Modeling of Biodegradation in an Old Unregulated European Landfill

In this note an example of modeling of biodegradation processes of an old abandoned municipal solid waste landfill for its simulation is illustrated using the landfill dynamic simulation tool MODUELO. In this program the waste biodegradation model is based on the quantification of organic matter, its chemical composition, biodegradability, accessibility to microorganisms, and the ratio nonbiodegradable leachable organic matter to gasifiable matter. Data from a characterization campaign, presented elsewhere, were used to determine these parameters. The experimental information was completed with safety factors (to compensate for sampling uncertainty) and literature values. The degradation rates were determined, after having calibrated the hydrological model, by fitting the temporal series of pollutants’ concentration measured in the leachate and the biogas composition. The achieved fit of the simulated series compared to the measured data is reported as the result of this work. Given the limited information available, the obtained simulation model is considered an acceptable tool to study the future evolution of the landfill in different circumstances.     

Composite Compressibility Model for Municipal Solid Waste

Three important mechanisms that contribute to the compression of municipal solid waste are instantaneous compression in response to applied load, secondary mechanical creep, and time-dependent biological decomposition. A composite compressibility model that explicitly takes these mechanisms into account was developed and implemented in a computer program to calculate landfill settlements. The model performance was assessed using data from the Bandeirantes Landfill, which is a well-documented landfill located in Sao Paulo, Brazil, and upon which an instrumented test fill was constructed. Model parameter values were obtained by nonlinear regression analysis, and it was found that the composite model tracked observed patterns of landfill settlement very well. Furthermore, the average parameter values from nonlinear regression analyses for 20 instruments exhibited small deviations between calculated and observed settlements, indicating that a single set of parameter values can provide reasonably good representation of all the waste in the vicinity of the test fill. Recommendations for applying the model to other landfills are provided.     

Unit Weight of Municipal Solid Waste

The unit weight of municipal solid waste (MSW) is an important parameter in engineering analyses of landfill performance, but significant uncertainty currently exists regarding its value. A careful review of reliable field data shows that individual landfills have a characteristic MSW unit weight profile. Based on in situ unit weight data and trends observed in large-scale laboratory tests, a hyperbolic relationship was developed to represent this characteristic MSW unit weight profile. Within the context of this characteristic profile, landfill-specific values of MSW unit weight depend primarily on waste composition, operational practices (i.e., compaction, cover soil placement, and liquids management), and confining stress. Guidance is provided for developing landfill-specific MSW unit weight profiles, including procedures for performing large-scale tests for in situ measurement of MSW unit weight at a landfill.     

Estimation of Soil–Water Characteristic Curve of Clayey Till Using Measured Pore-Size Distributions

The soil–water characteristic curve (SWCC) of fine-grained soils is usually determined experimentally. In the design of mine waste covers and landfill liners, the unsaturated hydraulic conductivity function, k(h), is often derived theoretically from the measured SWCC. Implicit in these derivations is the transformation of the SWCC to a pore-size distribution (PSD), typically assumed to be constant and monomodal. However, PSD measurements of a clayey till compacted at various water contents after compaction, after flexible-wall permeability testing and before and after SWCC tests show that the PSD of the same material varies significantly under the stated physical conditions. Predictions of the SWCCs using PSDs measured both before and after the SWCC tests significantly underpredicted the values measured. By applying a simple transformation to the PSD to account for the scaling effect from the porosimetry samples (approximately 1 g dry weight) to the SWCC test samples (approximately 200 g dry weight), the predicted SWCCs were found to envelop the measured values. A simple model that simulates the change in PSD during the SWCC test predicted water contents close (1% root mean square error) to the measured SWCCs.     

Performance of North American Bioreactor Landfills. I: Leachate Hydrology and Waste Settlement

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?L/m2?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.     

Potential use of Kraft pulp mill and flat glass cutting wastes in red ceramic products

This study assessed the incorporation of green liquor dregs, an inorganic solid waste from Kraft pulp mill, and flat glass cutting waste (FGCW) into red ceramic formulations. Since in Brazil sanitary landfills are still the main destination of industrial wastes such as those used in this research, a survey was conducted to identify the number of landfills in the region of origin of each waste and the amount of waste that could have this destination avoided. The effects of firing temperature and simultaneous incorporation of both industrial wastes were analyzed to optimize heat treatment and waste content in the formulation to manufacture red ceramic products. The influence of green liquor dregs and FGCW incorporation into clayey mass was evaluated varying waste content between 0 and 50 wt%. The specimens were prepared by uniaxial pressing, fired at 850 and 950 °C, and had their physical-mechanical properties and mineralogical and microstructural characteristics analyzed. The best results were obtained for the formulation with 10 wt% green liquor dregs and 30 wt% FGCW fired at 950 °C. This result highlights the potential of using green liquor dregs, a waste difficult to be recycled due to its chemical composition, associated with FGCW, which acts as a fluxing agent in ceramic formulations.     

Thermal Analysis of Cover Systems in Municipal Solid Waste Landfills

Cover temperature variations were determined at four municipal solid waste landfills located in different climatic regions in North America: Michigan, New Mexico, Alaska, and British Columbia. Cover temperatures varied seasonally similarly to air temperatures and demonstrated amplitude decrement and phase lag with depth. Elevated temperatures in the underlying wastes resulted in warmer temperatures and low frost penetration in the covers compared to surrounding subgrade soils. The ranges of measured temperatures decreased and average temperatures generally increased (approximately 2°C/m) with depth. The ranges of measured temperatures (Tmax?Tmin) were 18–30°C and 13–21°C and the average temperatures were 13–18°C and 14–23°C at 1 and 2?m depths, respectively. For soil and geosynthetic barrier materials around 1?m depth, the maximum and minimum temperatures were 22–25°C and 3–4°C, respectively. Frost depths were determined to be approximately 50% of those for soils at ambient conditions. The main direction of heat flow in the covers was upward (negative gradients). The cover gradients varied between ?18 and 14°C/m, with averages of ?7?to?1°C/m. The gradients for soil and geosynthetic barrier materials around 1?m depth varied between ?11 and 9°C/m with an average of ?2°C/m. Cover thawing n-factors ranged between 1.0 and 1.4 and the cover freezing n-factor was 0.6. Design charts and guidelines are provided for cover thermal analyses for variable climatic conditions.     

Municipal Solid Waste Landfill Settlement: Postclosure Perspectives

This paper presents settlement mechanisms and the methods for estimating settlements of municipal solid waste landfills, including bioreactor landfills. Based on results of field monitoring and data in published literature, coefficients of secondary compression for solid waste due to self-weight and external load are estimated. Special considerations are given to bioreactor landfills. Uses of these coefficients for long-term settlement estimation and their application to postclosure maintenance and development plans are discussed. Four case histories illustrating the use of these coefficients are presented. Methods of landfill treatment to reduce settlements are also presented.     

Long Term Landfill Primary and Secondary Leachate Production

This study evaluated long term primary and secondary leachate production from operating landfills in the northeastern United States. The data were obtained for periods when the landfills were in use (open) and were covered (closed). During the open period of operation, primary leachate production was 64% of the precipitation that fell on the site. After landfill cell closure, the primary leachate production declined and, four years after closure, such production reached quasi-equilibrium and averaged 2% of the precipitation. For secondary leachate production during the open and closed period, such production was 1 and 0.25% of the precipitation, respectively.     

Shear Strength Parameters of Municipal Solid Waste with Leachate Recirculation

The objective of this study was to characterize relative changes in waste shear strength parameters during waste decomposition. Twelve direct shear tests (100?mm diameter by 50?mm thickness) were performed on waste specimens ranging from fresh to well-decomposed residential refuse. In addition, nine direct shear tests were performed on selected waste components including fresh paper, partially decomposed refuse, and plastics. Results indicate that the friction angle of refuse decreased with decomposition. As refuse decomposed, the plastic content increased, which contributed to a decrease in friction angle as the friction angle of plastics is 18–19° as compared to 33° for fresh shredded waste. The extent of refuse decomposition was characterized by the cellulose plus hemicellulose to lignin ratio [(C+H)/L]. The measured friction angle decreased from 32 to 24° as (C+H)/L decreased from 1.29 to 0.25. The shearing pattern for decomposed refuse showed a peak, followed by residual, which was then followed by a steady increase in shear stresses with displacement; the final rate of increase was similar to that observed in fresh paper specimens. Results from this work were comparable to data from previous reports, though it is important to characterize the extent of solids decomposition for a valid comparison with published studies.