emissions for the dataset reviewed, and would provide a more accurate estimate of landfill gas emissions where measurements are unavailable.

Electrolysing mud: Membraneless electrolysis of water for hydrogen production using montmorillonite-rich marine mud

This paper describes a design for a low-cost membraneless water electrolyser for the production of green hydrogen that used a viscous electrolyte of naturally abundant montmorillonite-rich marine mud in a DEFT (divergent electrode flow through) geometry with stainless steel (304) mesh electrodes. The ratio of smectite to non-swelling clays in the mud was 1:2. The electrolyte was prepared by resuspending the mud in tap-water to remove the salt, and NaOH 1 M added to enhance the ionic conductivity, as measured by both Electrochemical Impedance Spectroscopy (EIS) and by the slope of DC current/voltage curves. Successful separation and collection of the hydrogen and oxygen gas was inferred from the ratio of 2:1 in the volumes of hydrogen and oxygen collected. Both acid and alkali treatments were trialled and it was found that, whereas acid treatment flocculated the mud, adding NaOH increased the dispersion, conductivity and viscosity, and reduced clogging. The conductivity of both the 24% dry mass alkali mud and a control 4% dry mass alkali bentonite suspension increased to that of pure NaOH 1 M when repeatedly electrolysed. Hydrogen and oxygen gas was collected for 10% and 24% dry mass muds. The less viscous 10% dry mass mud showed turbulent liquid-like behaviour which led to gas mixing but the 24% mud showed stable, solid-like flow and reliable gas separation. Three components of the energy efficiency of the electrolysis process are reported and discussed – the voltage efficiency of 42%, a gas collection efficiency of 50% and the auxiliary power efficiency of 60%. The overall energy efficiency due to these three contributing efficiencies, was 13% of the Higher Heating Value of 142 MJ/kg H2 for a current density of 45 mA/cm2. This mud electrolyser may still be considered worth developing for an off-grid, low budget site with a low-power source of renewable energy.

A review on the methane emission detection during offshore natural gas hydrate production

Due to the high energy density, large potential reserves and only release CO2 and water after combustion, natural gas hydrate (NGH) is considered as the most likely new clean energy source to replace traditional fossil energy (crude oil, natural gas, etc.). However, unlike the exploitation of traditional fossil energy, the essence of natural gas hydrate exploitation is to induce the production of methane by artificially decompose the natural gas hydrate and to simultaneously collect the generated methane. Because of the uncontrollable decomposition, the methane percolation and the gas collection efficiency, methane emission is inevitably occurred during natural gas hydrate exploitation, which could significantly affect the environmental friendliness of natural gas hydrate. In this review, the methane emission detection was divided into three interfaces: Seafloor and sediment, seawater, atmosphere. Meanwhile, according the summary and analysis of existing methane emission detection technologies and devices, it was concluded that the existing detection technologies can identify and quantify the methane emission and amount in the three interfaces, although the accuracy is different. For natural gas hydrate exploitation, quantifying the environmental impact of methane emission and predicting the diffusion path of methane, especially the methane diffusion in strata and seawater, should be the focus of subsequent research.

Life cycle GHG emissions of MSW landfilling versus Incineration: Expected outcomes based on US landfill gas collection regulations

From a GHG perspective, most LCA studies find incineration (MSWI) to be preferred over landfilling because of high energy recovery offsets. In some studies, however, landfilling results in less greenhouse gases (GHG) emissions than MSWI. We investigated using LCA, the landfill gas (LFG) collection efficiencies and waste composition that led to landfills resulting in less GHG emissions. Then, we explored what theoretical minimum lifetime gas collection efficiencies can be expected when following US LFG regulations. Only landfills with high LFG collection efficiencies (at least 81%) and recovery of methane for energy resulted in less GHG emissions compared to the management of the same waste stream in MSWI; required efficiency increased to 93% without LFG energy recovery. Expected theoretical lifetime LFG collection efficiencies were modeled in the range of 30–80%, with the lower rates associated with landfills having smaller input masses, high decay rates, and low concentrations of nonmethane organic compounds (CNMOC). Our modeling found that only under a limited combination of conditions (e.g., high CNMOC, high waste input rate, low decay rate) could a landfill expect to achieve a LFG collection efficiency as high as 80%, and that this value falls just under the 81–93% collection efficiency threshold needed for a landfill to result in less GHG emissions than MSWI. When exploring the influence of higher oxidation rates, changing decay rates, varying electricity grids, and inclusion of nonferrous metals recovery offsets the collection effciency range needed increased in nearly all cases; the electricity grid and nonferrous metals offsets had the greatest influence.

Efficiency of gas collection systems at Danish landfills and implications for regulations

Globally, landfills are an important source of anthropogenic methane emissions. Regulations require landfill gas be managed to reduce emissions, and some landfills have therefore installed gas collection systems to recover energy and mitigate methane emissions. However, the efficiency of such systems is seldom evaluated. This paper presents the gas collection efficiencies of 23 Danish landfills and suggests how these values could be used to regulate landfill methane emissions in Denmark. Methane emissions from all sites were measured using the tracer gas dispersion method, and gas collection efficiencies were calculated using the ratio of the methane collection rate to the sum of the collection and emission (and oxidation) rates. Gas collection efficiencies ranged between 13 and 86% with an average of 50% – a value lower than for Swedish (58%), UK (64%) and US (63%) landfills. Possible reasons for the inefficiency of gas collection systems in Denmark include shallow gas collection pipes, leakage from installations (e.g. leachate wells, gas engines), low gas recovery due to minimal gas production or a lack of gas collection in active waste cells. It is suggested to use gas collection efficiency to regulate landfills and help them reach a particular methane mitigation goal. Gas collection efficiency that falls below the target mitigation rate would in turn trigger actions to reduce landfill methane emissions. At sites where the quality of the collected gas is too low to operate a gas engine, the installed gas collection system could be retrofitted to a biocover system designed for methane oxidation.

Novel Graphene Wool Gas Adsorbent for Volatile and Semivolatile Organic Compounds.

Volatile and semivolatile organic compounds in ambient air and occupational settings are of great concern due to their associated adverse human health and environmental impacts. Novel graphene wool samplers have been developed and tested to overcome limitations of commercially available sorbents that can only be used once and typically require solvent extraction. Graphene wool (GW) was synthesized by non-catalytic chemical vapor deposition with optimized conditions, resulting in a novel fibrous graphene wool that is very easy to manage and less rigid than other forms of graphene, lending itself to a wide range of potential applications. Here, the air pollutant sampling capabilities of the GW were of interest. The optimal packing weight of GW inside a glass tube (length 178 mm, i.d. 4 mm, o.d. 6 mm) was investigated by the adsorption of vaporized alkane standards on the GW, using a condensation aerosol generator in a temperature-controlled chamber and subsequent detection using a flame ionization detector. The optimized GW packing density was found to be 0.19 mg mm–3 at a flow rate of 500 mL min–1, which provided a gas collection efficiency of >90% for octane, decane, and hexadecane. The humidity uptake of the sampler is less than 1% (m/m) for ambient humidities <70%. Breakthrough studies showed the favorable adsorption of polar molecules, which is attributed to the defective nature of the graphene and the inhomogeneous coating of the graphene layers on the quartz wool, suggesting that the polar versus non-polar uptake potential of the GW can be tuned by varying the graphene layering on the quartz wool substrate during synthesis. Oxidized domains at the irregular edges of the graphene layers, due to a broken, non-pristine sp2 carbon network, allow for adsorption of polar molecules. The GW was applied and used in a combustion sampling campaign where the samplers proved to be comparable to frequently used polydimethylsiloxane sorbents in terms of sampling and thermal desorption of non-polar semivolatile organic compounds. The total alkane concentrations detected after thermal desorption of GW and PDMS samplers were found to be 17.96 ± 13.27 and 18.30 ± 16.42 μg m–3, respectively; thus, the difference in the alkane sampling concentration between the two sorbent systems was negligible. GW provides a new, exciting possibility for the monitoring of organic air pollutants with numerous advantages, including high sampling efficiencies, simple and cost-effective synthesis of the thermally stable GW, solvent-free and environmentally friendly analysis, and, importantly, the reusability of samplers.

En Route to a Unified Model for Photoelectrochemical Reactor Optimization. II–Geometric Optimization of Perforated Photoelectrodes

Results have been reported previously of a model describing the performance of photoelectrochemical reactors, which utilize semiconductor | liquid junctions. This model was developed and verified using SnIV-doped α-Fe2O3 as photoanodes. Hematite films were fully characterized to obtain parameter inputs to a model predicting photocurrent densities. Thus, measured photocurrents were described and validated by the model in terms of measurable quantities. The complete reactor model, developed in COMSOL Multiphysics, accounted for gas evolution and desorption in the system. Hydrogen fluxes, charge yields and gas collection efficiencies in a photoelectrochemical reactor were estimated, revealing a critical need for geometric optimization to minimize H2-O2 product recombination as well as undesirable spatial distributions of current densities and “overpotentials” across the electrodes. Herein, the model was implemented in a 3D geometry and validated using solid and perforated 0.1 × 0.1 m2 planar photoanodes in an up-scaled photoelectrochemical reactor of 2 dm3. The same model was then applied to a set of simulated electrode geometries and electrode configurations to identify the electrode design that would maximize current densities and H2 fluxes. The electrode geometry was modified by introducing circular perforations of different sizes, relative separations and arrangements into an otherwise solid planar sheet for the purpose of providing ionic shortcuts. We report the simulated effects of electrode thickness and the presence or absence of a membrane to separate oxygen and hydrogen gases. In a reactor incorporating a membrane and a photoanode at 1.51 V vs RHE and pH 13.6, an optimized hydrogen flux was predicted for a perforation geometry with a separation-to-diameter ratio of 4.5 ± 0.5; the optimal perforation diameter was 50 µm. For reactors without a membrane, this ratio was 6.5 and 8.5 for a photoanode in a “wired” (monopolar) and “wireless” (photo-bipolar) design, respectively. The results and methodologies presented here will serve as a framework to optimize composite photoelectrodes (semiconductor | membrane | electrolyte), and photoelectrochemical reactors in general, for the production of hydrogen (and oxygen) from water using solar energy.

Sensitivity analysis and improvements of the recycling rate in municipal solid waste life cycle assessment: Focus on a Latin American developing context.

The life cycle assessment (LCA) of municipal solid waste (MSW) systems in developing countries is a matter of research. Obtain reliable results is challenging since field data and local databases are not always available. The research presented in this paper explores this issue in La Paz (Bolivia), where six environmental impact categories were assessed. The LCA, related to the formal MSW management system of the city, involves a sensitivity analysis of ten parameters and the scenario assessment in relation to the increase of the recycling rate. Results report that the environmental impacts are mostly sensitive in relation to landfill gas collection efficiency, use of plastic bags, the transportation distances of collected waste, and the replacement rate of virgin materials. Global warming potential is the impact category most variable (341.38-551.95kg CO2-eq tMSW-1), although it is not considerably reduced by recycling, which contributed mostly to the human toxicity and freshwater aquatic ecotoxicity. Doubling the amount of MSW recycled, from 235t to about 473t per year, human toxicity potential reduces of about 18% while freshwater aquatic ecotoxicity of about 12%. This research contributes for evaluating the most sensitive parameters in an MSW-LCA and to support policymakers towards waste recycling and sustainable development in Latin America developing cities.

The Evaluation System of the Sustainable Development of Municipal Solid Waste Landfills and Its Application

Improving the understanding of the stabilization process is of great significance to guide the sustainable development of municipal solid waste (MSW) landfills. An evaluation system of the stabilization process of MSW landfills has been established. The indices of the evaluation system involve the degradation degree of MSW, the release of landfill gas production potential, and the settlement of landfills. Based on the biochemical-consolidation-solute migration coupled model, an evaluation method of the MSW landfill stabilization process is proposed by combining field tests with numerical simulation. The stabilization process of the Jiangcungou landfill in China is investigated by using the proposed method. The analyzed results show that the stabilization process of high kitchen waste content landfills can be divided into three stages, which is different from the stabilization process of landfills in developed countries. For the Jiangcungou landfill, the ratio of cellulose to lignin in MSW decreases rapidly during the fast degradation stage when obvious settlement occurs. During the slow degradation stage, the hydrolysis rate is slow and settlement develops slowly. When the landfill reaches the stabilization stage, the ratio of cellulose to lignin of MSW changes very slowly; most of the landfill gas potential has been released; the settlement stabilization is completed basically. The change processes of the three evaluation indices are different, of which the degradation stabilization index is the main one. According to the findings above, leachate recirculation is recommended to adjust the degradation environment in the landfill, which can be helpful to avoid acidification at the fast degradation stage. Temporary cover is suggested to improve landfill gas collection efficiency at the beginning of the stable methanogenic stage. The landfill site closure should be operated when the settlement rate is low.

Power generation from municipal solid waste landfilled in the Beijing-Tianjin-Hebei region

The present study assesses the electricity generation potential of landfill gas to energy projects in the Beijing-Tianjin-Hebei region. The study used historical data on municipal solid waste disposed of in landfills in the Beijing-Tianjin-Hebei region from 2004 to 2018. The Landfill Gas Emission Model (LandGEM) software version 3.02 was used to evaluate the methane generation potential of the municipal solid waste. An economic feasibility analysis was conducted on the landfill gas to energy projects using economic indicators such as the net present value, investment payback period, and levelized cost of energy. Also, a sensitivity analysis was performed to determine the influence of variation in the discount rate, landfill gas collection efficiency, capacity factor, and power generation efficiency on the economic viability of the project. The main findings of the study show that the total electricity generation potential from landfill methane in the region is 12,525.2 GWh. The highest total electricity generation potential is in Beijing, while the lowest is in Tianjin. It was realized from the economic analysis that the project is feasible at all the locations in the Beijing-Tianjin-Hebei region. However, the project is highly feasible in Beijing, with a more positive net present value, lower investment payback period, and lower levelized cost of energy. It was found that the investment payback period of the project in the region is 11.3 y to 14.3 y, and the levelized cost of energy is $0.1402/kWh to $0.2260/kWh. The sensitivity analysis shows that at a discount rate exceeding 15%, the project is infeasible in the Beijing municipality and Hebei province, while it is infeasible at a discount rate of more than 10% in Tianjin. This study could provide technical guidance for investment in landfill gas to energy projects in the Beijing-Tianjin-Hebei region and other parts of China.

A techno-economic assessment of landfill gas emissions and energy recovery potential of different landfill areas in Turkey

Landfills are a widespread application for the management of municipal solid waste and the production of energy. However, landfill gas estimations, analysis of its energy capacity, and economic analyses need to be performed properly for a landfill project area. Although there are many gas prediction models in the literature, the default values in the model such as the methane production capacity (Lo) and the methane production rate (k) need to be recalculated according to the climate and waste composition of the region in order to obtain a more accurate gas estimation. Furthermore, the energy project from waste is expected to evaluate the through lifetime with variables (landfill operation, gas collection efficiency, different combustion engines, etc.) for an optimum plant capacity. In this study, it is aimed to investigate the landfill gas and methane production potential that can be obtained in landfill areas in different provinces of Turkey and to determine an optimum plant capacity by performing energy production cost analysis. To achieve this, the LandGEM 3.02 version was used to estimate long-term landfill gas potential in this study. The Lo value was calculated by using the IPCC (Intergovernmental Panel on Climate Change) methodology, and the k value was determined by considering the meteorological data of the regions (precipitation amount, etc.). The future population of the selected regions was estimated using the arithmetic increase method. According to this estimation, the solid waste quantity to be generated in the future was calculated. Energy capacities of these areas were calculated using internal combustion reciprocating engines with six different capacities. The unit energy production cost was evaluated by employing the levelized cost method. The optimum plant capacity was found by evaluating the energy production costs obtained for each site and six different engines. As a result, it is observed that the energy production plant with the optimum capacity determined from waste is economically and ecologically feasible.

Investigation of fugitive methane and gas collection efficiency in Halton landfill in Ontario, Canada.

Methane gas is one of the significant contributors to global warming. A large portion of methane emissions comes from landfills. Developing reliable measurement methods for methane emissions from landfill sites has become very important. In this paper, the surface emissions of methane gas are quantified using a portable probe having a flame ionization detector (FID), a method proven to be successful in landfill gas measurement. Surface methane emissions from two closed cells in the Halton landfill in Ontario, Canada, were measured using the FID method. By analyzing the emissions within the perimeter of the landfill, hotspots of gas leakage were identified. The closed cells in the Halton landfill are equipped with gas extraction system for flaring and energy recovery and a clay topsoil cover. Emission concentrations of fugitive methane were found to range from 0.1 to 63ppm. The largest emissions were detected in locations next to the leachate extraction manholes and malfunctioning gas extraction wells. The landfill gas balance showed that the landfill gas recovery efficiency was 44%, resulting in an average amount of fugitive methane from the landfill of 6124m3/day. The results of the study were used to determine the methane generation potential (Lo) for municipal solid waste to further calibrate the USEPA LandGEM model for Ontario landfills. The model was calibrated by actual methane emission measurement and recovery data. The calibrated Lo was found to be 70m3/t, which is lower than the estimated values in previous studies.

An Assessment of the Dynamic Global Warming Impact Associated with Long-Term Emissions from Landfills.

Landfills are a major contributor of anthropogenic CH4 emissions. Since the greenhouse gas (GHG) emissions associated with landfilling waste can occur over decades to centuries, the standard static approach to estimating global warming impacts may not accurately represent the global warming impacts of landfills. The objective of this study is to assess the implications of using 100 yr and 20 yr static and dynamic global warming potential (GWP) approaches to estimate the global warming impacts from municipal solid waste landfills. A life-cycle model was developed to estimate GHG emissions for three gas treatment cases (passive venting, flare, CH4 conversion to electricity) and four decay rates. For the 100 yr GWP, other model uncertainties (e.g., static GWP values, decay rate, moisture content, or gas collection efficiency) generally had a larger effect on the estimated global warming impact than the choice of static versus dynamic GWP methods. This shows that when comparing single-point GWP values, the choice of static versus dynamic is relatively unimportant for most landfills. While dynamic GWPs consider temporal variance and provide useful estimates for the warming over a set time horizon, for most comparative analyses, static values provide reasonable bounds for the actual 100 yr warming impact.

Effect of collection efficiency and oxidation factor on greenhouse gas emission and life cycle cost of landfill distributed energy generation

The landfill gas obtainable from municipal solid waste landfills can be a useful energy carrier for distributed electricity generation if properly harnessed. The quantity of the landfill gas available for use can be greatly influenced by its collection efficiency and the oxidation factor. This paper therefore estimates the possible effect of landfill gas collection efficiency as well as the oxidation factor on the electricity generation potential, life cycle cost and greenhouse gas emission of a landfill distributed generation system. To achieve this objective(s), the municipal solid waste data of the city of Ibadan is used and the amount of landfill gas obtainable in the short and long terms from the decomposition of waste in the landfill is determined using the Landfill Emission Generation Model software. The results showed that the average landfill gas generation rate based on the estimated waste profile of the city was 0.2028 billion cubic metres per year which could produce about 372 Giga Watts hour per year of electricity. It also demonstrated that the collection efficiency and oxidation factor have reciprocating impact on the electricity generation potential obtainable from landfill sites. This study can be found useful for landfill operators, engineers, environmentalists and other stakeholders in waste management sector on the need to operate upgraded landfill sites for improved energy generation and environmental benefits.

Assessment of CH4 and CO2 surface emissions from Polesgo's landfill (Ouagadougou, Burkina Faso) based on static chamber method

Methane (CH4) and carbon dioxide (CO2) surface emissions from Polesgo's landfill (Ouagadougou, Burkina Faso) were measured using the static chamber technique in 2017 and 2018. The Polesgo's landfill was composed of four zones: Phase I, II, Phase III, and SP. The surface of Phase I was fully covered and its conditions are better for surface emission measurements. As results concerning the Phase I zone, the geospatial means flux rates of CH4 (657 mg m−2 h−1 in 2017 and 1210 mg m−2 h−1 in 2018, respectively) are measured higher than the tolerable value reported in literature. The emitted CH4 or CO2 have permitted to locate higher surface emissions which are related to the cover state. The calculated gas collection efficiency (27.4% in 2017 and 23.0% in 2018) is low compared to those reported for landfills integrating landfill gas (LFG) extraction system. The carbon footprint calculations (24,966 tCO2-eq 2017 and 40,025 tCO2-eq in 2018, respectively) shown that Polesgo's landfill is a significant source of greenhouse gases (GHG) and its important potential for organic recovery can contribute to reduce the carbon footprint.

Evaluation of optimal model parameters for prediction of methane generation from selected U.S. landfills

In practice, methane generation at U.S. landfills is typically predicted by using the EPA’s Landfill Gas Emissions Model (LandGEM), which includes two parameters, the methane production potential (L0, m3 CH4 Mg−1 wet waste) and the first-order decay rate constant (k, yr−1). Default parameters in LandGEM (L0 = 100 and k = 0.04) were determined using data that reflect landfill management practices in the 1990s. In this study, methane collection data from 21 U.S. landfills were used to estimate the best fit k by inverse modeling of measured methane collection data in consideration of a time-varying gas collection efficiency. Optimal values of k were identified at a range of L0s between 55 and 160. The best fit k was greater than the U.S. EPA’s default parameter of 0.04 yr−1 at 14 of the 21 landfills studied. Surprisingly, the best fit k was often observed at L0 values greater than 100 m3 CH4 Mg−1 wet waste which again is the U.S. EPA default. The results show that there is wide variation in the best estimate of k. While there was a tendency for landfills, or sections of landfills that received more moisture to exhibit higher decay rates, the results were not consistent. Some landfills exhibited high decay rates even though the data suggested that they were relatively dry while some wet landfills exhibited low decay rates. The results suggest that L0 captures many factors and that the data may be most useful for site specific analysis as opposed to general landfill predictions.

Life cycle assessment for solid waste management in Lebanon: Economic implications of carbon credit.

Solid waste management has witnessed much progress in recent years with considerable efforts targeting the reduction of associated impacts and carbon emissions. Such efforts remain relatively limited in developing economies due to inefficient management practices. In this study, a life cycle assessment (LCA) approach is adopted to identify integrated systems with minimal impacts and reduced emissions in a developing context coupled with an economic valuation and sensitivity analysis to assess the effect of varying influencing parameters individually. The results showed that the highest impact arises from landfilling with minimal material recovery for recycling and composting, while incineration coupled with energy recovery contributed to the least equivalent emissions (-111% with respect to baseline scenario) at a varying cost of -70% to +93% depending on the selected technology and the value of carbon credit. Optimizing material recycling, composting and landfilling with energy recovery contributed to 98% savings in emissions (with respect to baseline scenario) and remained economically attractive irrespective of the carbon credit exchange rate of 0.5-50 US$/MTCO2E. The sensitivity analysis showed that an improvement in landfill gas collection efficiency (up to 60%) can contribute to major savings in emissions (58%). The application of the LCA-based approach supports the development of integrated viable plans while quantifying advantages and disadvantages towards decision-making and policy-planning.

The influence of moisture enhancement on landfill gas generation in a full-scale landfill

The objective of this study was to investigate the influence of different moisture enhancement strategies on landfill gas generation in a full-scale solid waste landfill. Moisture enhancement strategies included leachate recirculation and liquid waste addition that were implemented to promote in situ waste decomposition. Waste mass disposed at the landfill and measured gas flow rates in the gas collection system were partitioned among four phases of the landfill that were operated with different moisture enhancement strategies. The gas collection system included extraction points in gas wells as well as in leachate clean-out pipes and leachate recirculation trenches. The measured gas flow rates were modeled with the U.S. EPA LandGEM to optimize the first-order decay rate (k). Model simulations were completed with an assumed constant methane generation potential and gas collection efficiency. The optimized k for the Site-Wide analysis was 0.078 1/yr, which was elevated relative to the default k = 0.04 1/yr for conventional solid waste landfills. Optimized k values for the four phases ranged between 0.025 and 0.127 1/yr. The optimized k values increased with increasing aggressiveness of the moisture enhancement strategy. Although unique relationships between k and parameters reflecting moisture enhancement (e.g., water content) were not identified, this case study can provide guidance on moisture enhancement techniques that result in increased landfill gas generation and improved solid waste decomposition.