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641.
Effect of dissolved oxygen on biological nutrient removal by denitrifying phosphorus-accumulating organisms in a continuous-flow system 总被引:1,自引:0,他引:1
A laboratory-scale continuous-flow system with an anaerobic/anoxic/aerobic configuration was set up to study the effect of oxygen in the internal recycle stream; of particular interest was its performance of denitrifying phosphorus-accumulating organisms (DPAOs). It was found that, by using a degas device, the dissolved oxygen in the nitrate recycle stream was effectively decreased from 0.1 +/- 0.02 to 0.01 +/- 0.01 mg/L. This provided a favorable condition for DPAOs to grow under an anoxic condition and thus be sustained successfully in the system. When the degas device was removed from the system, the dissolved oxygen concentration in the anoxic reactor increased to 0.1 +/- 0.02 mg/L. The proliferation of the denitrifying glycogen-accumulating organisms (DGAOs) population and deterioration of DPAOs performance was observed. The increased population of DGAO/GAOs, which competed for the carbon source with DPAO/ PAOs, resulted in a poor performance of biological phosphorus removal. 相似文献
642.
Mark Thompson Jan Vlok Mathieu Rouget M. T. Hoffman Andrew Balmford R. M. Cowling 《Environmental management》2009,43(4):585-596
Improved techniques for measuring and monitoring the state of biodiversity are required for reporting on national obligations
to international and regional conservation institutions. Measuring the extent of grazing-related degradation in semi-arid
ecosystems has proved difficult. Here we present an accurate and cost-effective method for doing this, and apply it in a South
African semi-arid region that forms part of a globally significant biodiversity hotspot. We grouped structurally and functionally
similar vegetation units, which were expert-mapped at the 1:50,000 scale, into four habitat types, and developed habitat-specific
degradation models. We quantified degradation into three categories, using differences between dry and wet season values of
the Normalized Difference Vegetation Index (NDVI) for the three succulent karoo habitats, and the difference between maximum
and mean NDVI values for the subtropical thicket habitat. Field evaluation revealed an accuracy of 86%. Overall, degradation
was high: 24% of the study area was modeled as severely degraded, and only 9% as intact. Levels of degradation were highest
for bottomland habitats that were most exposed to grazing impacts. In sharp contrast to our methods, a widely used, broad-scale
and snapshot assessment of land cover in South Africa was only 33% accurate, and it considerably underestimated the extent
of severely degraded habitat in the study area. While our approach requires a multidisciplinary team, and in particular expert
knowledge on the characteristics and spatial delimitation of vegetation types, it is repeatable, rapid, and relatively inexpensive.
Consequently, it holds great promise for monitoring and evaluation programs in semi-arid ecosystems, in Africa, and beyond. 相似文献
643.
644.
Sami Mynttinen Author Vitae Author Vitae Jan Vissers Author Vitae Author Vitae Kari Hakuli Author Vitae Author Vitae 《Journal of Safety Research》2009,40(4):301-309
Problem
This study examined novice drivers’ overconfidence by comparing their self-assessed driver competence with the assessments made by driving examiners.Method
A Finnish (n = 2,739) and a Dutch sample (n = 239) of drivers license candidates assessed their driver competence in six areas and took the driving test.Result and Discussion
In contrast to previous studies where drivers have assessed their skill in comparison to the average driver, a smaller proportion overestimated and a larger proportion made realistic self-assessments of their driver competence in the present study, where self-assessments were compared with examiner assessments. Between 40% and 50% of the candidates in both samples made realistic assessments and 30% to 40% overestimated their competence. The proportion of overestimation was greater in the Dutch than in the Finnish sample, which might be explained by greater possibilities for practicing self-assessment in the Finnish driver education system. Similar to other self-assessment studies that indicate that incompetence is related to overestimation, a larger proportion of candidates that failed the test overestimated their skill compared to those who passed. In contrast to other studies, males did not overestimate their skills more than females, and younger driver candidates were not more overconfident than older drivers.Impact on traffic safety
Although a great proportion of the candidates made a realistic assessment of their own driver competence, overestimation is still a problem that needs to be dealt with. To improve the accuracy of novice drivers’ self-assessment, methods for self-assessment training should be developed and implemented in the driver licensing process. 相似文献645.
Hansen M Krogh KA Brandt A Christensen JH Halling-Sørensen B 《Environmental pollution (Barking, Essex : 1987)》2009,157(2):474-480
The antibacterial potency of eight anticoccidial drugs was tested in a soil bacteria bioassay (pour plate method), EC50-values between 2.4 and 19.6 μM were obtained; however, one compound, nicarbazin exhibited an EC50-value above the maximum tested concentration (21 μM, 9.1 mg L−1). The potency of mixtures of two of the compounds, narasin and nicarbazin, was synergistic (more than additive) with 10-fold greater antibacterial potency of the mixture than can be explained by their individual EC50-values. The influence of pH, temperature, oxygen concentration and light on the transformation of robenidine and salinomycin was investigated. Robenidine was transformed by photolysis (DT50 of 4.1 days) and was unstable at low pH (DT50 of approximately 4 days); salinomycin was merely transformed at low pH, the latter into an unknown number of products. The antibacterial potency of the mixtures of transformation products of robenidine after photolysis and at low pH was comparable with that of the parent compound. Finally five photo-transformation products of robenidine were structural elucidated by accurate mass measurements, i-FIT values (isotopic pattern fit) and MS/MS fragmentation patterns. 相似文献
646.
This paper presents results of investigations on the influence of humic substances (humate, HS) on the biological treatment of wastewater containing heavy metals (Cr, Cu, Fe, Mn, Ni, and Zn). Respirometric studies indicated that the investigated system complied with the Haldane model for inhibitory wastes. Chemical analyses showed that, while the soluble COD removal was high (82%), only 7% of ammonia was oxidized to nitrate. An addition of HS (500 mg L−1) mitigated the inhibitory effect of the wastewater on the returned activated sludge. The system with HS complied with the Monod model for non-inhibitory wastes, and the removal of ammonia and metals was 99% and over 90%, respectively. It is suggested that an application of HS could be beneficial for treatment plants receiving wastewater streams containing heavy metals. 相似文献
647.
Interacting effects of sulphate pollution, sulphide toxicity and eutrophication on vegetation development in fens: A mesocosm experiment 总被引:1,自引:0,他引:1
Jeroen J.M. Geurts Judith M. Sarneel Jan G.M. Roelofs Leon P.M. Lamers 《Environmental pollution (Barking, Essex : 1987)》2009,157(7):2072-2081
Both eutrophication and SO4 pollution can lead to higher availability of nutrients and potentially toxic compounds in wetlands. To unravel the interaction between the level of eutrophication and toxicity at species and community level, effects of SO4 were tested in nutrient-poor and nutrient-rich fen mesocosms. Biomass production of aquatic and semi-aquatic macrophytes and colonization of the water layer increased after fertilization, leading to dominance of highly competitive species. SO4 addition increased alkalinity and sulphide concentrations, leading to decomposition and additional eutrophication. SO4 pollution and concomitant sulphide production considerably reduced biomass production and colonization, but macrophytes were less vulnerable in fertilized conditions. The experiment shows that competition between species, vegetation succession and terrestrialization are not only influenced by nutrient availability, but also by toxicity, which strongly interacts with the level of eutrophication. This implies that previously neutralized toxicity effects in eutrophied fens may appear after nutrient reduction measures have been taken. 相似文献
648.
Henner Hollert Sebastian Hudjetz Evelyn Claus Werner Manz Georg Reifferscheid Peter Heininger Jan Schwarzbauer Wolfgang Ahlf Thomas Braunbeck Werner Brack Tobias Schulze Andreas Sch?ffer und Hans-Toni Ratte 《Umweltwissenschaften und Schadstoff-Forschung》2009,21(3):235-237
Ohne Zusammenfassung
Verantwortliche Herausgeber: Jan Schwarzbauer · Peter Heininger · Evelyn Claus
相似文献
Henner Hollert (Corresponding author)Email: |
Evelyn ClausEmail: |
Peter HeiningerEmail: |
Jan SchwarzbauerEmail: |
649.
Conservation subdivision design has been promoted as a way to protect ecologically sensitive areas while maintaining housing densities comparable to standard subdivisions, but many developers and planners question the appeal of conservation design to consumers. This study was conducted to compare economic aspects of conservation subdivision design to standard subdivision design in the midwestern United States. Three methods were used to determine the value homebuyers have for embedded conservation features in residential areas: transactional analyses (to indicate the value homebuyers have expressed for such features in the past); hedonic analyses (to determine the proportion of present value of homes attributable to such features); and contingent valuation (to examine willingness to pay according to homebuyers' preferred features, an indicator of potential future investment). Transactional analyses were based on assessment and transaction data for homes in three conservation-oriented subdivisions and three standard subdivisions in Cedar Rapids, Iowa, United States. Hedonic price models were also derived from assessment and transaction data. Contingent valuation analyses were based on a survey of residents in the same six subdivisions. Transactional data indicated higher 5-year appreciation rates for conservation versus standard subdivision design. Hedonic price models revealed that well-integrated conservation features (e.g. protected stream corridors) within subdivisions have a positive effect on home prices. Sixty-six percent of all respondents indicated willingness to pay for more embedded open space. Maximum willingness to pay was related to several factors including income, gender, desired level of open space, and concern about urban development. Overall, these results indicate that consumer demand and willingness to pay for conservation subdivision design are positive and should not be considered a barrier to implementation. 相似文献
650.
Strategic assessment of the magnitude and impacts of sand mining in Poyang Lake, China 总被引:2,自引:0,他引:2
Jan de Leeuw David Shankman Guofeng Wu Willem Frederik de Boer James Burnham Qing He Herve Yesou Jing Xiao 《Regional Environmental Change》2010,10(2):95-102
Planning for the extraction of aggregates is typically dealt with at a case to case basis, without assessing environmental
impacts strategically. In this study we assess the impact of sand mining in Poyang Lake, where dredging began in 2001 after
sand mining in the Yangtze River had been banned. In April 2008 concern over the impact on the biodiversity led to a ban on
sand mining in Poyang Lake until further plans could be developed. Planning will require consideration of both sand extraction
in relation to available sediment resources and also environmental impacts within the context of future demand for sand in
the lower Yangtze Valley. We used pairs of near-infrared (NIR) Aster satellite imagery to estimate the number of vessels leaving
the lake. Based on this we calculated a rate of sand extraction of 236 million m3 year−1 in 2005–2006. This corresponds to 9% of the total Chinese demand for sand. It qualifies Poyang Lake as probably the largest
sand mining operation in the world. It also indicates that sand extraction currently dominates the sediment balance of the
lower Yangtze River. A positive relation between demand for sand and GDP, revealed by historic data from the USA, suggests
that the current per capita demand for sand in China might increase in the near future from 2 to 4 m3 year−1. We review various environmental impacts and question whether it will be possible to preserve the rich biodiversity of the
lake, while continuing at the same time satisfying the increasing Chinese demand for sand. Finally we review alternative options
for sand mining, in order to relieve the pressure from the Poyang Lake ecosystem. 相似文献