Landfill gas containing methane is produced by anaerobic degradation of organic waste. Methane is a strong greenhouse gas and landfills are one of the major anthropogenic sources of atmospheric methane. Landfill methane may be oxidized by methanotrophic microorganisms in soils or waste materials utilizing oxygen that diffuses into the cover layer from the atmosphere. The methane oxidation process, which is governed by several environmental factors, can be exploited in engineered systems developed for methane emission mitigation. Mathematical models that account for methane oxidation can be used to predict methane emissions from landfills. Additional research and technology development is needed before methane mitigation technologies utilizing microbial methane oxidation processes can become commercially viable and widely deployed.

[1] When the open system isotope method has been used to determine the methane oxidation efficiency of a landfill cover soil, it has been assumed that gas transport from the landfill is primarily driven by advection, a mechanism that is not associated with isotopic fractionation. A controlled laboratory experiment revealed that this approach underestimated the methane oxidation efficiency because it underestimated the importance of molecular diffusion during gas transport. In a worst-case scenario laboratory column experiment where diffusion was an important gas transport mode, a comparison between a mass balance and the open system isotope method revealed that the latter underestimated methane oxidation by a factor 2 to 4. The vertical profile of the d 13 C value of methane in the column confirmed that isotope fractionation associated with gas transport occurred. Similar profiles were observed in the field, but the effect was less pronounced. It is concluded that the isotope method as currently applied produces a conservative estimate of methane oxidation by landfill cover soils.

A considerable fraction of the methane that is produced by landfills is oxidized by its covering soil before it can reach the atmosphere. This process was studied in soil columns that simulate landfill cover soil environments. The methane uptake was followed as a function of time. In soils of agricultural origin, a maximum value of 10.7 mol m -2 column d -1 was observed. Mixing sugar beet leaves with the soil led to a temporary stimulation of the methane oxidation rate, whereas a wheat straw amendment led to permanent stimulation. Soil originating from a real landfill cover oxidized on the order of 15 mol m -2 column d -1 , the highest value found in the literature to date. The soil gas composition was studied as a function of depth. With a new batch incubation technique, methane oxidation kinetics were determined in samples taken from the soil column. By combining this kinetic data with the soil gas composition data, the actively methane oxidizing zone in the soil column could be determined and an in situ assessment of oxygen limitation could be performed. Methane oxidation takes place mainly in the top 30 cm of the covering soil.

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There has been a significant increase in municipal solid waste (MSW) generation in India during the last few decades and its management has become a major issue because the poor waste management practices affect the health and amenity of the cities. In the present study, various physico-chemical parameters of the MSW were analyzed to characterize the waste dumped at Gazipur landfill site in Delhi, India, which shows that it contains a high fraction of degradable organic components. The decomposition of organic components produces methane, a significant contributor to global warming. Based on the waste composition, waste age and the total amount dumped, a first-order decay model (FOD) was applied to estimate the methane generation potential of the Gazipur landfill site, which yields an estimate of 15.3 Gg/year. This value accounts to about 1-3% of existing Indian landfill methane emission estimates. Based on the investigation of Gazipur landfill, we estimate Indian landfill methane emissions at 1.25 Tg/year or 1.68 Tg/year of methane generation potential. These values are within the range of existing estimates. A comparison of FOD with a recently proposed triangular model was also performed and it shows that both models can be used for the estimation of methane generation. However, the decrease of the emission after closure is more gradual in the case of the first-order model, leading to larger gas production predictions after more than 10 years of closure. The regional and global implications of national landfill methane emission are also discussed.

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Coagulase-negative staphylococci (CNS) are the main cause of bovine intramammary infections (IMI) in many countries. Despite a high prevalence of CNS IMI at parturition, species-specific risk factor studies, relying on accurate identification methods, are lacking. Therefore, this observational study aimed at determining the prevalence and distribution of different CNS species causing IMI in fresh heifers and dairy cows in Flemish dairy herds and identifying associated species- and subgroup-specific risk factors at the herd, cow, and quarter level. The effect on udder health was investigated as well. Staphylococcus chromogenes, S. sciuri, and S. cohnii were the most frequently isolated species. The only CNS species causing IMI in fresh heifers and dairy cows in all herds was Staphylococcus chromogenes, whereas large between-herd differences in distribution were observed for the other species. Quarters from heifers and quarters with an inverted teat end had higher odds of being infected with S. chromogenes, S. simulans, or S. xylosus as well as with S. chromogenes solely. Prepartum teat apex colonization with S. chromogenes increased the likelihood of S. chromogenes IMI in the corresponding quarters at parturition. Quarters with dirty teat apices before calving were more likely to be infected with S. cohnii, S. equorum, S. saprophyticus, or S. sciuri, supporting the environmental nature of these CNS species. Three species (S. chromogenes, S. simulans, and S. xylosus) were associated with a higher quarter somatic cell count at parturition as compared with uninfected quarters.

The breakdown of benzene, ethylbenzene, styrene, and o-chlorotoluene in aqueous solution by 520 kHz ultrasonic waves was studied at various initial concentrations in the millimolar range. First-order reaction rates depend upon both initial concentration and sonication time. These variations can be explained by a model that combines some physical and chemical aspects of sonochemistry. The basic assumptions of the model are first-order pyrolysis in the cavitations yielding both reactive/volatile and inert/nonvolatile products, and lowering of the maximum cavitation temperature due to the presence of the organic compounds in the bubble phase. Despite the necessary assumptions and approximations in order to limit the number of adjustable parameters, the lack of fit standard deviation after regression was as low as 4−9.2%.