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21.
A low-cost alternative approach to reduce landfill gas (LFG) emissions is to integrate compost into the landfill cover design in order to establish a biocover that is optimized for biological oxidation of methane (CH4). A laboratory and field investigation was performed to quantify respiration in an experimental compost biocover in terms of oxygen (O2) consumption and carbon dioxide (CO2) production and emission rates. O2 consumption and CO2 production rates were measured in batch and column experiments containing compost sampled from a landfill biowindow at Fakse landfill in Denmark. Column gas concentration profiles were compared to field measurements. Column studies simulating compost respiration in the biowindow showed average CO2 production and O2 consumption rates of 107 ± 14 g m−2 d−1 and 63 ± 12 g m−2 d−1, respectively. Gas profiles from the columns showed elevated CO2 concentrations throughout the compost layer, and CO2 concentrations exceeded 20% at a depth of 40 cm below the surface of the biowindow. Overall, the results showed that respiration of compost material placed in biowindows might generate significant CO2 emissions. In landfill compost covers, methanotrophs carrying out CH4 oxidation will compete for O2 with other aerobic microorganisms. If the compost is not mature, a significant portion of the O2 diffusing into the compost layer will be consumed by non-methanotrophs, thereby limiting CH4 oxidation. The results of this study however also suggest that the consumption of O2 in the compost due to aerobic respiration might increase over time as a result of the accumulation of biomass in the compost after prolonged exposure to CH4. 相似文献
22.
Effect of tetracycline residues in pig manure slurry on tetracycline-resistant bacteria and resistance gene tet(M) in soil microcosms 总被引:1,自引:0,他引:1
Agersø Y Wulff G Vaclavik E Halling-Sørensen B Jensen LB 《Environment international》2006,32(7):876-882
Effects of tetracycline residues from pig manure slurry on the prevalence of tetracycline-resistant bacteria and the tetracycline resistance gene, tet(M), were studied in soil microcosms. Four types of soil microcosms were established for a period of 152 days, supplemented with combinations of pig manure slurry and a tetracycline-resistant Enterococcus faecalis, CG110, containing the tetracycline resistance gene tet(M) (on the conjugative transposon, Tn916). The prevalence of both tetracycline-resistant aerobic bacteria and tetracycline-resistant enterococci declined rapidly until day 45 where no significant differences in the levels of tetracycline-resistant bacteria in any of the four types of microcosms could be detected. tet(M) could be detected in microcosms supplemented with either pig manure slurry and/or E. faecalis CG110 (tet(M)) for the whole period (152 days). tet(M) could be detected longer than tetracycline-resistant enterococci could be isolated (limit of detection 100 CFU/g soil) probably due to viable but not culturable (VBNC) bacteria with tet(M), horizontal gene transfer of tet(M) to indigenous soil bacteria or presence of "free" DNA. The concentration of chlortetracycline and oxytetracycline were almost stable through out the experimental period, but the tetracycline concentrations had no effect on prevalence of tetracycline-resistant bacteria. The presented microcosm approach simulated natural farmland conditions well and supported results from previous field studies. 相似文献