Quantification of greenhouse gas emissions from windrow composting of garden waste.

Microbial degradation of organic wastes entails the production of various gases such as carbon dioxide (CO(2)), methane (CH(4)), nitrous oxide (N(2)O), and carbon monoxide (CO). Some of these gases are classified as greenhouse gases (GHGs), thus contributing to climate change. A study was performed to evaluate three methods for quantifying GHG emissions from central composting of garden waste. Two small-scale methods were used at a windrow composting facility: a static flux chamber method and a funnel method. Mass balance calculations based on measurements of the C content in the in- and out-going material showed that 91 to 94% of the C could not be accounted for using the small-scale methods, thereby indicating that these methods significantly underestimate GHG emissions. A dynamic plume method (total emission method) employing Fourier Transform Infra Red (FTIR) absorption spectroscopy was found to give a more accurate estimate of the GHG emissions, with CO(2) emissions measured to be 127 +/- 15% of the degraded C. Additionally, with this method, 2.7 +/- 0.6% and 0.34 +/- 0.16% of the degraded C was determined to be emitted as CH(4) and CO. In this study, the dynamic plume method was a more effective tool for accounting for C losses and, therefore, we believe that the method is suitable for measuring GHG emissions from composting facilities. The total emissions were found to be 2.4 +/- 0.5 kg CH(4)-C Mg(-1) wet waste (ww) and 0.06 +/- 0.03 kg N(2)O-N Mg(-1) ww from a facility treating 15,540 Mg of garden waste yr(-1), or 111 +/- 30 kg CO(2)-equivalents Mg(-1) ww.

Hazardous off-gassing of carbon monoxide and oxygen depletion during ocean transportation of wood pellets.

Five ocean vessels were investigated for the characterization and quantification of gaseous compounds emitted during ocean transportation of wood pellets in closed cargo hatches from Canada to Sweden. The study was initiated after a fatal accident with several injured during discharge in Sweden. The objective with the investigation was to better understand the off-gassing and issues related to workers' exposure. Air sampling was done during transport and immediately before discharge in the undisturbed headspace air above the wood pellets and in the staircase adjacent to each hatch. The samples were analyzed with Fourier transform infrared spectroscopy and direct reading instruments. The following compounds and ranges were detected in samples from the five ships: carbon monoxide (CO) 1460-14650 ppm, carbon dioxide (CO2) 2960-21570 ppm, methane 79.9-956 ppm, butane equivalents 63-842 ppm, ethylene 2-21.2 ppm, propylene 5.3-36 ppm, ethane 0-25 ppm and aldehydes 2.3-35 ppm. The oxygen levels were between 0.8 and 16.9%. The concentrations in the staircases were almost as high as in the cargo hatches, indicating a fairly free passage of air between the two spaces. A potentially dangerous atmosphere was reached within a week from loading. The conclusions are that ocean transportation of wood pellets in confined spaces may produce an oxygen deficient atmosphere and lethal levels of CO which may leak into adjacent access spaces. The dangerous combination of extremely high levels of CO and reduced oxygen produces a fast-acting toxic combination. Measurement of CO in combination with oxygen is essential prior to entry in spaces having air communication with cargo hatches of wood pellets. Forced ventilation of staircases prior to entry is necessary. Redesign, locking and labeling of access doors and the establishment of rigorous entry procedures and training of onboard crew as well as personnel boarding ocean vessels are also important.

Optical technologies applied alongside on-site and remote approaches for climate gas emission quantification at a wastewater treatment plant.

Plant-integrated and on-site gas emissions were quantified from a Swedish wastewater treatment plant by applying several optical analytical techniques and measurement methods. Plant-integrated CH4 emission rates, measured using mobile ground-based remote sensing methods, varied between 28.5 and 33.5 kg CH4 h-1, corresponding to an average emission factor of 5.9% as kg CH4 (kg CH4production) -1, whereas N2O emissions varied between 4.0 and 6.4 kg h-1, corresponding to an average emission factor of 1.5% as kg N2O-N (kg TN influent) -1. Plant-integrated NH3 emissions were around 0.4 kg h-1, corresponding to an average emission factor of 0.11% as kg NH3-N (kg TN removed) -1. On-site emission measurements showed that the largest proportions of CH4 (70%) and NH3 (66%) were emitted from the sludge treatment line (mainly biosolid stockpiles and the thickening and dewatering units), while most of the N2O (82%) was emitted from nitrifying trickling filters. In addition to being the most important CH4 source, stockpiles of biosolids exhibited different emissions when the sludge digesters were operated in series compared to in parallel, thus slightly increasing substrate retention time in the digesters. Lower CH4 emissions and generally higher N2O and NH3 emissions were observed when the digesters were operated in series. Loading biosolids onto trucks for off-site treatment generally resulted in higher CH4, N2O, and NH3 emissions from the biosolid stockpiles. On-site CH4 and N2O emission quantifications were approximately two-thirds of the plant-integrated emission quantifications, which may be explained by the different timeframes of the approaches and that not all emission sources were identified during on-site investigation. Off-site gas emission quantifications, using ground-based remote sensing methods, thus seem to provide more comprehensive total plant emissions rates, whereas on-site measurements provide insights into emissions from individual sources.

Emission quantification using the tracer gas dispersion method: The influence of instrument, tracer gas species and source simulation.

The tracer gas dispersion method (TDM) is a remote sensing method used for quantifying fugitive emissions by relying on the controlled release of a tracer gas at the source, combined with concentration measurements of the tracer and target gas plumes. The TDM was tested at a wastewater treatment plant for plant-integrated methane emission quantification, using four analytical instruments simultaneously and four different tracer gases. Measurements performed using a combination of an analytical instrument and a tracer gas, with a high ratio between the tracer gas release rate and instrument precision (a high release-precision ratio), resulted in well-defined plumes with a high signal-to-noise ratio and a high methane-to-tracer gas correlation factor. Measured methane emission rates differed by up to 18% from the mean value when measurements were performed using seven different instrument and tracer gas combinations. Analytical instruments with a high detection frequency and good precision were established as the most suitable for successful TDM application. The application of an instrument with a poor precision could only to some extent be overcome by applying a higher tracer gas release rate. A sideward misplacement of the tracer gas release point of about 250m resulted in an emission rate comparable to those obtained using a tracer gas correctly simulating the methane emission. Conversely, an upwind misplacement of about 150m resulted in an emission rate overestimation of almost 50%, showing the importance of proper emission source simulation when applying the TDM.

Quantification of methane emissions from 15 Danish landfills using the mobile tracer dispersion method.

Whole-site methane emissions from 15 Danish landfills were assessed using a mobile tracer dispersion method with either Fourier transform infrared spectroscopy (FTIR), using nitrous oxide as a tracer gas, or cavity ring-down spectrometry (CRDS), using acetylene as a tracer gas. The landfills were chosen to represent the different stages of the lifetime of a landfill, including open, active, and closed covered landfills, as well as those with and without gas extraction for utilisation or flaring. Measurements also included landfills with biocover for oxidizing any fugitive methane. Methane emission rates ranged from 2.6 to 60.8 kg h(-1), corresponding to 0.7-13.2 g m(-2)d(-1), with the largest emission rates per area coming from landfills with malfunctioning gas extraction systems installed, and the smallest emission rates from landfills closed decades ago and landfills with an engineered biocover installed. Landfills with gas collection and recovery systems had a recovery efficiency of 41-81%. Landfills where shredder waste was deposited showed significant methane emissions, with the largest emission from newly deposited shredder waste. The average methane emission from the landfills was 154 tons y(-1). This average was obtained from a few measurement campaigns conducted at each of the 15 landfills and extrapolating to annual emissions requires more measurements. Assuming that these landfills are representative of the average Danish landfill, the total emission from Danish landfills were calculated at 20,600 tons y(-1), which is significantly lower than the 33,300 tons y(-1) estimated for the national greenhouse gas inventory for 2011.

Quantifying methane emission from fugitive sources by combining tracer release and downwind measurements - a sensitivity analysis based on multiple field surveys.

Using a dual species methane/acetylene instrument based on cavity ring down spectroscopy (CRDS), the dynamic plume tracer dispersion method for quantifying the emission rate of methane was successfully tested in four measurement campaigns: (1) controlled methane and trace gas release with different trace gas configurations, (2) landfill with unknown emission source locations, (3) landfill with closely located emission sources, and (4) comparing with an Fourier transform infrared spectroscopy (FTIR) instrument using multiple trace gasses for source separation. The new real-time, high precision instrument can measure methane plumes more than 1.2 km away from small sources (about 5 kg h(-1)) in urban areas with a measurement frequency allowing plume crossing at normal driving speed. The method can be used for quantification of total methane emissions from diffuse area sources down to 1 kg per hour and can be used to quantify individual sources with the right choice of wind direction and road distance. The placement of the trace gas is important for obtaining correct quantification and uncertainty of up to 36% can be incurred when the trace gas is not co-located with the methane source. Measurements made at greater distances are less sensitive to errors in trace gas placement and model calculations showed an uncertainty of less than 5% in both urban and open-country for placing the trace gas 100 m from the source, when measurements were done more than 3 km away. Using the ratio of the integrated plume concentrations of tracer gas and methane gives the most reliable results for measurements at various distances to the source, compared to the ratio of the highest concentration in the plume, the direct concentration ratio and using a Gaussian plume model. Under suitable weather and road conditions, the CRDS system can quantify the emission from different sources located close to each other using only one kind of trace gas due to the high time resolution, while the FTIR system can measure multiple trace gasses but with a lower time resolution.

Mitigation of methane emission from an old unlined landfill in Klintholm, Denmark using a passive biocover system.

Methane generated at landfills contributes to global warming and can be mitigated by biocover systems relying on microbial methane oxidation. As part of a closure plan for an old unlined landfill without any gas management measures, an innovative biocover system was established. The system was designed based on a conceptual model of the gas emission patterns established through an initial baseline study. The study included construction of gas collection trenches along the slopes of the landfill where the majority of the methane emissions occurred. Local compost materials were tested as to their usefulness as bioactive methane oxidizing material and a suitable compost mixture was selected. Whole site methane emission quantifications based on combined tracer release and downwind measurements in combination with several local experimental activities (gas composition within biocover layers, flux chamber based emission measurements and logging of compost temperatures) proved that the biocover system had an average mitigation efficiency of approximately 80%. The study showed that the system also had a high efficiency during winter periods with temperatures below freezing. An economic analysis indicated that the mitigation costs of the biocover system were competitive to other existing greenhouse gas mitigation options.

Gas production, composition and emission at a modern disposal site receiving waste with a low-organic content.

AV Miljø is a modern waste disposal site receiving non-combustible waste with a low-organic content. The objective of the current project was to determine the gas generation, composition, emission, and oxidation in top covers on selected waste cells as well as the total methane (CH(4)) emission from the disposal site. The investigations focused particularly on three waste disposal cells containing shredder waste (cell 1.5.1), mixed industrial waste (cell 2.2.2), and mixed combustible waste (cell 1.3). Laboratory waste incubation experiments as well as gas modeling showed that significant gas generation was occurring in all three cells. Field analysis showed that the gas generated in the cell with mixed combustible waste consisted of mainly CH(4) (70%) and carbon dioxide (CO(2)) (29%) whereas the gas generated within the shredder waste, primarily consisted of CH(4) (27%) and nitrogen (N(2)) (71%), containing no CO(2). The results indicated that the gas composition in the shredder waste was governed by chemical reactions as well as microbial reactions. CH(4) mass balances from three individual waste cells showed that a significant part (between 15% and 67%) of the CH(4) generated in cell 1.3 and 2.2.2 was emitted through leachate collection wells, as a result of the relatively impermeable covers in place at these two cells preventing vertical migration of the gas. At cell 1.5.1, which is un-covered, the CH(4) emission through the leachate system was low due to the high gas permeability of the shredder waste. Instead the gas was emitted through the waste resulting in some hotspot observations on the shredder surface with higher emission rates. The remaining gas that was not emitted through surfaces or the leachate collection system could potentially be oxidized as the measured oxidation capacity exceeded the potential emission rate. The whole CH(4) emission from the disposal site was found to be 820 ± 202 kg CH(4)d(-1). The total emission rate through the leachate collection system at AV Miljø was found to be 211 kg CH(4)d(-1). This showed that approximately » of the emitted gas was emitted through the leachate collections system making the leachate collection system an important source controlling the overall gas migration from the site. The emission pathway for the remaining part of the gas was more uncertain, but emission from open cells where waste is being disposed of or being excavated for incineration, or from horizontal leachate drainage pipes placed in permeable gravel layers in the bottom of empty cells was likely.

Methane oxidation in Swedish landfills quantified with the stable carbon isotope technique in combination with an optical method for emitted methane.

Methane budgets (production = emissions + oxidation + recovery) were estimated for six landfill sites in Sweden. Methane oxidation was measured in downwind plumes with a stable isotope technique (Chanton, J. P., et al., Environ. Sci Technol. 1999, 33, 3755-3760.) Positions in plumes for isotope sampling as well as methane emissions were determined with an optical instrument (Fourier Transform InfraRed) in combination with N20 as tracer gas (Galle, B., et al., Environ. Sci Technol. 2001, 35, 21-25.) Two landfills had been closed for years prior to the measurements, while four were active. Measurements at comparable soil temperatures showed that the two closed landfills had a significantly higher fraction of oxidized methane (38-42% of emission) relative to the four active landfills (4.6-15% of emission). These results highlight the importance of installing and maintaining effective landfill covers and also indicate that substantial amounts of methane escape from active landfills. Based on these results we recommend that the IPCC default values for methane oxidation in managed landfills could be set to 10% for active sites and 20% for closed sites. Gas recovery was found to be highly variable at the different sites, with values from 14% up to 65% of total methane production. The variance can be attributed to different waste management practices.