Influence of hysteresis on tidal capillary fringe dynamics in a well-sorted sand

Nielsen and Perrochet [Adv. Water Resour. 23 (2000) 503] presented experimental data for cyclic water movement in the vadose zone above an oscillating watertable. The response of the watertable to cyclic forcing was characterised by the ratios of the forcing head to watertable amplitudes and their associated phase lag. They found that their non-hysteretic Richards' equation model failed to represent the observed behaviour of these parameters. This paper explores the effect on the simulated capillary fringe dynamics (in terms of these parameters) of including varying degrees of hysteresis in the moisture retention curve used in a numerical model of their experiment. It is clear that hysteresis can indeed account for observed discrepancies between simulation and experiment and that the effect of hysteresis varies with the frequency of oscillation. The use of a single-valued mean retention curve, as advocated by some authors, fails to provide a match between the simulated and observed behaviour of the Nielsen and Perrochet parameters, but is shown to be adequate for predicting time-averaged soil moisture profiles. (C) 2003 Elsevier Ltd. All rights reserved.

The influence of key chemical constituents in activated sludge on surface and flocculating properties

This paper examines the influence of the chemical constituents of activated sludge and extracted extracellular polymeric substances (EPS) on the surface properties, hydrophobicity, surface charge (SC) and flocculating ability (FA) of activated sludge floes. Activated sludge samples from 7 different full-scale wastewater treatment plants were examined. Protein and humic substances were found to be the dominant polymeric compounds in the activated sludges and the extracted EPS, and they significantly affected the FA and surface properties, hydrophobicity and SC, of the sludge floes. The polymeric compounds proteins, humic substances and carbohydrates in the sludge floes and the extracted EPS contributed to the negative SC, but correlated negatively to the hydrophobicity of sludge floes. The quantity of protein and carbohydrate within the sludge and the extracted EPS was correlated positively to the FA of the sludge floes, while increased amounts of humic substances resulted in lower FA. In contrast, increased amounts of total extracted EPS had a negative correlation to FA. The results reveal that the quality and quantity of the polymeric compounds within the sludge floes is more informative, with respect to understanding the mechanisms involved in flocculation, than if only the extracted EPS are considered. This is an important finding as it indicates that extracting EPS may be insufficient to characterise the EPS. This is due to the low extraction efficiency and difficulties involved in the separation of EPS from other organic compounds. Correlations were observed between the surface properties and FA of the sludge floes., This confirms that the surface properties of the, sludge flocs play an important role in the bioflocculation process but that also other interactions like polymer entanglement are important. (C) 2002 Elsevier Science Ltd. All rights reserved.

Impacts of structural characteristics on activated sludge floc stability

Activated sludge samples from seven full-scale plants were investigated in order to determine the relationship between floc structure and floc stability. Floc stability was determined by shear sensitivity and floc strength. Floc structure was considered in terms of two size scales, the micro- and macrostructure. The microstructure refers to the organization of the floc components, such as the individual microorganisms. The macrostructure refers to the overall floc. The floc macrostructure was characterized by filament index, sludge volume index, size, and fractal dimension. It had a significant impact on floc stability. Large and open floes with low fractal dimensions containing large number of filaments were more shear sensitive and had lower floc strength compared to small and dense floes. Fluorescent in situ hybridization analysis indicated that the organization of the bacterial cells might also have an effect on the floc stability. (C) 2003 Elsevier Ltd. All rights reserved.

Integrated control of nitrate recirculation and external carbon addition in a predenitrification system

The integrated control of nitrate recirculation and external carbon addition in a predenitrification biological wastewater treatment system is studied. The proposed control structure consists of four feedback control loops, which manipulate the nitrate recirculation and the carbon dosage flows in a highly coordinated manner such that the consumption of external carbon is minimised while the nitrate discharge limits (based on both grab and composite samples) are met. The control system requires the measurement of the nitrate concentrations at the end of both the anoxic and the aerobic zones. Distinct from ordinary control systems, which typically minimise the variation in the controlled variables, the proposed control system essentially maximises the diurnal variation of the effluent nitrate concentration and through this maximises the use of influent COD for denitrification, thus minimising the requirement for external carbon source. Simulation studies using a commonly accepted simulation benchmark show that the controlled system consistently achieves the designated effluent quality with minimum costs.

Relationship between flocculation of activated sludge and composition of extracellular polymeric substances

Activated sludge floes are a flocculated mass of microorganisms, extracellular polymeric substances (EPS) and adsorbed organic and inorganic material. The structure of the floes is very heterogeneous and floes with very different properties and morphologies may occur, depending on the conditions in the activated sludge treatment plant and wastewater composition. Present thinking suggests that cations, such as calcium, create cationic bridges with EPS excreted by the bacteria and thereby hold the various floe constituents together. However, due to the complex and heterogeneous nature of activated sludge, the mechanisms have neither been thoroughly investigated nor successfully quantified. A better understanding and description of the biological flocculation process is necessary in order to establish more efficient operational strategies. The main aim of this study was to get a comprehensive and unique insight into the floe properties of activated sludge and to assess the relative impact of chemical and physical parameters. A variety of sludges from full scale treatment plants with different settling properties were characterised. The interrelationships between floe parameters such as composition of EPS, surface properties and floe structure, and their effect on the flocculation and separation properties were assessed. The results indicate that the EPS, both in terms of quantity and quality, are very important for the floe properties of the activated sludge. However, presence of filaments may alter the physical properties of the floes considerably. The EPS showed positive correlations to sludge volume index (SVI) if only sludges with low or moderate numbers of filaments were included. The surface properties were more affected by the composition of the EPS than by the number of filaments. The EPS showed positive correlation to negative surface charge and a negative correlation to relative hydrophobicity and flocculation ability. The negative correlation between flocculation ability and amount of EPS was surprising. The shear sensitivity, measured as degree of erosion of floes when subjected to shear, was more affected by floe size and number of filaments than amount of EPS.

Simulation supplements field studies to determine no-till dryland corn population recommendations for semiarid western Nebraska

In a 2-yr multiple-site field study conducted in western Nebraska during 1999 and 2000, optimum dryland corn (Zea mays L.) population varied from less than 1.7 to more than 5.6 plants m(-2), depending largely on available water resources. The objective of this study was to use a modeling approach to investigate corn population recommendations for a wide range of seasonal variation. A corn growth simulation model (APSIM-maize) was coupled to long-term sequences of historical climatic data from western Nebraska to provide probabilistic estimates of dryland yield for a range of corn populations. Simulated populations ranged from 2 to 5 plants m(-2). Simulations began with one of three levels of available soil water at planting, either 80, 160, or 240 mm in the surface 1.5 m of a loam soil. Gross margins were maximized at 3 plants m(-2) when starting available water was 160 or 240 mm, and the expected probability of a financial loss at this population was reduced from about 10% at 160 mm to 0% at 240 mm. When starting available water was 80 mm, average gross margins were less than $15 ha(-1), and risk of financial loss exceeded 40%. Median yields were greatest when starting available soil water was 240 mm. However, perhaps the greater benefit of additional soil water at planting was reduction in the risk of making a financial loss. Dryland corn growers in western Nebraska are advised to use a population of 3 plants m(-2) as a base recommendation.

Methodologies for calibration and predictive analysis of a watershed model

The use of a fitted parameter watershed model to address water quantity and quality management issues requires that it be calibrated under a wide range of hydrologic conditions. However, rarely does model calibration result in a unique parameter set. Parameter nonuniqueness can lead to predictive nonuniqueness. The extent of model predictive uncertainty should be investigated if management decisions are to be based on model projections. Using models built for four neighboring watersheds in the Neuse River Basin of North Carolina, the application of the automated parameter optimization software PEST in conjunction with the Hydrologic Simulation Program Fortran (HSPF) is demonstrated. Parameter nonuniqueness is illustrated, and a method is presented for calculating many different sets of parameters, all of which acceptably calibrate a watershed model. A regularization methodology is discussed in which models for similar watersheds can be calibrated simultaneously. Using this method, parameter differences between watershed models can be minimized while maintaining fit between model outputs and field observations. In recognition of the fact that parameter nonuniqueness and predictive uncertainty are inherent to the modeling process, PEST's nonlinear predictive analysis functionality is then used to explore the extent of model predictive uncertainty.

The application of wave induced forces to a two-dimensional finite element long wave hydrodynamic model

This paper describes the modification of a two-dimensional finite element long wave hydrodynamic model in order to predict the net current and water levels attributable to the influences of waves. Tests examine the effects of the application of wave induced forces, including comparisons to a physical experiment. An example of a real river system is presented with comparisons to measured data, which demonstrate the importance of simulating the combined effects of tides and waves upon hydrodynamic behavior. (C) 2002 Elsevier Science Ltd. All rights reserved.

Improving the public management career: report for the ministry of planning, budgeting e management, federal government of Brazil

This report sets out the findings and recommendations of a review of the Public Management Career (EPPGG) undertaken between 5 and 9 January 2009. The purpose of the review was to clarify EPPGG???s role, functions and profile, and to develop proposals for improving its effectiveness and management, taking account of the context within which such improvements would have to be implemented. Specific objectives were to examine a number of human resources management (HRM) aspects of the career in the light of international practice, including recruitment; initial education; professional development; performance evaluation; deployment; mobility and networking.

Enquadramento de corpos de água em pequenas e micro bacias hidrográficas rurais de base agrícola familiar : subsídios à elaboração da fase diagnóstica

Este trabalho tem como proposta geral fornecer subsídios para o desenvolvimento da fase diagnóstica do processo de Enquadramento de corpos de água superficiais de pequenas e micro bacias hidrográficas (PMBH). Sua justificativa ampara-se no fato de que a implementação de processos de Enquadramento ainda é restrita, principalmente, no que tange as PMBH, escala de gestão ainda não considerada pelo gerenciamento de recursos hídricos. Apresenta como objetivos a identificação, análise e seleção de itens de diagnósticos adotados em processos de Enquadramento; avaliação quanto as particularidades / especificidade quanto à utilização desses itens de diagnóstico para a realidade de PMBH, e por fim, a proposição de diretrizes para o estabelecimento de procedimentos orientativos para avaliações diagnósticas para fins de Enquadramento de corpos de agua superficiais em PMBH. Metodologicamente, embasado por meio de análise de estudos técnicos e científicos, os itens de diagnóstico identificados foram agrupados de forma sistematizada, e realizada avaliação quanto a aplicabilidade desses itens na elaboração de diagnóstico para Enquadramento em PMBH. Como resultado, mostrou ser possível obter maior nível de detalhamento para os itens de diagnósticos sugeridos pela Resolução nº 91/08 do CNRH no Artigo 4º. Apresentou como produto, um de conjunto de itens de diagnóstico de referência para a fase de avaliações diagnósticas do Enquadramento. Também demonstrou haver, de fato, particularidades que devem ser levadas em consideração quanto ao desenvolvimento de estudos de Enquadramento em pequenas regiões hidrográficas. Além disso, com a proposição de diretrizes para o estabelecimento de procedimentos orientativos para a fase de diagnósticos do Enquadramento, verificou que os desafios para tornar realidade o Enquadramento de corpos de água superficiais em PMBH são de natureza financeira, política e técnico-científica.

Efeito da restrição hídrica sobre o crescimento de clones de eucalipto

O estabelecimento e o crescimento inicial de espécies florestais no campo são fortemente afetados pela disponibilidade de água no solo e pela época de plantio, por isso, o presente trabalho estuda o impacto do déficit hídrico no crescimento de mudas de dois clones do híbrido Eucalyptus grandis x Eucalyptus urophylla, ambos submetidos a 4 níveis de déficit hídrico, em duas épocas de plantio. O estudo foi realizado na área experimental do Núcleo de Estudos e Difusão de Tecnologia em Florestas, Recursos Hídricos e Agricultura Sustentável (NEDTEC), do Centro de Ciências Agrárias da Universidade Federal do Espírito Santo (CCA-UFES), localizado no município de Jerônimo Monteiro. O trabalho foi realizado em duas épocas distintas, sendo a primeira no período de 09 de fevereiro a 09 de junho de 2009 e a segunda no período de 11 de julho a 07 de novembro de 2009, visando à realização das observações em diferentes condições de regime de radiação, déficit de pressão do vapor do ar, temperatura, umidade relativa do ar e velocidade do vento. O delineamento experimental utilizado foi o inteiramente ao acaso em parcelas subdivididas 2 x 4, alocando-se os 4 níveis de déficits hídricos na parcela principal e as 2 épocas nas subparcelas, com três repetições. Os manejos hídricos aplicados foram: Déficit 0 (D0) sem déficit, Déficit 1(D1) corte da irrigação aos 30 dias de experimentação, permanecendo até o final do experimento, Déficit 2 (D2) corte da irrigação aos 30 dias de experimentação, suspensão da irrigação por 60 dias e posterior retomada da irrigação por mais 30 dias; Déficit 3 (D3) corte da irrigação aos 60 dias de experimentação, prolongando até o final do experimento. Os dados experimentais foram submetidos à análise de variância, e quando significativas, as médias foram comparadas pelo teste de média Tukey a 5% de probabilidade, para cada clone estudado. Com este trabalho, foi possível avaliar o impacto de diferentes déficits hídricos, no crescimento inicial das plantas, em duas épocas do ano e avaliar o incremento no desenvolvimento das plantas durante a aplicação dos tratamentos, com retiradas de amostras médias de cada tratamento a cada 30 dias. As variáveis medidas nos dois experimentos foram altura total da planta, diâmetro ao nível do coleto, número de folhas, área foliar, matéria seca de folhas, matéria seca de haste e ramos, matéria seca de raízes e matéria seca total. Foram avaliadas as variáveis climáticas durante todo o período experimental, nas duas épocas, a fim de determinar a condição do clima em cada época. Para os dois clones estudados, em geral, os déficits hídricos promoveram a redução das variáveis morfológicas estudadas e a época experimental foi o fator que mais influenciou a redução do crescimento das plantas. Sendo que a Época 1 foi a que proporcionou resultados superiores, e a Época 2 foi a que prejudicou mais o desenvolvimento das plantas, reduzindo significativamente todas as variáveis morfológicas em todos os déficits hídricos, inclusive o D0.