@article{sun_wang_decarolis_barlaz_2019, title={Evaluation of optimal model parameters for prediction of methane generation from selected US landfills}, volume={91}, ISSN={["0956-053X"]}, DOI={10.1016/j.wasman.2019.05.004}, abstractNote={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.}, journal={WASTE MANAGEMENT}, author={Sun, Wenjie and Wang, Xiaoming and DeCarolis, Joseph F. and Barlaz, Morton A.}, year={2019}, month={May}, pages={120–127} }
 @article{wang_barlaz_2016, title={Decomposition and carbon storage of hardwood and softwood branches in laboratory-scale landfills}, volume={557}, journal={Science of the Total Environment}, author={Wang, X. M. and Barlaz, M. A.}, year={2016}, pages={355–362} }
 @article{wang_nagpure_decarolis_barlaz_2015, title={Characterization of Uncertainty in Estimation of Methane Collection from Select US Landfills}, volume={49}, ISSN={["1520-5851"]}, DOI={10.1021/es505268x}, abstractNote={Methane is a potent greenhouse gas generated from the anaerobic decomposition of waste in landfills. If captured, methane can be beneficially used to generate electricity. To inventory emissions and assist the landfill industry with energy recovery projects, the U.S. EPA developed the Landfill Gas Emissions Model (LandGEM) that includes two key parameters: the first-order decay rate (k) and methane production potential (L0). By using data from 11 U.S. landfills, Monte Carlo simulations were performed to quantify the effect of uncertainty in gas collection efficiency and municipal solid waste fraction on optimal k values and collectable methane. A dual-phase model and associated parameters were also developed to evaluate its performance relative to a single-phase model (SPM) similar to LandGEM. The SPM is shown to give lower error in estimating methane collection, with site-specific best-fit k values. Most of the optimal k values are notably greater than the U.S. EPA's default of 0.04 yr(-1), which implies that the gas generation decreases more rapidly than predicted at the current default. We translated the uncertainty in collectable methane into uncertainty in engine requirements and potential economic losses to demonstrate the practical significance to landfill operators. The results indicate that landfill operators could overpay for engine capacity by $30,000-780,000 based on overestimates of collectable methane.}, number={3}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Wang, Xiaoming and Nagpure, Ajay S. and DeCarolis, Joseph F. and Barlaz, Morton A.}, year={2015}, month={Feb}, pages={1545–1551} }
 @article{wang_cruz_ximenes_barlaz_2015, title={Decomposition and carbon storage of selected paper products in laboratory-scale landfills}, volume={532}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2015.05.132}, abstractNote={The objective of this study was to measure the anaerobic biodegradation of different types of paper products in laboratory-scale landfill reactors. The study included (a) measurement of the loss of cellulose, hemicellulose, organic carbon, and (b) measurement of the methane yields for each paper product. The test materials included two samples each of newsprint (NP), copy paper (CP), and magazine paper (MG), and one sample of diaper (DP). The methane yields, carbon storage factors and the extent of cellulose and hemicellulose decomposition all consistently show that papers made from mechanical pulps (e.g., NPs) are less degradable than those made from chemical pulps where essentially all lignin was chemically removed (e.g., CPs). The diaper, which is not only made from chemical pulp but also contains some gel and plastic, exhibited limited biodegradability. The extent of biogenic carbon conversion varied from 21 to 96% among papers, which contrasts with the uniform assumption of 50% by the Intergovernmental Panel on Climate Change (IPCC) for all degradable materials discarded in landfills. Biochemical methane potential tests also showed that the solids to liquid ratio used in the test can influence the results.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, publisher={Elsevier BV}, author={Wang, Xiaoming and Cruz, Florentino B. and Ximenes, Fabiano and Barlaz, Morton A.}, year={2015}, month={Nov}, pages={70–79} }
 @article{wang_padgett_powell_barlaz_2013, title={Decomposition of forest products buried in landfills}, volume={33}, ISSN={["0956-053X"]}, DOI={10.1016/j.wasman.2013.07.009}, abstractNote={The objective of this study was to investigate the decomposition of selected wood and paper products in landfills. The decomposition of these products under anaerobic landfill conditions results in the generation of biogenic carbon dioxide and methane, while the un-decomposed portion represents a biogenic carbon sink. Information on the decomposition of these municipal waste components is used to estimate national methane emissions inventories, for attribution of carbon storage credits, and to assess the life-cycle greenhouse gas impacts of wood and paper products. Hardwood (HW), softwood (SW), plywood (PW), oriented strand board (OSB), particleboard (PB), medium-density fiberboard (MDF), newsprint (NP), corrugated container (CC) and copy paper (CP) were buried in landfills operated with leachate recirculation, and were excavated after approximately 1.5 and 2.5 yr. Samples were analyzed for cellulose (C), hemicellulose (H), lignin (L), volatile solids (VS), and organic carbon (OC). A holocellulose decomposition index (HOD) and carbon storage factor (CSF) were calculated to evaluate the extent of solids decomposition and carbon storage. Samples of OSB made from HW exhibited cellulose plus hemicellulose (C + H) loss of up to 38%, while loss for the other wood types was 0–10% in most samples. The C + H loss was up to 81%, 95% and 96% for NP, CP and CC, respectively. The CSFs for wood and paper samples ranged from 0.34 to 0.47 and 0.02 to 0.27 g OC g−1 dry material, respectively. These results, in general, correlated well with an earlier laboratory-scale study, though NP and CC decomposition measured in this study were higher than previously reported.}, number={11}, journal={WASTE MANAGEMENT}, author={Wang, Xiaoming and Padgett, Jennifer M. and Powell, John S. and Barlaz, Morton A.}, year={2013}, month={Nov}, pages={2267–2276} }
 @article{wang_nagpure_decarolis_barlaz_2013, title={Using observed data to improve estimated methane collection from select US landfills}, volume={47}, DOI={10.1021/es304565m}, abstractNote={The anaerobic decomposition of solid waste in a landfill produces methane, a potent greenhouse gas, and if recovered, a valuable energy commodity. Methane generation from U.S. landfills is usually estimated using the U.S. EPA's Landfill Gas Emissions Model (LandGEM). Default values for the two key parameters within LandGEM, the first-order decay rate (k) and the methane production potential (L0) are based on data collected in the 1990s. In this study, observed methane collection data from 11 U.S. landfills and estimates of gas collection efficiencies developed from site-specific gas well installation data were included in a reformulated LandGEM equation. Formal search techniques were employed to optimize k for each landfill to find the minimum sum of squared errors (SSE) between the LandGEM prediction and the observed collection data. Across nearly all landfills, the optimal k was found to be higher than the default AP-42 of 0.04 yr(-1) and the weighted average decay for the 11 landfills was 0.09 - 0.12 yr(-1). The results suggest that the default k value assumed in LandGEM is likely too low, which implies that more methane is produced in the early years following waste burial when gas collection efficiencies tend to be lower.}, number={7}, journal={Environmental Science & Technology}, author={Wang, X. M. and Nagpure, A. S. and DeCarolis, J. F. and Barlaz, Morton}, year={2013}, pages={3251–3257} }
 @article{wang_padgett_cruz_barlaz_2011, title={Wood Biodegradation in Laboratory-Scale Landfills}, volume={45}, ISSN={["1520-5851"]}, DOI={10.1021/es201241g}, abstractNote={The objective of this research was to characterize the anaerobic biodegradability of major wood products in municipal waste by measuring methane yields, decay rates, the extent of carbohydrate decomposition, carbon storage, and leachate toxicity. Tests were conducted in triplicate 8 L reactors operated to obtain maximum yields. Measured methane yields for red oak, eucalyptus, spruce, radiata pine, plywood (PW), oriented strand board (OSB) from hardwood (HW) and softwood (SW), particleboard (PB) and medium-density fiberboard (MDF) were 32.5, 0, 7.5, 0.5, 6.3, 84.5, 0, 5.6, and 4.6 mL CH(4) dry g(-1), respectively. The red oak, a HW, exhibited greater decomposition than either SW (spruce and radiata), a trend that was also measured for the OSB-HW relative to OSB-SW. However, the eucalyptus (HW) exhibited toxicity. Thus, wood species have unique methane yields that should be considered in the development of national inventories of methane production and carbon storage. The current assumption of uniform biodegradability is not appropriate. The ammonia release from urea formaldehyde as present in PB and MDF could contribute to ammonia in landfill leachate. Using the extent of carbon conversion measured in this research, 0-19.9%, predicted methane production from a wood mixture using the Intergovernmental Panel for Climate Change waste model is only 7.9% of that predicted using the 50% carbon conversion default.}, number={16}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, publisher={American Chemical Society (ACS)}, author={Wang, Xiaoming and Padgett, Jennifer M. and Cruz, Florentino B. and Barlaz, Morton A.}, year={2011}, month={Aug}, pages={6864–6871} }