根据腐殖填料生物滤池及石英砂普通生物滤池的氨氮去除效率、表面水力负荷及微生物量差异,比较两者氨氮降解速率及比降解速率,对腐殖填料生物滤池的氨氮降解特征进行分析。结果表明,在相同运行方式及外界环境下,腐殖填料滤池表面水力负荷数倍于石英砂普通生物滤池;腐殖填料生物滤池单位体积平均氨氮降解速率高达31.5 g NH4+-N/(m3.d),是石英砂普通生物滤池的5.4倍;腐殖填料生物滤池氨氮比降解速率为4.1×10-2μg NH4+-N/(g微生物碳.d),约为石英砂普通生物滤池的4倍。腐殖填料生物滤池能负载较高的生物量,抗堵塞性能较强,系统内特异微生物对氨氮降解能力较高,是一种优良的降解氨氮的生物滤池。 相似文献
Introduction: Driving under the influence (DUI) citations are still a serious concern among drivers aged 16–20 years and have been shown to be related to increased risk of fatal and nonfatal crashes. A battery of laws and policies has been enacted to address this concern. Though numerous studies have evaluated these policies, there is still a need for comprehensive policy evaluations that take into account a variety of contextual factors. Previous effort by this research team examined the impact of 20 minimum legal drinking age–21 laws in the state of California, as they impacted alcohol-related crash rates among drivers under 21 years of age while at the same time accounting for alcohol and gas taxes, unemployment rates, sex distribution among drivers, and sobriety checkpoints. The current research seeks to expand this evaluation to the county level (San Diego County). More specifically, we evaluate the impact of measures subject to county control such as retail beverage service (RBS) laws and social host (SH) laws, as well as media coverage, city employment, alcohol outlet density, number of sworn officers, alcohol consumption, and taxation policies, to determine the most effective point of intervention for communities seeking to reduce underage DUI citations.
Methods: Annual DUI citation data (2000 to 2013), RBS and SH policies, and city-wide demographic, economic, and environmental information were collected and applied to each of the 20 cities in San Diego County, California. A structural equation model was fit to estimate the relative contribution of the variables of interest to DUI citation rates.
Results: Alcohol consumption and alcohol outlet density both demonstrated a significant increase in DUI rates, whereas RBS laws, SH laws, alcohol tax rates, media clusters, gas tax rates, and unemployment rates demonstrated significant decreases in DUI rates.
Conclusions: At the county level, although RBS laws, SH laws, and media efforts were found to contribute to a significant reduction in DUI rates, the largest significant contributors to reducing DUI rates were alcohol and gas taxation rates. Policy makers interested in reducing DUI rates among teenagers should examine these variables within their specific communities and consider conducting community-specific research to determine the best way to do so. Future efforts should be made to develop models that represent specific communities who are interested in reducing DUI rates among drivers aged 16–20 years. 相似文献
This study, based on data collected from a representative sample of adults in the United States, explores the social cognitive variables that motivated Americans to validate rumours on social media about Hurricanes Harvey and Irma, both of which struck in August/September 2017. The results indicate that risk perception and negative emotions are positively related to systematic processing of relevant risk information, and that systematic processing is significantly related to rumour validation through search engines such as Google. In contrast, trust in information about the hurricane is significantly related to validation through official sources, such as FEMA (Federal Emergency Management Agency), and major news outlets such as The New York Times. Trust in information is also significantly related to systematic processing of risk information. The findings of this study suggest that ordinary citizens may be motivated to validate rumours on social media, which is an increasingly important issue in contemporary societies. 相似文献
Different nutrient media experimentally were N, P and Fe-limited conditions and a serial of diluted BGll media. The cell change of morphology and life history, cell number, cell color and cell area of Microcystis were analyzed quantitatively. First, the effects of nitrogen, phosphorus and iron depletion were distinctively different. Phosphorus and iron depletion caused more special division cells,slowly growth increasing, the easier change of bigger cell area. Second, the nitrogen and iron depletion could make the color of alga from green to brown. Finally, according to the resource competition and Monod equation, Microcystis kinetics of phosphorus and iron were also examined. Ks and μmax of phosphorus absorption were 0.0352 μmol/L, 0.493 d^-1 respectively; iron absorption: 0.00323 μmol/L, 0.483d^-1. In a word, some evidences of the Microcystis bloom dominance in certain nutrient conditions were indicated in the experiments. The dominances were determined as the reviving under the adverse circumstances through the special division, the various nitrogen resources,and the lower kinetics of phosphorus and iron than that of most of other algae. The conclusions provided the scientific basis for preventing and managing Microcystis bloom in freshwater. 相似文献
Dispersal of inert particles on a flame front is one of the techniques employed to suppress explosions. The current study investigates the influence of micron-sized (75–90 μm) inert (sand) particles on the laminar burning velocity of methane-air premixtures of different equivalence ratios (0.9–1.2) and reactant temperatures (297, 350, 400 K) using a Bunsen-burner type experimental apparatus. When an inert particle interacts with the flame zone, it extracts energy from the flame, thereby acting like a heat sink and hence reducing the flame temperature. Results show that for sand particle size in the range of 75–90 μm, a concentration of 380–520 g/m3 is necessary for extinction of a methane-air flame at ambient temperature. An increase in reactant temperature reduces the heat-sink effect necessitating a higher concentration of sand to extinguish the flame. A mathematical model is developed to generalize the results and make them applicable to a wide range of parameters. 相似文献