Composition of Municipal Solid Waste in the United States and Implications for Carbon Sequestration and Methane Yield

Eleven statewide waste characterization studies were compared to assess variation in the quantity and composition of waste after separation of recyclable and compostable materials, i.e., discarded waste. These data were also used to assess the impact of varying composition on sequestered carbon and methane yield. Inconsistencies in the designation of waste component categories and definitions were the primary differences between study methodologies; however, sampling methodologies were consistent with recommended protocols. The average municipal solid waste (MSW) discard rate based on the statewide studies was 1.90?kg?MSW?person?1?day?1, which was within the range of two national estimates: 2.35 and 1.46?kg?MSW?person?1?day?1. Dominant components in MSW discards were similar between studies. Organics (food waste, yard trimmings), paper, and plastic components averaged 23.6±4.9%, 28.5±6.5%, and 10.6±3.0% of discarded MSW, respectively. Construction and demolition (C&D) waste was 20.2±9.7% of total solid waste discards (i.e., MSW plus C&D). Based on average statewide waste composition data, a carbon sequestration factor (CSF) for MSW of 0.13 kg C dry kg?MSW?1 was calculated. For C&D waste, a CSF of 0.14 kg C dry kg C and D waste?1 was estimated. Ultimate methane yields (Lo) of 59.1 and 63.9?m3 CH4 wet Mg refuse?1 were computed using EPA and state characterization study data, respectively, and were lower than AP-42 guidelines. Recycling, combustion, and other management practices at the local level could significantly impact CSF and (Lo) estimates, which are sensitive to the relative fraction of organic components in discarded MSW and C&D waste.     

Pollution Management in the Twentieth Century

A literature review is presented on the evolution of water pollution management and its impact on land pollution from 1900 to 2000 within an hypothesis of whether we could have done more, sooner. Stream pollution science in the context of the fundamental sanitary engineering concepts of reasonable use and assimilative capacity is examined in light of evolving regulatory frameworks from the early 1900s, when regulation and standards were mostly lacking, to the zero discharge goals and comprehensive federal command/control regulations of the late Twentieth Century. Details on the interplay through the years of improving environmental analytical chemistry, environmental quality definitions, wastewater control technologies, municipal–industrial wastewater differences, and regulatory will/diligence are provided. The pressure exerted on land and groundwater pollution as a result of water pollution control is emphasized. The author’s conclusion is that more effective, faster pollution control evolution would have been difficult.     

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.     

Evaluating the Mobility of Arsenic in Synthetic Iron-Containing Solids Using a Modified Sequential Extraction Method

Many water treatment technologies for arsenic removal that are used today produce arsenic-bearing residuals which are disposed in nonhazardous landfills. Previous works have established that many of these residuals will release arsenic to a much greater extent than predicted by standard regulatory leaching tests (e.g., the toxicity characteristic leaching procedure) and, consequently, require stabilization to ensure benign behavior after disposal. In this work, a four-step sequential extraction method was developed in an effort to determine the proportion of arsenic in various phases in untreated as well as stabilized iron-based solid matrices. The solids synthesized using various potential stabilization techniques included: amorphous arsenic-iron sludge (ASL), reduced ASL via reaction with zero valent iron (RASL), amorphous ferrous arsenate (PFA), a mixture of PFA and SL (M1), crystalline ferrous arsenate (HPFA), and a mixture of HPFA and SL (M2). The overall arsenic mobility of the tested samples increased in the following order: ASL>RASL>PFA>M1>HPFA>M2.     

Life-Cycle Assessment of Waste Management Greenhouse Gas Emissions Using Municipal Waste Combustor Data

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.     

Results from 18 Years of In Situ Performance Testing of Landfill Cover Systems in Germany

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 2×10?10 to 9×10?8?m/s, the daily peaks of the leakage through the geosynthetic clay barriers from initial values around 2×10?11?to?2×10?7?m3/(m2?s). 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.     

Secondary Compression of Municipal Solid Wastes and a Compression Model for Predicting Settlement of Municipal Solid Waste Landfills

The estimation of the capacity and settlement of landfills is critical to successful site operation and future development of a landfill. This paper reports the results of a study on biodegradation behavior and the compression of municipal solid wastes. An experimental apparatus was developed which had a temperature-control system, a leachate recycling system, a loading system, and a gas and liquid collection system. Experiments were performed both with and without optimal biodegradation for comparative purposes. Test results indicated that settlement resulting from creep was relatively insignificant when the biodegradation process was inhibited. Compression due to decomposition under optimal biodegradation conditions was found to be much larger than compression associated with creep. The biodegradation process was significantly influenced by the operational temperature. A one-dimensional model is proposed for calculating settlement and estimating the capacity of the landfill under relatively optimal biodegradation conditions. The model was developed to accommodate the calculation of settlement in landfills when a multistep filling procedure was used. The calculation method is relatively simple and convenient for design purposes. Simulations of the physical processes showed that enhancing solid waste biodegradation during the filling stage can considerably increase the capacity of the landfill and reduce postclosure settlements.     

Compaction Characteristics of Municipal Solid Waste

Compaction characteristics of municipal solid waste (MSW) were determined in the laboratory and in the field as a function of moisture content, compactive effort, and seasonal effects. Laboratory tests were conducted on manufactured wastes using modified and 4X modified efforts. Field tests were conducted at a MSW landfill in Michigan on incoming wastes without modifications to size, shape, or composition, using typical operational compaction equipment and procedures. Field tests generally included higher efforts and resulted in higher unit weights at higher water contents than the laboratory tests. Moisture addition to wastes in the field was more effective in winter than in summer due to dry initial conditions and potential thawing and softening of wastes. The measured parameters in the laboratory were γdmax-mod = 5.2?kN/m3, wopt-mod = 65%, γdmax-4×mod = 6.0?kN/m3, and wopt-4×mod = 56%; in the field with effort were γdmax-low = 5.7?kN/m3, wopt-low = 70%; γdmax-high = 8.2?kN/m3, and wopt-high = 73%; and in the field with season were γdmax-cold = 8.2?kN/m3, wcold = 79.5%, γdmax-warm = 6.1?kN/m3, and wwarm = 70.5%. Soil compaction theory was reasonably applicable to wastes with the exception that the Gs of waste solids increased with compactive effort resulting in steep degree of saturation curves and low change in wopt between efforts. Moisture addition to wastes during compaction increased the workability, the unit weight, and the amount of incoming wastes disposed, and reduced the compaction time. The combined effects have significant environmental and economic implications for landfill operations.     

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.     

Clogging of Gravel Drainage Layers Permeated with Landfill Leachate

Ten flow cells, called mesocosms, are used to investigate the effect of different gravel sizes (38 and 19?mm) and operating conditions on clogging of leachate collection systems. These mesocosms simulated in real time and real scale the two-dimensional leachate flow conditions representative of a section of a continuous 300-mm-thick gravel drainage blanket adjacent to a leachate collection pipe in a primary leachate collection system. The tests were terminated after 6–12?years of operation. In some mesocosms the full 300?mm of gravel was saturated. In others, the leachate level was initially set at 100?mm and the upper 200?mm were unsaturated. Although the flow through all mesocosms was similar, the clogging in the fully saturated gravel was substantially more than in the partially saturated gravel. After 6?years of operation, typically, less than 10% of the initial pore space was filled with clog material in the unsaturated gravel. For the saturated zone, 45% of the initial pore space was filled with clog material in the fully saturated design as compared to only 31% in the partially saturated design. The 38?mm gravel performed much better than the 19?mm gravel. For example, it maintained a hydraulic conductivity that was higher than the 19?mm gravel even after operating for twice as long. Up to four mesocosms were placed in series, with the effluent from one mesocosm being the influent for another. The reduction in mass loading within the first mesocosm reduced the amount of clogging within the mesocosm later in series. There was a clear progression of decreasing amounts of initial pore space filled with clog material in the last mesocosm in series, and most of the clogging was due to the vertically percolating leachate.