Journal of Environmental Engineering

This paper compares life-cycle greenhouse gas (GHG) emissions from two municipal solid waste (MSW) management options, municipal waste combustion, and landfilling, using a U.S. EPA life-cycle assessment (LCA) model, the MSW Decision Support Tool. Unlike previously reported LCAs, key combustion model inputs—total MSW carbon content and its biogenic/fossil split—are determined not from MSW composition studies, but from measurements taken at operating municipal waste combustors (MWCs). MWC measurement data show U.S. MSW carbon content averages of 30% with a biogenic/fossil split of 66%/34%. The LCA also considers a range of landfilling scenarios which account not only for alternative landfill gas (LFG) management techniques, but also for the variability of landfill methane generation and capture. The LCA found that for the range of inputs and scenarios considered, municipal waste combustion outperforms landfilling in terms of GHG emissions, regardless of the LFG management technique.

Modern waste management practices encourage the recovery of energy from municipal solid waste after efforts to reduce, reuse, and recycle appropriate materials. Energy can be recovered through direct mass burn in a waste-to-energy (WTE) facility or through the collection and combustion of biogas generated in sanitary landfills. Many comparisons have been made although rarely using best practice assumptions for both technologies; WTE proponents tend to assume low collection efficiency while landfill proponents tend to assume low electrical conversion efficiency. In general, WTE plants can be considered to have a better environmental performance (reduced emissions) with landfill having lower total costs (social and environmental). Both strategies have similar costs when considering 77% collection efficiency and a high efficiency (30% electrical conversion) WTE plant that displaces electricity from coal. The introduction of carbon capture and storage (CCS) technologies to waste management changes the landscape by increasing the capital costs and improving the environmental performance. The air emissions are significantly reduced, practically eliminated with oxygen combustion, as the capture of ${\text{CO}}_2$ requires significant flue gas scrubbing. The introduction of CCS results in a net environmental benefit for WTE plants with a turnaround electricity price of $7/MWh, as compared to landfill gas with capture. The largest environmental cost for WTE plants is the classification of fly ash as chemical waste, which is reduced with oxygen combustion. The net cost of capturing ${\text{CO}}_2$ from WTE facilities is estimated at $39/t ${\text{CO}}_2$ , one-third of the cost of ${\text{CO}}_2$ capture from landfills.

The mobility of zinc in coastal landfill sites reclaimed by municipal solid waste incinerator ash (MSWIA) was modeled and investigated by conducting a large column test. Temporal and spatial variations in the pH, redox potential (Eh), total organic carbon, and microbial activity were measured in pore water to observe their influences on the mobility of heavy metals throughout the test. After 502 days, permeation was terminated. Then to determine the content and forms of Zn along the column, MSWIA and marine clay samples were analyzed by the community bureau of reference modified sequential extraction procedure. Zn was partitioned into four defined chemical fractions: exchangeable, reducible, oxidizable, and residual. The results showed that attenuation processes occurred within the ash layer, Zn mobility was minor, and coastal landfill conditions promoted the immobilization of heavy metals. Both pH and Eh were the main factors for controlling the solubility of Zn. Moreover, under reduced-alkaline conditions, the reducible fraction was affected, but the oxidizable fraction was slightly favored. The formation of zinc sulphides might be another attenuation mechanism for Zn.

In 2006, the U.S. Environmental Protection Agency posted a new test method on its website called Other Test Method 10 (OTM 10) which describes direct measurement of pollutant mass emission flux from area sources using ground-based optical remote sensing. The method has validated application to relatively small bounded area sources but additional guidance is needed for large area sources, such as landfills, where the emission zone can exceed the size of optical configuration leading to difficulties in relating measured fluxes to emissions per unit area. This paper presents the findings of a series of tracer-release experiments designed to improve the understanding of OTM 10 in landfill applications. OTM 10 plume capture efficiency data acquired at a variety of landfill sites under a range of meteorological conditions and measurement configurations are presented. Experiments indicate an overall capture efficiency factor of 0.81 with a standard deviation of 0.33. Lower capture efficiencies from side slope releases are noted (0.69). The combined data set is analyzed for factors influencing capture efficiency. A multiple linear regression is used to model the capture efficiency as a function of primary parameters including distance of the tracer release from the observing plane and wind speed. A simplified model based on the regression analysis is described and its use for approximating the area contributing to flux is presented.

The study presented in this paper has been initiated by the Veolia Environment research center for waste management and supported by the French Environmental Agency. A comparison of five field-scale measurement methods for measuring fugitive methane emissions has been conducted on a French landfill site. The five methods evaluated consisted of a tracer gas technique, laser radial plume mapping, inverse modeling technique, differential absorption light detection and ranging (LiDAR), and helicopter-borne spectroscopy. These methods are evaluated on their abilities to measure emissions from a practical user-oriented aspect (metrological, technical, and economical criteria). High disparities in terms of quantitative results and applicability were observed from all methods. Techniques that used Gaussian dispersion modeling appeared less applicable to landfill sites due to topographic complexity and did not provide high confidence in the results. However, the method using optical remote sensing (radial plume mapping) methods showed that a spatially detailed analysis is achievable (cell level), and the LiDAR method showed very promising approach and technical performances.

An experimental passive methane oxidation biocover (PMOB) was constructed within the existing final cover of the St-Nicéphore landfill. Its substrate consisted of a 0.80-m-thick mixture of sand and compost. The goal of this experiment was to evaluate the performance of the PMOB in reducing ${\text{CH}}_4$ emissions when submitted to an increasing methane load. The ${\text{CH}}_4$ load applied started with $9.3\text{g}{\text{CH}}_4{\text{m}}^{-2}{\text{d}}^{-1}$ . When the site had to be closed for the winter, the ${\text{CH}}_4$ input was $820\text{g}{\text{CH}}_4{\text{m}}^{-2}{\text{d}}^{-1}$ . Throughout the study, practically all the ${\text{CH}}_4$ input was oxidized; absolute removal rates were linearly correlated to methane loading; and the oxidation zone was established between 0.6–0.8 m. These results seem to indicate that the upper limit potential of this PMOB to oxidize ${\text{CH}}_4$ was not necessarily reached during the study period. Surface ${\text{CH}}_4$ concentration scans showed no signs of leaks. The substrate offered excellent conditions for the growth of methanotrophs, whose count averaged $3.91\times {10}^8\text{CFU}\text{g}{\text{dw}}^{-1}$ soil.

A method to control the increase in landfill liner temperature due to the heat generated by the waste is examined. The design involves installation of an array of cooling pipes beneath the waste. The feasibility of this system for cooling the liner was examined by performing a series of analyses for conditions based on the Tokyo Port Landfill. The results suggest that the introduction of a cooling system can substantially reduce liner temperature and consequently significantly increase the service life of a high-density polyethylene (HDPE) geomembrane liner in an engineered barrier system. The effects of pipe layout, pipe spacing, and coolant flow rate are examined. It is shown that a periodic pipe layout is the most efficient. Liner temperature decreases with increased coolant transfer flow rate

Long-term spatial and temporal variations in temperatures have been investigated in covers, wastes, and liners at four municipal solid waste landfills located in different climatic regions: Alaska, British Columbia, Michigan, and New Mexico. Temperatures were measured in wastes with a broad range of ages from newly placed to old (up to 40 years). The characteristic shape of waste temperature versus depth relationships consisted of a convex temperature profile with maximum temperatures observed at central locations within the middle third fraction of the depth of the waste mass. Lower temperatures were observed above and below this central zone, with seasonal fluctuations occurring near the surface and steady and elevated values (above mean annual earth temperature) near the base of the landfills. Heat gain and long-term temperatures were directly affected by placement temperatures. Sustained concave temperature profiles were observed for winter waste placement. The highest heat gain and resulting high temperatures were observed in Michigan followed by British Columbia, New Mexico, and Alaska. The high heat gain in Michigan was attributed to coupled precipitation/moisture content and waste density. The time-averaged waste temperature ranges were 0.9–33.0, 14.4–49.2, 14.8–55.6, and $20.5–33.6°\text{C}$ in Alaska, British Columbia, Michigan, and New Mexico, respectively. Temperature increases occurred rapidly (over multiple years) in British Columbia and then dissipated for tens of years. Longer periods of temperature increase were observed at the other sites. Temperatures, temperature increases, and heat gain were higher during anaerobic decomposition of wastes than aerobic decomposition. A parametric study indicated that use of insulating materials over covers decreased temperature variations compared to uninsulated conditions for prevention of frost penetration or desiccation and for optimum methane oxidation. Overall, thermal regime of landfills is controlled by climatic and operational conditions.

The water balances and the long-term performance of different landfill cover systems have been measured in situ in large-scale lysimeters on the landfill Hamburg-Georgswerder, Germany since 1988. The cover systems including different barrier components for water transport were constructed with state-of-the-art technology and have been excavated at several occasions especially to inspect the structure of the barriers. For the first time, the irreversible impact of crack formation in cohesive soil barriers and geosynthetic clay barriers due to desiccation, shrinkage, ion exchange, and plant root penetration has been observed and quantified in this study. After four years of good performance, these covers began to leak between 90 and 200 mm/year (average precipitation of 860 mm/year). The hydraulic conductivity of the cohesive soil barriers increased from $2\times {10}^{-10}$ to $9\times {10}^{-8}\text{m}/\text{s}$ , the daily peaks of the leakage through the geosynthetic clay barriers from initial values around $2\times {10}^{-11}\text{\hspace{0.17em}to\hspace{0.17em}}2\times {10}^{-7}{\text{m}}^3/\left({\text{m}}^2\text{s}\right)$ . The composite barriers with geomembranes above cohesive soil barriers performed very well, showing no leakage and only very little thermally induced water transport. A capillary barrier also performed well (average annual leakage of 18 mm/year). The data of the past 10 years prove that evapotranspiration can be increased significantly by planting bushes, which also limits the potential leakage through barrier layers.

An assessment of state-of-the-practice at five full-scale North American landfills operating as bioreactors is presented in this two-paper set. This paper focuses on effectiveness of liners and leachate collection systems, leachate generation rates, leachate recirculation practices and rates, effectiveness in moistening the waste, and settlement of the waste over time. Except in one case, the liner and leachate collection systems at the bioreactor landfills were similar to those used for landfills operated conventionally. Leachate generation rates increased approximately linearly with recirculation rate, but in all cases, the leachate generation rate was $<300\text{L}/{\text{m}}^2\text{year}$ . Leachate depths generally were maintained within regulatory requirements, even with the highest recirculation rates. Leakage rates from liners at bioreactor landfills, including alternative liner designs employing geosynthetic clay liners, are comparable to leakage rates from conventional landfills. Thus, based on the information gathered in this study, additional requirements or features for liners or leachate collection systems are not warranted for bioreactor landfills. Diminishing capacity of horizontal recirculation trenches is common. Experience at one landfill suggests that small doses at high frequency under substantial injection pressure can deter loss of trench capacity. Only those landfills that were aggressive in recirculation had achieved water contents near the field capacity. Increasing the amount of liquid that is added may be required to achieve field capacity at some landfills, particularly if a final cover is placed soon after waste grades are reached. The rate of time-dependent waste settlement attributed to biodegradation is about 1.6 times larger in bioreactor landfills than in conventional landfills, and increases as the recirculation dosage increases.

The objective of this research was to examine the performance of five North American bioreactor landfills. This paper represents the second of a two-part series and addresses biological and chemical aspects of bioreactor performance including gas production and management, and leachate chemistry. The data support accelerated methane generation at several landfills $\left(k=0.08–0.211/\text{year}\right)$ relative to the AP-42 default decay rate $\left(k=0.041/\text{year}\right)$ . While the data indicate that gas collection increases at bioreactor landfills, a general relationship between decay rate and moisture added or wet weight water content could not be identified. There was no indication that gas collection increases appreciably when the water content reaches 40%. Most of the leachates at the landfills in this study were commingled from cells operating as a bioreactor and conventionally. Nevertheless, trends in pH and BOD:COD in the bioreactor leachates were consistent with the impacts of enhanced biological activity. Ammonia concentrations also increased over time but remained below levels reported to be inhibitory. For both heavy metals and speciated organic chemicals, there was no indication that bioreactor landfill leachate is significantly different from leachate generated at conventional landfills.

Leachate from mixed glass cullet (crushed recycled glass containers) that is stockpiled before use as construction aggregate or sand substitute is a potential source of water pollution. Rainwater leaching through the stockpiles dissolves and suspends organic compounds and nutrients from the glass. The objectives of this study were to investigate the effect of forced aeration on leachate quantity and quality in the glass cullet stockpiles compared to mechanical turning/mixing. Three experimental stockpiles were set up in the field, two with forced aeration treatment (one with fine and the other with coarse cullet) and one (coarse cullet) with mechanical turning. The organic concentrations in the leachate in most cases were comparable to those of raw domestic wastewater. Organic constituents (e.g., ${\text{BOD}}_5$ ) were reduced $\text{by}>70\mathrm{\%}$ from the initial levels $\left(\sim 450\text{mg}{\text{L}}^{-1}\right)$ during a 1.5-month period with forced aeration, compared to an 85% decrease in the turned stockpile. Particle size affected temperature and oxygen levels under aeration conditions, resulting in more biodegradation of organic contaminants in the stockpile of coarse cullet than the fine cullet.