Empreinte eau

Résumé

Lempreinte eau (on parle également d'empreinte sur l'eau) est le volume total d'eau virtuelle utilisée pour produire un produit ou un service. Comme on le fait pour l'empreinte écologique, on peut également évaluer l'empreinte eau d'une entreprise, d'un pays, d'un individu, d'une ville etc. L'empreinte de l'eau ou Water footprint en anglais est un indicateur basé sur la consommation effective d’eau aux différents stades de la production d’un produit par le consommateur ou le producteur. On distingue l'eau verte, bleue et grise :

l'eau bleue est l'eau captée pour les usages domestiques et agricoles. Elle est aussi définie comme l'eau douce de surface ou souterraine, autrement dit l'eau douce des lacs, des rivières et des aquifères ;
l'eau verte est l'eau de pluie stockée dans le sol : elle est incorporée dans les végétaux, transpirée ou évaporée;
l'eau grise est l'eau polluée par les processus de production. Dans la terminologie émergente de l'empreinte eau

Source officielle

https://fr.wikipedia.org/wiki/Empreinte_eau

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Optimization of drip irrigation using a sensor network in Sahel Region (Burkina Faso) - Analysis of soil water and plant dynamics in the framework of project Info4Dourou 2.0

Tom Müller

The research project Info4Dourou 2.0 's main goal is to improve agriculture in semi-arid regions by developing a support system that optimizes agricultural production and water consumption based on continuous soil humidity measurements using a sensor network. In this context, the main purpose of the study was to give more scientific support to the agronomic model on which the sensor network is based. In particular the research aims at understanding the soil water and plant dynamics in order to give recommendations on the system design. The main feature of the system is to indicate when irrigation must be triggered and in which soil moisture conditions. The thesis developed a numerical model based on the software HYDRUS 2D to acquire a precise knowledge on the soil water dynamics and was calibrated and coupled with field experiments on two vegetable crops of eggplant and cabbage in Burkina Faso using drip kit irrigation systems. A great focus was given on the plant response to different irrigation schedules and to water stress, considering aerial biomass development, root distribution and final yields. Water stress was linked to continuous measurements of the soil matrix potential at different depth and locations. The field experiments showed that a daily irrigation frequency resulted to better canopy development during the first part of the growth but that great water savings are possible by optimizing the schedule. Water stress was difficult to track precisely by following daily sap flow behaviour which suggested that plant stress occurs before transpiration reduction, especially when biomass is building up. The adaptability of the root distribution was demonstrated and was clearly correlated with the wetted zone which depended on the irrigation schedule. From the numerical model, it was shown that using one sensor at a depth of about 10 cm was most appropriate in order to pilot irrigation during the whole crop growth. The analysis showed that most of the water savings could be achieved at relatively high threshold values and that low thresholds mainly resulted to transpiration reduction which was not advisable. A threshold of -20 kPa was proposed for the beginning of the growth stage which then decreases to a value of -50 kPa at full canopy development. These thresholds are believed to be adequate for most vegetable crops since they allow keeping the soil matrix potential in the root zone at values that are tolerated by most plants. An analysis of the influence of the soil texture also showed that similar values seem to perform well for most soils, if assuming an adaptation of the root distribution to the wetted zone. The study focused mainly on water stress but more research could be done on the impact of the irrigation system on nutrients availability for example.

2015

Chargement

THERMOECONOMIC ANALYSIS AND OPTIMISATION OF AIR-BASED BOTTOMING CYCLES FOR WATER-FREE HYBRID SOLAR GAS-TURBINE POWER PLANTS

Raphaël Michel Adrien Marie Sandoz

Among the plethora of alternatives available, concentrated solar power (CSP) appears as one of the most favourable options. The stability and dispatchability of production achievable by the integration of storage and fuel-solar hybridisation are amidst the major advantages of this technology. Nevertheless, conventional CSP plants are based on stream-turbine cycles which consume large amounts of water. In addition to the low thermodynamic efficiency of this type of cycle, the installation of such plants in water-scarce areas is complicated by their reliance on water resources. Thus, the study of new concepts that overcome these drawbacks is necessary for the future of this technology. The availability of high temperature solar receivers for solar tower systems opens the way for the use of gas-turbines in hybrid solar- natural gas configurations. In order to increase the efficiency of the cycle while keeping the water consumption as low as possible, a promising alternative to the recovery of the waste heat in steam-turbines is to use a low-temperature intercooled-recuperated gas-turbine cycle. This work focuses on the analysis and optimisation of the performance of an innovative hybrid solar gas-turbine power plant with an air-based bottoming cycle (ABHSGT). The evaluation considers thermodynamic performance, economic viability and environmental impact as interrelated concerns. With this in mind, detailed steady-state and dynamic models of the power plant have been developed and validated by comparison with existing components. A second model without bottoming cycle has been built for comparison. A multi-objective optimisation using an evolutionary algorithm has then been performed, optimising both capital cost and specific CO2 emissions and resulting in a Pareto-optimal set of possible designs. The analysis of the trade-off curves resulting from the optimisation reveals promising outcomes. The global minimum for the levelised cost of electricity, found at relatively high solar shares, proves the economic potential of the technology. The integration of the bottoming cycle decreases significantly the levelised cost of electricity and the CO2 emissions of the system compared to the reference plant, and higher efficiencies are achieved. The optimal design selected for an in-depth thermoeconomic and environmental analysis exhibits a levelised cost of electricity of 109 [USD/MWhe] for a solar share of 20% and an overall exergetic efficiency 38.5%. The specific CO2 emissions are reduced by 33% compared to those of a simple gas-fired power plant. The water consumption is kept at very low levels compared to other CSP plants, making the system suitable for the deployment in water-scarce areas. In addition, the environmental impact induced by the land use requirements is considerably lower than that of other renewable energy technologies. The sensitivity analysis performed to assess the consequence of changes in varying financial conditions on the levelised cost of electricity and the net present value reveals that the system studied represents a profitable investment in the presence of feed-in tariffs. In the light of the performance obtained in the three aspects considered (thermodynamic, economic and environmental), it can be concluded that the ABHSGT represents a promising alternative to other renewable energy technologies, especially in water-scarce areas.

2012

Chargement

Pressure on freshwater resources is increasingly covered by methodological developments addressing freshwater use in the field of Life Cycle Assessment (LCA). These developments ultimately lead to the publication of the ISO 14046 standard to define the principles, requirement and guidelines for a water footprint in August 2014. The objective of this thesis is to foster the application of water footprint by identifying good practices and developing operational approaches to assess and improve its discriminatory power. Indeed, academic development and LCA application by practitioners often evolve within distinct communities and with various practical constraints. For instance, newly developed methods are spatially differentiated to reduce model uncertainty, improve accuracy, precision and confidence in LCA results. However, models officially recommended by the European commission for product water footprints are generic (i.e., results do not depend on location), such as USEtox for the modelling of the human toxic and ecotoxic impacts. The trade-off between theoretical variability reduction and decrease of uncertainty in practice considering the level of geographical information available to the practitioner requires solutions meeting the needs of both LCA actors. This thesis answers the need to bridge methodological development and water footprint application through three main specific objectives: - Review existing and applicable inventory and impact assessment methods that address quantitative freshwater use in a life cycle perspective and provide preliminary application recommendations for practitioners - Analyse spatial differentiation of toxic emissions to water applied to USEtox at the inter-continental and intra-continental level and explore simplified spatial differentiation approaches such as spatial archetypes - Develop a fate and exposure characterization model and factors for toxic emissions into water with global coverage and fine resolution and test practical solutions to apply spatial characterization factors on a case study The first part of this thesis (Chapter 2) focuses on quantitative aspects of water use by providing a comprehensive review of existing and applicable inventory and impact assessment methods that address freshwater use. This analysis proves that a water footprint is already applicable for experienced practitioners relying on the current state-of-the-art methods. It provides a basis to reference the state-of-the-art of methods addressing water use in LCA already used and cited by several authors in the field of water management and specific water footprint case studies. Practical solutions to operationalize spatial differentiation are tested in Chapter 3 and 4, focusing on impact pathways generated by toxic emissions into water. Spatially differentiated landscapes and models are first developed as a reference to test simplified approaches: (1) landscape parameters are created for USEtox to develop continent and sub-continent specific boxes nested within the world and (2) a fate and exposure characterization model and factors are developed to assess toxic emissions into water with global coverage at 0.5°*0.5° resolution. The results of this work prove that using a generic model is acceptable to cover a low resolution such a continent, country, or sector when the detailed emission location is unknown while a finer resolution is essential for a regional impact score at the watershed or point source level.

EPFL2014

Chargement

Optimization of drip irrigation using a sensor network in Sahel Region (Burkina Faso) - Analysis of soil water and plant dynamics in the framework of project Info4Dourou 2.0

Tom Müller

2015

THERMOECONOMIC ANALYSIS AND OPTIMISATION OF AIR-BASED BOTTOMING CYCLES FOR WATER-FREE HYBRID SOLAR GAS-TURBINE POWER PLANTS

Raphaël Michel Adrien Marie Sandoz

2012

EPFL2014