Quantifying the effect of strong ignition sources on particle preconditioning and distribution in the 20-L chamber

Computational fluid dynamics is used to investigate the preconditioning aspect of overdriving in dust explosion testing. The results show that preconditioning alters both the particle temperature and distribution prior to flame propagation in the 20-L chamber. A parametric study gives the fluid pressure and temperature, and particle temperature and concentration at an assumed flame kernel development time (10 ms) for varying ignitor size and particle diameter. For the 10 kJ ignitor with 50% efficiency, polyethylene particles under 50 μm reach 400 K and may melt prior to flame propagation. Gases from the ignitor detonation displace the dust from the center of the chamber and may increase local particle concentration up to two times the nominal value being tested. These effects have important implications for explosive testing of dusts in the 20-L chamber and comparing to larger 1-m³ testing, where these effects may be negligible.     

Dynamic safety analysis of process systems by mapping bow-tie into Bayesian network

Among the various techniques used for safety analysis of process systems, bow-tie (BT) analysis is becoming a popular technique as it represents an accident scenario from causes to effects. However, the BT application in the dynamic safety analysis is limited due to the static nature of its components, i.e. fault tree and event tree. It is therefore difficult in BT to take accident precursors into account to update the probability of events and the consequent risk. Also, BT is unable to represent conditional dependency. Event dependency is common among primary events and safety barriers. The current paper illustrates how Bayesian network (BN) helps to overcome these limitations. It has also been shown that BN can be used in dynamic safety analysis of a wide range of accident scenarios due to its flexible structure. This paper also introduces the application of probability adapting in dynamic safety analysis rather than probability updating. A case study from the U.S. Chemical Safety Board has been used to illustrate the application of both BT and BN techniques, with a comparison of the results from each technique.     

Modelling the mitigation of a hydrogen deflagration in a nuclear waste silo ullage with water fog

During the decommissioning of certain legacy nuclear waste storage plants it is possible that significant releases of hydrogen gas could occur. Such an event could result in the formation of a flammable mixture within the silo ullage and, hence, the potential risk of ignition and deflagration occurring, threatening the structural integrity of the silo. Very fine water mist fogs have been suggested as a possible method of mitigating the overpressure rise, should a hydrogen–air deflagration occur. In the work presented here, the FLACS CFD code has been used to predict the potential explosion overpressure reduction that might be achieved using water fog mitigation for a range of scenarios where a hydrogen–air mixture, of a pre-specified concentration (containing 800 L of hydrogen), uniformly fills a volume located in a model silo ullage space, and is ignited giving rise to a vented deflagration. The simulation results suggest that water fog could significantly reduce the peak explosion overpressure, in a silo ullage, for lower concentration hydrogen–air mixtures up to 20%, but would require very high fog densities to be achieved to mitigate 30% hydrogen–air mixtures.     

Support of sustainable management of nitrogen contamination due to septic systems using numerical modeling methods

Nitrogen contamination is a serious concern to sustainable environmental management, and one important source of nitrogen contaminant is due to wastewater treatment using onsite sewage treatment and disposal systems (OSTDS, a.k.a., septic systems). This paper presents a study in which numerical modeling is used to support sustainable decision-making and management of nitrogen contamination by utilizing a recently developed GIS-based software, VZMOD, a Vadose Zone MODel for simulating nitrogen transformation and transport in vadose zone between drainfield of septic systems and water table. VZMOD is based on a physical model of unsaturated flow and nitrogen transformation and transport, and the model is solved numerically using the finite element methods. This is the major difference between VZMOD and other GIS-based software of nitrogen modeling. Using GIS techniques, VZMOD considers spatial variability of a number of hydrogeologic parameters such as hydraulic conductivity and porosity. A unique feature of VZMOD is that VZMOD addresses spatial variability of water table by using VZMOD together with ArcNLET, an ArcGIS-based software developed to simulate groundwater flow and nitrate load from septic systems to surface water bodies. VZMOD is designed to execute in different modes to be compatible with different levels of data availability in various management projects of nitrogen contamination. This paper presents an application of VZMOD at a neighborhood with hundreds of septic systems and heterogeneous hydraulic conductivity, porosity, and water table depth. The modeling results indicate that using septic systems at the considered neighborhood is unsustainable and more management means are necessary.     

Ecological Engineering Practices for the Reduction of Excess Nitrogen in Human-Influenced Landscapes: A Guide for Watershed Managers

Excess nitrogen (N) in freshwater systems, estuaries, and coastal areas has well-documented deleterious effects on ecosystems. Ecological engineering practices (EEPs) may be effective at decreasing nonpoint source N leaching to surface and groundwater. However, few studies have synthesized current knowledge about the functioning principles, performance, and cost of common EEPs used to mitigate N pollution at the watershed scale. Our review describes seven EEPs known to decrease N to help watershed managers select the most effective techniques from among the following approaches: advanced-treatment septic systems, low-impact development (LID) structures, permeable reactive barriers, treatment wetlands, riparian buffers, artificial lakes and reservoirs, and stream restoration. Our results show a broad range of N-removal effectiveness but suggest that all techniques could be optimized for N removal by promoting and sustaining conditions conducive to biological transformations (e.g., denitrification). Generally, N-removal efficiency is particularly affected by hydraulic residence time, organic carbon availability, and establishment of anaerobic conditions. There remains a critical need for systematic empirical studies documenting N-removal efficiency among EEPs and potential environmental and economic tradeoffs associated with the widespread use of these techniques. Under current trajectories of N inputs, land use, and climate change, ecological engineering alone may be insufficient to manage N in many watersheds, suggesting that N-pollution source prevention remains a critical need. Improved understanding of N-removal effectiveness and modeling efforts will be critical in building decision support tools to help guide the selection and application of best EEPs for N management.     

Environmental ascription in Worcester County,MA: toxic pollution and education outcomes

This paper argues that important issues of sustainable development have been addressed through single-issue landscape plans, and that these plans have carried little weight within the land use decision-making process. A more consolidated approach, based on multi-function landscape plans, is proposed. After reviewing the range of plans which, in the UK, cover woodland, farmscapes, visual amenity, coasts, catchments and biodiversity, the case is made for an integrative plan capable of addressing natural resource issues at the landscape scale. The preliminary character of an integrative plan is outlined. Whilst landscape plans have a relatively weak basis for implementation, it is concluded that a sufficient range of powers is available to ensure some progress.     

Home energy efficiency grants and advice: findings from the English Midlands

Research was conducted in Nottinghamshire, England to investigate public attitudes regarding home energy efficiency issues. Quantitative data were collected in the form of a postal survey, achieving over three hundred responses. Additionally, predominantly qualitative data were collected in semi-structured interviews in 15 homes. The issues investigated included the grant-funded energy efficiency measures installed by the public, the organisations providing grants, the means by which the recipients were referred to the organisations, and the public's preferences regarding energy efficiency advice. Findings were made about the local authority's success in encouraging the take-up of energy efficiency grants, about the public's preferences for the means by which advice should be provided, about trust relating to energy efficiency grants provided by gas and electricity suppliers, and about people's knowledge of the most effective energy efficiency measures. Additional findings were drawn about specific energy efficiency issues, including old heating systems and compact fluorescent light bulbs.     

The emergence of the transition movement in Canada: success and impact through the eyes of initiative leaders

ABSTRACT

Originating in the UK in 2006, the Transition movement is oriented to local grassroots citizen-led efforts that prepare for and support a societal energy transition to a low-carbon future in response to climate change, peak oil, ecological degradation, and economic instability. Overlapping significantly with relocalization, degrowth/slow growth, local food, and related movements, and based on permaculture principles and a distributed network model, it embraces the opportunity to turn crisis into an opportunity to build more resilient, convivial, and vibrant local communities, declaring that “if it’s not fun, it’s not sustainable”. The Transition approach has spread rapidly around the world, including initiatives in over 100 communities and cities in Canada. This paper reports on the methods and results of a Canadian community-based research study aimed at understanding how and where the movement has taken root across the country, what Transition practice looks like, challenges and opportunities encountered, and lessons learned that could be applied within the movement and by others interested in the role of citizen-led initiatives for sustainability transition. Utilising a practice theory lens, drawing on an extensive web-scan of the movement’s online presence, a survey and interviews with initiative (co)founders, an e-survey of Transition members/participants, regional “structured story-dialogue” workshops, and key informant interviews, and informed by input from a Movement Advisory Group, we describe the research process and explore what success and impact mean to those most active in the movement.     

Tales of local sustainability

Abstract

Local Agenda 21 (LA21) has emerged as the principal means of addressing sustainable development practice at the local government level. In the UK, progressive local authorities have emphasised the need for participatory processes and innovative policy options. This requires commitment and active involvement from a variety of individuals and organisations. Participants in LA21 have been interviewed to determine their motivations and perceptions, and their responses are represented in terms of the storylines of various constituencies of interest. The key themes seem to be those of actively promoting widespread participation, gaining competence in innovative techniques, taking a holistic approach to quality of life concerns, and claiming the legitimacy of local government as a key player in sustainable development.     

Export efficiency of large projects: The case of aluminium smelters

We draw attention to a number of key factors in the evaluation of major projects, such as smelters, which are highly capital- and energy-intensive as well as export-orientated. The practice of justifying such projects by upvaluing foreign exchange is considered, as is the cost of distortion. Export efficiency is introduced as the key criterion: the efficiency of some recent smelter proposals in Oceania was between 36 and 50 cents in the dollar. A correct power price is essential: hydropower (in contrast with hydroenergy) should be priced as a depletable resource.