Alkaline Degradation of Cellulose: Mechanisms and Kinetics

Cellulose powder and softwood sawdust were subjected to alkaline degradation under conditions representative of a cementitious environment for periods of 7 and 3 years, respectively. During the first 3 years, sampling was frequent, and data on the degradation of cellulose and production of isosaccharinic acid was used for establishing long-term prediction models. Samples after an additional period of 4 years were compared to the predicted values. The total rate of degradation was measured as the increase in total organic carbon (TOC) in corresponding solutions. A previously published theoretical model of degradation kinetics gave a good approximation of the present experimental data. Peeling-off, stopping, and alkaline hydrolysis reaction rate constants were obtained as model parameters, and the results suggested that the transformation of the glucose end group is the rate-limiting step in the cellulose peeling-off reaction and also determines the pH dependence of that reaction. After 3 years, isosaccharinic (ISA) acid represented 70–85% of all degradation products as quantified by capillary zone electrophoresis. The long-term prediction model indicated that all of the cellulose would be degraded after only 150–550 years. The control sampling after 7 years points toward a lower degradation of cellulose and production of ISA than predicted by the model, reflecting either a degradation of ISA that was faster than the production or a termination of the ISA production.     

Temporal Trends in Water Chemistry in the Turkey Lakes Watershed Ontario,Canada, 1982-1999

The Turkey Lakes Watershed (TLW) was established in 1980 as asite for study of the ecosystem effects of acidic deposition, andsince then there has been 40% reduction in North AmericanSO₂ emissions. Monitoring records for bulk deposition,shallow and deep ground water, two headwater streams and two lakeoutflows have been tested to identify statistically significantmonotonic trends. The TLW appears to be responding to decliningacidifying emissions because the most prevalent chemical trendacross sample types/stations was decreasing SO₄ ^2-. Increasing pH was detected in four of the seven data sets, butonly the H⁺ decrease in bulk deposition was of a magnitudeto be an important ionic compensation for the SO₄ ^2-decline. There is little evidence of acidification recovery inTLW waters however. Increasing alkalinity was found only in theoutflow of the penultimate lake of the basin, and in fact, deepground water and the other lake outflow had decreasing alkalinitytrends (i.e., continuing acidification). For the surface waterstations, the greater part of the ionic compensation fordeclining SO₄ ^2- was decreasing base cations, and as aresult, these waters are probably becoming more dilute with time,although only the headwater streams exhibited decliningconductivity. Five of seven data sets had increasing dissolvedorganic carbon concentrations. Increasing NO₃ ^- wasimportant in ground waters. Drought has strongly influencedtrends and delayed recovery by mobilizing S stored in catchmentwetlands and/or soils.     

HYDROLOGIC STAGE PERIODICITY OF THE MISSISSIPPI RIVER BEFORE AND AFTER SYSTEMATIC CHANNEL MODIFICATIONS1

ABSTRACT: Periodic flood disturbance is a well known controlling factor of in channel and floodplain ecosystem function. However, channel manipulations during the last century have potentially altered hydrologic fluctuations, and thus ecosystem function. We examined temporal river stage hydrology, through autocorrelation analysis, at seven gauges along the Mississippi River to quantify flow periodicity and effects of systematic channel modifications on flow periodicity. Intraannual variation follows a strong one‐year cycle of six months higher flow and six months lower flow for the entire Mississippi River drainage, with precipitation as a driving force. Interannual hydrologic variation differs between the upper and lower river segments. A clear quasi‐biennial oscillation pattern was evident throughout the lower river section. The effect of channel alterations was a decreased magnitude of differences between lower and higher flows. The upper section, however, suggests a 12‐to 14‐year periodicity prior to alterations and a decreased duration of lower flow years following systematic modifications. Interannual variograms clearly depict very different temporal hydrology between the upper Mississippi River and the lower Mississippi River, suggesting the simple transfer of knowledge from one segment to the other oversimplifies the complexity of a large river system.     

Emission Models and Inventories for Local Greenhouse Gas Emissions Assessment: Experience in the East Midlands Region of the Uk

This paper considers how regional greenhouse gas emissioninventories can be determined. It presents a greenhousegas emissions inventory, by source, for the East Midlandsthat has been compiled as part of a regional study intoclimate change impacts in the United Kingdom. This hasused available local data, and national emissions datawith appropriate scaling factors. Total greenhouse gasemissions for the region are estimated to be 59 milliontonnes of carbon dioxide equivalent (CO₂ equivalent)for 1997. Of these emissions, approximately 86% werecarbon dioxide emissions, 7% methane emissions, and 5%were nitrous oxide, with emissions of hydrofluorocarbons(HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride(SF₆) contributing less than 2% of total emissions.     

Investigating the Surface Energy Balance in Urban Areas – Recent Advances and Future Needs

Recent advances in understanding of the surface energy balance of urban areas, based on both experimental investigations andnumerical models, are reviewed. Particular attention is directedto the outcome of a COST-715 Expert Meeting held in April 2000,as well as experiments initiated by that action. In addition, recentcomplete parameterisations of urban effects in meso-scalemodels are reviewed. Given that neither the surface energybalance, nor its components, normally are directly measuredat meteorological stations, nor are there guidelines for theset-up of representative meteorological stations in urbanareas, this paper also provides recommendations to closethese gaps.     

A MODEL TO ENHANCE WETLAND DESIGN AND OPTIMIZE NONPOINT SOURCE POLLUTION CONTROL1

ABSTRACT: A dynamic, compartmental, simulation model (WETLAND) was developed for the design and evaluation of constructed wetlands to optimize nonpoint source (NPS) pollution control. The model simulates the hydrologic, nitrogen, carbon, dissolved oxygen (DO), bacteria, vegetative, phosphorous, and sediment cycles of a wetland system. Written in Fortran 77, the WETLAND models both free‐water surface (FWS) and subsurface flow (SSF) wetlands, and is designed in a modular manner that gives the user the flexibility to decide which cycles and processes to model. WETLAND differs from many existing wetland models in that the interactions between the different nutrient cycles are modeled, minimizing the number of assumptions concerning wetland processes. It also directly links microbial growth and death to the consumption and transformations of nutrients in the wetland system. The WETLAND model is intended to be utilized with an existing NPS hydro‐logic simulation model, such as ANSWERS or BASINS, but also may be used in situations where measured input data to the wetland are available. The model was calibrated and validated using limited data from a FWS wetland located at Benton, Kentucky. The WETLAND predictions were not statistically different from measured values for of five‐day biochemical oxygen demand (BOD₅), suspended sediment, nitrogen, and phosphorous. Effluent DO predictions were not always consistent with measured concentrations. A sensitivity analysis indicated the most significant input parameters to the model were those that directly affected bacterial growth and DO uptake and movement. The model was used to design a hypothetical constructed wetland in a subwatershed of the Nomini Creek watershed, located in Virginia. Two‐year simulations were completed for five separate wetland designs. Predicted percent reductions in BOD₅ (4 to 45 percent), total suspended solids (85 to 100 percent), total nitrogen (42 to 56 percent), and total phosphorous (38 to 57 percent) were similar to levels reported by previous research.     

SPATIALLY EXPLICIT HYDROLOGIC MODELING OF LAND USE CHANGE1

ABSTRACT: Using a Geographic Information System (GIS), a method is presented to develop a spatially explicit time series of land use in an urbanizing watershed. The method is prefaced on the existence of independent observations of land use at different times and data that describes the spatial‐temporal land use transition characteristics of the watershed between these two points in time. A method is then presented to generalize the TR‐55 graphical method, a common lumped hydrologic model for estimating peak discharge, for use in a spatially explicit scheme. This scheme predicts peak discharge throughout a watershed, rather than at a single selected watershed outlet. Coupling these two methods allows the engineer to model both the temporal and spatial evolution of peak discharge for the watershed. An illustrative watershed in a suburban area of Washington, DC is selected to demonstrate the methods. The model results from these analyses are presented graphically to highlight the complex features in peak discharge behavior that exist both spatially, as a function of position within the watershed drainage network, and temporally, as the watershed undergoes urbanization. These features are not commonly noted in most hydrologic analyses but are captured in these analyses because of the high spatial and temporal resolution of the methods presented. The physical implications of the modeled results are discussed in the context of the information content of a stream gauge located at the overall outlet of the illustrative watershed. This work shows that the common practice of transposition of gauge information to locations internal to the watershed would neglect internal variability in peak discharge behavior, and could potentially lead to the determination of inappropriate design discharges.     

The Prospect of Municipal Waste Landfill Diversion Depends on Geographical Location

This study reports on experimentation with municipal and industrial solid waste in Brazil, on mutual inspection of municipal sanitation models in selected Spanish and Brazilian towns, and on observations of municipal solid waste (MSW) management models effective in Argentina, Great Britain, Sweden, and Germany. The diversity of management strategies inhibits technology transfer. Judging by the models inspected, Sweden and Germany appear to be best prepared for stricter European landfill diversion targets in the near future. Experimentation in Brazil has resulted in a proactive MSW management model based on divided collection, which achieves 80 percent landfill diversion. This result, surprisingly, meets and exceeds European diversion targets in a South American context. As the gap in strategy and target narrows between South America and Europe, both technology and management methods may gain intercontinental mobility and thus enhance commercial ties between the two markets in the specific branch of MSW management.     

电除尘器集散控制系统的仿真研究

介绍了电除尘器集散控制系统的仿真研究。基于不同运行工况的需求，建立了一系列仿真数学模型；设计并开发了电除尘器集敢控制系统的仿真软件；通过仿真实验。验证了所建立的仿真数学模型正确合理。所开发的仿真软件能模拟电除尘器集散控制系统的全部功能。     

An improved methodology for assessing risk in aircraft operations at airports, applied to runway overruns

The paper addresses the need for models to assess risk at any particular airport, based on risk management principles used by the present risk management process, that use all available data on previous accidents. The case of runway overruns is taken as an example application, because new regulations require the provision of much longer Runway End Safety Areas than had previously been the norm. The paper presents models for overruns arising from both landings and aborted takeoffs. In each case models of overrun risk, of wreckage location and of the consequences are detailed. An example application of the models is then given in a hypothetical risk assessment.The models, though adding value to existing methods of assessing risk, are not as good as they could be, due to the lack of data on normal operations. It was therefore possible only to relate the rate of overruns to the rate of occurrence of the possible driving factors for a few factors where such comparable data on normal operations existed. It is recommended that effort be put into the collection of data to allow a more comprehensive analysis.