Enzymatic nitrous oxide emissions from wastewater treatment

Nitrous oxide (N₂O), a potent greenhouse gas, is emitted during nitrogen removal in wastewater treatment, significantly contributing to greenhouse effect. Nitrogen removal generally involves nitrification and denitrification catalyzed by specific enzymes. N₂O production and consumption vary considerably in response to specific enzyme-catalyzed nitrogen imbalances, but the mechanisms are not yet completely understood. Studying the regulation of related enzymes’ activity is essential to minimize N₂O emissions during wastewater treatment. This paper aims to review the poorly understood related enzymes that most commonly involved in producing and consuming N₂O in terms of their nature, structure and catalytic mechanisms. The pathways of N₂O emission during wastewater treatment are briefly introduced. The key environmental factors influencing N₂O emission through regulatory enzymes are summarized and the enzyme-based mechanisms are revealed. Several enzymebased techniques for mitigating N₂O emissions directly or indirectly are proposed. Finally, areas for further research on N₂O release during wastewater treatment are discussed.

Open image in new window

     

Fiji, land of tropical cyclones and hurricanes: A case study of agricultural rehabilitation

Tropical cyclones and hurricanes have a severe impact on the social and economic activities of affected communities. For small island nations in the Pacific region, the effects can be devastating because of their smallness. FQi and several other countries in the region are vulnerable to such disasters as they are situated in the zone where cyclones occur frequently.
During the last decade, the frequency of natural disasters and their adverse impact on die economic and social development of small nations like Fiji, has aroused awareness mat relief efforts must go beyond immediate "mopping up" operations to those which contribute to attaining longer term benefits through reconstruction and rehabilitation.
The paper outlines the 1985 agricultural rehabilitation program and discusses related issues and problems.     

Environmental Management of Quarries as Waste Disposal Facilities

Problems associated with the disposal of municipal solid waste have become a source of public concern worldwide as awareness of potential adverse environmental impacts and health threats from solid waste has increased. Communities are concerned about the generation and management of solid waste to the extent of refusing to allow new disposal facilities near their homes, often after witnessing the legacy of existing facilities. Under these conditions, the development of national policies for the management of solid waste becomes highly political, all while requiring appropriate technical solutions that ensure environmental protection and proper management plans that support an acceptable solution for the disposal of municipal solid waste. In some locations, the conversion of old quarries into well-engineered and controlled landfills appears as a promising solution to a continuously increasing problem, at least for many decades to come. This paper describes the environmental impacts associated with solid waste disposal in a converted quarry site and the mitigation measures that can be adopted to alleviate potential adverse impacts. Environmental management and monitoring plans are also discussed in the context of ensuring adequate environmental protection during and after the conversion process.     

Heavy gas dispersion by water spray curtains: A research methodology

The mitigation of the consequences of accidental releases of dangerous toxic and/or flammable cloud is a serious concern in the petro-chemical and gas industries. Nowadays, the water-curtain is recognized as a useful technique to mitigate a heavy gas cloud. The paper presents a research methodology, which has been established and undertaken to quantify the forced dispersion factor provided by a water-curtain with respect to its configuration.

The method involves medium-scale field tests, Wind-Gallery tests and numerical simulations. These different approaches are discussed and exemplified by typical results emphasizing the observed concentration reduction due to the water-curtain.     

Removal of atmospheric particles by leaves and twigs of urban trees: Some preliminary observations and assessment of research needs

This paper reviews the various lines of evidence that support the hypothesis that above-ground plant parts remove particulates from the atmosphere. Some scanning electron microscope observations of the particulate burden on leaves of London planetree are discussed. The authors present an outline of the kinds of research required to support or reject the hypothesis that urban woody plants are important air filters.     

Practitioner Perspectives on the Role of Science in Environmental Impact Assessment

A large body of literature addresses the role of science in environmental impact assessment (EIA) but less attention has been given to the views of practitioners themselves. In this research a survey of 31 EIA practitioners in Western Australia was undertaken to determine their perceptions of the quality and importance of science in EIA. The survey results are compared with previous theoretical, empirical, and survey studies of the role of science in EIA. Interview questions addressed the role of science in impact prediction, monitoring activities, mitigation and management, and EIA decision-making. It was clear from the interviews that many practitioners are satisfied with the quality of science currently used in EIA, but do not believe that it is given sufficient importance in the process. The quality and importance of science in the predecision stages of EIA was rated higher than in the postdecision stages. While science was perceived to provide the basis for baseline data collection, impact prediction, and mitigation design, it was seen to be less important during decision-making and ongoing project management. Science was seen to be just one input to decision-makers along with other factors such as sociopolitical and economic considerations. While time and budget constraints were seen to limit the scientific integrity of EIA activities, pressure from the public and regulatory authorities increased it. Improving the scientific component of EIA will require consideration of all these factors, not just the technical issues.     

极值动态新Ⅰ型分布函数的模型及在汕头抗风防灾上的应用

最大风速分布函数的选择是抗风减灾的重要因素,迄今为止国内外所有可选择的分布函数,虽然对一个国家一些城市是好的,但是对另一些城市却不好,好的城市中,拟合优度准则检验结果也不能达到最佳位或趋近为1.本文采用动态的观点,根据不同城市的数据可用不同的参数值,使其可达到优度最佳值或趋近为1,在此思想基础上,改进了现在国内外绝大多数国家规范所采用的极值Ⅰ型,成为极值动态新Ⅰ型,是对分布函数选择彻底改革的一次尝试。按此原理,对汕头1959～1993共35年最大风速数据进行了分析,对各种概率条件下的风速风压提出了应用的数值。     

Numerical analysis of hydrogen deflagration mitigation by venting through a duct

This paper presents a model and simulation results for the mitigation of a hydrogen–air deflagration by venting through a duct. A large eddy simulation (LES) model, applied previously to study both closed-vessel, and open atmosphere hydrogen–air deflagrations, was developed further to model a hydrogen–air explosion vented through a duct. Sub-grid scale (SGS) flame wrinkling factors were introduced to model major phenomena which contribute to the increase of flame surface area in vented deflagrations. Simulations were conducted to validate the model against 20% hydrogen–air mixture deflagrations (vent diameters 25 and 45 cm) and 10% hydrogen–air mixture deflagration (vent diameter 25 cm). There was reasonable correlation between the simulations and the experimental data. The comparative importance of different physical phenomena contributing to the flame wrinkling is discussed.     

Modelling impacts of alternative farming management practices on greenhouse gas emissions from a winter wheat–maize rotation system in China

Agricultural production plays an important role in affecting atmospheric greenhouse gas concentrations. Field measurements were conducted in Quzhou County, Hebei Province in the North China Plains to quantify carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions from a winter wheat–maize rotation field, a common cropping system across the Chinese agricultural regions. The observed flux data in conjunction with the local climate, soil and management information were utilized to test a process-based model, Denitrification–Decomposition or DNDC, for its applicability for the cropping system. The validated DNDC was then used for predicting impacts of three management alternatives (i.e., no-till, increased crop residue incorporation and reduced fertilizer application rate) on CO₂ and N₂O emissions from the target field. Results from the simulations indicated that (1) CO₂ emissions were significantly affected by temperature, initial SOC, tillage method, and quantity and quality of the organic matter added in the soils; (2) increases in temperature, initial SOC, total fertilizer N input, and manure amendment substantially increased N₂O emissions; and (3) temperature, initial SOC, tillage, and quantity and quality of the organic matter added in the soil all had significant effects on global warming. Finally, five 50-year scenarios were simulated with DNDC to predict their long-term impacts on crop yield, soil C dynamics, nitrate leaching losses, and N₂O emissions. The modelled results suggested that implementation of manure amendment or crop residue incorporation instead of increased fertilizer application rates would more efficiently mitigate GHG emissions from the tested agro-ecosystem. The multi-impacts provided a sound basis for comprehensive assessments on the management alternatives.     

《破坏性地震应急条例》修订若干问题研究

随着经济社会和防震减灾事业的发展,特别是《突发事件应对法》的发布实施和《防震减灾法》的修订,曾经为加强和规范地震应急管理,推进防震减灾事业全面发展,发挥了重要的制度保障作用的《破坏性地震应急条例》,在实施过程中出现了一些明显不适应的地方,对条例进行修订已迫在眉睫。本文阐述了条例修订的基本原则和意义,并就应急机构、应急预...