Determination of first-order landfill gas modeling parameters and uncertainties

Using first-order kinetic empirical models to estimate landfill gas (LFG) generation and collection rates is well recognized in the literature. The uncertainty in the estimated LFG generation rates is a major challenge in evaluating performance of LFG collection and LFG to energy facilities. In this investigation, four methods for quantifying first-order LFG generation model parameters, methane generation potential, L₀, and methane generation rate constant, k, were evaluated. It was found that the model is insensitive to the approach taken in quantifying the parameters. However, considering the recognition of using the model in the literature, the optimum method to estimate L₀ and k is to determine L₀ using disposed municipal solid waste composition and laboratory component specific methane potential values. The k value can be selected by model fitting and regression using the first-order model if LFG collection data are available. When such data are not available, k can be selected from technical literature, based on site conditions. For five Florida case-study landfills L₀ varied from 56 to 77 m³ Mg⁻¹, and k varied from 0.04 to 0.13 yr⁻¹ for the traditional landfills and was 0.10 yr⁻¹ for the wet cell. Model predictions of LFG collection rates were on average lower than actual collection. The uncertainty (coefficient of variation) in modeled LFG generation rates varied from ±11% to ±17% while landfills were open, ±9% to ±18% at the end of waste placement, and ±16% to ±203% 50 years after waste placement ended.     

Formation of toxic species and precursors of PCDD/F in thermal decomposition of alpha-cypermethrin

This article examines the thermal decomposition of alpha-cypermethrin, one of the most common pyrethroid pesticides. The objective was to identify its decomposition pathways and to gain an understanding into the formation of toxic species in the environment, including those that may behave in combustion systems, especially in fires in the environment, as precursors for PCDD/F (polychlorinated dibenzo-p-dioxins and dibenzofurans). The experiments were conducted under non-oxidative conditions using a tubular reactor housed in a three-zone heating furnace and operated with a dilute stream of alpha-cypermethrin in 99.999% nitrogen. The condensable products were identified and quantitated, after being collected in a cold solvent trap and in an activated charcoal cartridge. The study revealed the formation of pollutants including precursors of toxic PCDD/F such as diphenyl ether and phenol. It was also found that the decomposition of alpha-cypermethrin involved parallel pathways of an unusual vinylcyclopropane rearrangement-cum-aromatisation reaction transforming alpha-cypermethrin and a rupture of the C(O)OC(CN) linkage. The former is similar to that occurring in the decomposition of permethrin pesticide, whereas the latter constitutes a newly discovered channel for the formation of pollutants. Density functional theory (DFT) calculations allowed us to attribute the occurrence of the second pathway to the effect of the cyanide group in significantly weakening the OC bond.     

Geographic variation in tissue accumulation of endocrine disrupting compounds (EDCs) in grazing sheep

Muscle tissue was collected from ewes and lambs derived from farms throughout Scotland and sample concentrations of five endocrine disrupting compound groups were determined. Farms of origin were categorised according to geographic region. There were few statistically-significant differences with region or distance from cities. However, the magnitude of the difference between the highest and lowest mean values in ewe muscle from different regions exceeded 30% for 13 of the 15 compounds that were consistently detected in muscle, with animals derived from the industrialised region having the highest mean values for 11 of the 13 compounds. A less marked trend was apparent in the lamb muscle (8 of 13 highest were in the industrialised region). The physiological effects of such small differences in exposure to mixtures of pollutants remain to be determined.     

Adaptation to the Impacts of Sea Level Rise in Egypt

Assessment of the vulnerability and expected socioeconomic losses over the Nile delta coast due to the impact of sea level rise is carried out in details. Impacts of sea level rise over the Governorates of Alexandria and Port Said in particular, are evaluated quantitatively. Analysis of the results at Alexandria Governorate indicate that, if no action is taken, an area of about 30% of the city will be lost due to inundation. Almost 2 million people will have to abandon their homeland; 195,000 jobs will be lost and an economic loss of over $3.5 Billion is expected over the next century. At Port Said Governorate results indicate that beach areas are most severely affected (hence tourism), followed by urban areas. The agriculture sector is the least affected sector. It is estimated that the economic loss is over $ 2.0 Billion for 0.50 m SLR and may exceed $ 4.4 Billion for 1.25 m SLR. Options and costs of adaptation are analyzed and presented. Multi-criteria and decision matrix approaches, based on questionnaire surveys are carried out to identify priorities for the two cases. Analysis of these techniques of two options; the current policy (hard protection measures on some vulnerable areas) and no action (stopping these activities) have the lowest scores. Beach nourishment and integrated coastal zone management (ICZM) have the highest scores, however ICZM has high cost measures. The most cost-effective option is the land-use change, however with relatively very high cost measure. It is recommended that an ICZM approach be adopted since it provides a reasonable trade off between costs and cost effectiveness.     

Development of a chemical kinetic model for a biosolids fluidized-bed gasifier and the effects of operating parameters on syngas quality

In an effort to decrease the land disposal of sewage sludge biosolids and to recover energy, gasification has become a viable option for the treatment of waste biosolids. The process of gasification involves the drying and devolatilization and partial oxidation of biosolids, followed closely by the reduction of the organic gases and char in a single vessel. The products of gasification include a gaseous fuel composed largely of N₂, H₂O, CO₂, CO, H₂, CH₄, and tars, as well as ash and unburned solid carbon. A mathematical model was developed using published devolatilization, oxidation, and reduction reactions, and calibrated using data from three different experimental studies of laboratory-scale fluidized-bed sewage sludge gasifiers reported in the literature. The model predicts syngas production rate, composition, and temperature as functions of the biosolids composition and feed rate, the air input rate, and gasifier bottom temperature. Several data sets from the three independent literature sources were reserved for model validation, with a focus placed on five species of interest (CO, CO₂, H₂, CH₄, and C₆H₆). The syngas composition predictions from the model compared well with experimental results from the literature. A sensitivity analysis on the most important operating parameters of a gasifier (bed temperature and equivalence ratio) was performed as well, with the results of the analysis offering insight into the operations of a biosolids gasifier.

Implications:

As gasification becomes a more prominent waste disposal option, understanding the effects of feedstock composition and gasifier parameters on the production of syngas (rate and quality) becomes increasingly important. A model has been developed for the gasification of dried sewage sludge that will allow for prediction of changes in syngas quality (and energy recovery from the waste), and should be helpful in assessing the benefits of new gasification projects.     

Declining metal levels at Foundry Cove (Hudson River, New York): response to localized dredging of contaminated sediments

This study examines the effectiveness of remediating a well-recognized case of heavy metal pollution at Foundry Cove (FC), Hudson River, New York. This tidal freshwater marsh was polluted with battery-factory wastes (1953-1979) and dredged in 1994-1995. Eight years after remediation, dissolved and particulate metals (Cd, Co, Cu, Pb, Ni, and Ag) were found to be lower than levels in the lower Hudson near New York City. Levels of metals (Co, Ni, Cd) on suspended particles were comparatively high. Concentrations of surface sediment Cd throughout the marsh system remain high, but have decreased both in the dredged and undredged areas: Cd was 2.4-230mg/kg dw of sediment in 2005 vs. 109-1500mg/kg in the same area in 1983. The rate of tidal export of Cd from FC has decreased by >300-fold, suggesting that dredging successfully stemmed a major source of Cd to the Hudson River.